Transcriber's note: A few typographical errors have been corrected: they are listed at the end of the text. The Errata on page viii, which were in the original book, have been applied to this e-text. Page numbers within curly brackets (such as {iii} and {27} have been included so that the reader might use the index. THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION. by CHARLES DARWIN, M. A. , F. R. S. , &c. IN TWO VOLUMES. --VOL. II. With Illustrations. LONDON:John Murray, Albemarle Street. 1868. The right of Translation is reserved. London: Printed by William Clowes and Sons, Stamford Street, and CharingCross. {iii} CONTENTS OF VOLUME II. CHAPTER XII. INHERITANCE. WONDERFUL NATURE OF INHERITANCE--PEDIGREES OF OUR DOMESTICATEDANIMALS--INHERITANCE NOT DUE TO CHANCE--TRIFLING CHARACTERSINHERITED--DISEASES INHERITED--PECULIARITIES IN THE EYE INHERITED--DISEASESIN THE HORSE--LONGEVITY AND VIGOUR--ASYMMETRICAL DEVIATIONS OFSTRUCTURE--POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY DIGITS AFTERAMPUTATION--CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED FROM NON-AFFECTEDPARENTS--WEAK AND FLUCTUATING INHERITANCE: IN WEEPING TREES, IN DWARFNESS, COLOUR OF FRUIT AND FLOWERS, COLOUR OF HORSES--NON-INHERITANCE IN CERTAINCASES--INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE CONDITIONSOF LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY REVERSION--CONCLUSION... Page 1 CHAPTER XIII. INHERITANCE _continued_--REVERSION OR ATAVISM. DIFFERENT FORMS OF REVERSION--IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS--REVERSION IN FERALANIMALS AND PLANTS--REVERSION IN CROSSED VARIETIES AND SPECIES--REVERSIONTHROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR FRUIT--INDIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL--THE ACT OF CROSSING ADIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS--OTHERPROXIMATE CAUSES OF REVERSION--LATENT CHARACTERS--SECONDARY SEXUALCHARACTERS--UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY--APPEARANCEWITH ADVANCING AGE OF CHARACTERS DERIVED FROM A CROSS--THE GERM WITH ALLITS LATENT CHARACTERS A WONDERFUL OBJECT--MONSTROSITIES--PELORIC FLOWERSDUE IN SOME CASES TO REVERSION ... Page 28 CHAPTER XIV. INHERITANCE _continued_--FIXEDNESS OF CHARACTER--PREPOTENCY--SEXUALLIMITATION--CORRESPONDENCE OF AGE. FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OFINHERITANCE--PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY, IN CROSSED BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER;SOMETIMES DUE TO THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE BREEDAND LATENT IN THE OTHER--INHERITANCE AS LIMITED BY SEX--NEWLY-ACQUIREDCHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE SEX ALONE, SOMETIMES LOST BY ONE SEX ALONE--INHERITANCE AT CORRESPONDING PERIODS OFLIFE--THE IMPORTANCE OF THE PRINCIPLE WITH RESPECT TO EMBRYOLOGY; ASEXHIBITED IN DOMESTICATED ANIMALS; AS EXHIBITED IN THE APPEARANCE ANDDISAPPEARANCE OF INHERITED DISEASES; SOMETIMES SUPERVENING EARLIER IN THECHILD THAN IN THE PARENT--SUMMARY OF THE THREE PRECEDING CHAPTERS ... Page62 {iv} CHAPTER XV. ON CROSSING. FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS--WHENTHE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THEOTHER--THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BYTHE CONDITIONS OF LIFE, AND BY NATURAL SELECTION--ALL ORGANIC BEINGSOCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS--ON CERTAIN CHARACTERSINCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE SUDDENLYAPPEARED IN THE INDIVIDUAL--ON THE MODIFICATION OF OLD RACES, AND THEFORMATION OF NEW RACES, BY CROSSING--SOME CROSSED RACES HAVE BRED TRUE FROMTHEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT SPECIES IN RELATION TOTHE FORMATION OF DOMESTIC RACES ... Page 85 CHAPTER XVI. CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--INFLUENCE OFDOMESTICATION ON FERTILITY. DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED--VARIOUSCAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUALPREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED--VARIETIESOF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO, RENDERED INSOME DEGREE MUTUALLY STERILE--DOMESTICATION ELIMINATES THE TENDENCY TOSTERILITY NATURAL TO SPECIES WHEN CROSSED--ON THE INCREASED FERTILITY OFUNCROSSED ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION ... Page100 CHAPTER XVII. ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSEINTERBREEDING. DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBIDTENDENCIES--GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM CROSSING, ANDON THE EVIL EFFECTS FROM CLOSE INTERBREEDING--CATTLE, CLOSELY INTERBRED;HALF-WILD CATTLE LONG KEPT IN THE SAMEPARKS--SHEEP--FALLOW-DEER--DOGS--RABBITS--PIGS--MAN, ORIGIN OF HISABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS, GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS, FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED SIZEOF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON CERTAIN PLANTSWHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE, BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT INDIVIDUALSEITHER OF THE SAME OR ANOTHER SPECIES--CONCLUSION ... Page 114 {v} CHAPTER XVIII. ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE:STERILITY FROM VARIOUS CAUSES. ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OFLIFE--STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVECOUNTRY AND IN MENAGERIES--MAMMALS, BIRDS, AND INSECTS--LOSS OF SECONDARYSEXUAL CHARACTERS AND OF INSTINCTS--CAUSES OF STERILITY--STERILITY OFDOMESTICATED ANIMALS FROM CHANGED CONDITIONS--SEXUAL INCOMPATIBILITY OFINDIVIDUAL ANIMALS--STERILITY OF PLANTS FROM CHANGED CONDITIONS OFLIFE--CONTABESCENCE OF THE ANTHERS--MONSTROSITIES AS A CAUSE OFSTERILITY--DOUBLE FLOWERS--SEEDLESS FRUIT--STERILITY FROM THE EXCESSIVEDEVELOPMENT OF THE ORGANS OF VEGETATION--FROM LONG-CONTINUED PROPAGATION BYBUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESSFRUIT ... Page 145 CHAPTER XIX. SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM. ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ONFERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGEDCONDITIONS OF LIFE--VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON THEDIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONSWITH RESPECT TO HYBRIDISM--LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATEPROGENY OF DIMORPHIC AND TRIMORPHIC PLANTS--STERILITY OF CROSSED SPECIESDUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE SYSTEM--NOT ACCUMULATEDTHROUGH NATURAL SELECTION--REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLYSTERILE--TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE IN FERTILITYBETWEEN CROSSED SPECIES AND CROSSED VARIETIES--CONCLUSION ... Page 173 CHAPTER XX. SELECTION BY MAN. SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURALSELECTION--RESULTS OF METHODICAL SELECTION--CARE TAKEN INSELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS, ANDBY SEMI-CIVILISED PEOPLE--UNIMPORTANT CHARACTERS OFTEN ATTENDEDTO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OURDOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUSSELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB-VARIETY--PLANTSAS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF SELECTION AS SHOWN BY THEGREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN ... Page 192 {vi} CHAPTER XXI. SELECTION--_continued. _ NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICHAPPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES FAVOURABLETO SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THECONDITIONS--CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE--THE PRODUCTIONOF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE--WHEN NO SELECTIONIS APPLIED, DISTINCT RACES ARE NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TODEGENERATION--TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TOAN EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TOCONVERGENCE--CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICHTHEY HAVE ALREADY VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OFINTERMEDIATE VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMITTO THE POWER OF SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICHDOMESTIC RACES HAVE ORIGINATED--SUMMARY ... Page 224 CHAPTER XXII. CAUSES OF VARIABILITY. VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES ASSIGNED BYVARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF EVERY KIND DUE TOCHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH CHANGES--CLIMATE, FOOD, EXCESS OF NUTRIMENT--SLIGHT CHANGES SUFFICIENT--EFFECTS OF GRAFTING ON THEVARIABILITY OF SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TOCHANGED CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSEINTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSEVARIABILITY--CROSSING AS A CAUSE OF THE APPEARANCE OF NEWCHARACTERS--VARIABILITY FROM THE COMMINGLING OF CHARACTERS AND FROMREVERSION--ON THE MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH EITHERDIRECTLY, OR INDIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE VARIABILITY... Page 250 CHAPTER XXIII. DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF LIFE. SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGEDCONDITIONS, IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THETISSUES--LOCAL DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE ORFOOD, ETC. --PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THEINOCULATION OF POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC BEINGS IN ASTATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNALCONDITIONS--COMPARISON OF AMERICAN AND EUROPEAN TREES--GALLS--EFFECTS OFPARASITIC FUNGI--CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENTINFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL SERIES OFVARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OFCHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BYUNNATURAL TREATMENT--SUMMARY ... Page 271 {vii} CHAPTER XXIV. LAWS OF VARIATION--USE AND DISUSE, ETC. NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON THEEFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS OFLIFE--ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY WHICHTHIS CAN BE EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS ... Page293 CHAPTER XXV. LAWS OF VARIATION, _continued_--CORRELATED VARIABILITY. EXPLANATION OF TERM--CORRELATION AS CONNECTED WITHDEVELOPMENT--MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED SIZEOF PARTS--CORRELATED VARIATION OF HOMOLOGOUS PARTS--FEATHERED FEET IN BIRDSASSUMING THE STRUCTURE OF THE WINGS--CORRELATION BETWEEN THE HEAD AND THEEXTREMITIES--BETWEEN THE SKIN AND DERMAL APPENDAGES--BETWEEN THE ORGANS OFSIGHT AND HEARING--CORRELATED MODIFICATIONS IN THE ORGANS OFPLANTS--CORRELATED MONSTROSITIES--CORRELATION BETWEEN THE SKULL ANDEARS--SKULL AND CREST OF FEATHERS--SKULL AND HORNS--CORRELATION OF GROWTHCOMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL SELECTION--COLOUR ASCORRELATED WITH CONSTITUTIONAL PECULIARITIES ... Page 319 CHAPTER XXVI. LAWS OF VARIATION, _continued_--SUMMARY. ON THE AFFINITY AND COHESION OF HOMOLOGOUS PARTS--ON THE VARIABILITY OFMULTIPLE AND HOMOLOGOUS PARTS--COMPENSATION OF GROWTH--MECHANICALPRESSURE--RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS OF THEPLANT, AND OF SEEDS IN THE CAPSULE, AS INDUCING VARIATION--ANALOGOUS ORPARALLEL VARIETIES--SUMMARY OF THE THREE LAST CHAPTERS ... Page 339 CHAPTER XXVII. PROVISIONAL HYPOTHESIS OF PANGENESIS. PRELIMINARY REMARKS--FIRST PART:--THE FACTS TO BE CONNECTED UNDER A SINGLEPOINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION--THE DIRECT ACTIONOF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE FUNCTIONAL INDEPENDENCEOF THE ELEMENTS OR UNITS OF THE BODY--VARIABILITY--INHERITANCE--REVERSION. SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARYASSUMPTIONS ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THESEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART--CONCLUSION ... Page357 {viii} CHAPTER XXVIII. CONCLUDING REMARKS. DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE ANDDISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES FAVOURABLE TOSELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE QUESTION WHETHER EACHPARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED ... Page 405 INDEX ... Page 433 * * * * * ERRATA. Vol. II. , pp. 18, 232, 258, for Cratægus oxycantha, read oxyacantha. , p. 98, 8 lines from top, for Dianthus armoria read armeria. , , 156, 15 lines from bottom, for Casuarinus read Casuarius. , ,, 4 lines from bottom, for Grus cineria read cinerea. , , 168, 11 lines from top, for Oesculus read Æsculus. , , 300, 3 lines from top, for anastomising read anastomosing. , ,, foot-note, for Birckell read Brickell. * * * * * {1} THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION. * * * * * CHAPTER XII. INHERITANCE. WONDERFUL NATURE OF INHERITANCE--PEDIGREES OF OUR DOMESTICATED ANIMALS--INHERITANCE NOT DUE TO CHANCE--TRIFLING CHARACTERS INHERITED--DISEASES INHERITED--PECULIARITIES IN THE EYE INHERITED--DISEASES IN THE HORSE--LONGEVITY AND VIGOUR--ASYMMETRICAL DEVIATIONS OF STRUCTURE--POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY DIGITS AFTER AMPUTATION--CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED FROM NON-AFFECTED PARENTS--WEAK AND FLUCTUATING INHERITANCE: IN WEEPING TREES, IN DWARFNESS, COLOUR OF FRUIT AND FLOWERS, COLOUR OF HORSES--NON-INHERITANCE IN CERTAIN CASES--INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE CONDITIONS OF LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY REVERSION--CONCLUSION. The subject of inheritance is an immense one, and has been treated by manyauthors. One work alone, 'De l'Hérédité Naturelle, ' by Dr. Prosper Lucas, runs to the length of 1562 pages. We must confine ourselves to certainpoints which have an important bearing on the general subject of variation, both with domestic and natural productions. It is obvious that a variationwhich is not inherited throws no light on the derivation of species, nor isof any service to man, except in the case of perennial plants, which can bepropagated by buds. If animals and plants had never been domesticated, and wild ones alone hadbeen observed, we should probably never have heard the saying, that "likebegets like. " The proposition would have been as self-evident, as that allthe buds on the same tree are alike, though neither proposition is strictlytrue. For, as has often been remarked, probably no two individuals are {2}identically the same. All wild animals recognise each other, which showsthat there is some difference between them; and when the eye is wellpractised, the shepherd knows each sheep, and man can distinguish afellow-man out of millions on millions of other men. Some authors have goneso far as to maintain that the production of slight differences is as mucha necessary function of the powers of generation, as the production ofoffspring like their parents. This view, as we shall see in a futurechapter, is not theoretically probable, though practically it holds good. The saying that "like begets like" has in fact arisen from the perfectconfidence felt by breeders, that a superior or inferior animal willgenerally reproduce its kind; but this very superiority or inferiorityshows that the individual in question has departed slightly from its type. The whole subject of inheritance is wonderful. When a new character arises, whatever its nature may be, it generally tends to be inherited, at least ina temporary and sometimes in a most persistent manner. What can be morewonderful than that some trifling peculiarity, not primordially attached tothe species, should be transmitted through the male or female sexual cells, which are so minute as not to be visible to the naked eye, and afterwardsthrough the incessant changes of a long course of development, undergoneeither in the womb or in the egg, and ultimately appear in the offspringwhen mature, or even when quite old, as in the case of certain diseases? Oragain, what can be more wonderful than the well-ascertained fact that theminute ovule of a good milking cow will produce a male, from whom a cell, in union with an ovule, will produce a female, and she, when mature, willhave large mammary glands, yielding an abundant supply of milk, and evenmilk of a particular quality? Nevertheless, the real subject of surpriseis, as Sir H. Holland has well remarked, [1] not that a character should beinherited, but that any should ever fail to be inherited. In a futurechapter, devoted to an hypothesis which I have termed pangenesis, anattempt will be made to show the means by which characters of all kinds aretransmitted from generation to generation. {3} Some writers, [2] who have not attended to natural history, have attemptedto show that the force of inheritance has been much exaggerated. Thebreeders of animals would smile at such simplicity; and if theycondescended to make any answer, might ask what would be the chance ofwinning a prize if two inferior animals were paired together? They mightask whether the half-wild Arabs were led by theoretical notions to keeppedigrees of their horses? Why have pedigrees been scrupulously kept andpublished of the Shorthorn cattle, and more recently of the Hereford breed?Is it an illusion that these recently improved animals safely transmittheir excellent qualities even when crossed with other breeds? have theShorthorns, without good reason, been purchased at immense prices andexported to almost every quarter of the globe, a thousand guineas havingbeen given for a bull? With greyhounds pedigrees have likewise been kept, and the names of such dogs, as Snowball, Major, &c. , are as well known tocoursers as those of Eclipse and Herod on the turf. Even with the Gamecockpedigrees of famous strains were formerly kept, and extended back for acentury. With pigs, the Yorkshire and Cumberland breeders "preserve andprint pedigrees;" and to show how such highly-bred animals are valued, Imay mention that Mr. Brown, who won all the first prizes for small breedsat Birmingham in 1850, sold a young sow and boar of his breed to Lord Duciefor 43 guineas; the sow alone was afterwards sold to the Rev. F. Thursbyfor 65 guineas; who writes, "she paid me very well, having sold her producefor 300_l_. , and having now four breeding sows from her. "[3] Hard cash paiddown, over and over again, is an excellent test of inherited superiority. In fact, the whole art of breeding, from which such great results have beenattained during the present century, depends on the inheritance of eachsmall {4} detail of structure. But inheritance is not certain; for if itwere, the breeder's art[4] would be reduced to a certainty, and there wouldbe little scope left for all that skill and perseverance shown by the menwho have left an enduring monument of their success in the present state ofour domesticated animals. It is hardly possible, within a moderate compass, to impress on the mind ofthose who have not attended to the subject, the full conviction of theforce of inheritance which is slowly acquired by rearing animals, bystudying the many treatises which have been published on the variousdomestic animals, and by conversing with breeders. I will select a fewfacts of the kind, which, as far as I can judge, have most influenced myown mind. With man and the domestic animals, certain peculiarities haveappeared in an individual, at rare intervals, or only once or twice in thehistory of the world, but have reappeared in several of the children andgrandchildren. Thus Lambert, "the porcupine-man, " whose skin was thicklycovered with warty projections, which were periodically moulted, had allhis six children and two grandsons similarly affected. [5] The face and bodybeing covered with long hair, accompanied by deficient teeth (to which Ishall hereafter refer), occurred in three successive generations in aSiamese family; but this case is not unique, as a woman[6] with acompletely hairy face was exhibited in London in 1663, and another instancehas recently occurred. Colonel Hallam[7] has described a race of two-leggedpigs, "the hinder extremities being entirely wanting;" and this deficiencywas transmitted through three generations. In fact, all races presentingany remarkable peculiarity, such as solid-hoofed swine, Mauchamp sheep, niata cattle, &c. , are instances of the long-continued inheritance of raredeviations of structure. When we reflect that certain extraordinary peculiarities have {5} thusappeared in a single individual out of many millions, all exposed in thesame country to the same general conditions of life, and, again, that thesame extraordinary peculiarity has sometimes appeared in individuals livingunder widely different conditions of life, we are driven to conclude thatsuch peculiarities are not directly due to the action of the surroundingconditions, but to unknown laws acting on the organisation or constitutionof the individual;--that their production stands in hardly closer relationto the conditions than does life itself. If this be so, and the occurrenceof the same unusual character in the child and parent cannot be attributedto both having been exposed to the same unusual conditions, then thefollowing problem is worth consideration, as showing that the result cannotbe due, as some authors have supposed, to mere coincidence, but must beconsequent on the members of the same family inheriting something in commonin their constitution. Let it be assumed that, in a large population, aparticular affection occurs on an average in one out of a million, so thatthe _à priori_ chance that an individual taken at random will be soaffected is only one in a million. Let the population consist of sixtymillions, composed, we will assume, of ten million families, eachcontaining six members. On these data, Professor Stokes has calculated forme that the odds will be no less than 8333 millions to 1 that in the tenmillion families there will not be even a single family in which one parentand two children will be affected by the peculiarity in question. Butnumerous cases could be given, in which several children have been affectedby the same rare peculiarity with one of their parents; and in this case, more especially if the grandchildren be included in the calculation, theodds against mere coincidence become something prodigious, almost beyondenumeration. In some respects the evidence of inheritance is more striking when weconsider the reappearance of trifling peculiarities. Dr. Hodgkin formerlytold me of an English family in which, for many generations, some membershad a single lock differently coloured from the rest of the hair. I knew anIrish gentleman, who, on the right side of his head, had a small white lockin the midst of his dark hair: he assured me that his grandmother had {6} asimilar lock on the same side, and his mother on the opposite side. But itis superfluous to give instances; every shade of expression, which mayoften be seen alike in parents and children, tells the same story. On whata curious combination of corporeal structure, mental character, andtraining, must handwriting depend! yet every one must have noted theoccasional close similarity of the handwriting in father and son, althoughthe father had not taught his son. A great collector of franks assured methat in his collection there were several franks of father and son hardlydistinguishable except by their dates. Hofacker, in Germany, remarks on theinheritance of handwriting; and it has even been asserted that English boyswhen taught to write in France naturally cling to their English manner ofwriting. [8] Gait, gestures, voice, and general bearing are all inherited, as the illustrious Hunter and Sir A. Carlisle have insisted. [9] My fathercommunicated to me two or three striking instances, in one of which a mandied during the early infancy of his son, and my father, who did not seethis son until grown up and out of health, declared that it seemed to himas if his old friend had risen from the grave, with all his highly peculiarhabits and manners. Peculiar manners pass into tricks, and severalinstances could be given of their inheritance; as in the case, oftenquoted, of the father who generally slept on his back, with his right legcrossed over the left, and whose daughter, whilst an infant in the cradle, followed exactly the same habit, though an attempt was made to cureher. [10] I will give one instance which has fallen under my ownobservation, and which is curious from being a trick associated with apeculiar state of mind, namely, pleasurable emotion. A boy had the singularhabit, when pleased, of rapidly moving his fingers parallel to each other, and, when much excited, of raising both hands, with the fingers stillmoving, to the sides of his face on a level with the eyes; this boy, whenalmost an old man, could still hardly resist this trick when much pleased, but from its absurdity concealed it. He had eight children. Of these, agirl, when {7} pleased, at the age of four and a half years, moved herfingers in exactly the same way, and what is still odder, when muchexcited, the raised both her hands, with her fingers still moving, to thesides of her face, in exactly the same manner as her father had done, andsometimes even still continued to do when alone. I never heard of any oneexcepting this one man and his little daughter who had this strange habit;and certainly imitation was in this instance out of the question. Some writers have doubted whether those complex mental attributes, on whichgenius and talent depend, are inherited, even when both parents are thusendowed. But he who will read Mr. Galton's able paper[11] on hereditarytalent will have his doubts allayed. Unfortunately it matters not, as far as inheritance is concerned, howinjurious a quality or structure may be if compatible with life. No one canread the many treatises[12] on hereditary disease and doubt this. Theancients were strongly of this opinion, or, as Ranchin expresses it, _OmnesGræci, Arabes, et Latini in eo consentiunt_. A long catalogue could begiven of all sorts of inherited malformations and of predisposition tovarious diseases. With gout, fifty per cent. Of the cases observed inhospital practice are, according to Dr. Garrod, inherited, and a greaterpercentage in private practice. Every one knows how often insanity runs infamilies, and some of the cases given by Mr. Sedgwick are awful, --as of asurgeon, whose brother, father, and four paternal uncles were all insane, the latter dying by suicide; of a Jew, whose father, mother, and sixbrothers and sisters were all mad; and in some other cases several membersof the same family, during three or four successive generations, havecommitted suicide. Striking instances {8} have been recorded of epilepsy, consumption, asthma, stone in the bladder, cancer, profuse bleeding fromthe slightest injuries, of the mother not giving milk, and of badparturition being inherited. In this latter respect I may mention an oddcase given by a good observer, [13] in which the fault lay in the offspring, and not in the mother: in a part of Yorkshire the farmers continued toselect cattle with large hind-quarters, until they made a strain called"Dutch-buttocked, " and "the monstrous size of the buttocks of the calf wasfrequently fatal to the cow, and numbers of cows were annually lost incalving. " Instead of giving numerous details on various inherited malformations and diseases, I will confine myself to one organ, that which is the most complex, delicate, and probably best-known in the human frame, namely, the eye, with its accessory parts. To begin with the latter: I have heard of a family in which parents and children were affected by drooping eyelids, in so peculiar a manner, that they could not see without throwing their heads backwards; and Sir A. Carlisle[14] specifies a pendulous fold to the eyelids as inherited. "In a family, " says Sir H. Holland, [15] "where the father had a singular elongation of the upper eyelid, seven or eight children were born with the same deformity; two or three other children having it not. " Many persons, as I year from Mr. Paget, have two or three of the hairs in their eyebrows (apparently corresponding with the vibrissæ of the lower animals) much longer than the others; and even so trifling a peculiarity as this certainly runs in families. With respect to the eye itself, the highest authority in England, Mr. Bowman, has been so kind as to give me the following remarks on certain inherited imperfections. First, hypermetropia, or morbidly long sight: in this affection, the organ, instead of being spherical, is too flat from front to back, and is often altogether too small, so that the retina is brought too forward for the focus of the humours; consequently a convex glass is required for clear vision of near objects, and frequently even of distant ones. This state occurs congenitally, or at a very early age, often in several children of the same family, where one of the parents has presented it. [16] Secondly, myopia, or short-sight, in which the eye is egg-shaped, and too long from front to back; the retina in this case lies behind the focus, and is therefore fitted to see distinctly only very near objects. This condition is not commonly congenital, but comes on in youth, the liability to it being well known to be transmissible from parent to child. The change from the spherical to the ovoidal shape seems the immediate {9} consequence of something like inflammation of the coats, under which they yield, and there is ground for believing that it may often originate in causes acting directly on the individual affected, and may thenceforward become transmissible. When both parents are myopic Mr. Bowman has observed the hereditary tendency in this direction to be heightened, and some of the children to be myopic at an earlier age or in a higher degree than their parents. Thirdly, squinting is a familiar example of hereditary transmission: it is frequently a result of such optical defects as have been above mentioned; but the more primary and uncomplicated forms of it are also sometimes in a marked degree transmitted in a family. Fourthly, _Cataract_, or opacity of the crystalline lens, is commonly observed in persons whose parents have been similarly affected, and often at an earlier age in the children than in the parents. Occasionally more than one child in a family is thus afflicted, one of whose parents or other relation presents the senile form of the complaint. When cataract affects several members of a family in the same generation, it is often seen to commence at about the same age in each; _e. G. _, in one family several infants or young persons may suffer from it; in another, several persons of middle age. Mr. Bowman also informs me that he has occasionally seen, in several members of the same family, various defects in either the right or left eye; and Mr. White Cooper has often seen peculiarities of vision confined to one eye reappearing in the same eye in the offspring. [17] The following cases are taken from an able paper by Mr. W. Sedgwick, and from Dr. Prosper Lucas. [18] Amaurosis, either congenital or coming on late in life, and causing total blindness, is often inherited; it has been observed in three successive generations. Congenital absence of the iris has likewise been transmitted for three generations, a cleft-iris for four generations, being limited in this latter case to the males of the family. Opacity of the cornea and congenital smallness of the eyes have been inherited. Portal records a curious case, in which a father and two sons were rendered blind, whenever the head was bent downwards, apparently owing to the crystalline lens, with its capsule, slipping through an unusually large pupil into the anterior chamber of the eye. Day-blindness, or imperfect vision under a bright light, is inherited, as is night-blindness, or an incapacity to see except under a strong light: a case has been recorded, by M. Cunier, of this latter defect having affected eighty-five members of the same family during six generations. The singular incapacity of distinguishing colours, which has been called _Daltonism_, is notoriously hereditary, and has been traced through five generations, in which it was confined to the female sex. With respect to the colour of the iris: deficiency of colouring matter is well known to be hereditary in albinoes. The iris of one eye being of a different colour from that of the other, and the iris being spotted, are cases which have been inherited. Mr. Sedgwick gives, in addition, on the {10} authority of Dr. Osborne, [19] the following curious instance of strong inheritance: a family of sixteen sons and five daughters all had eyes "resembling in miniature the markings on the back of a tortoiseshell cat. " The mother of this large family had three sisters and a brother all similarly marked, and they derived this peculiarity from their mother, who belonged to a family notorious for transmitting it to their posterity. Finally, Dr. Lucas emphatically remarks that there is not one single faculty of the eye which is not subject to anomalies; and not one which is not subjected to the principle of inheritance. Mr. Bowman agrees with the general truth of this proposition; which of course does not imply that all malformations are necessarily inherited; this would not even follow if both parents were affected by an anomaly which in most cases was transmissible. Even if no single fact had been known with respect to the inheritance ofdisease and malformations by man, the evidence would have been ample in thecase of the horse. And this might have been expected, as horses breed muchquicker than man, are matched with care, and are highly valued. I haveconsulted many works, and the unanimity of the belief by veterinaries ofall nations in the transmission of various morbid tendencies is surprising. Authors, who have had wide experience, give in detail many singular cases, and assert that contracted feet, with the numerous contingent evils, ofring-bones, curbs, splints, spavin, founder and weakness of the front legs, roaring or broken and thick wind, melanosis, specific ophthalmia, andblindness (the great French veterinary Hazard going so far as to say that ablind race could soon be formed), crib-biting, jibbing, and ill-temper, areall plainly hereditary. Youatt sums up by saying "there is scarcely amalady to which the horse is subject which is not hereditary;" and M. Bernard adds that the doctrine "that there is scarcely a disease which doesnot run in the stock, is gaining new advocates every day. "[20] So it {11}is in regard to cattle, with consumption, good and bad teeth, fine skin, &c. &c. But enough, and more than enough, has been said on disease. AndrewKnight, from his own experience, asserts that disease is hereditary withplants; and this assertion is endorsed by Lindley. [21] Seeing how hereditary evil qualities are, it is fortunate that good health, vigour, and longevity are equally inherited. It was formerly a well-knownpractice, when annuities were purchased to be received during the lifetimeof a nominee, to search out a person belonging to a family of which manymembers had lived to extreme old age. As to the inheritance of vigour andendurance, the English race-horse offers an excellent instance. Eclipsebegot 334, and King Herod 497 winners. A "cock-tail" is a horse not purelybred, but with only one-eighth or one-sixteenth impure blood in his veins, yet very few instances have ever occurred of such horses having won a greatrace. They are sometimes as fleet for short distances as thoroughbreds, butas Mr. Robson, the great trainer, asserts, they are deficient in wind, andcannot keep up the pace. Mr. Lawrence also remarks, "perhaps no instancehas ever occurred of a three-part-bred horse saving his '_distance_' inrunning two miles with thoroughbred racers. " It has been stated by Cecil, that when unknown horses, whose parents were not celebrated, haveunexpectedly won great races, as in the case of Priam, they can always beproved to be descended on both sides, through many generations, fromfirst-rate ancestors. On the Continent, Baron Cameronn challenges, in aGerman veterinary periodical, the opponents of the English race-horse, toname one good horse on the Continent which has not some English race-bloodin his veins. [22] With respect to the transmission of the many slight, but {12} infinitelydiversified characters, by which the domestic races of animals and plantsare distinguished, nothing need be said; for the very existence ofpersistent races proclaims the power of inheritance. A few special cases, however, deserve some consideration. It might havebeen anticipated, that deviations from the law of symmetry would not havebeen inherited. But Anderson[23] states that a rabbit produced in a littera young animal having only one ear; and from this animal a breed was formedwhich steadily produced one-eared rabbits. He also mentions a bitch, with asingle leg deficient, and she produced several puppies with the samedeficiency. From Hofacker's account[24] it appears that a one-horned stagwas seen in 1781 in a forest in Germany, in 1788 two, and afterwards, fromyear to year, many were observed with only one horn on the right side ofthe head. A cow lost a horn by suppuration, [25] and she produced threecalves which had on the same side of the head, instead of a horn, a smallbony lump attached merely to the skin; but we here approach the doubtfulsubject of inherited mutilations. A man who is left-handed, and a shell inwhich the spire turns in the wrong direction, are departures from thenormal though a symmetrical condition, and they are well known to beinherited. _Polydactylism. _--Supernumerary fingers and toes are eminently liable, as various authors have insisted, to transmission, but they are noticed here chiefly on account of their occasional regrowth after amputation. Polydactylism graduates[26] by multifarious steps from a mere cutaneous appendage, not including any bone, to a double hand. But an additional digit, supported on a metacarpal bone, and furnished with all the proper muscles, nerves, and vessels, is sometimes so perfect, that it escapes detection, unless the fingers are actually counted. Occasionally there are several supernumerary digits; but usually only one, making the total number six. This one may represent either a thumb or finger, being attached to the inner or outer margin of the hand. Generally, through the law of correlation, both hands and feet are similarly affected. I have tabulated the cases recorded in various works or privately communicated {13} to me, of forty-six persons with extra digits on one or both hands and feet; if in each case all four extremities had been similarly affected, the table would have shown a total of ninety-two hands and ninety-two feet each with six digits. As it is, seventy-three hands and seventy-five feet were thus affected. This proves, in contradiction to the result arrived at by Dr. Struthers, [27] that the hands are not more frequently affected than the feet. The presence of more than five digits is a great anomaly, for this number is not normally exceeded by any mammal, bird, or existing reptile. [28] Nevertheless, supernumerary digits are strongly inherited; they have been transmitted through five generations; and in some cases, after disappearing for one, two, or even three generations, have reappeared through reversion. These facts are rendered, as Professor Huxley has observed, more remarkable from its being known in most cases that the affected person had not married one similarly affected. In such cases the child of the fifth generation would have only 1-32nd part of the blood of his first sedigitated ancestor. Other cases are rendered remarkable by the affection gathering force, as Dr. Struthers has shown, in each generation, though in each the affected person had married one not affected; moreover such additional digits are often amputated soon after birth, and can seldom have been strengthened by use. Dr. Struthers gives the following instance: in the first generation an additional digit appeared on one hand; in the second, on both hands; in the third, three brothers had both hands, and one of the brothers a foot affected; and in the fourth generation all four limbs were affected. Yet we must not over-estimate the force of inheritance. Dr. Struthers asserts that cases of non-inheritance and of the first appearance of additional digits in unaffected families are much more frequent than cases of inheritance. Many other deviations of structure, of a nature almost as anomalous as supernumerary digits, such as deficient phalanges, thickened joints, crooked fingers, &c. , are in like manner strongly inherited, and are equally subject to intermission with reversion, though in such cases there is no reason to suppose that both parents had been similarly affected. [29] {14} Additional digits have been observed in negroes as well as in other races of man, and in several of the lower animals. Six toes have been described on the hind feet of the newt (_Salamandra cristata_), and, as it is said, of the frog. It deserves notice from what follows, that the six-toed newt, though adult, had preserved some of its larval characters; for part of the hyoidal apparatus, which is properly absorbed during the act of metamorphosis, was retained. In the dog, six toes on the hinder feet have been transmitted through three generations; and I have heard of a race of six-toed cats. In several breeds of the fowl the hinder toe is double, and is generally transmitted truly, as is well shown when Dorkings are crossed with common four-toed breeds. [30] With animals which have properly less than five digits, the number is sometimes increased to five, especially in the front legs, though rarely carried beyond that number; but this is due to the development of a digit already existing in a more or less rudimentary state. Thus the dog has properly four toes behind, but in the larger breeds a fifth toe is commonly, though not perfectly, developed. Horses, which properly have one toe alone fully developed with rudiments of the others, have been described with each foot bearing two or three small separate hoofs: analogous facts have been noticed with sheep, goats, and pigs. [31] The most interesting point with respect to supernumerary digits is their occasional regrowth after amputation. Mr. White[32] describes a child, three years old, with a thumb double from the first joint. He removed the lesser thumb, which was furnished with a nail; but to his astonishment it grew again, and reproduced a nail. The child was then taken to an eminent London surgeon, and the newly-grown thumb was wholly removed by its socket-joint, but again it grew and reproduced a nail. Dr. Struthers mentions a case of partial regrowth of an additional thumb, amputated when the child was three months old; and the late Dr. Falconer communicated to me an analogous case which had fallen under his own observation. A gentleman, who first called my attention to this subject, has given me the following facts which occurred in his own family. He himself, two brothers, and a sister were born with an extra digit to each extremity. His parents were not affected, and there was no tradition in the family, or in the village in which the family had long resided, of any member having been thus affected. Whilst a child, both additional toes, which were attached by bones, were rudely cut off; but the stump of one grew again, and a second operation was performed in his thirty-third year. {15} He has had fourteen children, of whom three have inherited additional digits; and one of them, when about six weeks old, was operated on by an eminent surgeon. The additional finger, which was attached by bone to the outer side of the hand, was removed at the joint; the wound healed, but immediately the digit began growing; and in about three months' time the stump was removed for the second time by the root. But it has since grown again, and is now fully a third of an inch in length, including a bone; so that it will for the third time have to be operated on. Now the normal digits in adult man and other mammals, in birds, and, as I believe, in true reptiles, have no power of regrowth. The nearest approach to this power is exhibited by the occasional reappearance in man of imperfect nails on the stumps of his fingers after amputation. [33] But man in his embryonic condition has a considerable power of reproduction, for Sir J. Simpson[34] has several times observed arms which had been cut off in the womb by bands of false membrane, and which had grown again to a certain extent. In one instance, the extremity was "divided into three minute nodules, on two of which small points of nails could be detected;" so that these nodules clearly represented fingers in process of regrowth. When, however, we descend to the lower vertebrate classes, which are generally looked at as representing the higher classes in their embryonic condition, we find ample powers of regrowth. Spallanzani[35] cut off the legs and tail of a salamander six times, and Bonnet eight times, successively, and they were reproduced. An additional digit beyond the proper number was occasionally formed after Bonnet had cut off or had divided longitudinally the hand or foot, and in one instance three additional digits were thus formed. [36] These latter cases appear at first sight quite distinct from the congenital production of additional digits in the higher animals; but theoretically, as we shall see in a future chapter, they probably present no real difference. The larvæ or tadpoles of the tailless Batrachians, but not the adults, [37] are capable of reproducing lost members. [38] Lastly, as I have been informed by Mr. J. J. Briggs and Mr. F. Buckland, when portions of the pectoral and tail fins of various {16} fresh-water fish are cut off, they are perfectly reproduced in about six weeks' time. From these several facts we may infer that supernumerary digits in manretain to a certain extent an embryonic condition, and that they resemblein this respect the normal digits and limbs in the lower vertebrateclasses. They also resemble the digits of some of the lower animals in thenumber exceeding five; for no mammal, bird, existing reptile, or amphibian(unless the tubercle on the hind feet of the toad and other taillessBatrachians be viewed as a digit) has more than five; whilst fishessometimes have in their pectoral fins as many as twenty metacarpal andphalangeal bones, which, together with the bony filaments, apparentlyrepresent our digits with their nails. So, again, in certain extinctreptiles, namely, the Ichthyopterygia, "the digits may be seven, eight, ornine in number, a significant mark, " says Professor Owen, "of piscineaffinity. "[39] We encounter much difficulty in attempting to reduce these various facts toany rule or law. The inconstant number of the additional digits--theirirregular attachment to either the inner or outer margin of the hand--thegradation which can be traced from a mere loose rudiment of a single digitto a completely double hand--the occasional appearance of additional digitsin the salamander after a limb has been amputated--these various factsappear to indicate mere fluctuating monstrosity; and this perhaps is allthat can be safely said. Nevertheless, as supernumerary digits in thehigher animals, from their power of regrowth and from the number thusacquired exceeding five, partake of the nature of the digits in the lowervertebrate animals;--as they occur by no means rarely, and are transmittedwith remarkable strength, though perhaps not more strongly than some otheranomalies;--and as with animals which have fewer than five digits, when anadditional one appears it is generally due to the development of a visiblerudiment;--we are led in all cases to suspect, that, although no actualrudiment can be detected, yet that a latent tendency to the formation of anadditional digit exists in all mammals, including man. On this view, as weshall more plainly see in the {17} next chapter when discussing latenttendencies, we should have to look at the whole case as one of reversion toan enormously remote, lowly-organised, and multidigitate progenitor. * * * * * I may here allude to a class of facts closely allied to, but somewhatdifferent from, ordinary cases of inheritance. Sir H. Holland[40] statesthat brothers and sisters of the same family are frequently affected, oftenat about the same age, by the same peculiar disease, not known to havepreviously occurred in the family. He specifies the occurrence of diabetesin three brothers under ten years old; he also remarks that children of thesame family often exhibit in common infantile diseases the same peculiarsymptoms. My father mentioned to me the case of four brothers who diedbetween the ages of sixty and seventy, in the same highly peculiar comatosestate. An instance has been already given of supernumerary digits appearingin four children out of six in a previously unaffected family. Dr. Devaystates[41] that two brothers married two sisters, their first-cousins, noneof the four nor any relation being an albino; but the seven childrenproduced from this double marriage were all perfect albinoes. Some of thesecases, as Mr. Sedgwick[42] has shown, are probably the result of reversionto a remote ancestor, of whom no record had been preserved; and all thesecases are so far directly connected with inheritance that no doubt thechildren inherited a similar constitution from their parents, and, frombeing exposed to nearly similar conditions of life, it is not surprisingthat they should be affected in the same manner and at the same period oflife. * * * * * Most of the facts hitherto given have served to illustrate the force ofinheritance, but we must now consider cases, grouped as well as the subjectallows into classes, showing how feeble, capricious, or deficient the powerof inheritance sometimes is. When a new peculiarity first appears, we cannever predict whether it will be inherited. If both parents from theirbirth present {18} the same peculiarity, the probability is strong that itwill be transmitted to at least some of their offspring. We have seen thatvariegation is transmitted much more feebly by seed from a branch which hadbecome variegated through bud-variation, than from plants which werevariegated as seedlings. With most plants the power of transmissionnotoriously depends on some innate capacity in the individual: thusVilmorin[43] raised from a peculiarly coloured balsam some seedlings, whichall resembled their parent; but of these seedlings some failed to transmitthe new character, whilst others transmitted it to all their descendantsduring several successive generations. So again with a variety of the rose, two plants alone out of six were found by Vilmorin to be capable oftransmitting the desired character. The weeping or pendulous growth of trees is strongly inherited in some cases, and, without any assignable reason, feebly in other cases. I have selected this character as an instance of capricious inheritance, because it is certainly not proper to the parent-species, and because, both sexes being borne on the same tree, both tend to transmit the same character. Even supposing that there may have been in some instances crossing with adjoining trees of the same species, it is not probable that all the seedlings would have been thus affected. At Moccas Court there is a famous weeping oak; many of its branches "are 30 feet long, and no thicker in any part of this length than a common rope:" this tree transmits its weeping character, in a greater or less degree, to all its seedlings; some of the young oaks being so flexible that they have to be supported by props; others not showing the weeping tendency till about twenty years old. [44] Mr. Rivers fertilized, as he informs me, the flowers of a new Belgian weeping thorn (_Cratægus oxyacantha_) with pollen from a crimson not-weeping variety, and three young trees, "now six or seven years old, show a decided tendency to be pendulous, but as yet are not so much so as the mother-plant. " According to Mr. MacNab, [45] seedlings from a magnificent weeping birch (_Betula alba_), in the Botanic Garden at Edinburgh, grew for the first ten or fifteen years upright, but then all became weepers like their parent. A peach with pendulous branches, like those of the weeping willow, has been found capable of propagation by seed. [46] Lastly, a weeping and almost prostrate yew (_Taxus baccata_) was found in a hedge in Shropshire; it was a male, but one branch bore female flowers, and produced berries; these, {19} being sown, produced seventeen trees, all of which had exactly the same peculiar habit with the parent-tree. [47] These facts, it might have been thought, would have been sufficient to render it probable that a pendulous habit would in all cases be strictly inherited. But let us look to the other side. Mr. MacNab[48] sowed seeds of the weeping beech (_Fagus sylvanica_), but succeeded in raising only common beeches. Mr. Rivers, at my request, raised a number of seedlings from three distinct varieties of weeping elm; and at least one of the parent-trees was so situated that it could not have been crossed by any other elm; but none of the young trees, now about a foot or two in height, show the least signs of weeping. Mr. Rivers formerly sowed above twenty thousand seeds of the weeping ash (_Fraxinus excelsior_), and not a single seedling was in the least degree pendulous: in Germany, M. Borchmeyer raised a thousand seedlings, with the same result. Nevertheless, Mr. Anderson, of the Chelsea Botanic Garden, by sowing seed from a weeping ash, which was found before the year 1780, in Cambridgeshire, raised several pendulous trees. [49] Professor Henslow also informs me that some seedlings from a female weeping ash in the Botanic Garden at Cambridge were at first a little pendulous, but afterwards became quite upright: it is probable that this latter tree, which transmits to a certain extent its pendulous habit, was derived by a bud from the same original Cambridgeshire stock; whilst other weeping ashes may have had a distinct origin. But the crowning case, communicated to me by Mr. Rivers, which shows how capricious is the inheritance of a pendulous habit, is that a variety of another species of ash (_F. Lentiscifolia_) which was formerly pendulous, "now about twenty years old has long lost this habit, every shoot being remarkably erect; but seedlings formerly raised from it were perfectly prostrate, the stems not rising more than two inches above the ground. " Thus the weeping variety of the common ash, which has been extensively propagated by buds during a long period, did not, with Mr. Rivers, transmit its character to one seedling out of above twenty thousand; whereas the weeping variety of a second species of ash, which could not, whilst grown in the same garden, retain its own weeping character, transmitted to its seedlings the pendulous habit in excess! Many analogous facts could be given, showing how apparently capricious is the principle of inheritance. All the seedlings from a variety of the Barberry (_B. Vulgaris_) with red leaves inherited the same character; only about one-third of the seedlings of the copper Beech (_Fagus sylvatica_) had purple leaves. Not one out of a hundred seedlings of a variety of the _Cerasus padus_, with yellow fruit, bore yellow fruit: one-twelfth of the seedlings of the variety of _Cornus mascula_, with yellow fruit, came true:[50] and lastly, all the trees raised by my father from a yellow-berried holly (_Ilex aquifolium_), {20} found wild, produced yellow berries. Vilmorin[51] observed in a bed of _Saponaria calabrica_ an extremely dwarf variety, and raised from it a large number of seedlings; some of these partially resembled their parent, and he selected their seed; but the grandchildren were not in the least dwarfed: on the other hand, he observed a stunted and bushy variety of _Tagetes signata_ growing in the midst of the common varieties by which it was probably crossed; for most of the seedlings raised from this plant were intermediate in character, only two perfectly resembling their parent; but seed saved from these two plants reproduced the new variety so truly, that hardly any selection has since been necessary. Flowers transmit their colour truly, or most capriciously. Many annuals come true: thus I purchased German seeds of thirty-four named sub-varieties of one _race_ of ten-week stocks (_Matthiola annua_), and raised a hundred and forty plants, all of which, with the exception of a single plant, came true. In saying this, however, it must be understood that I could distinguish only twenty kinds out of the thirty-four named sub-varieties; nor did the colour of the flower always correspond with the name affixed to the packet; but I say that they came true, because in each of the thirty-six short rows every plant was absolutely alike, with the one single exception. Again, I procured packets of German seed of twenty-five named varieties of common and quilled asters, and raised a hundred and twenty-four plants; of these, all except ten were true in the above limited sense; and I considered even a wrong shade of colour as false. It is a singular circumstance that white varieties generally transmit their colour much more truly than any other variety. This fact probably stands in close relation with one observed by Verlot, [52] namely, that flowers which are normally white rarely vary into any other colour. I have found that the white varieties of _Delphinium consolida_ and of the Stock are the truest. It is, indeed, sufficient to look through a nurseryman's seed-list, to see the large number of white varieties which can be propagated by seed. The several coloured varieties of the sweet-pea (_Lathyrus odoratus_) are very true; but I hear from Mr. Masters, of Canterbury, who has particularly attended to this plant, that the white variety is the truest. The hyacinth, when propagated by seed, is extremely inconstant in colour, but "white hyacinths almost always give by seed white-flowered plants;"[53] and Mr. Masters informs me that the yellow varieties also reproduce their colour, but of different shades. On the other hand, pink and blue varieties, the latter being the natural colour, are not nearly so true: hence, as Mr. Masters has remarked to me, "we see that a garden variety may acquire a more permanent habit than a natural species;" but it should have been added, that this occurs under cultivation, and therefore under changed conditions. With many flowers, especially perennials, nothing can be more fluctuating than the colour of the seedlings, as is notoriously the case with verbenas, carnations, dahlias, cinerarias, and others. [54] I sowed seed of twelve {21} named varieties of Snapdragon (_Antirrhinum majus_), and utter confusion was the result. In most cases the extremely fluctuating colour of seedling plants is probably in chief part due to crosses between differently-coloured varieties during previous generations. It is almost certain that this is the case with the polyanthus and coloured primrose (_Primula veris_ and _vulgaris_), from their reciprocally dimorphic structure;[55] and these are plants which florists speak of as never come true by seed: but if care be taken to prevent crossing, neither species is by any means very inconstant in colour; thus I raised twenty-three plants from a purple primrose, fertilised by Mr. J. Scott with its own pollen, and eighteen came up purple of different shades, and only five reverted to the ordinary yellow colour: again, I raised twenty plants from a bright-red cowslip, similarly treated by Mr. Scott, and every one perfectly resembled its parent in colour, as likewise did, with the exception of a single plant, 73 grandchildren. Even with the most variable flowers, it is probable that each delicate shade of colour might be permanently fixed so as to be transmitted by seed, by cultivation in the same soil, by long-continued selection, and especially by the prevention of crosses. I infer this from certain annual larkspurs (_Delphinium consolida_ and _ajacis_), of which common seedlings present a greater diversity of colour than any other plant known to me; yet on procuring seed of five named German varieties of _D. Consolida_, only nine plants out of ninety-four were false; and the seedlings of six varieties of _D. Ajacis_ were true in the same manner and degree as with the stocks above described. A distinguished botanist maintains that the annual species of Delphinium are always self-fertilised; therefore I may mention that thirty-two flowers on a branch of _D. Consolida_, enclosed in a net, yielded twenty-seven capsules, with an average of 17. 2 seed in each; whilst five flowers, under the same net, which were artificially fertilised, in the same manner as must be effected by bees during their incessant visits, yielded five capsules with an average of 35. 2 fine seed; and this shows that the agency of insects is necessary for the full fertility of this plant. Analogous facts could be given with respect to the crossing of many other flowers, such as carnations, &c. , of which the varieties fluctuate much in colour. As with flowers, so with our domesticated animals, no character is more variable than colour, and probably in no animal more so than with the horse. Yet with a little care in breeding, it appears that races of any colour might soon be formed. Hofacker gives the result of matching two hundred and sixteen mares of four different colours with like-coloured stallions, without regard to the colour of their ancestors; and of the two hundred and sixteen colts born, eleven alone failed to inherit the colour of their parents: Autenrieth and Ammon assert that, after two generations, colts of a uniform colour are produced with certainty. [56] In a few rare cases peculiarities fail to be inherited, apparently from theforce of inheritance being too strong. I have been assured by breeders ofthe canary-bird that to get a good {22} jonquil-coloured bird it does notanswer to pair two jonquils, as the colour then comes out too strong, or iseven brown. So again, if two crested canaries are paired, the young birdsrarely inherit this character:[57] for in crested birds a narrow space ofbare skin is left on the back of the head, where the feathers are up-turnedto form the crest, and, when both parents are thus characterised, thebareness becomes excessive, and the crest itself fails to be developed. Mr. Hewitt, speaking of Laced Sebright Bantams, says[58] that, "why this shouldbe so, I know not, but I am confident that those that are best lacedfrequently produce offspring very far from perfect in their markings, whilst those exhibited by myself, which have so often proved successful, were bred from the union of heavily-laced birds with those that werescarcely sufficiently laced. " It is a singular fact that, although several deaf-mutes often occur in thesame family, and though their cousins and other relations are often in thesame condition, yet their parents are very rarely deaf-mutes. To give asingle instance: not one scholar out of 148, who were at the same time inthe London Institution, was the child of parents similarly afflicted. Soagain, when a male or a female deaf-mute marries a sound person, theirchildren are most rarely affected: in Ireland out of 203 children thusproduced one alone was mute. Even when both parents have been deaf-mutes, as in the case of forty-one marriages in the United States and of six inIreland, only two deaf and dumb children were produced. Mr. Sedgwick, [59]in commenting on this remarkable and fortunate failure in the power oftransmission in the direct line, remarks that it may possibly be owing to"excess having reversed the action of some natural law in development. " Butit is safer in the present state of our knowledge to look at the whole caseas simply unintelligible. * * * * * With respect to the inheritance of structures mutilated by injuries oraltered by disease it is difficult to come to any {23} definite conclusion. In some cases mutilations have been practised for a vast number ofgenerations without any inherited result. Godron has remarked[60] thatdifferent races of man have from time immemorial knocked out their upperincisors, cut off joints of their fingers, made holes of immense sizethrough the lobes of their ears or through their nostrils, made deep gashesin various parts of their bodies, and there is no reason whatever tosuppose that these mutilations have ever been inherited. Adhesions due toinflammation and pits from the small-pox (and formerly many consecutivegenerations must have been thus pitted) are not inherited. With respect toJews, I have been assured by three medical men of the Jewish faith thatcircumcision, which has been practised for so many ages, has produced noinherited effect; Blumenbach, on the other hand, asserts[61] that inGermany Jews are often born in a condition rendering circumcisiondifficult, so that a name is here applied to them signifying "borncircumcised. " The oak and other trees must have borne galls from primevaltimes, yet they do not produce inherited excrescences; many other suchfacts could be adduced. On the other hand, various cases have been recorded of cats, dogs, andhorses, which have had their tails, legs, &c. , amputated or injured, producing offspring with the same parts ill-formed; but as it is not at allrare for similar malformations to appear spontaneously, all such cases maybe due to mere coincidence. Nevertheless, Dr. Prosper Lucas has given, ongood authorities, such a long list of inherited injuries, that it isdifficult not to believe in them. Thus, a cow that had lost a horn from anaccident with consequent suppuration, produced three calves which werehornless on the same side of the head. With the horse, there seems hardly adoubt that bony exostoses on the legs, caused by too much travelling onhard roads, are inherited. Blumenbach records the case of a man who had hislittle finger on the right hand almost cut off, and which in consequencegrew crooked, and his sons had the same finger on the same hand similarlycrooked. A soldier, fifteen years before his marriage, lost his left eyefrom purulent ophthalmia, and his {24} two sons were microphthalmic on thesame side. [62] In all such cases, if truthfully reported, in which theparent has had an organ injured on one side, and more than one child hasbeen born with the same organ affected on the same side, the chancesagainst mere coincidence are enormous. But perhaps the most remarkable andtrustworthy fact is that given by Dr. Brown-Séquard, [63] namely, that manyyoung guinea-pigs inherited an epileptic tendency from parents which hadbeen subjected to a particular operation, inducing in the course of a fewweeks a convulsive disease like epilepsy: and it should be especially notedthat this eminent physiologist bred a large number of guinea-pigs fromanimals which had not been operated on, and not one of these manifested theepileptic tendency. On the whole, we can hardly avoid admitting, thatinjuries and mutilations, especially when followed by disease, or perhapsexclusively when thus followed, are occasionally inherited. Although many congenital monstrosities are inherited, of which exampleshave already been given, and to which may be added the lately recorded caseof the transmission during a century of hare-lip with a cleft-palate in thewriter's own family, [64] yet other malformations are rarely or neverinherited. Of these later cases, many are probably due to injuries in thewomb or egg, and would come under the head of non-inherited injuries ormutilations. With plants, a long catalogue of inherited monstrosities ofthe most serious and diversified nature could easily be given; and withplants, there is no reason to suppose that monstrosities are caused bydirect injuries to the seed or embryo. _Causes of Non-inheritance. _ A large number of cases of non-inheritance are intelligible on theprinciple, that a strong tendency to inheritance does exist, but {25} thatit is overborne by hostile or unfavourable conditions of life. No one wouldexpect that our improved pigs, if forced during several generations totravel about and root in the ground for their own subsistence, wouldtransmit, as truly as they now do, their tendency to fatten, and theirshort muzzles and legs. Dray-horses assuredly would not long transmit theirgreat size and massive limbs, if compelled to live on a cold, dampmountainous region; we have indeed evidence of such deterioration in thehorses which have run wild on the Falkland Islands. European dogs in Indiaoften fail to transmit their true character. Our sheep in tropicalcountries lose their wool in a few generations. There seems also to be aclose relation between certain peculiar pastures and the inheritance of anenlarged tail in fat-tailed sheep, which form one of the most ancientbreeds in the world. With plants, we have seen that the American varietiesof maize lose their proper character in the course of two or threegenerations, when cultivated in Europe. Our cabbages, which here come sotrue by seed, cannot form heads in hot countries. Under changedcircumstances, periodical habits of life soon fail to be transmitted, asthe period of maturity in summer and winter wheat, barley, and vetches. Soit is with animals; for instance, a person whose statement I can trust, procured eggs of Aylesbury ducks from that town, where they are kept inhouses and are reared as early as possible for the London market; the ducksbred from these eggs in a distant part of England, hatched their firstbrood on January 24th, whilst common ducks, kept in the same yard andtreated in the same manner, did not hatch till the end of March; and thisshows that the period of hatching was inherited. But the grandchildren ofthese Aylesbury ducks completely lost their early habit of incubation, andhatched their eggs at the same time with the common ducks of the sameplace. Many cases of non-inheritance apparently result from the conditions of lifecontinually inducing fresh variability. We have seen that when the seeds ofpears, plums, apples, &c. , are sown, the seedlings generally inherit somedegree of family likeness from the parent-variety. Mingled with theseseedlings, a few, and sometimes many, worthless, wild-looking plantscommonly appear; and their appearance may be attributed to the principle ofreversion. But scarcely a single seedling will be found {26} perfectly toresemble the parent-form; and this, I believe, may be accounted for byconstantly recurring variability induced by the conditions of life. Ibelieve in this, because it has been observed that certain fruit-treestruly propagate their kind whilst growing on their own roots, but whengrafted on other stocks, and by this process their natural state ismanifestly affected, they produce seedlings which vary greatly, departingfrom the parental type in many characters. [65] Metzger, as stated in theninth chapter, found that certain kinds of wheat brought from Spain andcultivated in Germany, failed during many years to reproduce themselvestruly; but that at last, when accustomed to their new conditions, theyceased to be variable, --that is, they became amenable to the power ofinheritance. Nearly all the plants which cannot be propagated with anyapproach to certainty by seed, are kinds which have long been propagated bybuds, cuttings, offsets, tubers, &c. , and have in consequence beenfrequently exposed during their individual lives to widely diversifiedconditions of life. Plants thus propagated become so variable, that theyare subject, as we have seen in the last chapter, even to bud-variation. Our domesticated animals, on the other hand, are not exposed during theirindividual lives to such extremely diversified conditions, and are notliable to such extreme variability; therefore they do not lose the power oftransmitting most of their characteristic features. In the foregoingremarks on non-inheritance, crossed breeds are of course excluded, as theirdiversity mainly depends on the unequal development of characters derivedfrom either parent, modified by the principles of reversion and prepotency. _Conclusion. _ It has, I think, been shown in the early part of this chapter how stronglynew characters of the most diversified nature, whether normal or abnormal, injurious or beneficial, whether affecting organs of the highest or mosttrifling importance, are inherited. Contrary to the common opinion, it isoften sufficient for the inheritance of some peculiar character, that oneparent alone should possess it, as in most cases in which the rarer {27}anomalies have been transmitted. But the power of transmission is extremelyvariable: in a number of individuals descended from the same parents, andtreated in the same manner, some display this power in a perfect manner, and in some it is quite deficient; and for this difference no reason can beassigned. In some cases the effects of injuries or mutilations apparentlyare inherited; and we shall see in a future chapter that the effects of thelong-continued use and disuse of parts are certainly inherited. Even thosecharacters which are considered the most fluctuating, such as colour, arewith rare exceptions transmitted much more forcibly than is generallysupposed. The wonder, indeed, in all cases is not that any character shouldbe transmitted, but that the power of inheritance should ever fail. Thechecks to inheritance, as far as we know them, are, firstly, circumstanceshostile to the particular character in question; secondly, conditions oflife incessantly inducing fresh variability; and lastly, the crossing ofdistinct varieties during some previous generation, together with reversionor atavism--that is, the tendency in the child to resemble itsgrand-parents or more remote ancestors instead of its immediate parents. This latter subject will be fully discussed in the following chapter. * * * * * {28} CHAPTER XIII. INHERITANCE _continued_--REVERSION OR ATAVISM. DIFFERENT FORMS OF REVERSION--IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS--REVERSION IN FERAL ANIMALS AND PLANTS--REVERSION IN CROSSED VARIETIES AND SPECIES--REVERSION THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR FRUIT--IN DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL--THE ACT OF CROSSING A DIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS--OTHER PROXIMATE CAUSES OF REVERSION--LATENT CHARACTERS--SECONDARY SEXUAL CHARACTERS--UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY--APPEARANCE WITH ADVANCING AGE OF CHARACTERS DERIVED FROM A CROSS--THE GERM WITH ALL ITS LATENT CHARACTERS A WONDERFUL OBJECT--MONSTROSITIES--PELORIC FLOWERS DUE IN SOME CASES TO REVERSION. The great principle of inheritance to be discussed in this chapter has beenrecognised by agriculturists and authors of various nations, as shown bythe scientific term _Atavism_, derived from atavus, an ancestor; by theEnglish terms of _Reversion_, or _Throwing back_; by the French_Pas-en-arrière_; and by the German _Rück-schlag_, or _Rück-schritt_. Whenthe child resembles either grandparent more closely than its immediateparents, our attention is not much arrested, though in truth the fact ishighly remarkable; but when the child resembles some remote ancestor, orsome distant member in a collateral line, --and we must attribute the lattercase to the descent of all the members from a common progenitor, --we feel ajust degree of astonishment. When one parent alone displays somenewly-acquired and generally inheritable character, and the offspring donot inherit it, the cause may lie in the other parent having the power ofprepotent transmission. But when both parents are similarly characterised, and the child does not, whatever the cause may be, inherit the character inquestion, but resembles its grandparents, we have one of the simplest casesof reversion. We continually see another and even more simple case ofatavism, though not generally included under this head, namely, when {29}the son more closely resembles his maternal than his paternal grandsire insome male attribute, as in any peculiarity in the beard of man, the hornsof the bull, the hackles or comb of the cock, or, as in certain diseasesnecessarily confined to the male sex; for the mother cannot possess orexhibit such male attributes, yet the child has inherited them, through herblood, from his maternal grandsire. The cases of reversion may be divided into two main classes, which, however, in some instances, blend into each other; namely, first, thoseoccurring in a variety or race which has not been crossed, but has lost byvariation some character that it formerly possessed, and which afterwardsreappears. The second class includes all cases in which a distinguishableindividual, sub-variety, race, or species, has at some former period beencrossed with a distinct form, and a character derived from this cross, after having disappeared during one or several generations, suddenlyreappears. A third class, differing only in the manner of reproduction, might be formed to include all cases of reversion effected by means ofbuds, and therefore independent of true or seminal generation. Perhaps evena fourth class might be instituted, to include reversions by segments inthe same individual flower or fruit, and in different parts of the body inthe same individual animal as it grows old. But the two first main classeswill be sufficient for our purpose. * * * * * _Reversion to lost Characters by pure or uncrossed forms. _--Strikinginstances of this first class of cases were given in the sixth chapter, namely, of the occasional reappearance, in variously-coloured pure breedsof the pigeon, of blue birds with all the marks which characterise the wild_Columba livia_. Similar cases were given in the case of the fowl. With thecommon ass, as we now know that the legs of the wild progenitor arestriped, we may feel assured that the occasional appearance of such stripesin the domestic animal is a case of simple reversion. But I shall becompelled to refer again to these cases, and therefore will here pass themover. The aboriginal species from which our domesticated cattle and sheep aredescended, no doubt possessed horns; but several hornless breeds are nowwell established. Yet in these--for instance, {30} in Southdown sheep--"itis not unusual to find among the male lambs some with small horns. " Thehorns, which thus occasionally reappear in other polled breeds, either"grow to the full size, or are curiously attached to the skin alone andhang loosely down, or drop off. "[66] The Galloways and Suffolk cattle havebeen hornless for the last 100 or 150 years, but a horned calf, with thehorn often loosely attached, is occasionally born. [67] There is reason to believe that sheep in their early domesticated conditionwere "brown or dingy black;" but even in the time of David certain flockswere spoken of as white as snow. During the classical period the sheep ofSpain are described by several ancient authors as being black, red, ortawny. [68] At the present day, notwithstanding the great care which istaken to prevent it, particoloured lambs and some entirely black areoccasionally dropped by our most highly improved and valued breeds, such asthe Southdowns. Since the time of the famous Bakewell, during the lastcentury, the Leicester sheep have been bred with the most scrupulous care;yet occasionally grey-faced, or black-spotted, or wholly black lambsappear. [69] This occurs still more frequently with the less improvedbreeds, such as the Norfolks. [70] As bearing on this tendency in sheep torevert to dark colours, I may state (though in doing so I trench on thereversion of crossed breeds, and likewise on the subject of prepotency)that the Rev. W. D. Fox was informed that seven white Southdown ewes wereput to a so-called Spanish ram, which had two small black spots on hissides, and they produced thirteen lambs, all perfectly black. Mr. Foxbelieves that this ram belonged to a breed which he has himself kept, andwhich is always spotted with black and white; and he finds that Leicestersheep crossed by rams of this breed always produce black lambs: he has goneon recrossing these crossed sheep with pure white Leicesters during threesuccessive {31} generations, but always with the same result. Mr. Fox wasalso told by the friend from whom the spotted breed was procured, that helikewise had gone on for six or seven generations crossing with whitesheep, but still black lambs were invariably produced. Similar facts could be given with respect to tailless breeds of variousanimals. For instance, Mr. Hewitt[71] states that chickens bred from someRumpless fowls, which were reckoned so good that they won a prize at anexhibition, "in a considerable number of instances were furnished withfully developed tail-feathers. " On inquiry, the original breeder of thesefowls stated that, from the time when he had first kept them, they hadoften produced fowls furnished with tails; but that these latter wouldagain reproduce rumpless chickens. Analogous cases of reversion occur in the vegetable kingdom; thus "fromseeds gathered from the finest cultivated varieties of Heartsease (_Violatricolor_), plants perfectly wild both in their foliage and their flowersare frequently produced;"[72] but the reversion in this instance is not toa very ancient period, for the best existing varieties of the heartseaseare of comparatively modern origin. With most of our cultivated vegetablesthere is some tendency to reversion to what is known to be, or may bepresumed to be, their aboriginal state; and this would be more evident ifgardeners did not generally look over their beds of seedlings, and pull upthe false plants or "rogues" as they are called. It has already beenremarked, that some few seedling apples and pears generally resemble, butapparently are not identical with, the wild trees from which they aredescended. In our turnip[73] and carrot-beds a few plants often"break"--that is, flower too soon; and their roots are generally found tobe hard and stringy, as in the parent-species. By the aid of a littleselection, carried on during a few generations, most of our cultivatedplants could probably be brought back, without any great change in theirconditions of life, to a wild or nearly wild condition: Mr. Buckman haseffected this with the parsnip;[74] {32} and Mr. Hewett C. Watson, as heinforms me, selected, during three generations, "the most diverging plantsof Scotch kail, perhaps one of the least modified varieties of the cabbage;and in the third generation some of the plants came very close to the formsnow established in England about old castle-walls, and called indigenous. " * * * * * _Reversion in Animals and Plants which have run wild. _--In the caseshitherto considered, the reverting animals and plants have not been exposedto any great or abrupt change in their conditions of life which could haveinduced this tendency; but it is very different with animals and plantswhich have become feral or run wild. It has been repeatedly asserted in themost positive manner by various authors, that feral animals and plantsinvariably return to their primitive specific type. It is curious on whatlittle evidence this belief rests. Many of our domesticated animals couldnot subsist in a wild state; thus, the more highly improved breeds of thepigeon will not "field" or search for their own food. Sheep have neverbecome feral, and would be destroyed by almost every beast of prey. Inseveral cases we do not know the aboriginal parent-species, and cannotpossibly tell whether or not there has been any close degree of reversion. It is not known in any instance what variety was first turned out; severalvarieties have probably in some cases run wild, and their crossing alonewould tend to obliterate their proper character. Our domesticated animalsand plants, when they run wild, must always be exposed to new conditions oflife, for, as Mr. Wallace[75] has well remarked, they have to obtain theirown food, and are exposed to competition with the native productions. Underthese circumstances, if our domesticated animals did not undergo change ofsome kind, the result would be quite opposed to the conclusions arrived atin this work. Nevertheless, I do not doubt that the simple fact of animalsand plants becoming feral, does cause some tendency to reversion to theprimitive state; though this tendency has been much exaggerated by someauthors. {33} I will briefly run through the recorded cases. With neither horses nor cattle is the primitive stock known; and it has been shown in former chapters that they have assumed different colours in different countries. Thus the horses which have run wild in South America are generally brownish-bay, and in the East dun-coloured; their heads have become larger and coarser, and this may be due to reversion. No careful description has been given of the feral goat. Dogs which have run wild in various countries have hardly anywhere assumed a uniform character; but they are probably descended from several domestic races, and aboriginally from several distinct species. Feral cats, both in Europe and La Plata, are regularly striped; in some cases they have grown to an unusually large size, but do not differ from the domestic animal in any other character. When variously-coloured tame rabbits are turned out in Europe, they generally reacquire the colouring of the wild animal; there can be no doubt that this does really occur, but we should remember that oddly-coloured and conspicuous animals would suffer much from beasts of prey and from being easily shot; this at least was the opinion of a gentleman who tried to stock his woods with a nearly white variety; and when thus destroyed, they would in truth be supplanted by, instead of being transformed into, the common rabbit. We have seen that the feral rabbits of Jamaica, and especially of Porto Santo, have assumed new colours and other new characters. The best known case of reversion, and that on which the widely-spread belief in its universality apparently rests, is that of pigs. These animals have run wild in the West Indies, South America, and the Falkland Islands, and have everywhere acquired the dark colour, the thick bristles, and great tusks of the wild boar; and the young have reacquired longitudinal stripes. But even in the case of the pig, Roulin describes the half-wild animals in different parts of South America as differing in several respects. In Louisiana the pig[76] has run wild, and is said to differ a little in form, and much in colour, from the domestic animal, yet does not closely resemble the wild boar of Europe. With pigeons and fowls, [77] it is not known what variety was first turned out, nor what character the feral birds have assumed. The guinea-fowl in the West Indies, when feral, seems to vary more than in the domesticated state. With respect to plants run wild, Dr. Hooker[78] has strongly insisted on what slight evidence the common belief in their power of reversion rests. Godron[79] describes wild turnips, carrots, and celery; but these plants in their cultivated state hardly differ from their wild prototypes, except in the {34} succulency and enlargement of certain parts, --characters which would be surely lost by plants growing in a poor soil and struggling with other plants. No cultivated plant has run wild on so enormous a scale as the cardoon (_Cynara cardunculus_) in La Plata. Every botanist who has seen it growing there, in vast beds, as high as a horse's back, has been struck with its peculiar appearance; but whether it differs in any important point from the cultivated Spanish form, which is said not to be prickly like its American descendant, or whether it differs from he wild Mediterranean species, which is said not to be social, I do not know. * * * * * _Reversion to Characters derived from a Cross, in the case ofSub-varieties, Races, and Species. _--When an individual having somerecognizable peculiarity unites with another of the same sub-variety, nothaving the peculiarity in question, it often reappears in the descendantsafter an interval of several generations. Every one must have noticed, orheard from old people of children closely resembling in appearance ormental disposition, or in so small and complex a character as expression, one of their grandparents, or some more distant collateral relation. Verymany anomalies of structure and diseases, [80] of which instances have beengiven in the last chapter, have come into a family from one parent, andhave reappeared in the progeny after passing over two or three generations. The following case has been communicated to me on good authority, and may, I believe, be fully trusted: a pointer-bitch produced seven puppies; fourwere marked with blue and white, which is so unusual a colour with pointersthat she was thought to have played false with one of the greyhounds, andthe whole litter was condemned; but the gamekeeper was permitted to saveone as a curiosity. Two years afterwards a friend of the owner saw theyoung dog, and declared that he was the image of his old pointer-bitchSappho, the only blue and white pointer of pure descent which he had everseen. This led to close inquiry, and it was proved that he was thegreat-great-grandson of Sappho; so that, according to the commonexpression, he had only 1-16th of her blood in his veins. Here it canhardly be doubted that a character derived from a cross with an individualof the same variety reappeared after passing over three generations. {35} When two distinct races are crossed, it is notorious that the tendency inthe offspring to revert to one or both parent-forms is strong, and enduresfor many generations. I have myself seen the clearest evidence of this incrossed pigeons and with various plants. Mr. Sidney[81] states that, in alitter of Essex pigs, two young ones appeared which were the image of theBerkshire boar that had been used twenty-eight years before in giving sizeand constitution to the breed. I observed in the farmyard at Betley Hallsome fowls showing a strong likeness to the Malay breed, and was told byMr. Tollet that he had forty years before crossed his birds with Malays;and that, though he had at first attempted to get rid of this strain, hehad subsequently given up the attempt in despair, as the Malay characterwould reappear. This strong tendency in crossed breeds to revert has given rise to endlessdiscussions in how many generations after a single cross, either with adistinct breed or merely with an inferior animal, the breed may beconsidered as pure, and free from all danger of reversion. No one supposesthat less than three generations suffices, and most breeders think thatsix, seven, or eight are necessary, and some go to still greaterlengths. [82] But neither in the case of a breed which has been contaminatedby a single cross, nor when, in the attempt to form an intermediate breed, half-bred animals have been matched together during many generations, canany rule be laid down how soon the tendency to reversion will beobliterated. It depends on the difference in the strength or prepotency oftransmission in the two parent-forms, on their actual amount of difference, and on the nature of the conditions of life to which the crossed offspringare exposed. But we must be careful not to confound these cases ofreversion to characters gained from a cross, with those given under thefirst class, in which characters originally common to _both_ parents, butlost at some former period, reappear; for such characters may recur afteran almost indefinite number of generations. {36} The law of reversion is equally powerful with hybrids, when they aresufficiently fertile to breed together, or when they are repeatedly crossedwith either pure parent-form, as with mongrels. It is not necessary to giveinstances, for in the case of plants almost every one who has worked onthis subject from the time of Kölreuter to the present day has insisted onthis tendency. Gärtner has recorded some good instances; but no one hasgiven more striking cases than Naudin. [83] The tendency differs in degreeor strength in different groups, and partly depends, as we shall presentlysee, on the fact of the parent-plants having been long cultivated. Althoughthe tendency to reversion is extremely general with nearly all mongrels andhybrids, it cannot be considered as invariably characteristic of them;there is, also, reason to believe that it may be mastered by long-continuedselection; but these subjects will more properly be discussed in a futurechapter on Crossing. From what we see of the power and scope of reversion, both in pure races and when varieties or species are crossed, we may inferthat characters of almost every kind are capable of reappearance afterhaving been lost for a great length of time. But it does not follow fromthis that in each particular case certain characters will reappear: forinstance, this will not occur when a race is crossed with another endowedwith prepotency of transmission. In some few cases the power of reversionwholly fails, without our being able to assign any cause for the failure:thus it has been stated that in a French family in which 85 out of above600 members, during six generations, had been subject to night-blindness, "there has not been a single example of this affection in the children ofparents who were themselves free from it. "[84] * * * * * _Reversion through Bud-propagation--Partial Reversion, by segments in thesame flower or fruit, or in different parts of the {37} body in the sameindividual animal. _--In the eleventh chapter, many cases of reversion bybuds, independently of seminal generation, were given--as when a leaf-budon a variegated, curled, or laciniated variety suddenly reassumes itsproper character; or as when a Provence-rose appears on a moss-rose, or apeach on a nectarine-tree. In some of these cases only half the flower orfruit, or a smaller segment, or mere stripes, reassumed their formercharacter; and here we have with buds reversion by segments. Vilmorin[85]has also recorded several cases with plants derived from seed, of flowersreverting by stripes or blotches to their primitive colours: he states thatin all such cases a white or pale-coloured variety must first be formed, and, when this is propagated for a length of time by seed, stripedseedlings occasionally make their appearance; and these can afterwards bycare be multiplied by seed. The stripes and segments just referred to are not due, as far as is known, to reversion to characters derived from a cross, but to characters lost byvariation. These cases, however, as Naudin[86] insists in his discussion ondisjunction of character, are closely analogous with those given in theeleventh chapter, in which crossed plants are known to have producedhalf-and-half or striped flowers and fruit, or distinct kinds of flowers onthe same root resembling the two parent-forms. Many piebald animalsprobably come under this same head. Such cases, as we shall see in thechapter on Crossing, apparently result from certain characters not readilyblending together, and, as a consequence of this incapacity for fusion, theoffspring either perfectly resemble one of their two parents, or resembleone parent in one part and the other parent in another part; or whilstyoung are intermediate in character, but with advancing age revert whollyor by segments to either parent-form, or to both. Thus young trees of the_Cytisus adami_ are intermediate in foliage and flowers between the twoparent-forms; but when older the buds continually revert either partiallyor wholly to both forms. The cases given in the eleventh chapter on thechanges which occurred during growth {38} in crossed plants of Tropæolum, Cereus, Datura, and Lathyrus are all analogous. As however these plants arehybrids of the first generation, and as their buds after a time come toresemble their parents and not their grandparents, these cases do not atfirst appear to come under the law of reversion in the ordinary sense ofthe word; nevertheless, as the change is effected through a succession ofbud-generations on the same plant, they may be thus included. Analogous facts have been observed in the animal kingdom, and are moreremarkable, as they occur strictly in the same individual, and not as withplants through a succession of bud-generations. With animals the act ofreversion, if it can be so designated, does not pass over a truegeneration, but merely over the early stages of growth in the sameindividual. For instance, I crossed several white hens with a black cock, and many of the chickens were during the first year perfectly white, butacquired during the second year black feathers; on the other hand, some ofthe chickens which were at first black became during the second yearpiebald with white. A great breeder[87] says, that a Pencilled Brahma henwhich has any of the blood of the Light Brahma in her, will "occasionallyproduce a pullet well pencilled during the first year, but she will mostlikely moult brown on the shoulders and become quite unlike her originalcolours in the second year. " The same thing occurs with Light Brahmas if ofimpure blood. I have observed exactly similar cases with the crossedoffspring from differently coloured pigeons. But here is a more remarkablefact: I crossed a turbit, which has a frill formed by the feathers beingreversed on its breast, with a trumpeter; and one of the young pigeons thusraised showed at first not a trace of the frill, but, after moultingthrice, a small yet unmistakably distinct frill appeared on its breast. According to Girou, [88] calves produced from a red cow by a black bull, orfrom a black cow by a red bull, are not rarely born red, and subsequentlybecome black. In the foregoing cases, the characters which appear with advancing age arethe result of a cross in the previous or some {39} former generation; butin the following cases, the characters which thus reappear formerlyappertained to the species, and were lost at a more or less remote epoch. Thus, according to Azara, [89] the calves of a hornless race of cattle whichoriginated in Corrientes, though at first quite hornless, as they becomeadult sometimes acquire small, crooked, and loose horns; and these insucceeding years occasionally become attached to the skull. White and blackbantams, both of which generally breed true, sometimes assume as they growold a saffron or red plumage. For instance, a first-rate black bantam hasbeen described, which during three seasons was perfectly black, but thenannually became more and more red; and it deserves notice that thistendency to change, whenever it occurs in a bantam, "is almost certain toprove hereditary. "[90] The cuckoo or blue-mottled Dorking cock, when old, is liable to acquire yellow or orange hackles in place of his properbluish-grey hackles. [91] Now, as _Gallus bankiva_ is coloured red andorange, and as Dorking fowls and both kinds of bantams are descended fromthis species, we can hardly doubt that the change which occasionally occursin the plumage of these birds as their age advances, results from atendency in the individual to revert to the primitive type. * * * * * _Crossing as a direct cause of Reversion. _--It has long been notorious thathybrids and mongrels often revert to both or to one of their parent-forms, after an interval of from two to seven or eight, or according to someauthorities even a greater number of generations. But that the act ofcrossing in itself gives an impulse towards reversion, as shown by thereappearance of long-lost characters, has never, I believe, been hithertoproved. The proof lies in certain peculiarities, which do not characterisethe immediate parents, and therefore cannot have been derived from them, frequently appearing in the offspring of two breeds when crossed, whichpeculiarities never appear, or appear with extreme rarity, in these samebreeds, as long as they are {40} precluded from crossing. As thisconclusion seems to me highly curious and novel, I will give the evidencein detail. My attention was first called to this subject, and I was led to make numerous experiments, by MM. Boitard and Corbié having stated that, when they crossed certain breeds, pigeons coloured like the wild _C. Livia_, or the common dovecot, namely, slaty-blue, with double black wing-bars, sometimes chequered with black, white loins, the tail barred with black, with the outer feathers edged with white, were almost invariably produced. The breeds which I crossed, and the remarkable results attained, have been fully described in the sixth chapter. I selected pigeons, belonging to true and ancient breeds, which had not a trace of blue or any of the above specified marks; but when crossed, and their mongrels recrossed, young birds were continually produced, more or less plainly coloured slaty-blue, with some or all of the proper characteristic marks. I may recall to the reader's memory one case, namely, that of a pigeon, hardly distinguishable from the wild Shetland species, the grandchild of a red-spot, white fantail, and two black barbs, from any of which, when purely-bred, the production of a pigeon coloured like the wild _C. Livia_ would have been almost a prodigy. I was thus led to make the experiments, recorded in the seventh chapter, on fowls. I selected long-established, pure breeds, in which there was not a trace of red, yet in several of the mongrels feathers of this colour appeared; and one magnificent bird, the offspring of a black Spanish cock and white Silk hen, was coloured almost exactly like the wild _Gallus bankiva_. All who know anything of the breeding of poultry will admit that tens of thousands of pure Spanish and of pure white Silk fowls might have been reared without the appearance of a red feather. The fact, given on the authority of Mr. Tegetmeier, of the frequent appearance, in mongrel fowls, of pencilled or transversely-barred feathers, like those common to many gallinaceous birds, is likewise apparently a case of reversion to a character formerly possessed by some ancient progenitor of the family. I owe to the kindness of this same excellent observer the inspection of some neck-hackles and tail-feathers from a hybrid between the common fowl and a very distinct species, the _Gallus varius_; and these feathers are transversely striped in a conspicuous manner with dark metallic blue and grey, a character which could not have been derived from either immediate parent. I have been informed by Mr. B. P. Brent, that he crossed a white Aylesbury drake and a black so-called Labrador duck, both of which are true breeds, and he obtained a young drake closely like the mallard (_A. Boschas_). Of the musk-duck (_A. Moschata_, Linn. ) there are two sub-breeds, namely, white and slate-coloured; and these I am informed breed true, or nearly true. But the Rev. W. D. Fox tells me that, by putting a white drake to a slate-coloured duck, black birds, pied with white, like the wild musk-duck, were always produced. We have seen in the fourth chapter, that the so-called Himalayan rabbit, with its snow-white body, black ears, nose, tail, and feet, breeds {41} perfectly true. This race is known to have been formed by the union of two varieties of silver-grey rabbits. Now, when a Himalayan doe was crossed by a sandy-coloured buck, a silver-grey rabbit was produced; and this is evidently a case of reversion to one of the parent varieties. The young of the Himalayan rabbit are born snow-white, and the dark marks do not appear until some time subsequently; but occasionally young Himalayan rabbits are born of a light silver-grey, which colour soon disappears; so that here we have a trace of reversion, during an early period of life, to the parent-varieties, independently of any recent cross. In the third chapter is was shown that at an ancient period some breeds of cattle in the wilder parts of Britain were white with dark ears, and that the cattle now kept half wild in certain parks, and those which have run quite wild in two distant parts of the world, are likewise thus coloured. Now, an experienced breeder, Mr. J. Beasley, of Northamptonshire, [92] crossed some carefully selected West Highland cows with purely-bred shorthorn bulls. The bulls were red, red and white, or dark roan; and the Highland cows were all of a red colour, inclining to a light or yellow shade. But a considerable number of the offspring--and Mr. Beasley calls attention to this as a remarkable fact--were white, or white with red ears. Bearing in mind that none of the parents were white, and that they were purely-bred animals, it is highly probable that here the offspring reverted, in consequence of the cross, to the colour either of the aboriginal parent-species or of some ancient and half-wild parent-breed. The following case, perhaps, comes under the same head: cows in their natural state have their udders but little developed, and do not yield nearly so much milk as our domesticated animals. Now there is some reason to believe[93] that cross-bred animals between two kinds, both of which are good milkers, such as Alderneys and Shorthorns, often turn out worthless in this respect. In the chapter on the Horse reasons were assigned for believing that the primitive stock was striped and dun-coloured; and details were given, showing that in all parts of the world stripes of a dark colour frequently appear along the spine, across the legs, and on the shoulders, where they are occasionally double or treble, and even sometimes on the face and body of horses of all breeds and of all colours. But the stripes appear most frequently on the various kinds of duns. They may sometimes plainly be seen on foals, and subsequently disappear. The dun-colour and the stripes are strongly transmitted when a horse thus characterised is crossed with any other; but I was not able to prove that striped duns are generally produced from the crossing of two distinct breeds, neither of which are duns, though this does sometimes occur. The legs of the ass are often striped, and this may be considered as a reversion to the wild parent-form, the _Asinus tæniopus_ of Abyssinia, [94] which is thus striped. In the domestic animal the stripes on the shoulder are occasionally double, or forked at the extremity, as in certain zebrine {42} species. There is reason to believe that the foal is frequently more plainly striped on the legs than the adult animal. As with the horse, I have not acquired any distinct evidence that the crossing of differently-coloured varieties of the ass brings out the stripes. But now let us turn to the result of crossing the horse and ass. Although mules are not nearly so numerous in England as asses, I have seen a much greater number with striped legs, and with the stripes far more conspicuous than in either parent-form. Such mules are generally light-coloured, and might be called fallow-duns. The shoulder-stripe in one instance was deeply forked at the extremity, and in another instance was double, though united in the middle. Mr. Martin gives a figure of a Spanish mule with strong zebra-like marks on its legs, [95] and remarks, that mules are particularly liable to be thus striped on their legs. In South America, according to Roulin, [96] such stripes are more frequent and conspicuous in the mule than in the ass. In the United States, Mr. Gosse, [97] speaking of these animals, says, "that in a great number, perhaps in nine out of every ten, the legs are banded with transverse dark stripes. " Many years ago I saw in the Zoological Gardens a curious triple hybrid, from a bay mare, by a hybrid from a male ass and female zebra. This animal when old had hardly any stripes; but I was assured by the superintendent, that when young it had shoulder-stripes, and faint stripes on its flanks and legs. I mention this case more especially as an instance of the stripes being much plainer during youth than in old age. As the zebra has such conspicuously striped legs, it might have been expected that the hybrids from this animal and the common ass would have had their legs in some degree striped; but it appears from the figures given in Dr. Gray's 'Knowsley Gleanings, ' and still more plainly from that given by Geoffroy and F. Cuvier, [98] that the legs are much more conspicuously striped than the rest of the body; and this fact is intelligible only on the belief that the ass aids in giving, through the power of reversion, this character to its hybrid offspring. The quagga is banded over the whole front part of its body like a zebra, but has no stripes on its legs, or mere traces of them. But in the famous hybrid bred by Lord Morton, [99] from a chesnut, nearly purely-bred, Arabian mare, by a male quagga, the stripes were "more strongly defined and darker than those on the legs of the quagga. " The mare was subsequently put to a black Arabian horse, and bore two colts, both of which, as formerly stated, were plainly striped on the legs, and one of them likewise had stripes on the neck and body. The _Asinus Indicus_[100] is characterised by a spinal stripe, without shoulder {43} or leg stripes; but traces of these latter stripes may occasionally be seen even in the adult;[101] and Colonel S. Poole, who has had ample opportunities for observation, informs me that in the foal, when first born, the head and legs are often striped, but the shoulder-stripe is not so distinct as in the domestic ass; all these stripes, excepting that along the spine, soon disappear. Now a hybrid, raised at Knowsley[102] from a female of this species by a male domestic ass, had all four legs transversely and conspicuously striped, had three short stripes on each shoulder, and had even some zebra-like stripes on its face! Dr. Gray informs me that he has seen a second hybrid of the same parentage similarly striped. From these facts we see that the crossing of the several equine speciestends in a marked manner to cause stripes to appear on various parts of thebody, especially on the legs. As we do not know whether the primordialparent of the genus was striped, the appearance of the stripes can onlyhypothetically be attributed to reversion. But most persons, afterconsidering the many undoubted cases of variously coloured marksreappearing by reversion in crossed pigeons, fowls, ducks, &c. , will cometo the same conclusion with respect to the horse-genus; and in this case wemust admit that the progenitor of the group was striped on the legs, shoulders, face, and probably over the whole body, like a zebra. If wereject this view, the frequent and almost regular appearance of stripes inthe several foregoing hybrids is left without any explanation. * * * * * It would appear that with crossed animals a similar tendency to therecovery of lost characters holds good even with instincts. There are somebreeds of fowls which are called "everlasting layers, " because they havelost the instinct of incubation; and so rare is it for them to incubatethat I have seen notices published in works on poultry, when hens of suchbreeds have taken to sit. [103] Yet the aboriginal species was of course agood incubator; for with birds in a state of nature hardly any {44}instinct is so strong as this. Now, so many cases have been recorded of thecrossed offspring from two races, neither of which are incubators, becomingfirst-rate sitters, that the reappearance of this instinct must beattributed to reversion from crossing. One author goes so far as to say, "that a cross between two non-sitting varieties almost invariably producesa mongrel that becomes broody, and sits with remarkable steadiness. "[104]Another author, after giving a striking example, remarks that the fact canbe explained only on the principle that "two negatives make a positive. " Itcannot, however, be maintained that hens produced from a cross between twonon-sitting breeds invariably recover their lost instinct, any more thanthat crossed fowls or pigeons invariably recover the red or blue plumage oftheir prototypes. I raised several chickens from a Polish hen by a Spanishcock, --breeds which do not incubate, --and none of the young hens at firstrecovered their instinct, and this appeared to afford a well-markedexception to the foregoing rule; but one of these hens, the only one whichwas preserved, in the third year sat well on her eggs and reared a brood ofchickens. So that here we have the appearance with advancing age of aprimitive instinct, in the same manner as we have seen that the red plumageof the _Gallus bankiva_ is sometimes reacquired by crossed and purely-bredfowls of various kinds as they grow old. The parents of all our domesticated animals were of course aboriginallywild in disposition; and when a domesticated species is crossed with adistinct species, whether this is a domesticated or only tamed animal, thehybrids are often wild {45} to such a degree, that the fact is intelligibleonly on the principle that the cross has caused a partial return to theprimitive disposition. The Earl of Powis formerly imported some thoroughly domesticated humpedcattle from India, and crossed them with English breeds, which belong to adistinct species; and his agent remarked to me, without any question havingbeen asked, how oddly wild the cross-bred animals were. The European wildboar and the Chinese domesticated pig are almost certainly specificallydistinct: Sir F. Darwin crossed a sow of the latter breed with a wildAlpine boar which had become extremely tame, but the young, though havinghalf-domesticated blood in their veins, were "extremely wild inconfinement, and would not eat swill like common English pigs. " Mr. Hewitt, who has had great experience in crossing tame cock-pheasants with fowlsbelonging to five breeds, gives as the character of all "extraordinarywildness;"[105] but I have myself seen one exception to this rule. Mr. S. J. Salter, [106] who raised a large number of hybrids from a bantam-henby _Gallus Sonneratii_, states that "all were exceedingly wild. " Mr. Waterton[107] bred some wild ducks from eggs hatched under a common duck, and the young were allowed to cross freely both amongst themselves and withthe tame ducks; they were "half wild and half tame; they came to thewindows to be fed, but still they had a wariness about them quiteremarkable. " On the other hand, mules from the horse and ass are certainly not in theleast wild, yet they are notorious for obstinacy and vice. Mr. Brent, whohas crossed canary-birds with many kinds of finches, has not observed, ashe informs me, that the hybrids were in any way remarkably wild. Hybridsare often raised between the common and musk duck, and I have been assuredby three persons, who have kept these crossed birds, that they were notwild; but Mr. Garnett[108] observed that his female hybrids exhibited"migratory propensities, " of which there is not a vestige in the common ormusk duck. No case is {46} known of this latter bird having escaped andbecome wild in Europe or Asia, except, according to Pallas, on the CaspianSea; and the common domestic duck only occasionally becomes wild indistricts where large lakes and fens abound. Nevertheless, a large numberof cases have been recorded[109] of hybrids from these two ducks, althoughso few are reared in comparison with purely-bred birds of either species, having been shot in a completely wild state. It is improbable that any ofthese hybrids could have acquired their wildness from the musk-duck havingpaired with a truly wild duck; and this is known not to be the case inNorth America; hence we must infer that they have reacquired, throughreversion, their wildness, as well as renewed powers of flight. These latter facts remind us of the statements, so frequently made bytravellers in all parts of the world, on the degraded state and savagedisposition of crossed races of man. That many excellent and kind-heartedmulattos have existed no one will dispute; and a more mild and gentle setof men could hardly be found than the inhabitants of the island of Chiloe, who consist of Indians commingled with Spaniards in various proportions. Onthe other hand, many years ago, long before I had thought of the presentsubject, I was struck with the fact that, in South America, men ofcomplicated descent between Negroes, Indians, and Spaniards, seldom had, whatever the cause might be, a good expression. [110] Livingstone, --and amore unimpeachable authority cannot be quoted, --after speaking of ahalf-caste man on the Zambesi, described by the Portuguese as a raremonster of inhumanity, remarks, "It is unaccountable why half-castes, suchas he, are so much more cruel than the Portuguese, but such is undoubtedlythe case. " An inhabitant remarked to Livingstone, "God made white men, andGod made black men, but the Devil made half-castes. "[111] When two races, both {47} low in the scale, are crossed, the progeny seems to be eminentlybad. Thus the noble-hearted Humboldt, who felt none of that prejudiceagainst the inferior races now so current in England, speaks in strongterms of the bad and savage disposition of Zambos, or half-castes betweenIndians and Negroes; and this conclusion has been arrived at by variousobservers. [112] From these facts we may perhaps infer that the degradedstate of so many half-castes is in part due to reversion to a primitive andsavage condition, induced by the act of crossing, as well as to theunfavourable moral conditions under which they generally exist. * * * * * _Summary on the proximate causes leading to Reversion. _--When purely-bredanimals or plants reassume long-lost characters, --when the common ass, forinstance, is born with striped legs, when a pure race of black or whitepigeons throws a slaty-blue bird, or when a cultivated heartsease withlarge and rounded flowers produces a seedling with small and elongatedflowers, --we are quite unable to assign any proximate cause. When animalsrun wild, the tendency to reversion, which, though it has been greatlyexaggerated, no doubt exists, is sometimes to a certain extentintelligible. Thus, with feral pigs, exposure to the weather will probablyfavour the growth of the bristles, as is known to be the case with the hairof other domesticated animals, and through correlation the tusks will tendto be redeveloped. But the reappearance of coloured longitudinal stripes onyoung feral pigs cannot be attributed to the direct action of externalconditions. In this case, and in many others, we can only say that changedhabits of life apparently have favoured a tendency, inherent or latent inthe species, to return to the primitive state. It will be shown in a future chapter that the position of flowers on thesummit of the axis, and the position of seeds within the capsule, sometimesdetermine a tendency towards reversion; and this apparently depends on theamount of sap or nutriment which the flower-buds and seeds receive. Theposition, also, of buds, either on branches or on roots, sometimesdetermines, as was formerly shown, the transmission of the {48} propercharacter of the variety, or its reversion to a former state. We have seen in the last section that when two races or species are crossedthere is the strongest tendency to the reappearance in the offspring oflong-lost characters, possessed by neither parent nor immediate progenitor. When two white, or red, or black pigeons, of well-established breeds, areunited, the offspring are almost sure to inherit the same colours; but whendifferently-coloured birds are crossed, the opposed forces of inheritanceapparently counteract each other, and the tendency which is inherent inboth parents to produce slaty-blue offspring becomes predominant. So it isin several other cases. But when, for instance, the ass is crossed with _A. Indicus_ or with the horse, --animals which have not striped legs, --and thehybrids have conspicuous stripes on their legs and even on their faces, allthat can be said is, that an inherent tendency to reversion is evolvedthrough some disturbance in the organisation caused by the act of crossing. Another form of reversion is far commoner, indeed is almost universal withthe offspring from a cross, namely, to the characters proper to either pureparent-form. As a general rule, crossed offspring in the first generationare nearly intermediate between their parents, but the grandchildren andsucceeding generations continually revert, in a greater or lesser degree, to one or both of their progenitors. Several authors have maintained thathybrids and mongrels include all the characters of both parents, not fusedtogether, but merely mingled in different proportions in different parts ofthe body; or, as Naudin[113] has expressed it, a hybrid is a livingmosaic-work, in which the eye cannot distinguish the discordant elements, so completely are they intermingled. We can hardly doubt that, in a certainsense, this is true, as when we behold in a hybrid the elements of bothspecies segregating themselves into segments in the same flower or fruit, by a process of self-attraction or self-affinity; this segregation takingplace either by seminal or by bud-propagation. Naudin further believes thatthe segregation of the two specific elements or essences is eminentlyliable to occur in the male and female reproductive matter; and he thusexplains the almost {49} universal tendency to reversion in successivehybrid generations. For this would be the natural result of the union ofpollen and ovules, in both of which the elements of the same species hadbeen segregated by self-affinity. If, on the other hand, pollen whichincluded the elements of one species happened to unite with ovulesincluding the elements of the other species, the intermediate or hybridstate would still be retained, and there would be no reversion. But itwould, as I suspect, be more correct to say that the elements of bothparent-species exist in every hybrid in a double state, namely, blendedtogether and completely separate. How this is possible, and what the termspecific essence or element may be supposed to express, I shall attempt toshow in the hypothetical chapter on pangenesis. But Naudin's view, as propounded by him, is not applicable to thereappearance of characters lost long ago by variation; and it is hardlyapplicable to races or species which, after having been crossed at someformer period with a distinct form, and having since lost all traces of thecross, nevertheless occasionally yield an individual which reverts (as inthe case of the great-great-grandchild of the pointer Sappho) to thecrossing form. The most simple case of reversion, namely, of a hybrid ormongrel to its grandparents, is connected by an almost perfect series withthe extreme case of a purely-bred race recovering characters which had beenlost during many ages; and we are thus led to infer that all the cases mustbe related by some common bond. Gärtner believed that only those hybrid plants which are highly sterileexhibit any tendency to reversion to their parent-forms. It is rash todoubt so good an observer, but this conclusion must I think be an error;and it may perhaps be accounted for by the nature of the genera observed byhim, for he admits that the tendency differs in different genera. Thestatement is also directly contradicted by Naudin's observations, and bythe notorious fact that perfectly fertile mongrels exhibit the tendency ina high degree, --even in a higher degree, according to Gärtner himself, thanhybrids. [114] Gärtner further states that reversions rarely occur with {50} hybrid plantsraised from species which have not been cultivated, whilst, with thosewhich have been long cultivated, they are of frequent occurrence. Thisconclusion explains a curious discrepancy: Max Wichura, [115] who workedexclusively on willows, which had not been subjected to culture, never sawan instance of reversion; and he goes so far as to suspect that the carefulGärtner had not sufficiently protected his hybrids from the pollen of theparent-species: Naudin, on the other hand, who chiefly experimented oncucurbitaceous and other cultivated plants, insists more strenuously thanany other author on the tendency to reversion in all hybrids. Theconclusion that the condition of the parent-species, as affected byculture, is one of the proximate causes leading to reversion, agrees fairlywell with the converse case of domesticated animals and cultivated plantsbeing liable to reversion when they become feral; for in both cases theorganisation or constitution must be disturbed, though in a very differentway. Finally, we have seen that characters often reappear in purely-bred raceswithout our being able to assign any proximate cause; but when they becomeferal this is either indirectly or directly induced by the change in theirconditions of life. With crossed breeds, the act of crossing in itselfcertainly leads to the recovery of long-lost characters, as well as ofthose derived from either parent-form. Changed conditions, consequent oncultivation, and the relative position of buds, flowers, and seeds on theplant, all apparently aid in giving this same tendency. Reversion may occureither through seminal or bud generation, generally at birth, but sometimesonly with an advance of age. Segments or portions of the individual mayalone be thus affected. That a being should be born resembling in certaincharacters an ancestor removed by two or three, and in some cases byhundreds or even thousands of generations, is assuredly a wonderful fact. In these cases the child is commonly said to inherit such charactersdirectly from its grandparents or more remote ancestors. But this view ishardly conceivable. If, however, we suppose that every character is derived{51} exclusively from the father or mother, but that many characters lielatent in both parents during a long succession of generations, theforegoing facts are intelligible. In what manner characters may beconceived to lie latent, will be considered in a future chapter to which Ihave lately alluded. * * * * * _Latent Characters. _--But I must explain what is meant by characters lyinglatent. The most obvious illustration is afforded by secondary sexualcharacters. In every female all the secondary male characters, and in everymale all the secondary female characters, apparently exist in a latentstate, ready to be evolved under certain conditions. It is well known thata large number of female birds, such as fowls, various pheasants, partridges, peahens, ducks, &c. , when old or diseased, or when operated on, partly assume the secondary male characters of their species. In the caseof the hen-pheasant this has been observed to occur far more frequentlyduring certain seasons than during others. [116] A duck ten years old hasbeen known to assume both the perfect winter and summer plumage of thedrake. [117] Waterton[118] gives a curious case of a hen which had ceasedlaying, and had assumed the plumage, voice, spurs, and warlike dispositionof the cock; when opposed to an enemy she would erect her hackles and showfight. Thus every character, even to the instinct and manner of fighting, must have lain dormant in this hen as long as her ovaria continued to act. The females of two kinds of deer, when old, have been known to acquirehorns; and, as Hunter has remarked, we see something of an analogous naturein the human species. On the other hand, with male animals, it is notorious that the secondarysexual characters are more or less completely lost when they are subjectedto castration. Thus, if the operation be performed on a young cock, henever, as Yarrell states, crows {52} again; the comb, wattles, and spurs donot grow to their full size, and the hackles assume an intermediateappearance between true hackles and the feathers of the hen. Cases arerecorded of confinement alone causing analogous results. But charactersproperly confined to the female are likewise acquired; the capon takes tositting on eggs, and will bring up chickens; and what is more curious, theutterly sterile male hybrids from the pheasant and the fowl act in the samemanner, "their delight being to watch when the hens leave their nests, andto take on themselves the office of a sitter. "[119] That admirable observerRéaumur[120] asserts that a cock, by being long confined in solitude anddarkness, can be taught to take charge of young chickens; he then utters apeculiar cry, and retains during his whole life this newly acquiredmaternal instinct. The many well-ascertained cases of various male mammalsgiving milk, show that their rudimentary mammary glands retain thiscapacity in a latent condition. We thus see that in many, probably in all cases, the secondary charactersof each sex lie dormant or latent in the opposite sex, ready to be evolvedunder peculiar circumstances. We can thus understand how, for instance, itis possible for a good milking cow to transmit her good qualities throughher male offspring to future generations; for we may confidently believethat these qualities are present, though latent, in the males of eachgeneration. So it is with the game-cock, who can transmit his superiorityin courage and vigour through his female to his male offspring; and withman it is known [121] that diseases, such as hydrocele, necessarilyconfined to the male sex, can be transmitted through the female to thegrandson. Such cases as these offer, as was remarked at the commencement ofthis chapter, the simplest possible examples of reversion; and they areintelligible on the belief that characters common to the grandparent andgrandchild of the same sex are present, though latent, in the intermediateparent of the opposite sex. The subject of latent characters is so important, as we shall see in afuture chapter, that I will give another illustration. {53} Many animalshave the right and left sides of their body unequally developed: this iswell known to be the case with flat-fish, in which the one side differs inthickness and colour, and in the shape of the fins, from the other; andduring the growth of the young fish one eye actually travels, as shown bySteenstrup, from the lower to the upper surface. [122] In most flat-fishesthe left is the blind side, but in some it is the right; though in bothcases "wrong fishes, " which are developed in a reversed manner to what isusual, occasionally occur, and in _Platessa flesus_ the right or left sideis indifferently developed, the one as often as the other. With gasteropodsor shell-fish, the right and left sides are extremely unequal; the fargreater number of species are dextral, with rare and occasional reversalsof development, and some few are normally sinistral; but certain species ofBulimus, and, many Achatinellæ, [123] are as often sinistral as dextral. Iwill give an analogous case in the great Articulate kingdom: the two sidesof Verruca[124] are so wonderfully unlike, that without careful dissectionit is extremely difficult to recognise the corresponding parts on theopposite sides of the body; yet it is apparently a mere matter of chancewhether it be the right or the left side that undergoes so singular anamount of change. One plant is known to me[125] in which the flower, according as it stands on the one or other side of the spike, is unequallydeveloped. In all the foregoing cases the two sides of the animal areperfectly symmetrical at an early period of growth. Now, whenever a speciesis as liable to be unequally developed on the one as on the other side, wemay infer that the capacity for such development is present, though latent, in the undeveloped side. And as a reversal of development occasionallyoccurs in animals of many kinds, this latent capacity is probably verycommon. The best yet simplest instances of characters lying dormant are, perhaps, those previously given, in which chickens and {54} young pigeons, raisedfrom a cross between differently coloured birds, are at first of onecolour, but in a year or two acquire feathers of the colour of the otherparent; for in this case the tendency to a change of plumage is clearlylatent in the young bird. So it is with hornless breeds of cattle, some ofwhich acquire, as they grow old, small horns. Purely bred black and whitebantams, and some other fowls, occasionally assume, with advancing years, the red feathers of the parent-species. I will here add a somewhatdifferent case, as it connects in a striking manner latent characters oftwo classes. Mr. Hewitt[126] possessed an excellent Sebright gold-laced henbantam, which, as she became old, grew diseased in her ovaria, and assumedmale characters. In this breed the males resemble the females in allrespects except in their combs, wattles, spurs, and instincts; hence itmight have been expected that the diseased hen would have assumed onlythose masculine characters which are proper to the breed, but she acquired, in addition, well-arched tail sickle-feathers quite a foot in length, saddle-feathers on the loins, and hackles on the neck, --ornaments which, asMr. Hewitt remarks, "would be held as abominable in this breed. " TheSebright bantam is known[127] to have originated about the year 1800 from across between a common bantam and a Polish fowl, recrossed by a hen-tailedbantam, and carefully selected; hence there can hardly be a doubt that thesickle-feathers and hackles which appeared in the old hen were derived fromthe Polish fowl or common bantam; and we thus see that not only certainmasculine characters proper to the Sebright bantam, but other masculinecharacters derived from the first progenitors of the breed, removed by aperiod of above sixty years, were lying latent in this hen-bird, ready tobe evolved as soon as her ovaria became diseased. From these several facts it must be admitted that certain characters, capacities, and instincts may lie latent in an individual, and even in asuccession of individuals, without our being able to detect the least signsof their presence. We have {55} already seen that the transmission of acharacter from the grandparent to the grandchild, with its apparentomission in the intermediate parent of the opposite sex, becomes simple onthis view. When fowls, pigeons, or cattle of different colours are crossed, and their offspring change colour as they grow old, or when the crossedturbit acquired the characteristic frill after its third moult, or whenpurely-bred bantams partially assume the red plumage of their prototype, wecannot doubt that these qualities were from the first present, thoughlatent, in the individual animal, like the characters of a moth in thecaterpillar. Now, if these animals had produced offspring before they hadacquired with advancing age their new characters, nothing is more probablethan that they would have transmitted them to some of their offspring, which in this case would in appearance have received such characters fromtheir grandparents or more distant progenitors. We should then have had acase of reversion, that is, of the reappearance in the child of anancestral character, actually present, though during youth completelylatent, in the parent; and this we may safely conclude is what occurs withreversions of all kinds to progenitors however remote. This view of the latency in each generation of all the characters whichappear through reversion, is also supported by their actual presence insome cases during early youth alone, or by their more frequent appearanceand greater distinctness at this age than during maturity. We have seenthat this is often the case with the stripes on the legs and faces of theseveral species of the horse-genus. The Himalayan rabbit, when crossed, sometimes produces offspring which revert to the parent silver-grey breed, and we have seen that in purely bred animals pale-grey fur occasionallyreappears during early youth. Black cats, we may feel assured, wouldoccasionally produce by reversion tabbies; and on young black kittens, witha pedigree[128] known to have been long pure, faint traces of stripes mayalmost always be seen which afterwards disappear. Hornless Suffolk cattleoccasionally produce by reversion horned animals; and Youatt[129] assertsthat even in hornless individuals {56} "the rudiment of a horn may be oftenfelt at an early age. " No doubt it appears at first sight in the highest degree improbable that inevery horse of every generation there should be a latent capacity andtendency to produce stripes, though these may not appear once in a thousandgenerations; that in every white, black, or other coloured pigeon, whichmay have transmitted its proper colour during centuries, there should be alatent capacity in the plumage to become blue and to be marked with certaincharacteristic bars; that in every child in a six-fingered family thereshould be the capacity for the production of an additional digit; and so inother cases. Nevertheless there is no more inherent improbability in thisbeing the case than in a useless and rudimentary organ, or even in only atendency to the production of a rudimentary organ, being inherited duringmillions of generations, as is well known to occur with a multitude oforganic beings. There is no more inherent improbability in each domesticpig, during a thousand generations, retaining the capacity and tendency todevelop great tusks under fitting conditions, than in the young calf havingretained for an indefinite number of generations rudimentary incisor teeth, which never protrude through the gums. I shall give at the end of the next chapter a summary of the threepreceding chapters; but as isolated and striking cases of reversion havehere been chiefly insisted on, I wish to guard the reader against supposingthat reversion is due to some rare or accidental combination ofcircumstances. When a character, lost during hundreds of generations, suddenly reappears, no doubt some such combination must occur; butreversions may be constantly observed, at least to the immediatelypreceding generations, in the offspring of most unions. This has beenuniversally recognised in the case of hybrids and mongrels, but it has beenrecognised simply from the difference between the united forms renderingthe resemblance of the offspring to their grandparents or more remoteprogenitors of easy detection. Reversion is likewise almost invariably therule, as Mr. Sedgwick has shown, with certain diseases. Hence we mustconclude that a tendency to this peculiar form of transmission is anintegral part of the general law of inheritance. {57} * * * * * _Monstrosities. _--A large number of monstrous growths and of lesseranomalies are admitted by every one to be due to an arrest of development, that is to the persistence of an embryonic condition. If every horse or asshad striped legs whilst young, the stripes which occasionally appear onthese animals when adult would have to be considered as due to theanomalous retention of an early character, and not as due to reversion. Now, the leg-stripes in the horse-genus, and some other characters inanalogous cases, are apt to occur during early youth and then to disappear;thus the persistence of early characters and reversion are brought intoclose connexion. But many monstrosities can hardly be considered as the result of an arrestof development; for parts of which no trace can be detected in the embryo, but which occur in other members of the same class of animals or plants, occasionally appear, and these may probably with truth be attributed toreversion. For instance: supernumerary mammæ, capable of secreting milk, are not extremely rare in women; and as many as five have been observed. When four are developed, they are generally arranged symmetrically on eachside of the chest; and in one instance a woman (the daughter of anotherwith supernumerary mammæ) had one mamma, which yielded milk, developed inthe inguinal region. This latter case, when we remember the position of themammæ in some of the lower animals on both the chest and inguinal region, is highly remarkable, and leads to the belief that in all cases theadditional mammæ in woman are due to reversion. The facts given in the lastchapter on the tendency in supernumerary digits to regrowth afteramputation, indicate their relation to the digits of the lower vertebrateanimals, and lead to the suspicion that their appearance may in some mannerbe connected with reversion. But I shall have to recur, in the chapter onpangenesis, to the abnormal multiplication of organs, and likewise to theiroccasional transposition. The occasional development in man of thecoccygeal vertebræ into a short and free tail, though it thus becomes inone sense more perfectly developed, may at the same time be considered asan arrest of development, and as a case of reversion. The greater frequencyof a monstrous kind of proboscis in the pig than in any other mammal, considering the position of the pig {58} in the mammalian series, haslikewise been attributed, perhaps truly, to reversion. [130] When flowers which are properly irregular in structure become regular or peloric, the change is generally looked at by botanists as a return to the primitive state. But Dr. Maxwell Masters, [131] who has ably discussed this subject, remarks that when, for instance, all the sepals of a Tropæolum become green and of the same shape, instead of being coloured with one alone prolonged into a spur, or when all the petals of a Linaria become simple and regular, such cases may be due merely to an arrest of development; for in these flowers all the organs during their earliest condition are symmetrical, and, if arrested at this stage of growth, they would not become irregular. If, moreover, the arrest were to take place at a still earlier period of development, the result would be a simple tuft of green leaves; and no one probably would call this a case of reversion. Dr. Masters designates the cases first alluded to as regular peloria; and others, in which all the corresponding parts assume a similar form of irregularity, as when all the petals in a Linaria become spurred, as irregular peloria. We have no right to attribute these latter cases to reversion, until it can be shown to be probable that the parent-form, for instance, of the genus Linaria had had all its petals spurred; for a change of this nature might result from the spreading of an anomalous structure, in accordance with the law, to be discussed in a future chapter, of homologous parts tending to vary in the same manner. But as both forms of peloria frequently occur on the same individual plant of the Linaria, [132] they probably stand in some close relation to each other. On the doctrine that peloria is simply the result of an arrest of development, it is difficult to understand how an organ arrested at a very early period of growth should acquire its full functional perfection;--how a petal, supposed to be thus arrested, should acquire its brilliant colours, and serve as an envelope to the flower, or a stamen produce efficient pollen; yet this occurs with many peloric flowers. That pelorism is not due to mere chance variability, but either to an arrest of development or to reversion, we may infer from an observation made by Ch. Morren, [133] namely, that families which have irregular flowers often "return by these monstrous growths to their regular form; whilst we never see a regular flower realise the structure of an irregular one. " Some flowers have almost certainly become more or less completely peloric through reversion. _Corydalis tuberosa_ properly has one of its two nectaries colourless, destitute of nectar, only half the size of the other, and {59} therefore, to a certain extent, in a rudimentary state; the pistil is curved towards the perfect nectary, and the hood, formed of the inner petals, slips off the pistil and stamens in one direction alone, so that, when a bee sucks the perfect nectary, the stigma and stamens are exposed and rubbed against the insect's body. In several closely allied genera, as in Dielytra, &c. , there are two perfect nectaries, the pistil is straight, and the hood slips off on either side, according as the bee sucks either nectary. Now, I have examined several flowers of _Corydalis tuberosa_, in which both nectaries were equally developed and contained nectar; in this we see only the redevelopment of a partially aborted organ; but with this redevelopment the pistil becomes straight, and the hood slips off in either direction; so that these flowers have acquired the perfect structure, so well adapted for insect agency, of Dielytra and its allies. We cannot attribute these coadapted modifications to chance, or to correlated variability; we must attribute them to reversion to a primordial condition of the species. The peloric flowers of Pelargonium have their five petals in all respects alike, and there is no nectary; so that they resemble the symmetrical flowers of the closely allied Geranium-genus; but the alternate stamens are also sometimes destitute of anthers, the shortened filaments being left as rudiments, and in this respect they resemble the symmetrical flowers of the closely allied genus, Erodium. Hence we are led to look at the peloric flowers of Pelargonium as having probably reverted to the state of some primordial form, the progenitor of the three closely related genera of Pelargonium, Geranium, and Erodium. In the peloric form of _Antirrhinum majus_, appropriately called the "_Wonder_, " the tubular and elongated flowers differ wonderfully from those of the common snapdragon; the calyx and the mouth of the corolla consist of six equal lobes, and include six equal instead of four unequal stamens. One of the two additional stamens is manifestly formed by the development of a microscopically minute papilla, which may be found at the base of the upper lip of the flower in all common snapdragons, at least in nineteen plants examined by me. That this papilla is a rudiment of a stamen was well shown by its various degrees of development in crossed plants between the common and peloric Antirrhinum. Again, a peloric _Galeobdolon luteum_, growing in my garden, had five equal petals, all striped like the ordinary lower lip, and included five equal instead of four unequal stamens; but Mr. R. Keeley, who sent me this plant, informs me that the flowers vary greatly, having from four to six lobes to the corolla, and from three to six stamens. [134] Now, as the members of the two great families to which the Antirrhinum and Galeobdolon belong are properly pentamerous, with some of the parts confluent and others suppressed, we ought not to look at the sixth stamen and the sixth lobe to the corolla in either case as due to reversion, any more than the additional petals in double flowers in these same two families. But the case is different with the fifth stamen in the peloric Antirrhinum, which {60} is produced by the redevelopment of a rudiment always present, and which probably reveals to us the state of the flower, as far as the stamens are concerned, at some ancient epoch. It is also difficult to believe that the other four stamens and the petals, after an arrest of development at a very early embryonic age, would have come to full perfection in colour, structure, and function, unless these organs had at some former period normally passed through a similar course of growth. Hence it appears to me probable that the progenitor of the genus Antirrhinum must at some remote epoch have included five stamens and borne flowers in some degree resembling those now produced by the peloric form. Lastly, I may add that many instances have been recorded of flowers, not generally ranked as peloric, in which certain organs, normally few in number, have been abnormally augmented. As such an increase of parts cannot be looked at as an arrest of development, nor as due to the redevelopment of rudiments, for no rudiments are present, and as these additional parts bring the plant into closer relationship with its natural allies, they ought probably to be viewed as reversions to a primordial condition. These several facts show us in an interesting manner how intimately certainabnormal states are connected together; namely, arrests of developmentcausing parts to become rudimentary or to be wholly suppressed, --theredevelopment of parts at present in a more or less rudimentarycondition, --the reappearance of organs of which not a vestige can now bedetected, --and to these may be added, in the case of animals, the presenceduring youth, and subsequent disappearance, of certain characters whichoccasionally are retained throughout life. Some naturalists look at allsuch abnormal structures as a return to the ideal state of the group towhich the affected being belongs; but it is difficult to conceive what ismeant to be conveyed by this expression. Other naturalists maintain, withgreater probability and distinctness of view, that the common bond ofconnection between the several foregoing cases is an actual, thoughpartial, return to the structure of the ancient progenitor of the group. Ifthis view be correct, we must believe that a vast number of characters, capable of evolution, lie hidden in every organic being. But it would be amistake to suppose that the number is equally great in all beings. We know, for instance, that plants of many orders occasionally become peloric; butmany more cases have been observed in the Labiatæ and Scrophulariaceæ thanin any other order; and in one genus of the Scrophulariaceæ, namelyLinaria, no less {61} than thirteen species have been described in apeloric condition. [135] On this view of the nature of peloric flowers, andbearing in mind what has been said with respect to certain monstrosities inthe animal kingdom, we must conclude that the progenitors of most plantsand animals, though widely different in structure, have left an impressioncapable of redevelopment on the germs of their descendants. The fertilised germ of one of the higher animals, subjected as it is to sovast a series of changes from the germinal cell to old age, --incessantlyagitated by what Quatrefages well calls the _tourbillon vital_, --is perhapsthe most wonderful object in nature. It is probable that hardly a change ofany kind affects either parent, without some mark being left on the germ. But on the doctrine of reversion, as given in this chapter, the germbecomes a far more marvellous object, for, besides the visible changes towhich it is subjected, we must believe that it is crowded with invisiblecharacters, proper to both sexes, to both the right and left side of thebody, and to a long line of male and female ancestors separated by hundredsor even thousands of generations from the present time; and thesecharacters, like those written on paper with invisible ink, all lie readyto be evolved under certain known or unknown conditions. * * * * * {62} CHAPTER XIV. INHERITANCE _continued_--FIXEDNESS OF CHARACTER--PREPOTENCY--SEXUALLIMITATION--CORRESPONDENCE OF AGE. FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF INHERITANCE--PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY, IN CROSSED BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER; SOMETIMES DUE TO THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE BREED AND LATENT IN THE OTHER--INHERITANCE AS LIMITED BY SEX--NEWLY-ACQUIRED CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE SEX ALONE, SOMETIMES LOST BY ONE SEX ALONE--INHERITANCE AT CORRESPONDING PERIODS OF LIFE--THE IMPORTANCE OF THE PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS EXHIBITED IN DOMESTICATED ANIMALS; AS EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF INHERITED DISEASES; SOMETIMES SUPERVENING EARLIER IN THE CHILD THAN IN THE PARENT--SUMMARY OF THE THREE PRECEDING CHAPTERS. In the two last chapters the nature and force of Inheritance, thecircumstances which interfere with its power, and the tendency toReversion, with its many remarkable contingencies, were discussed. In thepresent chapter some other related phenomena will be treated of, as fullyas my materials permit. _Fixedness of Character. _ It is a general belief amongst breeders that the longer any character hasbeen transmitted by a breed, the more firmly it will continue to betransmitted. I do not wish to dispute the truth of the proposition, thatinheritance gains strength simply through long continuance, but I doubtwhether it can be proved. In one sense the proposition is little betterthan a truism; if any character has remained constant during manygenerations, it will obviously be little likely, the conditions of liferemaining the same, to vary during the next generation. So, again, inimproving a breed, if care be taken for a length of time to exclude allinferior individuals, the breed will obviously tend to become truer, as itwill not have been crossed during many generations by an inferior animal. We have previously seen, {63} but without being able to assign any cause, that, when a new character appears, it is occasionally from the first wellfixed, or fluctuates much, or wholly fails to be transmitted. So it is withthe aggregate of slight differences which characterise a new variety, forsome propagate their kind from the first much truer than others. Even withplants multiplied by bulbs, layers, &c. , which may in one sense be said toform parts of the same individual, it is well known that certain varietiesretain and transmit through successive bud-generations their newly-acquiredcharacters more truly than others. In none of these, nor in the followingcases, does there appear to be any relation between the force with which acharacter is transmissible and the length of time during which it hasalready been transmitted. Some varieties, such as white and yellowhyacinths and white sweet-peas, transmit their colours more faithfully thando the varieties which have retained their natural colour. In the Irishfamily, mentioned in the twelfth chapter, the peculiar tortoiseshell-likecolouring of the eyes was transmitted far more faithfully than any ordinarycolour. Ancon and Mauchamp sheep and niata cattle, which are allcomparatively modern breeds, exhibit remarkably strong powers ofinheritance. Many similar cases could be adduced. As all domesticated animals and cultivated plants have varied, and yet aredescended from aboriginally wild forms, which no doubt had retained thesame character from an immensely remote epoch, we see that scarcely anydegree of antiquity ensures a character being transmitted perfectly true. In this case, however, it may be said that changed conditions of lifeinduce certain modifications, and not that the power of inheritance fails;but in every case of failure, some cause, either internal or external, mustinterfere. It will generally be found that the parts in our domesticatedproductions which have varied, or which still continue to vary, --that is, which fail to retain their primordial state, --are the same with the partswhich differ in the natural species of the same genus. As, on the theory ofdescent with modification, the species of the same genus have been modifiedsince they branched off from a common progenitor, it follows that thecharacters by which they differ from each other have varied whilst otherparts of the organisation have remained unchanged; and it might be arguedthat {64} these same characters now vary under domestication, or fail to beinherited, owing to their lesser antiquity. But we must believe structures, which have already varied, would be more liable to go on varying, ratherthan structures which during an immense lapse of time have remainedunaltered; and this variation is probably the result of certain relationsbetween the conditions of life and the organisation, quite independently ofthe greater or less antiquity of each particular character. Fixedness of character, or the strength of inheritance, has often beenjudged of by the preponderance of certain characters in the crossedoffspring between distinct races; but prepotency of transmission here comesinto play, and this, as we shall immediately see, is a very differentconsideration from the strength or weakness of inheritance. It has oftenbeen observed[136] that breeds of animals inhabiting wild and mountainouscountries cannot be permanently modified by our improved breeds; and asthese latter are of modern origin, it has been thought that the greaterantiquity of the wilder breeds has been the cause of their resistance toimprovement by crossing; but it is more probably due to their structure andconstitution being better adapted to the surrounding conditions. Whenplants are first subjected to culture, it has been found that, duringseveral generations, they transmit their characters truly, that is, do notvary, and this has been attributed to ancient characters being stronglyinherited; but it may with equal or greater probability be consequent onchanged conditions of life requiring a long time for their accumulativeaction. Notwithstanding these considerations, it would perhaps be rash todeny that characters become more strongly fixed the longer they aretransmitted; but I believe that the proposition resolves itself intothis, --that all characters of all kinds, whether new or old, tend to beinherited, and that those which have already withstood all counteractinginfluences and been truly transmitted, will, as a general rule, continue towithstand them, and consequently be faithfully inherited. {65} _Prepotency in the Transmission of Character. _ When individuals distinct enough to be recognised, but of the same family, or when two well-marked races, or two species, are crossed, the usualresult, as stated in the previous chapter, is, that the offspring in thefirst generation are intermediate between their parents, or resemble oneparent in one part and the other parent in another part. But this is by nomeans the invariable rule; for in many cases it is found that certainindividuals, races, and species are prepotent in transmitting theirlikeness. This subject has been ably discussed by Prosper Lucas, [137] butis rendered extremely complicated by the prepotency sometimes runningequally in both sexes, and sometimes more strongly in one sex than in theother; it is likewise complicated by the presence of secondary sexualcharacters, which render the comparison of mongrels with theirparent-breeds difficult. It would appear that in certain families some one ancestor, and after himothers in the same family, must have had great power in transmitting theirlikeness through the male line; for we cannot otherwise understand how thesame features should so often be transmitted after marriages with variousfemales, as has been the case with the Austrian Emperors, and as, accordingto Niebuhr, formerly occurred in certain Roman families with their mentalqualities. [138] The famous bull Favourite is believed[139] to have had aprepotent influence on the shorthorn race. It has also been observed[140]with English race-horses that certain mares have generally transmittedtheir own character, whilst other mares of equally pure blood have allowedthe character of the sire to prevail. The truth of the principle of prepotency comes out more clearly when certain races are crossed. The improved Shorthorns, notwithstanding that the breed is comparatively modern, are generally acknowledged to possess great power in impressing their likeness on all other breeds; and it is chiefly in consequence of this power that they are so highly valued {66} for exportation. [141] Godine has given a curious case of a ram of a goat-like breed of sheep from the Cape of Good Hope, which produced offspring hardly to be distinguished from himself, when crossed with ewes of twelve other breeds. But two of these half-bred ewes, when put to a merino ram, produced lambs closely resembling the merino breed. Girou de Buzareingues[142] found that of two races of French sheep the ewes of one, when crossed during successive generations with merino rams, yielded up their character far sooner than the ewes of the other race. Sturm and Girou have given analogous cases with other breeds of sheep and with cattle, the prepotency running in these cases through the male side; but I was assured on good authority in South America, that when niata cattle are crossed with common cattle, though the niata breed is prepotent whether males or females are used, yet that the prepotency is strongest through the female line. The Manx cat is tailless and has long hind legs; Dr. Wilson crossed a male Manx with common cats, and, out of twenty-three kittens, seventeen were destitute of tails; but when the female Manx was crossed by common male cats all the kittens had tails, though they were generally short and imperfect. [143] In making reciprocal crosses between pouter and fantail pigeons, the pouter-race seemed to be prepotent through both sexes over the fantail. But this is probably due to weak power in the fantail rather than to any unusually strong power in the pouter, for I have observed that barbs also preponderated over fantails. This weakness of transmission in the fantail, though the breed is an ancient one, is said[144] to be general; but I have observed one exception to the rule, namely, in a cross between a fantail and laugher. The most curious instance known to me of weak power in both sexes is in the trumpeter pigeon. This breed has been well known for at least 130 years: it breeds perfectly true, as I have been assured by those who have long kept many birds: it is characterised by a peculiar tuft of feathers over the beak, by a crest on the head, by a most peculiar coo quite unlike that of any other breed, and by much-feathered feet. I have crossed both sexes with turbits of two sub-breeds, with almond tumblers, spots, and runts, and reared many mongrels and recrossed them; and though the crest on the head and feathered feet were inherited (as is generally the case with most breeds), I have never seen a vestige of the tuft over the beak or heard the peculiar coo. Boitard and Corbié[145] assert that this is the invariable result of crossing trumpeters with any other breed: Neumeister, [146] however, states that in Germany mongrels have been obtained, though very rarely, which were furnished with the tuft and would trumpet: but a pair of these mongrels with a tuft, which I imported, never trumpeted. Mr. Brent states[147] that the crossed offspring of a trumpeter were crossed {67} with trumpeters for three generations, by which time the mongrels had 7-8ths of this blood in their veins, yet the tuft over the beak did not appear. At the fourth generation the tuft appeared, but the birds, though now having 15-16ths trumpeter's blood, still did not trumpet. This case well shows the wide difference between inheritance and prepotency; for here we have a well-established old race which transmits it characters faithfully, but which, when crossed with any other race, has the feeblest power of transmitting its two chief characteristic qualities. I will give one other instance with fowls and pigeons of weakness and strength in the transmission of the same character to their crossed offspring. The Silk-fowl breeds true, and there is reason to believe is a very ancient race; but when I reared a large number of mongrels from a Silk-hen by a Spanish cock, not one exhibited even a trace of the so-called silkiness. Mr. Hewitt also asserts that in no instance are the silky feathers transmitted by this breed when crossed with any other variety. But three birds out of many raised by Mr. Orton from a cross between a silk-cock and a bantam-hen, had silky feathers. [148] So that it is certain that this breed very seldom has the power of transmitting its peculiar plumage to its crossed progeny. On the other hand, there is a silk sub-variety of the fantail pigeon, which has its feathers in nearly the same state as in the Silk-fowl: now we have already seen that fantails, when crossed, possess singularly weak power in transmitting their general qualities; but the silk sub-variety when crossed with any other small-sized race invariably transmits its silky feathers![149] The law of prepotency comes into action when species are crossed, as with races and individuals. Gärtner has unequivocally shown[150] that this is the case with plants. To give one instance: when _Nicotiana paniculata_ and _vincæflora_ are crossed, the character of _N. Paniculata_ is almost completely lost in the hybrid; but if _N. Quadrivalvis_ be crossed with _N. Vincæflora_, this later species, which was before so prepotent, now in its turn almost disappears under the power of _N. Quadrivalvis_. It is remarkable that the prepotency of one species over another in transmission is quite independent, as shown by Gärtner, of the greater or less facility with which the one fertilises the other. With animals, the jackal is prepotent over the dog, as is stated by Flourens who made many crosses between these animals; and this was likewise the case with a hybrid which I once saw between a jackal and terrier. I cannot doubt, from the observations of Colin and others, that the ass is prepotent over the horse; the prepotency in this instance running more strongly through the male than through the female ass; so that the mule resembles the ass more closely than does the hinny. [151] The {68} male pheasant, judging from Mr. Hewitt's descriptions, [152] and from the hybrids which I have seen, preponderates over the domestic fowl; but the latter, as far as colour is concerned, has considerable power of transmission, for hybrids raised from five differently coloured hens differed greatly in plumage. I formerly examined some curious hybrids in the Zoological Gardens, between the Penguin variety of the common duck and the Egyptian goose (_Tadorna Ægyptiaca_); and although I will not assert that the domesticated variety preponderated over the natural species, yet it had strongly impressed its unnatural upright figure on these hybrids. I am aware that such cases as the foregoing have been ascribed by various authors, not to one species, race, or individual being prepotent over the other in impressing it character on its crossed offspring, but to such rules as that the father influences the external characters and the mother the internal or vital organs. But the great diversity of the rules given by various authors almost proves their falseness. Dr. Prosper Lucas has fully discussed this point, and has shown[153] that none of the rules (and I could add others to those quoted by him) apply to all animals. Similar rules have been enounced for plants, and have been proved by Gärtner[154] to be all erroneous. If we confine our view to the domesticated races of a single species, or perhaps even to the species of the same genus, some such rules may hold good; for instance, it seems that in reciprocally crossing various breeds of fowls the male generally gives colour;[155] but conspicuous exceptions have passed under my own eyes. In sheep it seems that the ram usually gives its peculiar horns and fleece to its crossed offspring, and the bull the presence or absence of horns. In the following chapter on Crossing I shall have occasion to show that certain characters are rarely or never blended by crossing, but are {69} transmitted in an unmodified state from either parent-form; I refer to this fact here because it is sometimes accompanied on the one side by prepotency, which thus acquires the false appearance of unusual strength. In the same chapter I shall show that the rate at which a species or breed absorbs and obliterates another by repeated crosses, depends in chief part on prepotency in transmission. In conclusion, some of the cases above given, --for instance, that of thetrumpeter pigeon, --prove that there is a wide difference between mereinheritance and prepotency. This latter power seems to us, in ourignorance, to act in most cases quite capriciously. The very samecharacter, even though it be an abnormal or monstrous one, such as silkyfeathers, may be transmitted by different species, when crossed, eitherwith prepotent force or singular feebleness. It is obvious, that apurely-bred form of either sex, in all cases in which prepotency does notrun more strongly in one sex than the other, will transmit its characterwith prepotent force over a mongrelized and already variable form. [156]From several of the above-given cases we may conclude that mere antiquityof character does not by any means necessarily make it prepotent. In somecases prepotency apparently depends on the same character being present andvisible in one of the two breeds which are crossed, and latent or invisiblein the other breed; and in this case it is natural that the character whichis potentially present in both should be prepotent. Thus, we have reason tobelieve that there is a latent tendency in all horses to be dun-colouredand striped; and when a horse of this kind is crossed with one of any othercolour, it is said that the offspring are almost sure to be striped. Sheephave a similar latent tendency to become dark-coloured, and we have seenwith what prepotent force a ram with a few black spots, when crossed withsheep of various breeds, coloured its offspring. All pigeons have a latenttendency to become slaty-blue, with certain characteristic marks, and it isknown that, when a bird thus coloured is crossed with one of any othercolour, it is most difficult afterwards to eradicate the blue tint. Anearly parallel case is offered by those black bantams which, as they grow{70} old, develop a latent tendency to acquire red feathers. But there areexceptions to the rule: hornless breeds of cattle possess a latent capacityto reproduce horns, yet when crossed with horned breeds they do notinvariably produce offspring bearing horns. We meet with analogous cases with plants. Striped flowers, though they canbe propagated truly by seed, have a latent tendency to become uniformlycoloured, but when once crossed by a uniformly coloured variety, they everafterwards fail to produce striped seedlings. [157] Another case is in somerespects more curious: plants bearing peloric or regular flowers have sostrong a latent tendency to reproduce their normally irregular flowers, that this often occurs by buds when a plant is transplanted into poorer orricher soil. [158] Now I crossed the peloric snapdragon (_Antirrhinummajus_), described in the last chapter, with pollen of the common form; andthe latter, reciprocally, with peloric pollen. I thus raised two great bedsof seedlings, and not one was peloric. Naudin[159] obtained the same resultfrom crossing a peloric Linaria with the common form. I carefully examinedthe flowers of ninety plants of the crossed Antirrhinum in the two beds, and their structure had not been in the least affected by the cross, exceptthat in a few instances the minute rudiment of the fifth stamen, which isalways present, was more fully or even completely developed. It must not besupposed that this entire obliteration of the peloric structure in thecrossed plants can be accounted for by any incapacity of transmission; forI raised a large bed of plants from the peloric Antirrhinum, artificiallyfertilised by its own pollen, and sixteen plants, which alone survived thewinter, were all as perfectly peloric as the parent-plant. Here we have agood instance of the wide difference between the inheritance of a characterand the power of transmitting it to crossed offspring. The crossed plants, which perfectly resembled the common snapdragon, were allowed to sowthemselves, and, out of a hundred and twenty-seven seedlings, eighty-eightproved to be common snapdragons, two were in an intermediate conditionbetween the peloric and normal state, {71} and thirty-seven were perfectlypeloric, having reverted to the structure of their one grandparent. Thiscase seems at first sight to offer an exception to the rule formerly given, namely, that a character which is present in one form and latent in theother is generally transmitted with prepotent force when the two forms arecrossed. For in all the Scrophulariaceæ, and especially in the generaAntirrhinum and Linaria, there is, as was shown in the last chapter, astrong latent tendency to become peloric; and there is also, as we havejust seen, a still stronger tendency in all peloric plants to reacquiretheir normal irregular structure. So that we have two opposed latenttendencies in the same plants. Now, with the crossed Antirrhinums thetendency to produce normal or irregular flowers, like those of the commonSnapdragon, prevailed in the first generation; whilst the tendency topelorism, appearing to gain strength by the intermission of a generation, prevailed to a large extent in the second set of seedlings. How it ispossible for a character to gain strength by the intermission of ageneration, will be considered in the chapter on pangenesis. On the whole, the subject of prepotency is extremely intricate, --from itsvarying so much in strength, even in regard to the same character, indifferent animals, --from its running either equally in both sexes, or, asfrequently is the case with animals, but not with plants, much stronger inthe one sex than the other, --from the existence of secondary sexualcharacters, --from the transmission of certain characters being limited, aswe shall immediately see, by sex, --from certain characters not blendingtogether, --and, perhaps, occasionally from the effects of a previousfertilisation on the mother. It is therefore not surprising that every onehitherto has been baffled in drawing up general rules on the subject ofprepotency. _Inheritance as limited by Sex. _ New characters often appear in one sex, and are afterwards transmitted tothe same sex, either exclusively or in a much greater degree than to theother. This subject is important, because with animals of many kinds in astate of nature, both high and low in the scale, secondary sexualcharacters, not in {72} any way directly connected with the organs ofreproduction, are often conspicuously present. With our domesticatedanimals, also, these same secondary characters are often found to differgreatly from the state in which they exist in the parent-species. And theprinciple of inheritance as limited by sex shows how such characters mighthave been first acquired and subsequently modified. Dr. P. Lucas, who has collected many facts on this subject, shows[160] that when a peculiarity, in no manner connected with the reproductive organs, appears in either parent, it is often transmitted exclusively to the offspring of the same sex, or to a much greater number of them than of the opposite sex. Thus, in the family of Lambert, the horn-like projections on the skin were transmitted from the father to his sons and grandsons alone; so it has been with other cases of ichthyosis, with supernumerary digits, with a deficiency of digits and phalanges, and in a lesser degree with various diseases, especially with colour-blindness, and a hæmorrhagic diathesis, that is, an extreme liability to profuse and uncontrollable bleeding from trifling wounds. On the other hand, mothers have transmitted, during several generations, to their daughters alone, supernumerary and deficient digits, colour-blindness, and other peculiarities. So that we see that the very same peculiarity may become attached to either sex, and be long inherited by that sex alone; but the attachment in certain cases is much more frequent to one than the other sex. The same peculiarities also may be promiscuously transmitted to either sex. Dr. Lucas gives other cases, showing that the male occasionally transmits his peculiarities to his daughters alone, and the mother to her sons alone; but even in this case we see that inheritance is to a certain extent, though inversely, regulated by sex. Dr. Lucas, after weighing the whole evidence, comes to the conclusion that every peculiarity, according to the sex in which it first appears, tends to be transmitted in a greater or lesser degree to that sex. A few details from the many cases collected by Mr. Sedgwick, [161] may be here given. Colour-blindness, from some unknown cause, shows itself much oftener in males than in females; in upwards of two hundred cases collected by Mr. Sedgwick, nine-tenths related to men; but it is eminently liable to be transmitted through women. In the case given by Dr. Earle, members of eight related families were affected during five generations: these families consisted of sixty-one individuals, namely, of thirty-two males, of whom nine-sixteenths were incapable of distinguishing colour, and of twenty-nine females, of whom only one-fifteenth were thus affected. {73} Although colour-blindness thus generally clings to the male sex, nevertheless, in one instance in which it first appeared in a female, it was transmitted during five generations to thirteen individuals, all of whom were females. A hæmorrhagic diathesis, often accompanied by rheumatism, has been known to affect the males alone during five generations, being transmitted, however, through the females. It is said that deficient phalanges in the fingers have been inherited by the females alone during ten generations. In another case, a man thus deficient in both hands and feet, transmitted the peculiarity to his two sons and one daughter; but in the third generation, out of nineteen grandchildren, twelve sons had the family defect, whilst the seven daughters were free. In ordinary cases of sexual limitation, the sons or daughters inherit the peculiarity, whatever it may be, from their father or mother, and transmit it to their children of the same sex; but generally with the hæmorrhagic diathesis, and often with colour-blindness, and in some other cases, the sons never inherit the peculiarity directly from their fathers, but the daughters, and the daughters alone, transmit the latent tendency, so that the sons of the daughters alone exhibit it. Thus, the father, grandson, and great-great-grandson will exhibit a peculiarity, --the grandmother, daughter, and great-granddaughter having transmitted it in a latent state. Hence we have, as Mr. Sedgwick remarks, a double kind of atavism or reversion; each grandson apparently receiving and developing the peculiarity from his grandfather, and each daughter apparently receiving the latent tendency from her grandmother. From the various facts recorded by Dr. Prosper Lucas, Mr. Sedgwick, and others, there can be no doubt that peculiarities first appearing in either sex, though not in any way necessarily or invariably connected with that sex, strongly tend to be inherited by the offspring of the same sex, but are often transmitted in a latent state through the opposite sex. Turning now to domesticated animals, we find that certain characters not proper to the parent-species are often confined to, and inherited by, one sex alone; but we do not know the history of the first appearance of such characters. In the chapter on Sheep, we have seen that the males of certain races differ greatly from the females in the shape of their horns, these being absent in the ewes of some breeds, in the development of fat in the tail in certain fat-tailed breeds, and in the outline of the forehead. These differences, judging from the character of the allied wild species, cannot be accounted for by supposing that they have been derived from distinct parent-forms. There is, also, a great difference between the horns of the two sexes in one Indian breed of goats. The bull zebu is said to have a larger hump than the cow. In the Scotch deer-hound the two sexes differ in size more than in any other variety of the dog, [162] and, judging from analogy, more than in the aboriginal parent-species. The peculiar colour called tortoise-shell is very rarely seen in a male cat; the males of this variety being of a rusty tint. A tendency to baldness in man before the advent of old age is certainly inherited; and in the European, or at least in the {74} Englishman, is an attribute of the male sex, and may almost be ranked as an incipient secondary sexual character. In various breeds of the fowl the males and females often differ greatly; and these differences are far from being the same with those which distinguish the two sexes in the parent-species, the _Gallus bankiva_; and consequently have originated under domestication. In certain sub-varieties of the Game race we have the unusual case of the hens differing from each other more than the cocks. In an Indian breed of a white colour stained with soot, the hens invariably have black skins, and their bones are covered by a black periosteum, whilst the cocks are never or most rarely thus characterised. Pigeons offer a more interesting case; for the two sexes rarely differ throughout the whole great family, and the males and females of the parent-form, the _C. Livia_, are undistinguishable; yet we have seen that with Pouters the male has the characteristic quality of pouting more strongly developed than the female; and in certain sub-varieties[163] the males alone are spotted or striated with black. When male and female English carrier-pigeons are exhibited in separate pens, the difference in the development of the wattle over the beak and round the eyes is conspicuous. So that here we have instances of the appearance of secondary sexual characters in the domesticated races of a species in which such differences are naturally quite absent. On the other hand, secondary sexual characters which properly belong to thespecies are sometimes quite lost, or greatly diminished, underdomestication. We see this in the small size of the tusks in our improvedbreeds of the pig, in comparison with those of the wild boar. There aresub-breeds of fowls in which the males have lost the fine flowingtail-feathers and hackles; and others in which there is no difference incolour between the two sexes. In some cases the barred plumage, which ingallinaceous birds is commonly the attribute of the hen, has beentransferred to the cock, as in the cuckoo sub-breeds. In other casesmasculine characters have been partly transferred to the female, as withthe splendid plumage of the golden-spangled Hamburgh hen, the enlarged combof the Spanish hen, the pugnacious disposition of the Game hen, and as inthe well-developed spurs which occasionally appear in the hens of variousbreeds. In Polish fowls both sexes are ornamented with a topknot, that ofthe male being formed of hackle-like feathers, and this is a new malecharacter in the genus Gallus. On the whole, as far as I can judge, newcharacters are more apt {75} to appear in the males of our domesticatedanimals than in the females, and afterwards to be either exclusively ormore strongly inherited by the males. Finally, in accordance with theprinciple of inheritance as limited by sex, the appearance of secondarysexual characters in natural species offers no especial difficulty, andtheir subsequent increase and modification, if of any service to thespecies, would follow through that form of selection which in my 'Origin ofSpecies' I have called sexual selection. _Inheritance at corresponding periods of Life. _ This is an important subject. Since the publication of my 'Origin ofSpecies, ' I have seen no reason to doubt the truth of the explanation theregiven of perhaps the most remarkable of all the facts in biology, namely, the difference between the embryo and the adult animal. The explanation is, that variations do not necessarily or generally occur at a very earlyperiod of embryonic growth, and that such variations are inherited at acorresponding age. As a consequence of this the embryo, even when theparent-form undergoes a great amount of modification, is left only slightlymodified; and the embryos of widely-different animals which are descendedfrom a common progenitor remain in many important respects like each otherand their common progenitor. We can thus understand why embryology shouldthrow a flood of light on the natural system of classification, for thisought to be as far as possible genealogical. When the embryo leads anindependent life, that is, becomes a larva, it has to be adapted to thesurrounding conditions in its structure and instincts, independently ofthose of its parents; and the principle of inheritance at correspondingperiods of life renders this possible. This principle is, indeed, in one way so obvious that it escapes attention. We possess a number of races of animals and plants, which, when comparedwith each other and with their parent-forms, present conspicuousdifferences, both in the immature and mature states. Look at the seeds ofthe several kinds of peas, beans, maize, which can be propagated truly, andsee how they differ in size, colour, and shape, whilst the {76} full-grownplants differ but little. Cabbages on the other hand differ greatly infoliage and manner of growth, but hardly at all in their seeds; andgenerally it will be found that the differences between cultivated plantsat different periods of growth are not necessarily closely connectedtogether, for plants may differ much in their seeds and little whenfull-grown, and conversely may yield seeds hardly distinguishable, yetdiffer much when full-grown. In the several breeds of poultry, descendedfrom a single species, differences in the eggs and chickens, in the plumageat the first and subsequent moults, in the comb and wattles duringmaturity, are all inherited. With man peculiarities in the milk and secondteeth, of which I have received the details, are inheritable, and with manlongevity is often transmitted. So again with our improved breeds of cattleand sheep, early maturity, including the early development of the teeth, and with certain breeds of fowl the early appearance of secondary sexualcharacters, all come under the same head of inheritance at correspondingperiods. Numerous analogous facts could be given. The silk-moth, perhaps, offers thebest instance; for in the breeds which transmit their characters truly, theeggs differ in size, colour, and shape;--the caterpillars differ, inmoulting three or four times, in colour, even in having a dark-colouredmark like an eyebrow, and in the loss of certain instincts;--the cocoonsdiffer in size, shape, and in the colour and quality of the silk; theseseveral differences being followed by slight or barely distinguishabledifferences in the mature moth. But it may be said that, if in the above cases a new peculiarity isinherited, it must be at the corresponding stage of development; for an eggor seed can resemble only an egg or seed, and the horn in a full-grown oxcan resemble only a horn. The following cases show inheritance atcorresponding periods more plainly, because they refer to peculiaritieswhich might have supervened, as far as we can see, earlier or later inlife, yet are inherited at the same period at which they first appeared. In the Lambert family the porcupine-like excrescences appeared in the father and sons at the same age, namely, about nine weeks after {77} birth. [164] In the extraordinary hairy family described by Mr. Crawfurd, [165] children were produced during three generations with hairy ears; in the father the hair began to grow over his body at six years old; in his daughter somewhat earlier, namely, at one year; and in both generations the milk teeth appeared late in life, the permanent teeth being afterwards singularly deficient. Greyness of hair at an unusually early age has been transmitted in some families. These cases border on diseases inherited at corresponding periods of life, to which I shall immediately refer. It is a well-known peculiarity with almond-tumbler pigeons, that the full beauty and peculiar character of the plumage does not appear until the bird has moulted two or three times. Neumeister describes and figures a breed of pigeons in which the whole body is white except the breast, neck, and head; but before the first moult all the white feathers acquire coloured edges. Another breed is more remarkable: its first plumage is black, with rusty-red wing-bars and a crescent-shaped mark on the breast; these marks then became white, and remain so during three or four moults; but after this period the white spreads over the body, and the bird loses its beauty. [166] Prize canary-birds have their wings and tail black: "this colour, however, is only retained until the first moult, so that they must be exhibited ere the change takes place. Once moulted, the peculiarity has ceased. Of course all the birds emanating from this stock have black wings and tails the first year. "[167] A curious and somewhat analogous account has been given[168] of a family of wild pied rooks which were first observed in 1798, near Chalfont, and which every year from that date up to the period of the published notice, viz. 1837, "have several of their brood particoloured, black and white. This variegation of the plumage, however, disappears with the first moult; but among the next young families there are always a few pied ones. " These changes of plumage, which appear and are inherited at various corresponding periods of life in the pigeon, canary-bird, and rook, are remarkable, because the parent-species undergo no such change. Inherited diseases afford evidence in some respects of less value than the foregoing cases, because diseases are not necessarily connected with any change in structure; but in other respects of more value, because the periods have been more carefully observed. Certain diseases are communicated to the child apparently by a process like inoculation, and the child is from the first affected; such cases may be here passed over. Large classes of diseases usually appear at certain ages, such as St. Vitus's dance in youth, consumption in early mid-life, gout later, and apoplexy still later; and these are naturally inherited at the same period. But even in diseases of this class, instances have been recorded, as with St. Vitus's {78} dance, showing that an unusually early or late tendency to the disease is inheritable. [169] In most cases the appearance of any inherited disease is largely determined by certain critical periods in each person's life, as well as by unfavourable conditions. There are many other diseases, which are not attached to any particular period, but which certainly tend to appear in the child at about the same age at which the parent was first attacked. An array of high authorities, ancient and modern, could be given in support of this proposition. The illustrious Hunter believed in it; and Piorry[170] cautions the physician to look closely to the child at the period when any grave inheritable disease attacked the parent. Dr. Prosper Lucas, [171] after collecting facts from every source, asserts that affections of all kinds, though not related to any particular period of life, tend to reappear in the offspring at whatever period of life they first appeared in the progenitor. As the subject is important, it may be well to give a few instances, simply as illustrations, not as proof; for proof, recourse must be had to the authorities above quoted. Some of the following cases have been selected for the sake of showing that, when a slight departure from the rule occurs, the child is affected somewhat earlier in life than the parent. In the family of Le Compte blindness was inherited during three generations, and no less than thirty-seven children and grandchildren were all affected at about the same age, namely seventeen or eighteen. [172] In another case a father and his four children all became blind at twenty-one years old; in another, a grandmother grew blind at thirty-five, her daughter at nineteen, and three grandchildren at the ages of thirteen and eleven. [173] So with deafness, two brothers, their father and paternal grandfather, all became deaf at the age of forty. [174] Esquirol gives several striking instances of insanity coming on at the same age, as that of a grandfather, father, and son, who all committed suicide near their fiftieth year. Many other cases could be given, as of a whole family who became insane at the age of forty. [175] Other cerebral affections sometimes follow the same rule, --for instance, epilepsy and apoplexy. A woman died of the latter disease when sixty-three years old; one of her daughters at forty-three, and the other at sixty-seven: the latter had twelve children, who all died from tubercular meningitis. [176] I mention this latter case because it illustrates a frequent occurrence, namely, a change in the precise nature of an inherited disease, though still affecting the same organ. {79} Asthma has attacked several members of the same family when forty years old, and other families during infancy. The most different diseases, as angina pectoris, stone in the bladder, and various affections of the skin, have appeared in successive generations at nearly the same age. The little finger of a man began from some unknown cause to grow inwards, and the same finger in his two sons began at the same age to bend inwards in a similar manner. Strange and inexplicable neuralgic affections have caused parents and children to suffer agonies at about the same period of life. [177] I will give only two other cases, which are interesting as illustrating the disappearance as well as the appearance of disease at the same age. Two brothers, their father, their paternal uncles, seven cousins, and their paternal grandfather, were all similarly affected by a skin-disease, called pityriasis versicolor; "the disease, strictly limited to the males of the family (though transmitted through the females), usually appeared at puberty, and disappeared at about the age of forty or forty-five years. " The second case is that of four brothers, who when about twelve years old suffered almost every week from severe headaches, which were relieved only by a recumbent position in a dark room. Their father, paternal uncles, paternal grandfather, and paternal granduncles all suffered in the same way from headaches, which ceased at the age of fifty-four or fifty-five in all those who lived so long. None of the females of the family were affected. [178] It is impossible to read the foregoing accounts, and the many others whichhave been recorded, of diseases coming on during three or even moregenerations, at the same age in several members of the same family, especially in the case of rare affections in which the coincidence cannotbe attributed to chance, and doubt that there is a strong tendency toinheritance in disease at corresponding periods of life. When the rulefails, the disease is apt to come on earlier in the child than in theparent; the exceptions in the other direction being vey much rarer. Dr. Lucas[179] alludes to several cases of inherited diseases coming on at anearlier period. I have already given one striking instance with blindnessduring three generations; and Mr. Bowman remarks that this frequentlyoccurs with cataract. With cancer there seems to be a peculiar liability toearlier inheritance: Mr. Paget, who has particularly {80} attended to thissubject, and tabulated a large number of cases, informs me that he believesthat in nine cases out of ten the later generation suffers from the diseaseat an earlier period than the previous generation. He adds, "In theinstances in which the opposite relation holds, and the members of latergenerations have cancer at a later age than their predecessors, I think itwill be found that the non-cancerous parents have lived to extreme oldages. " So that the longevity of a non-affected parent seems to have thepower of determining in the offspring the fatal period; and we thusapparently get another element of complexity in inheritance. The facts, showing that with certain diseases the period of inheritanceoccasionally or even frequently advances, are important with respect to thegeneral descent-theory, for they render it in some degree probable that thesame thing would occur with ordinary modifications of structure. The finalresult of a long series of such advances would be the gradual obliterationof characters proper to the embryo and larva, which would thus come toresemble more and more closely the mature parent-form. But any structurewhich was of service to the embryo or larva would be preserved by thedestruction at this stage of growth of each individual which manifested anytendency to lose at too early an age its own proper character. Finally, from the numerous races of cultivated plants and domestic animals, in which the seed or eggs, the young or old, differ from each other andfrom their parent-species;--from the cases in which new characters haveappeared at a particular period, and afterwards have been inherited at thesame period;--and from what we know with respect to disease, we mustbelieve in the truth of the great principle of inheritance at correspondingperiods of life. * * * * * _Summary of the three preceding Chapters. _--Strong as is the force ofinheritance, it allows the incessant appearance of new characters. These, whether beneficial or injurious, of the most trifling importance, such as ashade of colour in a flower, a coloured lock of hair, or a mere gesture; orof the highest importance, as when affecting the brain or an organ soperfect {81} and complex as the eye; or of so grave a nature as to deserveto be called a monstrosity, or so peculiar as not to occur normally in anymember of the same natural class, are all sometimes strongly inherited byman, the lower animals, and plants. In numberless cases it suffices for theinheritance of a peculiarity that one parent alone should be thuscharacterised. Inequalities in the two sides of the body, though opposed tothe law of symmetry, may be transmitted. There is a considerable body ofevidence showing that even mutilations, and the effects of accidents, especially or perhaps exclusively when followed by disease, areoccasionally inherited. There can be no doubt that the evil effects oflong-continued exposure in the parent to injurious conditions are sometimestransmitted to the offspring. So it is, as we shall see in a futurechapter, with the effects of the use and disuse of parts, and of mentalhabits. Periodical habits are likewise transmitted, but generally, as itwould appear, with little force. Hence we are led to look at inheritance as the rule, and non-inheritance asthe anomaly. But this power often appears to us in our ignorance to actcapriciously, transmitting a character with inexplicable strength orfeebleness. The very same peculiarity, as the weeping habit of trees, silky-feathers, &c. , may be inherited either firmly or not at all bydifferent members of the same group, and even by different individuals ofthe same species, though treated in the same manner. In this latter case wesee that the power of transmission is a quality which is merely individualin its attachment. As with single characters, so it is with the severalconcurrent slight differences which distinguish sub-varieties or races; forof these, some can be propagated almost as truly as species, whilst otherscannot be relied on. The same rule holds good with plants, when propagatedby bulbs, offsets, &c. , which in one sense still form parts of the sameindividual, for some varieties retain or inherit through successivebud-generations their character far more truly than others. Some characters not proper to the parent-species have certainly beeninherited from an extremely remote epoch, and may therefore be consideredas firmly fixed. But it is doubtful whether length of inheritance in itselfgives fixedness of character; {82} though the chances are obviously infavour of any character which has long been transmitted true or unaltered, still being transmitted true as long as the conditions of life remain thesame. We know that many species, after having retained the same characterfor countless ages, whilst living under their natural conditions, whendomesticated have varied in the most diversified manner, that is, havefailed to transmit their original form; so that no character appears to beabsolutely fixed. We can sometimes account for the failure of inheritanceby the conditions of life being opposed to the development of certaincharacters; and still oftener, as with plants cultivated by grafts andbuds, by the conditions causing new and slight modifications incessantly toappear. In this latter case it is not that inheritance wholly fails, butthat new characters are continually superadded. In some few cases, in whichboth parents are similarly characterised, inheritance seems to gain so muchforce by the combined action of the two parents, that it counteracts itsown power, and a new modification is the result. In many cases the failure of the parents to transmit their likeness is dueto the breed having been at some former period crossed; and the child takesafter his grandparent or more remote ancestor of foreign blood. In othercases, in which the breed has not been crossed, but some ancient characterhas been lost through variation, it occasionally reappears throughreversion, so that the parents apparently fail to transmit their ownlikeness. In all cases, however, we may safely conclude that the childinherits all its characters from its parents, in whom certain charactersare latent, like the secondary sexual characters of one sex in the other. When, after a long succession of bud-generations, a flower or fruit becomesseparated into distinct segments, having the colours or other attributes ofboth parent-forms, we cannot doubt that these characters were latent in theearlier buds, though they could not then be detected, or could be detectedonly in an intimately commingled state. So it is with animals of crossedparentage, which with advancing years occasionally exhibit charactersderived from one of their two parents, of which not a trace could at firstbe perceived. Certain monstrosities, which resemble what naturalists callthe typical form of the group in question, {83} apparently come under thesame law of reversion. It is assuredly an astonishing fact that the maleand female sexual elements, that buds, and even full-grown animals, shouldretain characters, during several generations in the case of crossedbreeds, and during thousands of generations in the case of pure breeds, written as it were in invisible ink, yet ready at any time to be evolvedunder the requisite conditions. What these conditions are, we do not in many cases at all know. But the actof crossing in itself, apparently from causing some disturbance in theorganisation, certainly gives a strong tendency to the reappearance oflong-lost characters, both corporeal and mental, independently of thosederived from the cross. A return of any species to its natural conditionsof life, as with feral animals and plants, favours reversion; though it iscertain that this tendency exists, we do not know how far it prevails, andit has been much exaggerated. On the other hand, the crossed offspring ofplants which have had their organisation disturbed by cultivation, are moreliable to reversion than the crossed offspring of species which have alwayslived under their natural conditions. When distinguishable individuals of the same family, or races, or speciesare crossed, we see that the one is often prepotent over the other intransmitting its own character. A race may possess a strong power ofinheritance, and yet when crossed, as we have seen with trumpeter-pigeons, yield to the prepotency of every other race. Prepotentcy of transmissionmay be equal in the two sexes of the same species, but often runs morestrongly in one sex. It plays an important part in determining the rate atwhich one race can be modified or wholly absorbed by repeated crosses withanother. We can seldom tell what makes one race or species prepotent overanother; but it sometimes depends on the same character being present andvisible in one parent, and latent or potentially present in the other. Characters may first appear in either sex, but oftener in the male than inthe female, and afterwards be transmitted to the offspring of the same sex. In this case we may feel confident that the peculiarity in question isreally present though latent in the opposite sex; hence the father maytransmit through his daughter any character to his grandson; and the mother{84} conversely to her granddaughter. We thus learn, and the fact is animportant one, that transmission and development are distinct powers. Occasionally these two powers seem to be antagonistic, or incapable ofcombination in the same individual; for several cases have been recorded inwhich the son has not directly inherited a character from his father, ordirectly transmitted it to his son, but has received it by transmissionthrough his non-affected mother, and transmitted it through hisnon-affected daughter. Owing to inheritance being limited by sex, we cansee how secondary sexual characters may first have arisen under nature;their preservation and accumulation being dependent on their service toeither sex. At whatever period of life a new character first appears, it generallyremains latent in the offspring until a corresponding age is attained, andthen it is developed. When this rule fails, the child generally exhibitsthe character at an earlier period than the parent. On this principle ofinheritance at corresponding periods, we can understand how it is that mostanimals display from the germ to maturity such a marvellous succession ofcharacters. Finally, though much remains obscure with respect to Inheritance, we maylook at the following laws as fairly well established. Firstly, a tendencyin every character, new and old, to be transmitted by seminal and budgeneration, though often counteracted by various known and unknown causes. Secondly, reversion or atavism, which depends on transmission anddevelopment being distinct powers: it acts in various degrees and mannersthrough both seminal and bud generation. Thirdly, prepotency oftransmission, which may be confined to one sex, or be common to both sexesof the prepotent form. Fourthly, transmission, limited by sex, generally tothe same sex in which the inherited character first appeared. Fifthly, inheritance at corresponding periods of life, with some tendency to theearlier development of the inherited character. In these laws ofInheritance, as displayed under domestication, we see an ample provisionfor the production, through variability and natural selection, of newspecific forms. * * * * * {85} CHAPTER XV. ON CROSSING. FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS--WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THE OTHER--THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BY THE CONDITIONS OF LIFE, AND BY NATURAL SELECTION--ALL ORGANIC BEINGS OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS--ON CERTAIN CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE SUDDENLY APPEARED IN THE INDIVIDUAL--ON THE MODIFICATION OF OLD RACES, AND THE FORMATION OF NEW RACES, BY CROSSING--SOME CROSSED RACES HAVE BRED TRUE FROM THEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES. In the two previous chapters, when discussing reversion and prepotency, Iwas necessarily led to give many facts on crossing. In the present chapterI shall consider the part which crossing plays in two opposeddirections, --firstly, in obliterating characters, and consequently inpreventing the formation of new races; and secondly, in the modification ofold races, or in the formation of new and intermediate races, by acombination of characters. I shall also show that certain characters areincapable of fusion. The effects of free or uncontrolled breeding between the members of thesame variety or of closely allied varieties are important; but are soobvious that they need not be discussed at much length. It is freeintercrossing which chiefly gives uniformity, both under nature and underdomestication, to the individuals of the same species or variety, when theylive mingled together and are not exposed to any cause inducing excessivevariability. The prevention of free crossing, and the intentional matchingof individual animals, are the corner-stones of the breeder's art. No manin his senses would expect to improve or modify a breed in any particularmanner, or keep an old breed true and distinct, unless he separated hisanimals. The killing of inferior animals in each generation comes to the{86} same thing as their separation. In savage and semi-civilisedcountries, where the inhabitants have not the means of separating theiranimals, more than a single breed of the same species rarely or neverexists. In former times, even in a country so civilised as North America, there were no distinct races of sheep, for all had been mingledtogether. [180] The celebrated agriculturist Marshall[181] remarks that"sheep that are kept within fences, as well as shepherded flocks in opencountries, have generally a similarity, if not a uniformity, of characterin the individuals of each flock;" for they breed freely together, and areprevented from crossing with other kinds; whereas in the unenclosed partsof England the unshepherded sheep, even of the same flock, are far fromtrue or uniform, owing to various breeds having mingled and crossed. Wehave seen that the half-wild cattle in the several British parks areuniform in character in each; but in the different parks, from not havingmingled and crossed during many generations, they differ in a slightdegree. We cannot doubt that the extraordinary number of varieties andsub-varieties of the pigeon, amounting to at least one hundred and fifty, is partly due to their remaining, differently from other domesticatedbirds, paired for life when once matched. On the other hand, breeds of catsimported into this country soon disappear, for their nocturnal and ramblinghabits render it hardly possible to prevent free crossing. Rengger[182]gives an interesting case with respect to the cat in Paraguay: in all thedistant parts of the kingdom it has assumed, apparently from the effects ofthe climate, a peculiar character, but near the capital this change hasbeen prevented, owing, as he asserts, to the native animal frequentlycrossing with cats imported from Europe. In all cases like the foregoing, the effects of an occasional cross will be augmented by the increasedvigour and fertility of the crossed offspring, of which fact evidence willhereafter be given; for this will lead to the mongrels increasing morerapidly than the pure parent-breeds. {87} When distinct breeds are allowed to cross freely, the result will be aheterogenous body; for instance, the dogs in Paraguay are far from uniform, and can no longer be affiliated to their parent-races. [183] The characterwhich a crossed body of animals will ultimately assume must depend onseveral contingencies, --namely, on the relative numbers of the individualsbelonging to the two or more races which are allowed to mingle; on theprepotency of one race over the other in the transmission of character; andon the conditions of life to which they are exposed. When two commingledbreeds exist at first in nearly equal numbers, the whole will sooner orlater become intimately blended, but not so soon, both breeds being equallyfavoured in all respects, as might have been expected. The followingcalculation[184] shows that this is the case: if a colony with an equalnumber of black and white men were founded, and we assume that they marryindiscriminately, are equally prolific, and that one in thirty annuallydies and is born; then "in 65 years the number of blacks, whites, andmulattoes would be equal. In 91 years the whites would be 1-10th, theblacks 1-10th, and the mulattoes, or people of intermediate degrees ofcolour, 8-10ths of the whole number. In three centuries not 1-100th part ofthe whites would exist. " When one of two mingled races exceeds the other greatly in number, thelatter will soon be wholly, or almost wholly, absorbed and lost. [185] ThusEuropean pigs and dogs have been largely introduced into the islands of thePacific Ocean, and the native races have been absorbed and lost in thecourse of about fifty or sixty years;[186] but the imported races no doubtwere favoured. Rats may be considered as semi-domesticated animals. Somesnake-rats (_Mus alexandrinus_) escaped in the Zoological Gardens ofLondon, "and for a long time afterwards the keepers frequently caughtcross-bred rats, at first half-breds, afterwards with less and less of thecharacter of the snake-rat, till at length all traces of itdisappeared. "[187] On the other hand, {88} in some parts of London, especially near the docks, where fresh rats are frequently imported, anendless variety of intermediate forms may be found between the brown, black, and snake rat, which are all three usually ranked as distinctspecies. How many generations are necessary for one species or race to absorbanother by repeated crosses has often been discussed;[188] and therequisite number has probably been much exaggerated. Some writers havemaintained that a dozen, or score, or even more generations, are necessary;but this in itself is improbable, for in the tenth generation there will beonly 1-1024th part of foreign blood in the offspring. Gärtner found, [189]that with plants one species could be made to absorb another in from threeto five generations, and he believes that this could always be effected infrom six to seventh generations. In one instance, however, Kölreuter[190]speaks of the offspring of _Mirabilis vulgaris_, crossed during eightsuccessive generations by _M. Longiflora_, as resembling this latterspecies so closely, that the most scrupulous observer could detect "vixaliquam notabilem differentiam;"--he succeeded, as he says, "ad plenariamfere transmutationem. " But this expression shows that the act of absorptionwas not even then absolutely complete, though these crossed plantscontained only the 1-256th part of _M. Vulgaris_. The conclusions of suchaccurate observers as Gärtner and Kölreuter are of far higher worth thanthose made without scientific aim by breeders. The most remarkablestatement which I have met with of the persistent endurance of the effectsof a single cross is given by Fleischmann, [191] who, in reference to Germansheep, says "that the original coarse sheep have 5500 fibres of wool on asquare inch; grades of the third or fourth Merino cross produced about8000, the twentieth cross 27, 000, the perfect pure Merino blood 40, 000 to48, 000. " So that in this case common German sheep crossed twenty timessuccessively with Merinos have not by any means acquired wool as fine asthat of the pure breed. In all cases, the rate of absorption will {89}depend largely on the conditions of life being favourable to any particularcharacter; and we may suspect that there would be under the climate ofGermany a constant tendency to degeneration in the wool of Merinos, unlessprevented by careful selection; and thus perhaps the foregoing remarkablecase may be explained. The rate of absorption must also depend on theamount of distinguishable difference between the two forms which arecrossed, and especially, as Gärtner insists, on prepotency of transmissionin the one form over the other. We have seen in the last chapter that oneof two French breeds of sheep yielded up its character, when crossed withMerinos, very much slower than the other; and the common German sheepreferred to by Fleischmann may present an analogous case. But in all casesthere will be during many subsequent generations more or less liability toreversion, and it is this fact which has probably led authors to maintainthat a score or more of generations are requisite for one race to absorbanother. In considering the final result of the commingling of two or morebreeds, we must not forget that the act of crossing in itself tends tobring back long-lost characters not proper to the immediate parent-forms. With respect to the influence of the conditions of life on any two breedswhich are allowed to cross freely, unless both are indigenous and have longbeen accustomed to the country where they live, they will, in allprobability, be unequally affected by the conditions, and this will modifythe result. Even with indigenous breeds, it will rarely or never occur thatboth are equally well adapted to the surrounding circumstances; moreespecially when permitted to roam freely, and not carefully tended, as willgenerally be the case with breeds allowed to cross. As a consequence ofthis, natural selection will to a certain extent come into action, and thebest fitted will survive, and this will aid in determining the ultimatecharacter of the commingled body. How long a time it would require before such a crossed body of animalswould assume within a limited area a uniform character no one can say; thatthey would ultimately become uniform from free intercrossing, and from thesurvival of the fittest, we may feel assured; but the character thusacquired would rarely or never, as we may infer from the several previous{90} considerations, be exactly intermediate between that of the twoparent-breeds. With respect to the very slight differences by which theindividuals of the same sub-variety, or even of allied varieties, arecharacterised, it is obvious that free crossing would soon obliterate suchsmall distinctions. The formation of new varieties, independently ofselection, would also thus be prevented; except when the same variationcontinually recurred from the action of some strongly predisposing cause. Hence we may conclude that free crossing has in all cases played animportant part in giving to all the members of the same domestic race, andof the same natural species, uniformity of character, though largelymodified by natural selection and by the direct action of the surroundingconditions. _On the possibility of all organic beings occasionally intercrossing. _--Butit may be asked, can free crossing occur with hermaphrodite animals andplants? All the higher animals, and the few insects which have beendomesticated, have separated sexes, and must inevitably unite for eachbirth. With respect to the crossing of hermaphrodites, the subject is toolarge for the present volume, and will be more properly treated in asucceeding work. In my 'Origin of Species, ' however, I have given a shortabstract of the reasons which induce me to believe that all organic beingsoccasionally cross, though perhaps in some cases only at long intervals oftime. [192] I will here just recall the fact that many plants, thoughhermaphrodite in structure, are unisexual in function;--such as thosecalled by C. K. Sprengel _dichogamous_, in which the pollen and stigma ofthe same flower are matured at different periods; or those called by me_reciprocally dimorphic_, in which the flower's own pollen is not fitted tofertilise its own stigma; or again, the many kinds in which curiousmechanical contrivances exist, effectually preventing self-fertilisation. There are, however, many hermaphrodite plants which are not in any wayspecially constructed to favour intercrossing, but which neverthelesscommingle almost as freely as animals with separated sexes. This is thecase with cabbages, radishes, and onions, as I know from {91} havingexperimented on them: even the peasants of Liguria say that cabbages mustbe prevented "from falling in love" with each other. In the orange tribe, Gallesio[193] remarks that the amelioration of the various kinds is checkedby their continual and almost regular crossing. So it is with numerousother plants. Nevertheless some cultivated plants can be named which rarely intercross, as the common pea, or which never intercross, as I have reason to believeis the case with the sweet-pea (_Lathyrus odoratus_); yet the structure ofthese flowers certainly favours an occasional cross. The varieties of thetomato and aubergine (_Solanum_) and pimenta (_Pimenta vulgaris?_) aresaid[194] never to cross, even when growing alongside each other. But itshould be observed that these are all exotic plants, and we do not know howthey would behave in their native country when visited by the properinsects. It must also be admitted that some few natural species appear under ourpresent state of knowledge to be perpetually self-fertilised, as in thecase of the Bee Ophrys (_O. Apifera_), though adapted in its structure tobe occasionally crossed. The _Leersia oryzoides_ produces minute enclosedflowers which cannot possibly be crossed, and these alone, to the exclusionof the ordinary flowers, have as yet been known to yield seed. [195] A fewadditional and analogous cases could be advanced. But these facts do notmake me doubt that it is a general law of nature that the individuals ofthe same species occasionally intercross, and that some great advantage isderived from this act. It is well known (and I shall hereafter have to giveinstances) that some plants, both indigenous and naturalised, rarely ornever produce flowers; or, if they flower, never produce seeds. But no oneis thus led to doubt that it is a general law of nature that phanerogamicplants should produce flowers, and that these flowers should produce seed. When they fail, we believe that such plants would perform their properfunctions under different conditions, or that they formerly did so and willdo so again. On analogous grounds, I believe that the few flowers {92}which do not now intercross, either would do so under different conditions, or that they formerly fertilised each other at intervals--the means foreffecting this being generally still retained--and they will do so again atsome future period, unless indeed they become extinct. On this view alone, many points in the structure and action of the reproductive organs inhermaphrodite plants and animals are intelligible, --for instance, the maleand female organs never being so completely enclosed as to render accessfrom without impossible. Hence we may conclude that the most important ofall the means for giving uniformity to the individuals of the same species, namely, the capacity of occasionally intercrossing, is present, or has beenformerly present, with all organic beings. _On certain Characters not blending. _--When two breeds are crossed their characters usually become intimately fused together; but some characters refuse to blend, and are transmitted in an unmodified state either from both parents or from one. When grey and white mice are paired, the young are not piebald nor of an intermediate tint, but are pure white or of the ordinary grey colour: so it is when white and common collared turtle-doves are paired. In breeding Game fowls, a great authority, Mr. J. Douglas, remarks, "I may here state a strange fact: if you cross a black with a white game, you get birds of both breeds of the clearest colour. " Sir R. Heron crossed during many years white, black, brown, and fawn-coloured Angora rabbits, and never once got these colours mingled in the same animal, but often all four colours in the same litter. [196] Additional cases could be given, but this form of inheritance is very far from universal even with respect to the most distinct colours. When turnspit dogs and ancon sheep, both of which have dwarfed limbs, are crossed with common breeds, the offspring are not intermediate in structure, but take after either parent. When tailless or hornless animals are crossed with perfect animals, it frequently, but by no means invariably, happens that the offspring are {93} either perfectly furnished with these organs or are quite destitute of them. According to Rengger, the hairless condition of the Paraguay dog is either perfectly or not at all transmitted to its mongrel offspring; but I have seen one partial exception in a dog of this parentage which had part of its skin hairy, and part naked; the parts being distinctly separated as in a piebald animal. When Dorking fowls with five toes are crossed with other breeds, the chickens often have five toes on one foot and four on the other. Some crossed pigs raised by Sir R. Heron between the solid-hoofed and common pig had not all four feet in an intermediate condition, but two feet were furnished with properly divided, and two with united hoofs. Analogous facts have been observed with plants: Major Trevor Clarke crossed the little, glabrous-leaved, annual stock (_Matthiola_), with pollen of a large, red-flowered, rough-leaved, biennial stock, called _cocardeau_ by the French, and the result was that half the seedlings had glabrous and the other half rough leaves, but none had leaves in an intermediate state. That the glabrous seedlings were the product of the rough-leaved variety, and not accidentally of the mother-plant's own pollen, was shown by their tall and strong habit of growth. [197] In the succeeding generations raised from the rough-leaved crossed seedlings, some glabrous plants appeared, showing that the glabrous character, though incapable of blending with and modifying the rough leaves, was all the time latent in this family of plants. The numerous plants formerly referred to, which I raised from reciprocal crosses between the peloric and common Antirrhinum, offer a nearly parallel case; for in the first generation all the plants resembled the common form, and in the next generation, out of one hundred and thirty-seven plants, two alone were in an intermediate condition, the others perfectly resembling either the peloric or common form. Major Trevor Clarke also fertilised the above-mentioned red-flowered stock with pollen from the purple Queen stock, and about half the seedlings scarcely differed in habit, and not at all in the red colour of the flower, from the mother-plant, the other half bearing blossoms of a rich purple, closely like those of the paternal plant. Gärtner crossed many white and yellow-flowered species and varieties of Verbascum; and these colours were never blended, but the offspring bore either pure white or pure yellow blossoms; the former in the larger proportion. [198] Dr. Herbert raised many seedlings, as he informed me, from Swedish turnips crossed by two other varieties, and these never produced flowers of an intermediate tint, but always like one of their parents. I fertilised the purple sweet-pea (_Lathyrus odoratus_), which has a dark reddish-purple standard-petal and violet-coloured wings and keel, with pollen of the painted-lady sweet-pea, which has a pale cherry-coloured standard, and almost white wings and keel; and from the same pod I twice raised plants perfectly resembling both sorts; the greater number resembling the father. So perfect was the resemblance, that I should have thought there had {94} been some mistake, if the plants which were at first identical with the paternal variety, namely, the painted-lady, had not later in the season produced, as mentioned in a former chapter, flowers blotched and streaked with dark purple. I raised grandchildren and great-grandchildren from these crossed plants, and they continued to resemble the painted-lady, but during the later generations became rather more blotched with purple, yet none reverted completely to the original mother-plant, the purple sweet-pea. The following case is slightly different, but still shows the same principle: Naudin[199] raised numerous hybrids between the yellow _Linaria vulgaris_ and the purple _L. Purpurea_, and during three successive generations the colours kept distinct in different parts of the same flower. From such cases as the foregoing, in which the offspring of the first generation perfectly resemble either parent, we come by a small step to those cases in which differently coloured flowers borne on the same root resemble both parents, and by another step to those in which the same flower or fruit is striped or blotched with the two parental colours, or bears a single stripe of the colour or other characteristic quality of one of the parent-forms. With hybrids and mongrels it frequently or even generally happens that one part of the body resembles more or less closely one parent and another part the other parent; and here again some resistance to fusion, or, what comes to the same thing, some mutual affinity between the organic atoms of the same nature, apparently comes into play, for otherwise all parts of the body would be equally intermediate in character. So again, when the offspring of hybrids or mongrels, which are themselves nearly intermediate in character, revert either wholly or by segments to their ancestors, the principle of the affinity of similar, or the repulsion of dissimilar atoms, must come into action. To this principle, which seems to be extremely general, we shall recur in the chapter on pangenesis. It is remarkable, as has been strongly insisted upon by Isidore Geoffroy St. Hilaire in regard to animals, that the transmission of characters without fusion occurs most rarely when species are crossed; I know of one exception alone, namely, with the hybrids naturally produced between the common and hooded crow (_Corvus corone_ and _cornix_), which, however, are closely allied species, differing in nothing except colour. Nor have I met with any well-ascertained cases of transmission of this kind, even when one form is strongly prepotent over another, when two races are crossed which have been slowly formed by man's selection, and therefore resemble to a certain extent natural species. Such cases as puppies in the same litter closely resembling two distinct breeds, are probably due to super-foetation, --that is, to the influence of two fathers. All the characters above enumerated, which are transmitted in a perfect state to some of the offspring and not to others, --such as distinct colours, nakedness of skin, smoothness of leaves, absence of horns or tail, additional toes, pelorism, dwarfed structure, &c. , --have all been known to appear suddenly in individual animals and plants. From this fact, and from the several slight, aggregated differences which distinguish domestic races and species from {95} each other, not being liable to this peculiar form of transmission, we may conclude that it is in some way connected with the sudden appearance of the characters in question. _On the Modification of old Races and the Formation of new Races byCrossing. _--We have hitherto chiefly considered the effects of crossing ingiving uniformity of character; we must now look to an opposite result. There can be no doubt that crossing, with the aid of rigorous selectionduring several generations, has been a potent means in modifying old races, and in forming new ones. Lord Orford crossed his famous stud of greyhoundsonce with the bulldog, which breed was chosen from being deficient inscenting powers, and from having what was wanted, courage and perseverance. In the course of six or seven generations all traces of the external formof the bulldog were eliminated, but courage and perseverance remained. Certain pointers have been crossed, as I hear from the Rev. W. D. Fox, withthe foxhound, to give them dash and speed. Certain strains of Dorking fowlshave had a slight infusion of Game blood; and I have known a great fancierwho on a single occasion crossed his turbit-pigeons with barbs, for thesake of gaining greater breadth of beak. In the foregoing cases breeds have been crossed once, for the sake ofmodifying some particular character; but with most of the improved races ofthe pig, which now breed true, there have been repeated crosses, --forinstance, the improved Essex owes its excellence to repeated crosses withthe Neapolitan, together probably with some infusion of Chinese blood. [200]So with our British sheep: almost all the races, except the Southdown, havebeen largely crossed; "this, in fact, has been the history of our principalbreeds. "[201] To give an example, the "Oxfordshire Downs" now rank as anestablished breed. [202] They were produced about the year 1830 by crossing"Hampshire and in some instances Southdown ewes with Cotswold rams:" nowthe Hampshire ram was itself produced by repeated crosses between thenative {96} Hampshire sheep and Southdowns; and the long-woolled Cotswoldwere improved by crosses with the Leicester, which latter again is believedto have been a cross between several long-woolled sheep. Mr. Spooner, afterconsidering the various cases which have been carefully recorded, concludes"that from a judicious pairing of cross-bred animals it is practicable toestablish a new breed. " On the Continent the history of several crossedraces of cattle and of other animals has been well ascertained. To give oneinstance: the King of Wurtemberg, after twenty-five years' carefulbreeding, that is after six or seven generations, made a new breed ofcattle from a cross between a Dutch and Swiss breed, combined with otherbreeds. [203] The Sebright bantam, which breeds as true as any other kind offowl, was formed about sixty years ago by a complicated cross. [204] DarkBrahmas, which are believed by some fanciers to constitute a distinctspecies, were undoubtedly formed[205] in the United States, within a recentperiod, by a cross between Chittagongs and Cochins. With plants I believethere is little doubt that some kinds of turnips, now extensivelycultivated, are crossed races; and the history of a variety of wheat whichwas raised from two very distinct varieties, and which after six years'culture presented an even sample, has been recorded on good authority. [206] Until quite lately, cautious and experienced breeders, though not averse toa single infusion of foreign blood, were almost universally convinced thatthe attempt to establish a new race, intermediate between two widelydistinct races, was hopeless: "they clung with superstitious tenacity tothe doctrine of purity of blood, believing it to be the ark in which alonetrue safety could be found. "[207] Nor was this conviction unreasonable:when two distinct races are crossed, the offspring of the first generationare generally nearly uniform in character; but even this sometimes fails tobe the case, especially with crossed dogs and fowls, the young of whichfrom the first are sometimes much {97} diversified. As cross-bred animalsare generally of large size and vigorous, they have been raised in greatnumbers for immediate consumption. But for breeding they are found to beutterly useless; for though they may be themselves uniform in character, when paired together they yield during many generations offspringastonishingly diversified. The breeder is driven to despair, and concludesthat he will never form an intermediate race. But from the cases alreadygiven, and from others which have been recorded, it appears that patiencealone is necessary; as Mr. Spooner remarks, "nature opposes no barrier tosuccessful admixture; in the course of time, by the aid of selection andcareful weeding, it is practicable to establish a new breed. " After six orseven generations the hoped-for result will in most cases be obtained; buteven then an occasional reversion, or failure to keep true, may beexpected. The attempt, however, will assuredly fail if the conditions oflife be decidedly unfavourable to the characters of eitherparent-breed. [208] Although the grandchildren and succeeding generations of cross-bred animalsare generally variable in an extreme degree, some curious exceptions to therule have been observed, both with crossed races and species. Thus Boitardand Corbié[209] assert that from a Pouter and a Runt "a Cavalier willappear, which we have classed amongst pigeons of pure race, because ittransmits all its qualities to its posterity. " The editor of the 'PoultryChronicle'[210] bred some bluish fowls from a black Spanish cock and aMalay hen; and these remained true to colour "generation after generation. "The Himalayan breed of rabbits was certainly formed by crossing twosub-varieties of the silver-grey rabbit; although it suddenly assumed itspresent character, which differs much from that of either parent-breed, yetit has ever since been easily and truly propagated. I crossed some Labradorand Penguin ducks, and recrossed the mongrels with Penguins; afterwards, most of the ducks reared during three generations were nearly uniform incharacter, being brown with a white crescentic mark on the lower part ofthe breast, {98} and with some white spots at the base of the beak; so thatby the aid of a little selection a new breed might easily have been formed. In regard to crossed varieties of plants, Mr. Beaton remarks[211] that"Melville's extraordinary cross between the Scotch kale and an earlycabbage is as true and genuine as any on record;" but in this case no doubtselection was practised. Gärtner[212] has given five cases of hybrids, inwhich the progeny kept constant; and hybrids between _Dianthus armeria_ and_deltoides_ remained true and uniform to the tenth generation. Dr. Herbertlikewise showed me a hybrid from two species of Loasa which from its firstproduction had kept constant during several generations. We have seen in the earlier chapters, that some of our domesticatedanimals, such as dogs, cattle, pigs, &c. , are almost certainly descendedfrom more than one species, or wild race, if any one prefers to apply thislatter term to forms which were enabled to keep distinct in a state ofnature. Hence the crossing of aboriginally distinct species probably cameinto play at an early period in the formation of our present races. FromRütimeyer's observations there can be little doubt that this occurred withcattle; but in most cases some one of the forms which were allowed to crossfreely, will, it is probable, have absorbed and obliterated the others. Forit is not likely that semi-civilized men would have taken the necessarypains to modify by selection their commingled, crossed, and fluctuatingstock. Nevertheless, those animals which were best adapted to theirconditions of life would have survived through natural selection; and bythis means crossing will often have indirectly aided in the formation ofprimeval domesticated breeds. Within recent times, as far as animals are concerned, the crossing ofdistinct species has done little or nothing in the formation ormodification of our races. It is not yet known whether the species ofsilk-moth which have been recently crossed in France will yield permanentraces. In the fourth chapter I alluded with some hesitation to thestatement that a new breed, between the hare and rabbit, called leporides, had been formed in France, and was found capable of propagating {99}itself; but it is now positively affirmed[213] that this is an error. Withplants which can be multiplied by buds and cuttings, hybridisation has donewonders, as with many kinds of Roses, Rhododendrons, Pelargoniums, Calceolarias, and Petunias. Nearly all these plants can be propagated byseed; most of them freely; but extremely few or none come true by seed. Some authors believe that crossing is the chief cause of variability, --thatis, of the appearance of absolutely new characters. Some have gone so faras to look at it as the sole cause; but this conclusion is disproved bysome of the facts given in the chapter on Bud-variation. The belief thatcharacters not present in either parent or in their ancestors frequentlyoriginate from crossing is doubtful; that they occasionally thus arise isprobable; but this subject will be more conveniently discussed in a futurechapter on the causes of Variability. A condensed summary of this and of the three following chapters, togetherwith some remarks on Hybridism, will be given in the nineteenth chapter. * * * * * {100} CHAPTER XVI. CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--INFLUENCE OFDOMESTICATION ON FERTILITY. DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED--VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUAL PREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED--VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO, RENDERED IN SOME DEGREE MUTUALLY STERILE--DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY NATURAL TO SPECIES WHEN CROSSED--ON THE INCREASED FERTILITY OF UNCROSSED ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION. The domesticated races of both animals and plants, when crossed, are withextremely few exceptions quite prolific, --in some cases even more so thanthe purely bred parent-races. The offspring, also, raised from such crossesare likewise, as we shall see in the following chapter, generally morevigorous and fertile than their parents. On the other hand, species whencrossed, and their hybrid offspring, are almost invariability in somedegree sterile; and here there seems to exist a broad and insuperabledistinction between races and species. The importance of this subject asbearing on the origin of species is obvious; and we shall hereafter recurto it. It is unfortunate how few precise observations have been made on thefertility of mongrel animals and plants during several successivegenerations. Dr. Broca[214] has remarked that no one has observed whether, for instance, mongrel dogs, bred _inter se_, are indefinitely fertile; yet, if a shade of infertility be detected by careful observation in theoffspring of natural forms when crossed, it is thought that their specificdistinction is proved. But so many breeds of sheep, cattle, pigs, dogs, andpoultry, have been crossed and recrossed in various ways, that anysterility, if it had existed, would from being injurious {101} almostcertainly have been observed. In investigating the fertility of crossedvarieties many sources of doubt occur. Whenever the least trace ofsterility between two plants, however closely allied, was observed byKölreuter, and more especially by Gärtner, who counted the exact number ofseed in each capsule, the two forms were at once ranked as distinctspecies; and if this rule be followed, assuredly it will never be provedthat varieties when crossed are in any degree sterile. We have formerlyseen that certain breeds of dogs do not readily pair together; but noobservations have been made whether, when paired, they produce the fullnumber of young, and whether the latter are perfectly fertile _inter se_;but, supposing that some degree of sterility were found to exist, naturalists would simply infer that these breeds were descended fromaboriginally distinct species; and it would be scarcely possible toascertain whether or not this explanation was the true one. The Sebright Bantam is much less prolific than any other breed of fowls, and is descended from a cross between two very distinct breeds, recrossedby a third sub-variety. But it would be extremely rash to infer that theloss of fertility was in any manner connected with its crossed origin, forit may with more probability be attributed either to long-continued closeinterbreeding, or to an innate tendency to sterility correlated with theabsence of hackles and sickle tail-feathers. Before giving the few recorded cases of forms, which must be ranked asvarieties, being in some degree sterile when crossed, I may remark thatother causes sometimes interfere with varieties freely intercrossing. Thusthey may differ too greatly in size, as with some kinds of dogs and fowls:for instance, the editor of the 'Journal of Horticulture, &c. , '[215] saysthat he can keep Bantams with the larger breeds without much danger oftheir crossing, but not with the smaller breeds, such as Games, Hamburgs, &c. With plants a difference in the period of flowering serves to keepvarieties distinct, as with the various kinds of maize and wheat: thusColonel Le Couteur[216] remarks, "the Talavera wheat, from flowering muchearlier than any other kind, is sure to continue pure. " In different partsof {102} the Falkland Islands the cattle are breaking up into herds ofdifferent colours; and those on the higher ground, which are generallywhite, usually breed, as I am informed by Admiral Sulivan, three monthsearlier than those on the lowlands; and this would manifestly tend to keepthe herds from blending. Certain domestic races seem to prefer breeding with their own kind; andthis is a fact of some importance, for it is a step towards thatinstinctive feeling which helps to keep closely allied species in a stateof nature distinct. We have now abundant evidence that, if it were not forthis feeling, many more hybrids would be naturally produced than is thecase. We have seen in the first chapter that the alco dog of Mexicodislikes dogs of other breeds; and the hairless dog of Paraguay mixes lessreadily with the European races, than the latter do with each other. InGermany the female Spitz-dog is said to receive the fox more readily thanwill other dogs; a female Australian Dingo in England attracted the wildmale foxes. But these differences in the sexual instinct and attractivepower of the various breeds may be wholly due to their descent fromdistinct species. In Paraguay the horses have much freedom, and anexcellent observer[217] believes that the native horses of the same colourand size prefer associating with each other, and that the horses which havebeen imported from Entre Rios and Banda Oriental into Paraguay likewiseprefer associating together. In Circassia six sub-races of the horse areknown and have received distinct names; and a native proprietor ofrank[218] asserts that horses of three of these races, whilst living a freelife, almost always refuse to mingle and cross, and will even attack eachother. It has been observed, in a district stocked with heavy Lincolnshire andlight Norfolk sheep, that both kinds, though bred together, when turnedout, "in a short time separate to a sheep;" the Lincolnshires drawing offto the rich soil, and the Norfolks to their own dry light soil; and as longas there is plenty of grass, "the two breeds keep themselves as distinct asrooks and pigeons. " In this case different habits of {103} life tend tokeep the races distinct. On one of the Faroe islands, not more than half amile in diameter, the half-wild native black sheep are said not to havereadily mixed with the imported white sheep. It is a more curious fact thatthe semi-monstrous ancon sheep of modern origin "have been observed to keeptogether, separating themselves from the rest of the flock, when put intoenclosures with other sheep. "[219] With respect to fallow deer, which livein a semi-domesticated condition, Mr. Bennett[220] states that the dark andpale coloured herds, which have long been kept together in the Forest ofDean, in High Meadow Woods, and in the New Forest, have never been known tomingle: the dark-coloured deer, it may be added, are believed to have beenfirst brought by James I. From Norway, on account of their greaterhardiness. I imported from the island of Porto Santo two of the feralrabbits, which differ, as described in the fourth chapter, from commonrabbits; both proved to be males, and, though they lived during some yearsin the Zoological Gardens, the superintendent, Mr. Bartlett, in vainendeavoured to make them breed with various tame kinds; but whether thisrefusal to breed was due to any change in instinct, or simply to theirextreme wildness; or whether confinement had rendered them sterile, asoften occurs, cannot be told. Whilst matching for the sake of experiment many of the most distinct breedsof pigeons, it frequently appeared to me that the birds, though faithful totheir marriage vow, retained some desire after their own kind. AccordinglyI asked Mr. Wicking, who has kept a larger stock of various breeds togetherthan any man in England, whether he thought that they would prefer pairingwith their own kind, supposing that there were males and females enough ofeach; and he without hesitation answered that he was convinced that thiswas the case. It has often been noticed that the dovecot pigeon seems tohave an actual aversion towards the several fancy breeds;[221] yet all have{104} certainly sprung from a common progenitor. The Rev. W. D. Fox informsme that his flocks of white and common Chinese geese kept distinct. These facts and statements, though some of them are incapable of proof, resting only on the opinion of experienced observers, show that somedomestic races are led by different habits of life to keep to a certainextent separate, and that others prefer coupling with their own kind, inthe same manner as species in a state of nature, though in a much lessdegree. With respect to sterility from the crossing of domestic races, I know of no well-ascertained case with animals. This fact, seeing the great difference in structure between some breeds of pigeons, fowls, pigs, dogs, &c. , is extraordinary, in contrast with the sterility of many closely allied natural species when crossed; but we shall hereafter attempt to show that it is not so extraordinary as it at first appears. And it may be well here to recall to mind that the amount of external difference between two species will not safely guide us in foretelling whether or not they will breed together, --some closely allied species when crossed being utterly sterile, and others which are extremely unlike being moderately fertile. I have said that no case of sterility in crossed races rests on satisfactory evidence; but here is one which at first seems trustworthy. Mr. Youatt, [222] and a better authority cannot be quoted, states, that formerly in Lancashire crosses were frequently made between longhorn and shorthorn cattle; the first cross was excellent, but the produce was uncertain; in the third or fourth generation the cows were bad milkers; "in addition to which, there was much uncertainty whether the cows would conceive; and full one-third of the cows among some of these half-breds failed to be in calf. " This at first seems a good case; but Mr. Wilkinson states, [223] that a breed derived from this same cross was actually established in another part of England; and if it had failed in fertility, the fact would surely have been noticed. Moreover, supposing that Mr. Youatt had proved his case, it might be argued that the sterility was wholly due to the two parent-breeds being descended from primordially distinct species. I will give a case with plants, to show how difficult it is to get sufficient evidence. Mr. Sheriff, who has been so successful in the formation of new races of wheat, fertilised the Hopetoun with the Talavera; in the first and second generations the produce was intermediate in character, but in the fourth generation "it was found to consist of many varieties; nine-tenths of the florets proved barren, and many of the seeds seemed shrivelled abortions, void of vitality, and the whole race was evidently verging to extinction. "[224] Now, considering how little these {105} varieties of wheat differ in any important character, it seems to me very improbable that the sterility resulted, as Mr. Sheriff thought, from the cross, but from some quite distinct cause. Until such experiments are many times repeated, it would be rash to trust them; but unfortunately they have been rarely tried even once with sufficient care. Gärtner has recorded a more remarkable and trustworthy case: he fertilised thirteen panicles (and subsequently nine others) on a dwarf maize bearing yellow seed[225] with pollen of a tall maize having red seed; and one head alone produced good seed, only five in number. Though these plants are monoecious, and therefore do not require castration, yet I should have suspected some accident in the manipulation had not Gärtner expressly stated that he had during many years grown these two varieties together, and they did not spontaneously cross; and this, considering that the plants are monoecious and abound with pollen, and are well known generally to cross freely, seems explicable only on the belief that these two varieties are in some degree mutually infertile. The hybrid plants raised from the above five seed were intermediate in structure, extremely variable, and perfectly fertile. [226] No one, I believe, has hitherto suspected that these varieties of maize are distinct species; but had the hybrids been in the least sterile, no doubt Gärtner would at once have so classed them. I may here remark, that with undoubted species there is not necessarily any close relation between the sterility of a first cross and that of the hybrid offspring. Some species can be crossed with facility, but produce utterly sterile hybrids; others can be crossed with extreme difficulty, but the hybrids when produced are moderately fertile. I am not aware, however, of any instance quite like this of the maize with natural species, namely, of a first cross made with difficulty, but yielding perfectly fertile hybrids. The following case is much more remarkable, and evidently perplexed Gärtner, whose strong wish it was to draw a broad line of distinction between species and varieties. In the genus Verbascum, he made, during eighteen years, a vast number of experiments, and crossed no less than 1085 flowers and counted their seeds. Many of these experiments consisted in crossing white and yellow varieties of both _V. Lychnitis_ and _V. Blattaria_ with nine other species and their hybrids. That the white and yellow flowered plants of these two species are really varieties, no one has doubted; and Gärtner actually raised in the case of both species one variety from the seed of the other. Now in two of his works[227] he distinctly asserts that crosses between similarly-coloured flowers yield more seed than between dissimilarly-coloured; so that the yellow-flowered variety of either species (and conversely with the white-flowered variety), when crossed with pollen of its own kind, yields more seed than when crossed with that of the white variety; and so it is when differently coloured species are crossed. The general results may be seen in the Table at the {106} end of his volume. In one instance he gives[228] the following details; but I must premise that Gärtner, to avoid exaggerating the degree of sterility in his crosses, always compares the _maximum_ number obtained from a cross with the _average_ number naturally given by the pure mother-plant. The white-variety of _V. Lychnitis_, naturally fertilised by its own pollen, gave from an _average_ of twelve capsules ninety-six good seeds in each; whilst twenty flowers fertilised with pollen from the yellow variety of this same species, gave as the _maximum_ only eighty-nine good seed; so that we have the proportion of 1000 to 908, according to Gärtner's usual scale. I should have thought it possible that so small a difference in fertility might have been accounted for by the evil effects of the necessary castration; but Gärtner shows that the white variety of _V. Lychnitis_, when fertilised first by the white variety of _V. Blattaria_, and then by the yellow variety of this species, yielded seed in the proportion of 622 to 438; and in both these cases castration was performed. Now the sterility which results from the crossing of the differently coloured varieties of the same species, is fully as great as that which occurs in many cases when distinct species are crossed. Unfortunately Gärtner compared the results of the first unions alone, and not the sterility of the two sets of hybrids produced from the white variety of _V. Lychnitis_ when fertilised by the white and yellow varieties of _V. Blattaria_, for it is probable that they would have differed in this respect. Mr. J. Scott has given me the results of a series of experiments on Verbascum, made by him in the Botanic Gardens of Edinburgh. He repeated some of Gärtner's experiments on distinct species, but obtained only fluctuating results; some confirmatory, but the greater number contradictory; nevertheless these seem hardly sufficient to overthrow the conclusions arrived at by Gärtner from experiments tried on a much larger scale. In the second place Mr. Scott experimented on the relative fertility of unions between similarly and dissimilarly-coloured varieties of the same species. Thus he fertilised six flowers of the yellow variety of _V. Lychnitis_ by its own pollen, and obtained six capsules, and calling, for the sake of having a standard of comparison, the average number of good seed in each one hundred, he found that this same yellow variety, when fertilised by the white variety, yielded from seven capsules an average of ninety-four seed. On the same principle, the white variety of _V. Lychnitis_ by its own pollen (from six capsules), and by the pollen of the yellow variety (eight capsules), yielded seed in the proportion of 100 to 82. The yellow variety of _V. Thapsus_ by its own pollen (eight capsules), and by that of the white variety (only two capsules), yielded seed in the proportion of 100 to 94. Lastly, the white variety of _V. Blattaria_ by its own pollen (eight capsules), and by that of the yellow variety (five capsules), yielded seed in the proportion of 100 to 79. So that in every case the unions of dissimilarly-coloured varieties of the same species were less fertile than the unions of similarly-coloured varieties; when all the cases are grouped together, the difference of fertility is as 86 to 100. Some additional trials were made, and altogether thirty-six similarly-coloured unions yielded thirty-five good {107} capsules; whilst thirty-five dissimilarly-coloured unions yielded only twenty-six good capsules. Besides the foregoing experiments, the purple _V. Phoeniceum_ was crossed by a rose-coloured and a white variety of the same species; these two varieties were also crossed together, and these several unions yielded less seed than _V. Phoeniceum_ by its own pollen. Hence it follows from Mr. Scott's experiments, that in the genus Verbascum the similarly and dissimilarly-coloured varieties of the same species behave, when crossed, like closely allied but distinct species. [229] This remarkable fact of the sexual affinity of similarly-coloured varieties, as observed by Gärtner and Mr. Scott, may not be of very rare occurrence; for the subject has not been attended to by others. The following case is worth giving, partly to show how difficult it is to avoid error. Dr. Herbert[230] has remarked that variously-coloured double varieties of the hollyhock (_Althæa rosea_) may be raised with certainty by seed from plants growing close together. I have been informed that nurserymen who raise seed for sale do not separate their plants; accordingly I procured seed of eighteen named varieties; of these, eleven varieties produced sixty-two plants all perfectly true to their kind; and seven produced forty-nine plants, half of which were true and half false. Mr. Masters of Canterbury has given me a more striking case; he saved seed from a great bed of twenty-four named varieties planted in closely adjoining rows, and each variety reproduced itself truly with only sometimes a shade of difference in tint. Now in the hollyhock the pollen, which is abundant, is matured and nearly all shed before the stigma of the same flower is ready to receive it;[231] and as bees covered with pollen incessantly fly from plant to plant, it would appear that adjoining varieties could not escape being crossed. As, however, this does not occur, it appeared to me probable that the pollen {108} of each variety was prepotent on its own stigma over that of all other varieties. But Mr. C. Turner of Slough, well known for his success in the cultivation of this plant, informs me that it is the doubleness of the flowers which prevents the bees gaining access to the pollen and stigma; and he finds that it is difficult even to cross them artificially. Whether this explanation will fully account for varieties in close proximity propagating themselves so truly by seed, I do not know. The following cases are worth giving, as they relate to monoecious forms, which do not require, and consequently have not been injured by, castration. Girou de Buzareingues crossed what he designates three varieties of gourd, [232] and asserts that their mutual fertilisation is less easy in proportion to the difference which they present. I am aware how imperfectly the forms in this group were until recently known; but Sageret, [233] who ranked them according to their mutual fertility, considers the three forms above alluded to as varieties, as does a far higher authority, namely, M. Naudin. [234] Sageret[235] has observed that certain melons have a greater tendency, whatever the cause may be, to keep true than others; and M. Naudin, who has had such immense experience in this group, informs me that he believes that certain varieties intercross more readily than others of the same species; but he has not proved the truth of this conclusion; the frequent abortion of the pollen near Paris being one great difficulty. Nevertheless, he has grown close together, during seven years, certain forms of Citrullus, which, as they could be artificially crossed with perfect facility and produced fertile offspring, are ranked as varieties; but these forms when not artificially crossed kept true. Many other varieties, on the other hand, in the same group cross with such facility, as M. Naudin repeatedly insists, that without being grown far apart they cannot be kept in the least true. Another case, though somewhat different, may be here given, as it is highly remarkable, and is established on excellent evidence. Kölreuter minutely describes five varieties of the common tobacco, [236] which were reciprocally crossed, and the offspring were intermediate in character and as fertile as their parents: from this fact Kölreuter inferred that they are really varieties; and no one, as far as I can discover, seems to have doubted that such is the case. He also crossed reciprocally these five varieties with _N. Glutinosa_, and they yielded very sterile hybrids; but those raised from the _var. Perennis_, whether used as the father or mother plant, were not so sterile as the hybrids from the four other varieties. [237] So that the sexual {109} capacity of this one variety has certainly been in some degree modified, so as to approach in nature that of _N. Glutinosa_. [238] These facts with respect to plants show that in some few cases certainvarieties have had their sexual powers so far modified, that they crosstogether less readily and yield less seed than other varieties of the samespecies. We shall presently see that the sexual functions of most animalsand plants are eminently liable to be affected by the conditions of life towhich they are exposed; and hereafter we shall briefly discuss the conjointbearing of this and other facts on the difference in fertility betweencrossed varieties and crossed species. _Domestication eliminates the tendency to Sterility which is general withSpecies when crossed. _ This hypothesis was first propounded by Pallas, [239] and has been adoptedby several authors. I can find hardly any direct facts in its support; butunfortunately no one has compared, in the case of either animals or plants, the fertility of anciently domesticated varieties, when crossed with adistinct species, with that of the wild parent-species when similarlycrossed. No one has compared, for instance, the fertility of _Gallusbankiva_ and of the domesticated fowl, when crossed with a distinct speciesof Gallus or Phasianus; and the {110} experiment would in all cases besurrounded by many difficulties. Dureau de la Malle, who has so closelystudied classical literature, states[240] that in the time of the Romansthe common mule was produced with more difficulty than at the present day;but whether this statement may be trusted I know not. A much moreimportant, though somewhat different, case is given by M. Groenland, [241]namely, that plants, known from their intermediate character and sterilityto be hybrids between Ægilops and wheat, have perpetuated themselves underculture since 1857, _with a rapid but varying increase of fertility in eachgeneration_. In the fourth generation the plants, still retaining theirintermediate character, had become as fertile as common cultivated wheat. The indirect evidence in favour of the Pallasian doctrine appears to me tobe extremely strong. In the earlier chapters I have attempted to show thatour various breeds of dogs are descended from several wild species; andthis probably is the case with sheep. There can no longer be any doubt thatthe Zebu or humped Indian ox belongs to a distinct species from Europeancattle: the latter, moreover, are descended from two or three forms, whichmay be called either species or wild races, but which co-existed in a stateof nature and kept distinct. We have good evidence that our domesticatedpigs belong to at least two specific types, _S. Scrofa_ and _Indica_, whichprobably lived together in a wild state in South-eastern Europe. Now, awidely-extended analogy leads to the belief that if these several alliedspecies, in the wild state or when first reclaimed, had been crossed, theywould have exhibited, both in their first unions and in their hybridoffspring, some degree of sterility. Nevertheless the several domesticatedraces descended from them are now all, as far as can be ascertained, perfectly fertile together. If this reasoning be trustworthy, and it isapparently sound, we must admit the Pallasian doctrine that long-continueddomestication tends to eliminate that sterility which is natural to specieswhen crossed in their aboriginal state. {111} _On increased Fertility from Domestication and Cultivation. _ Increased fertility from domestication, without any reference to crossing, may be here briefly considered. This subject bears indirectly on two orthree points connected with the modification of organic beings. As Buffonlong ago remarked, [242] domestic animals breed oftener in the year andproduce more young at a birth than wild animals of the same species; they, also, sometimes breed at an earlier age. The case would hardly havedeserved further notice, had not some authors lately attempted to show thatfertility increases and decreases in an inverse ratio with the amount offood. This strange doctrine has apparently arisen from individual animalswhen supplied with an inordinate quantity of food, and from plants of manykinds when grown on excessively rich soil, as on a dunghill, becomingsterile; but to this latter point I shall have occasion presently toreturn. With hardly an exception, our domesticated animals, which have longbeen habituated to a regular and copious supply of food, without the labourof searching for it, are more fertile than the corresponding wild animals. It is notorious how frequently cats and dogs breed, and how many young theyproduce at a birth. The wild rabbit is said generally to breed four timesyearly, and to produce from four to eight young; the tame rabbit breeds sixor seven times yearly, and produces from four to eleven young. The ferret, though generally so closely confined, is more prolific than its supposedwild prototype. The wild sow is remarkably prolific, for she often breedstwice in the year, and produces from four to eight and sometimes eventwelve young at a birth; but the domestic sow regularly breeds twice ayear, and would breed oftener if permitted; and a sow that produces lessthan eight at a birth "is worth little, and the sooner she is fattened forthe butcher the better. " The amount of food affects the fertility even ofthe same individual: thus sheep, which on mountains never produce more thanone lamb at a birth, when brought {112} down to lowland pastures frequentlybear twins. This difference apparently is not due to the cold of the higherland, for sheep and other domestic animals are said to be extremelyprolific in Lapland. Hard living, also, retards the period at which animalsconceive; for it has been found disadvantageous in the northern islands ofScotland to allow cows to bear calves before they are four years old. [243] Birds offer still better evidence of increased fertility from domestication: the hen of the wild _Gallus bankiva_ lays from six to ten eggs, a number which would be thought nothing of with the domestic hen. The wild duck lays from five to ten eggs; the tame one in the course of the year from eighty to one hundred. The wild grey-lag goose lays from five to eight eggs; the tame from thirteen to eighteen, and she lays a second time; as Mr. Dixon has remarked, "high-feeding, care, and moderate warmth induce a habit of prolificacy which becomes in some measure hereditary. " Whether the semi-domesticated dovecot pigeon is more fertile than the wild rock-pigeon _C. Livia_, I know not; but the more thoroughly domesticated breeds are nearly twice as fertile as dovecots: the latter, however, when caged and highly fed, become equally fertile with house pigeons. The peahen alone of domesticated birds is rather more fertile, according to some accounts, when wild in its native Indian home, than when domesticated in Europe and exposed to our much colder climate. [244] With respect to plants, no one would expect wheat to tiller more, and each ear to produce more grain, in poor than in rich soil; or to get in poor soil a heavy crop of peas or beans. Seeds vary so much in number {113} that it is difficult to estimate them; but on comparing beds of carrots saved for seed in a nursery garden with wild plants, the former seemed to produce about twice as much seed. Cultivated cabbages yielded thrice as many pods by measure as wild cabbages from the rocks of South Wales. The excess of berries produced by the cultivated Asparagus in comparison with the wild plant is enormous. No doubt many highly cultivated plants, such as pears, pineapples, bananas, sugar-cane, &c. , are nearly or quite sterile; and I am inclined to attribute this sterility to excess of food and to other unnatural conditions; but to this subject I shall presently recur. In some cases, as with the pig, rabbit, &c. , and with those plants whichare valued for their seed, the direct selection of the more fertileindividuals has probably much increased their fertility; and in all casesthis may have occurred indirectly, from the better chance of the morenumerous offspring produced by the more fertile individuals havingsurvived. But with cats, ferrets, and dogs, and with plants like carrots, cabbages, and asparagus, which are not valued for their prolificacy, selection can have played only a subordinate part; and their increasedfertility must be attributed to the more favourable conditions of lifeunder which they have long existed. * * * * * {114} CHAPTER XVII. ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSEINTERBREEDING. DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID TENDENCIES--GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM CROSSING, AND ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING--CATTLE, CLOSELY INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME PARKS--SHEEP--FALLOW-DEER--DOGS--RABBITS--PIGS--MAN, ORIGIN OF HIS ABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS, GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS, FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED SIZE OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON CERTAIN PLANTS WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE, BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES--CONCLUSION. The gain in constitutional vigour, derived from an occasional cross betweenindividuals of the same variety, but belonging to distinct families, orbetween distinct varieties, has not been so largely or so frequentlydiscussed, as have the evil effects of too close interbreeding. But theformer point is the more important of the two, inasmuch as the evidence ismore decisive. The evil results from close interbreeding are difficult todetect, for they accumulate slowly, and differ much in degree withdifferent species; whilst the good effects which almost invariably follow across are from the first manifest. It should, however, be clearlyunderstood that the advantage of close interbreeding, as far as theretention of character is concerned, is indisputable, and often outweighsthe evil of a slight loss of constitutional vigour. In relation to thesubject of domestication, the whole question is of some importance, as tooclose interbreeding interferes with the improvement of old races, andespecially with the formation of new ones. It is important as indirectlybearing on Hybridism; and perhaps on the extinction of species, when anyform has become so rare that only a few individuals {115} remain within aconfined area. It bears in an important manner on the influence of freeintercrossing, in obliterating individual differences, and thus givinguniformity of character to the individuals of the same race or species; forif additional vigour and fertility be thus gained, the crossed offspringwill multiply and prevail, and the ultimate result will be far greater thanotherwise would have occurred. Lastly, the question is of high interest, asbearing on mankind. Hence I shall discuss this subject at full length. Asthe facts which prove the evil effects of close interbreeding are morecopious, though less decisive, than those on the good effects of crossing, I shall, under each group of beings, begin with the former. There is no difficulty in defining what is meant by a cross; but this is byno means easy in regard to "breeding in and in" or "too closeinterbreeding, " because, as we shall see, different species of animals aredifferently affected by the same degree of interbreeding. The pairing of afather and daughter, or mother and son, or brothers and sisters, if carriedon during several generations, is the closest possible form ofinterbreeding. But some good judges, for instance Sir J. Sebright, believethat the pairing of a brother and sister is closer than that of parents andchildren; for when the father is matched with his daughter he crosses, asis said, with only half his own blood. The consequences of closeinterbreeding carried on for too long a time, are, as is generallybelieved, loss of size, constitutional vigour, and fertility, sometimesaccompanied by a tendency to malformation. Manifest evil does not usuallyfollow from pairing the nearest relations for two, three, or even fourgenerations; but several causes interfere with our detecting the evil--suchas the deterioration being very gradual, and the difficulty ofdistinguishing between such direct evil and the inevitable augmentation ofany morbid tendencies which may be latent or apparent in the relatedparents. On the other hand, the benefit from a cross, even when there hasnot been any very close interbreeding, is almost invariably at onceconspicuous. There is reason to believe, and this was the opinion of thatmost experienced observer Sir J. Sebright, [245] that the evil effects ofclose interbreeding may be checked by the related individuals {116} beingseparated during a few generations and exposed to different conditions oflife. That evil directly follows from any degree of close interbreeding has beendenied by many persons; but rarely by any practical breeder; and never, asfar as I know, by one who has largely bred animals which propagate theirkind quickly. Many physiologists attribute the evil exclusively to thecombination and consequent increase of morbid tendencies common to bothparents: that this is an active source of mischief there can be no doubt. It is unfortunately too notorious that men and various domestic animalsendowed with a wretched constitution, and with a strong hereditarydisposition to disease, if not actually ill, are fully capable ofprocreating their kind. Close interbreeding, on the other hand, inducessterility; and this indicates something quite distinct from theaugmentation of morbid tendencies common to both parents. The evidenceimmediately to be given convinces me that it is a great law of nature, thatall organic beings profit from an occasional cross with individuals notclosely related to them in blood; and that, on the other hand, long-continued close interbreeding is injurious. Various general considerations have had much influence in leading me tothis conclusion; but the reader will probably rely more on special factsand opinions. The authority of experienced observers, even when they do notadvance the grounds of their belief, is of some little value. Now almostall men who have bred many kinds of animals and have written on thesubject, such as Sir J. Sebright, Andrew Knight, &c. , [246] have expressedthe strongest conviction on the impossibility of long-continued closeinterbreeding. Those who have compiled works on agriculture, and haveassociated much with breeders, such as the sagacious Youatt, Low, &c. , havestrongly declared their opinion to the same effect. Prosper Lucas, trustinglargely to French authorities, has come to a similar conclusion. Thedistinguished German agriculturist Hermann von Nathusius, who has writtenthe most able treatise on this subject which I have met with, concurs; andas I shall have to quote from {117} this treatise, I may state thatNathusius is not only intimately acquainted with works on agriculture inall languages, and knows the pedigrees of our British breeds better thanmost Englishmen, but has imported many of our improved animals, and ishimself an experienced breeder. Evidence of the evil effects of close interbreeding can most readily beacquired in the case of animals, such as fowls, pigeons, &c. , whichpropagate quickly, and, from being kept in the same place, are exposed tothe same conditions. Now I have inquired of very many breeders of thesebirds, and I have hitherto not met with a single man who was not thoroughlyconvinced that an occasional cross with another strain of the samesub-variety was absolutely necessary. Most breeders of highly-improved orfancy birds value their own strain, and are most unwilling, at the risk, intheir opinion, of deterioration, to make a cross. The purchase of afirst-rate bird of another strain is expensive, and exchanges aretroublesome; yet all breeders, as far as I can hear, excepting those whokeep large stocks at different places for the sake of crossing, are drivenafter a time to take this step. Another general consideration which has had great influence on my mind is, that with all hermaphrodite animals and plants, which it might have beenthought would have perpetually fertilised themselves, and thus have beensubjected for long ages to the closest interbreeding, there is no singlespecies, as far as I can discover, in which the structure ensuresself-fertilisation. On the contrary, there are in a multitude of cases, asbriefly stated in the fifteenth chapter, manifest adaptations which favouror inevitably lead to an occasional cross between one hermaphrodite andanother of the same species; and these adaptive structures are utterlypurposeless, as far as we can see, for any other end. With _Cattle_ there can be no doubt that extremely close interbreeding may be long carried on, advantageously with respect to external characters and with no manifestly apparent evil as far as constitution is concerned. The same remark is applicable to sheep. Whether these animals have gradually been rendered less susceptible than others to this evil, in order to permit them to live in herds, --a habit which leads the old and vigorous males to expel all intruders, and in consequence often to pair with their own daughters, I will not pretend to decide. The case of Bakewell's Long-horns, which were closely interbred for a long period, has often been {118} quoted; yet Youatt says[247] the breed "had acquired a delicacy of constitution inconsistent with common management, " and "the propagation of the species was not always certain. " But the Shorthorns offer the most striking case of close interbreeding; for instance, the famous bull Favourite (who was himself the offspring of a half-brother and sister from Foljambe) was matched with his own daughter, granddaughter, and great-granddaughter; so that the produce of this last union, or the great-great-granddaughter, had 15-16ths, or 93. 75 per cent. Of the blood of Favourite in her veins. This cow was matched with the bull Wellington, having 62. 5 per cent. Of Favourite blood in his veins, and produced Clarissa; Clarissa was matched with the bull Lancaster, having 68. 75 of the same blood, and she yielded valuable offspring. [248] Nevertheless Collings, who reared these animals, and was a strong advocate for close breeding, once crossed his stock with a Galloway, and the cows from this cross realised the highest prices. Bates's herd was esteemed the most celebrated in the world. For thirteen years he bred most closely in and in; but during the next seventeen years, though he had the most exalted notion of the value of his own stock, he thrice infused fresh blood into his herd: it is said that he did this, not to improve the form of his animals, but on account of their lessened fertility. Mr. Bates's own view, as given by a celebrated breeder, [249] was, that "to breed in and in from a bad stock was ruin and devastation; yet that the practice may be safely followed within certain limits when the parents so related are descended from first-rate animals. " We thus see that there has been extremely close interbreeding with Shorthorns; but Nathusius, after the most careful study of their pedigrees, says that he can find no instance of a breeder who has strictly followed this practice during his whole life. From this study and his own experience, he concludes that close interbreeding is necessary to ennoble the stock; but that in effecting this the greatest care is necessary, on account of the tendency to infertility and weakness. It may be added, that another high authority[250] asserts that many more calves are born cripples from Shorthorns than from other and less closely interbred races of cattle. Although by carefully selecting the best animals (as Nature effectually does by the law of battle) close interbreeding may be long carried on with cattle, yet the good effects of a cross between almost any two breeds is at once shown by the greater size and vigour of the offspring; as Mr. Spooner writes to me, "crossing distinct breeds certainly improves cattle for the butcher. " Such crossed animals are of course of no value to the breeder; but they have been raised during many years in several {119} parts of England to be slaughtered;[251] and their merit is now so fully recognised, that at fat-cattle shows a separate class has been formed for their reception. The best fat ox at the great show at Islington in 1862 was a crossed animal. The half-wild cattle, which have been kept in British parks probably for 400 or 500 years, or even for a longer period, have been advanced by Culley and others as a case of long-continued interbreeding within the limits of the same herd without any consequent injury. With respect to the cattle at Chillingham, the late Lord Tankerville owned that they were bad breeders. [252] The agent, Mr. Hardy, estimates (in a letter to me, dated May, 1861) that in the herd of about fifty the average number annually slaughtered, killed by fighting, and dying, is about ten, or one in five. As the herd is kept up to nearly the same average number, the annual rate of increase must be likewise about one in five. The bulls, I may add, engage in furious battles, of which battles the present Lord Tankerville has given me a graphic description, so that there will always be rigorous selection of the most vigorous males. I procured in 1855 from Mr. D. Gardner, agent to the Duke of Hamilton, the following account of the wild cattle kept in the Duke's park in Lanarkshire, which is about 200 acres in extent. The number of cattle varies from sixty-five to eighty; and the number annually killed (I presume by all causes) is from eight to ten; so that the annual rate of increase can hardly be more than one in six. Now in South America, where the herds are half-wild, and therefore offer a nearly fair standard of comparison, according to Azara the natural increase of the cattle on an estancia is from one-third to one-fourth of the total number, or one in between three and four; and this, no doubt, applies exclusively to adult animals fit for consumption. Hence the half-wild British cattle which have long interbred within the limits of the same herd are relatively far less fertile. Although in an unenclosed country like Paraguay there must be some crossing between the different herds, yet even there the inhabitants believe that the occasional introduction of animals from distant localities is necessary to prevent "degeneration in size and diminution of fertility. "[253] The decrease in size from ancient times in the Chillingham and Hamilton cattle must have been prodigious, for Professor Rütimeyer has shown that they are almost certainly the descendants of the gigantic _Bos primigenius_. No doubt this decrease in size may be largely attributed to less favourable conditions of life; yet animals roaming over large parks, and fed during severe winters, can hardly be considered as placed under very unfavourable conditions. With _Sheep_ there has often been long-continued interbreeding within the limits of the same flock; but whether the nearest relations have been matched so frequently as in the case of Shorthorn cattle, I do not know. The Messrs. Brown during fifty years have never infused fresh blood into their excellent flock of Leicesters. Since 1810 Mr. Barford has acted on the same principle with the Foscote flock. He asserts that half a century {120} of experience has convinced him that when two nearly related animals are quite sound in constitution, in-and-in breeding does not induce degeneracy; but he adds that he "does not pride himself on breeding from the nearest affinities. " In France the Naz flock has been bred for sixty years without the introduction of a single strange ram. [254] Nevertheless, most great breeders of sheep have protested against close interbreeding prolonged for too great a length of time. [255] The most celebrated of recent breeders, Jonas Webb, kept five separate families to work on, thus "retaining the requisite distance of relationship between the sexes. "[256] Although by the aid of careful selection the near interbreeding of sheep may be long continued without any manifest evil, yet it has often been the practice with farmers to cross distinct breeds to obtain animals for the butcher, which plainly shows that good is derived from this practice. Mr. Spooner sums up his excellent Essay on Crossing by asserting that there is a direct pecuniary advantage in judicious cross-breeding, especially when the male is larger than the female. A former celebrated breeder, Lord Somerville, distinctly states that his half-breeds from Ryelands and Spanish sheep were larger animals than either the pure Ryelands or pure Spanish sheep. [257] As some of our British parks are ancient, it occurred to me that there must have been long-continued close interbreeding with the fallow deer (_Cervus dama_) kept in them; but on inquiry I find that it is a common practice to infuse new blood by procuring bucks from other parks. Mr. Shirley, [258] who has carefully studied the management of deer, admits that in some parks there has been no admixture of foreign blood from a time beyond the memory of man. But he concludes "that in the end the constant breeding in-and-in is sure to tell to the disadvantage of the whole herd, though it may take a very long time to prove it; moreover, when we find, as is very constantly the case, that the introduction of fresh blood has been of the very greatest use to deer, both by improving their size and appearance, and particularly by being of service in removing the taint of 'rickback, ' if not of other diseases, to which deer are sometimes subject when the blood has not been changed, there can, I think, be no doubt but that a judicious cross with a good stock is of the greatest consequence, and is indeed essential, sooner or later, to the prosperity of every well-ordered park. " Mr. Meynell's famous foxhounds have been adduced, as showing that no ill effects follow from close interbreeding; and Sir J. Sebright ascertained from him that he frequently bred from father and daughter, mother and {121} son, and sometimes even from brothers and sisters. Sir J. Sebright, however, declares, [259] that by breeding _in-and-in_, by which he means matching brothers and sisters, he has actually seen strong spaniels become weak and diminutive lapdogs. The Rev. W. D. Fox has communicated to me the case of a small lot of bloodhounds, long kept in the same family, which had become very bad breeders, and nearly all had a bony enlargement in the tail. A single cross with a distinct strain of bloodhounds restored their fertility, and drove away the tendency to malformation in the tail. I have heard the particulars of another case with bloodhounds, in which the female had to be held to the male. Considering how rapid is the natural increase of the dog, it is difficult to understand the high price of most highly improved breeds, which almost implies long-continued close interbreeding, except on the belief that this process lessens fertility and increases liability to distemper and other diseases. A high authority, Mr. Scrope, attributes the rarity and deterioration in size of the Scotch deerhound (the few individuals now existing throughout the country being all related) in large part to close interbreeding. With all highly-bred animals there is more or less difficulty in getting them to procreate quickly, and all suffer much from delicacy of constitution; but I do not pretend that these effects ought to be wholly attributed to close interbreeding. A great judge of rabbits[260] says, "the long-eared does are often too highly bred or forced in their youth to be of much value as breeders, often turning out barren or bad mothers. " Again: "Very long-eared bucks will also sometimes prove barren. " These highly-bred rabbits often desert their young, so that it is necessary to have nurse-rabbits. With _Pigs_ there is more unanimity amongst breeders on the evil effects of close interbreeding than, perhaps, with any other large animal. Mr. Druce, a great and successful breeder of the Improved Oxfordshires (a crossed race), writes, "without a change of boars of a different tribe, but of the same breed, constitution cannot be preserved. " Mr. Fisher Hobbs, the raiser of the celebrated Improved Essex breed, divided his stock into three separate families, by which means he maintained the breed for more than twenty years, "by judicious selection from the _three distinct families_. "[261] Lord Western was the first importer of a Neapolitan boar and sow. "From this pair he bred in-and-in, until the breed was in danger of becoming extinct, a sure result (as Mr. Sidney remarks) of in-and-in breeding. " Lord Western then crossed his Neapolitan pigs with the old Essex, and made the first great step towards the Improved Essex breed. Here is a more interesting case. Mr. J. Wright, well known as a breeder, crossed[262] the same boar with the daughter, granddaughter, and great-granddaughter, and so on for seven generations. The result was, that in many instances the offspring failed to breed; in others they produced few that lived; and of the latter many were idiotic, without sense {122} even to suck, and when attempting to move could not walk straight. Now it deserves especial notice, that the two last sows produced by this long course of interbreeding were sent to other boars, and they bore several litters of healthy pigs. The best sow in external appearance produced during the whole seven generations was one in the last stage of descent; but the litter consisted of this one sow. She would not breed to her sire, yet bred at the first trial to a stranger in blood. So that, in Mr. Wright's case, long-continued and extremely close interbreeding did not affect the external form or merit of the young; but with many of them the general constitution and mental powers, and especially the reproductive functions, were seriously affected. Nathusius gives[263] an analogous and even more striking case: he imported from England a pregnant sow of the large Yorkshire breed, and bred the product closely in-and-in for three generations: the result was unfavourable, as the young were weak in constitution, with impaired fertility. One of the latest sows, which he esteemed a good animal, produced, when paired with her own uncle (who was known to be productive with sows of other breeds), a litter of six, and a second time a litter of only five weak young pigs. He then paired this sow with a boar of a small black breed, which he had likewise imported from England, and which boar, when matched with sows of his own breed, produced from seven to nine young: now, the sow of the large breed, which was so unproductive when paired with her own uncle, yielded to the small black boar, in the first litter twenty-one, and in the second litter eighteen young pigs; so that in one year she produced thirty-nine fine young animals! As in the case of several other animals already mentioned, even when no injury is perceptible from moderately close interbreeding, yet, to quote the words of Mr. Coate, a most successful breeder (who five times won the annual gold medal of the Smithfield Club Show for the best pen of pigs), "Crosses answer well for profit to the farmer, as you get more constitution and quicker growth; but for me, who sell a great number of pigs for breeding purposes, I find it will not do, as it requires many years to get anything like purity of blood again. "[264] Before passing on to Birds, I ought to refer to man, though I am unwillingto enter on this subject, as it is surrounded by natural prejudices. It hasmoreover been discussed by various authors under many points of view. [265]Mr. Tylor[266] has shown {123} that with widely different races, in themost distant quarters of the world, marriages between relations--evenbetween distant relations--have been strictly prohibited. A few exceptionalcases can be specified, especially with royal families; and these have beenenlarged on in a learned article[267] by Mr. W. Adam, and formerly in 1828by Hofacker. Mr. Tylor is inclined to believe that the almost universalprohibition of closely-related marriages has arisen from their evil effectshaving been observed, and he ingeniously explains some apparent anomaliesin the prohibition not extending equally to the relations on both the maleand female side. He admits, however, that other causes, such as theextension of friendly alliances, may have come into play. Mr. W. Adam, onthe other hand, concludes that related marriages are prohibited and viewedwith repugnance from the confusion which would thus arise in the descent ofproperty, and from other still more recondite reasons; but I cannot acceptthis view, seeing that the savages of Australia and South America, [268] whohave no property to bequeath or fine moral feelings to confuse, hold thecrime of incest in abhorrence. It would be interesting to know, if it could be ascertained, as throwinglight on this question with respect to man, what occurs with the higheranthropomorphous apes--whether the young males and females soon wander awayfrom their parents, or whether the old males become jealous of their sonsand expel them, or whether any inherited instinctive feeling, from beingbeneficial, has been generated, leading the young males and females of thesame family to prefer pairing with distinct families, and to dislikepairing with each other. A considerable body of evidence has already beenadvanced, showing that the offspring from parents which are not related aremore vigorous and fertile than those from parents which are closelyrelated; hence any slight feeling, arising from the sexual excitement ofnovelty or other cause, which led to the former rather than to the latterunions, would be augmented through natural selection, and thus might becomeinstinctive; for those individuals which had an innate preference of thiskind would increase in number. It seems more probable, that degradedsavages should {124} thus unconsciously have acquired their dislike andeven abhorrence of incestuous marriages, rather than that they should havediscovered by reasoning and observation the evil results. The abhorrenceoccasionally failing is no valid argument against the feeling beinginstinctive, for any instinct may occasionally fail or become vitiated, assometimes occurs with parental love and the social sympathies. In the caseof man, the question whether evil follows from close interbreeding willprobably never be answered by direct evidence, as he propagates his kind soslowly and cannot be subjected to experiment; but the almost universalpractice of all races at all times of avoiding closely-related marriages isan argument of considerable weight; and whatever conclusion we arrive at inregard to the higher animals may be safely extended to man. Turning now to Birds: in the case of the _Fowl_ a whole array of authorities could be given against too close interbreeding. Sir J. Sebright positively asserts that he made many trials, and that his fowls, when thus treated, became long in the legs, small in the body, and bad breeders. [269] He produced the famous Sebright Bantams by complicated crosses, and by breeding in-and-in; and since his time there has been much close interbreeding with these Bantams; and they are now notoriously bad breeders. I have seen Silver Bantams, directly descended from his stock, which had become almost as barren as hybrids; for not a single chicken had been that year hatched from two full nests of eggs. Mr. Hewitt says that with these Bantams the sterility of the male stands, with rare exceptions, in the closest relation with their loss of certain secondary male characters: he adds, "I have noticed, as a general rule, that even the slightest deviation from feminine character in the tail of the male Sebright--say the elongation by only half an inch of the two principal tail-feathers--brings with it improved probability of increased fertility. "[270] Mr. Wright states[271] that Mr. Clark, "whose fighting-cocks were so notorious, continued to breed from his own kind till they lost their disposition to fight, but stood to be cut up without making any resistance, and were so reduced in size as to be under those weights required for the best prizes; but on obtaining a cross from Mr. Leighton, they again resumed their former courage and weight. " It should be borne in mind that game-cocks before they fought were always weighed, so that nothing was left to the imagination about any reduction or increase of {125} weight. Mr. Clark does not seem to have bred from brothers and sisters, which is the most injurious kind of union; and he found, after repeated trials, that there was a greater reduction in weight in the young from a father paired with his daughter, than from a mother with her son. I may add that Mr. Eyton, of Eyton, the well-known ornithologist, who is a large breeder of Grey Dorkings, informs me that they certainly diminish in size, and become less prolific, unless a cross with another strain is occasionally obtained. So it is with Malays, according to Mr. Hewitt, as far as size is concerned. [272] An experienced writer[273] remarks that the same amateur, as is well known, seldom long maintains the superiority of his birds; and this, he adds, undoubtedly is due to all his stock "being of the same blood;" hence it is indispensable that he should occasionally procure a bird of another strain. But this is not necessary with those who keep a stock of fowls at different stations. Thus, Mr. Ballance, who has bred Malays for thirty years, and has won more prizes with these birds than any other fancier in England, says that breeding in-and-in does not necessarily cause deterioration; "but all depends upon how this is managed. " "My plan has been to keep about five or six distinct runs, and to rear about two hundred or three hundred chickens each year, and select the best birds from each run for crossing. I thus secure sufficient crossing to prevent deterioration. "[274] We thus see that there is almost complete unanimity with poultry-breeders that, when fowls are kept at the same place, evil quickly follows from interbreeding carried on to an extent which would be disregarded in the case of most quadrupeds. On the other hand, it is a generally received opinion that cross-bred chickens are the hardiest and most easily reared. [275] Mr. Tegetmeier, who has carefully attended to poultry of all breeds, says[276] that Dorking hens, allowed to run with Houdan or Crevecoeur cocks, "produce in the early spring chickens that for size, hardihood, early maturity, and fitness for the market, surpass those of any pure breed that we have ever raised. " Mr. Hewitt gives it as a general rule with fowls, that crossing the breed increases their size. He makes this remark after stating that hybrids from the pheasant and fowl are considerably larger than either progenitor: so again, hybrids from the male golden pheasant and hen common pheasant "are of far larger size than either parent-bird. "[277] To this subject of the increased size of hybrids I shall presently return. With _Pigeons_, breeders are unanimous, as previously stated, that it is absolutely indispensable, notwithstanding the trouble and expense thus caused, occasionally to cross their much-prized birds with individuals of another strain, but belonging, of course, to the same variety. It deserves {126} notice that, when large size is one of the desired characters, as with pouters, [278] the evil effects of close interbreeding are much sooner perceived than when small birds, such as short-faced tumblers, are valued. The extreme delicacy of the high fancy breeds, such as these tumblers and improved English carriers, is remarkable; they are liable to many diseases, and often die in the egg or during the first moult; and their eggs have generally to be hatched under foster-mothers. Although these highly-prized birds have invariably been subjected to much close interbreeding, yet their extreme delicacy of constitution cannot perhaps be thus fully explained. Mr. Yarrell informed me that Sir J. Sebright continued closely interbreeding some owl-pigeons, until from their extreme sterility he as nearly as possible lost the whole family. Mr. Brent[279] tried to raise a breed of trumpeters, by crossing a common pigeon, and recrossing the daughter, granddaughter, great-granddaughter, and great-great-granddaughter, with the same male trumpeter, until he obtained a bird with 15/16ths of trumpeter's blood; but then the experiment failed, for "breeding so close stopped reproduction. " The experienced Neumeister[280] also asserts that the offspring from dovecotes and various other breeds are "generally very fertile and hardy birds:" so again, MM. Boitard and Corbié, [281] after forty-five years' experience, recommend persons to cross their breeds for amusement; for, if they fail to make interesting birds, they will succeed under an economical point of view, "as it is found that mongrels are more fertile than pigeons of pure race. " I will refer only to one other animal, namely, the Hive-bee, because a distinguished entomologist has advanced this as a case of inevitable close interbreeding. As the hive is tenanted by a single female, it might have been thought that her male and female offspring would always have bred together, more especially as bees of different hives are hostile to each other; a strange worker being almost always attacked when trying to enter another hive. But Mr. Tegetmeier has shown[282] that this instinct does not apply to drones, which are permitted to enter any hive; so that there is no _à priori_ improbability of a queen receiving a foreign drone. The fact of the union invariably and necessarily taking place on the wing, during the queen's nuptial flight, seems to be a special provision against continued interbreeding. However this may be, experience has shown, since the introduction of the yellow-banded Ligurian race into Germany and England, that bees freely cross: Mr. Woodbury, who introduced Ligurian bees into Devonshire, found during a single season that three stocks, at distances of from one to two miles from his hives, were crossed by his drones. In one case the Ligurian drones must have flown over the city of Exeter, and over several intermediate hives. On another occasion several common black queens were crossed by Ligurian drones at a distance of from one to three and a half miles. [283] {127} _Plants. _ When a single plant of a new species is introduced into any country, if propagated by seed, many individuals will soon be raised, so that if the proper insects be present there will be crossing. With newly-introduced trees or other plants not propagated by seed we are not here concerned. With old-established plants it is an almost universal practice occasionally to make exchanges of seed, by which means individuals which have been exposed to different conditions of life, --and this, as we have seen, diminishes the evil from close interbreeding, --will occasionally be introduced into each district. Experiments have not been tried on the effects of fertilising flowers with their own pollen during _several_ generations. But we shall presently see that certain plants, either normally or abnormally, are more or less sterile, even in the first generation, when fertilised by their own pollen. Although nothing is directly known on the evil effects of long-continued close interbreeding with plants, the converse proposition that great good is derived from crossing is well established. With respect to the crossing of individuals belonging to the same sub-variety, Gärtner, whose accuracy and experience exceeded that of all other hybridisers, states[284] that he has many times observed good effects from this step, especially with exotic genera, of which the fertility is somewhat impaired, such as Passiflora, Lobelia, and Fuchsia. Herbert also says, [285] "I am inclined to think that I have derived advantage from impregnating the flower from which I wished to obtain seed with pollen from another individual of the same variety, or at least from another flower, rather than with its own. " Again, Professor Lecoq asserts that he has ascertained that crossed offspring are more vigorous and robust than their parents. [286] General statements of this kind, however, can seldom be fully trusted; consequently I have begun a series of experiments, which, if they continue to give the same results as hitherto, will for ever settle the question of the good effects of crossing two distinct plants of the same variety, and of the evil effects of self-fertilisation. A clear light will thus also be thrown on the fact that flowers are invariably constructed so as to permit, or favour, or necessitate the union of two individuals. We shall clearly understand why monoecious and dioecious, --why dimorphic and trimorphic plants exist, and many other such cases. The plan which I have followed in my experiments is to grow plants in the same pot, or in pots of the same size, or close together in the open ground; to carefully exclude insects; and then to fertilise some of the flowers with pollen from the same flower, and others on the same plant with pollen from a distinct but adjoining plant. In many, but not all, of these experiments, the crossed plants yielded much more seed than the self-fertilised plants; and I have never seen the {128} reversed case. The self-fertilised and crossed seeds thus obtained were allowed to germinate in the same glass vessel on damp sand; and as the seeds successively germinated, they were planted in pairs on opposite sides of the same pot, with a superficial partition between them, and were placed so as to be equally exposed to the light. In other cases the self-fertilised and crossed seeds were simply sown on opposite sides of the same small pot. I have, in short, followed different plans, but in every case have taken all the precautions which I could think of, so that the two lots should be equally favoured. Now, I have carefully observed the growth of plants raised from crossed and self-fertilised seed, from their germination to maturity, in species of the following genera, namely, Brassica, Lathyrus, Lupinus, Lobelia, Lactuca, Dianthus, Myosotis, Petunia, Linaria, Calceolaria, Mimulus, and Ipomoea, and the difference in their powers of growth, and of withstanding in certain cases unfavourable conditions, was most manifest and strongly marked. It is of importance that the two lots of seed should be sown or planted on opposite sides of the same pot, so that the seedlings may struggle against each other; for if sown separately in ample and good soil, there is often but little difference in their growth. I will briefly describe the two most striking cases as yet observed by me. Six crossed and six self-fertilised seeds of _Ipomoea purpurea_, from plants treated in the manner above described, were planted as soon as they had germinated, in pairs on opposite sides of two pots, and rods of equal thickness were given them to twine up. Five of the crossed plants grew from the first more quickly than the opposed self-fertilised plants; the sixth, however, was weakly and was for a time beaten, but at last its sounder constitution prevailed and it shot ahead of its antagonist. As soon as each crossed plant reached the top of its seven-foot rod its fellow was measured, and the result was that, when the crossed plants were seven feet high, the self-fertilised had attained the average height of only five feet four and a half inches. The crossed plants flowered a little before, and more profusely than the self-fertilised plants. On opposite sides of another _small_ pot a large number of crossed and self-fertilised seeds were sown, so that they had to struggle for bare existence; a single rod was given to each lot: here again the crossed plants showed from the first their advantage; they never quite reached the summit of the seven-foot rod, but relatively to the self-fertilised plants their average height was as seven feet to five feet two inches. The experiment was repeated in the two following generations with plants raised from the self-fertilised and crossed plants, treated in exactly the same manner, and with nearly the same result. In the second generation, the crossed plants, which were again crossed, produced 121 seed-capsules, whilst the self-fertilised plants, again self-fertilised, produced only 84 capsules. Some flowers of the _Mimulus luteus_ were fertilised with their own pollen, and others were crossed with pollen from distinct plants growing in the same pot. The seeds after germinating were thickly planted on opposite sides of a pot. The seedlings were at first equal in height; but when the young crossed plants were exactly half an inch, the {129} self-fertilised plants were only a quarter of an inch high. But this inequality did not continue, for, when the crossed plants were four and a half inches high, the self-fertilised were three inches; and they retained the same relative difference till their growth was complete. The crossed plants looked far more vigorous than the uncrossed, and flowered before them; they produced also a far greater number of flowers, which yielded capsules (judging, however, from only a few) containing more seeds. As in the former case, the experiment was repeated in the same manner during the next two generations, and with exactly the same result. Had I not watched these plants of the Mimulus and Ipomoea during their whole growth, I could not have believed it possible, that a difference apparently so slight, as that of the pollen being taken from the same flower, and from a distinct plant growing in the same small pot, could have made so wonderful a difference in the growth and vigour of the plants thus produced. This, under a physiological point of view, is a most remarkable phenomenon. * * * * * With respect to the benefit derived from crossing distinct varieties, plenty of evidence has been published. Sageret[287] repeatedly speaks in strong terms of the vigour of melons raised by crossing different varieties, and adds that they are more easily fertilised than common melons, and produce numerous good seed. Here follows the evidence of an English gardener:[288] "I have this summer met with better success in my cultivation of melons, in an unprotected state, from the seeds of hybrids (_i. E. _ mongrels) obtained by cross impregnation, than with old varieties. The offspring of three different hybridisations (one more especially, of which the parents were the two most dissimilar varieties I could select) each yielded more ample and finer produce than any one of between twenty and thirty established varieties. " Andrew Knight[289] believed that his seedlings from crossed varieties of the apple exhibited increased vigour and luxuriance; and M. Chevreul[290] alludes to the extreme vigour of some of the crossed fruit-trees raised by Sageret. By crossing reciprocally the tallest and shortest peas, Knight[291] says, "I had in this experiment a striking instance of the stimulative effects of crossing the breeds; for the smallest variety, whose height rarely exceeded two feet, was increased to six feet; whilst the height of the large and luxuriant kind was very little diminished. " Mr. Laxton gave me seed-peas produced from crosses between four distinct kinds; and the plants thus raised were extraordinarily vigorous, being in each case from one to two or three feet taller than the parent-forms growing close alongside them. {130} Wiegmann[292] made many crosses between several varieties of cabbage; and he speaks with astonishment of the vigour and height of the mongrels, which excited the amazement of all the gardeners who beheld them. Mr. Chaundy raised a great number of mongrels by planting together six distinct varieties of cabbage. These mongrels displayed an infinite diversity of character; "But the most remarkable circumstance was, that, while all the other cabbages and borecoles in the nursery were destroyed by a severe winter, these hybrids were little injured, and supplied the kitchen when there was no other cabbage to be had. " Mr. Maund exhibited before the Royal Agricultural Society[293] specimens of crossed wheat, together with their parent varieties; and the editor states that they were intermediate in character, "united with that greater vigour of growth, which it appears, in the vegetable as in the animal world, is the result of a first cross. " Knight also crossed several varieties of wheat, [294] and he says "that in the years 1795 and 1796, when almost the whole crop of corn in the island was blighted, the varieties thus obtained, and these only, escaped in this neighbourhood, though sown in several different soils and situations. " Here is a remarkable case: M. Clotzsch[295] crossed _Pinus sylvestris_ and _nigricans_, _Quercus robur_ and _pedunculata, Alnus glutinosa_ and _incana_, _Ulmus campestris_ and _effusa_; and the cross-fertilised seeds, as well as seeds of the pure parent-trees, were all sown at the same time and in the same place. The result was, that after an interval of eight years, the hybrids were one-third taller than the pure trees! * * * * * The facts above given refer to undoubted varieties, excepting the trees crossed by Clotzsch, which are ranked by various botanists as strongly-marked races, sub-species, or species. That true hybrids raised from entirely distinct species, though they lose in fertility, often gain in size and constitutional vigour, is certain. It would be superfluous to quote any facts; for all experimenters, Kölreuter, Gärtner, Herbert, Sageret, Lecoq, and Naudin, have been struck with the wonderful vigour, height, size, tenacity of life, precocity, and hardiness of their hybrid productions. Gärtner[296] sums up his conviction on this head in the strongest terms. Kölreuter[297] gives numerous precise measurements of the weight and height of his hybrids in comparison with measurements of both parent-forms; and speaks with astonishment of their "_statura portentosa_, " their "_ambitus vastissimus ac altitudo valde conspicua_. " Some exceptions to the rule in the case of very sterile hybrids have, however, been noticed by Gärtner and {131} Herbert; but the most striking exceptions are given by Max Wichura, [298] who found that hybrid willows were generally tender in constitution, dwarf, and short-lived. Kölreuter explains the vast increase in the size of the roots, stems, &c. , of his hybrids, as the result of a sort of compensation due to their sterility, in the same way as many emasculated animals are larger than the perfect males. This view seems at first sight extremely probable, and has been accepted by various authors;[299] but Gärtner[300] has well remarked that there is much difficulty in fully admitting it; for with many hybrids there is no parallelism between the degree of their sterility and their increased size and vigour. The most striking instances of luxuriant growth have been observed with hybrids which were not sterile in any extreme degree. In the genus Mirabilis, certain hybrids are unusually fertile, and their extraordinary luxuriance of growth, together with their enormous roots, [301] have been transmitted to their progeny. The increased size of the hybrids produced between the fowl and pheasant, and between the distinct species of pheasants, has been already noticed. The result in all cases is probably in part due to the saving of nutriment and vital force through the sexual organs not acting, or acting imperfectly, but more especially to the general law of good being derived from a cross. For it deserves especial attention that mongrel animals and plants, which are so far from being sterile that their fertility is often actually augmented, have, as previously shown, their size, hardiness, and constitutional vigour generally increased. It is not a little remarkable that an accession of vigour and size should thus arise under the opposite contingencies of increased and diminished fertility. It is a perfectly well ascertained fact[302] that hybrids will invariably breed more readily with either pure parent, and not rarely with a distinct species, than with each other. Herbert is inclined to explain even this fact by the advantage derived from a cross; but Gärtner more justly accounts for it by the pollen of the hybrid, and probably its ovules, being in some degree vitiated, whereas the pollen and ovules of both pure parents and of any third species are sound. Nevertheless there are some well-ascertained and remarkable facts, which, as we shall immediately see, show that the act of crossing in itself undoubtedly tends to increase or re-establish the fertility of hybrids. _On certain Hermaphrodite Plants which, either normally or abnormally, require to be fertilised by pollen from a distinct individual or species. _ The facts now to be given differ from those hitherto detailed, as theself-sterility does not here result from long-continued, {132} closeinterbreeding. These facts are, however, connected with our presentsubject, because a cross with a distinct individual is shown to be eithernecessary or advantageous. Dimorphic and trimorphic plants, though they arehermaphrodites, must be reciprocally crossed, one set of forms by theother, in order to be fully fertile, and in some cases to be fertile in anydegree. But I should not have noticed these plants, had it not been for thefollowing cases given by Dr. Hildebrand:[303]-- _Primula sinensis_ is a reciprocally dimorphic species: Dr. Hildebrand fertilised twenty-eight flowers of both forms, each by pollen of the other form, and obtained the full number of capsules containing on an average 42. 7 seed per capsule; here we have complete and normal fertility. He then fertilised forty-two flowers of both forms with pollen of the same form, but taken from a distinct plant, and all produced capsules containing on an average only 19. 6 seed. Lastly, and here we come to our more immediate point, he fertilised forty-eight flowers of both forms with pollen of the same form, taken from the same flower, and now he obtained only thirty-two capsules, and these contained on an average 18. 6 seed, or one less per capsule than in the former case. So that, with these illegitimate unions, the act of impregnation is less assured, and the fertility slightly less, when the pollen and ovules belong to the same flower, than when belonging to two distinct individuals of the same form. Dr. Hildebrand has recently made analogous experiments on the long-styled form of _Oxalis rosea_, with the same result. [304] It has recently been discovered that certain plants, whilst growing intheir native country under natural conditions, cannot be fertilised withpollen from the same plant. They are sometimes so utterly self-impotent, that, though they can readily be fertilised by the pollen of a distinctspecies or even distinct genus, yet, wonderful as the fact is, they neverproduce a single seed by their own pollen. In some cases, moreover, theplant's own pollen and stigma mutually act on each other in a deleteriousmanner. Most of the facts to be given relate to Orchids, but I willcommence with a plant belonging to a widely different family. Sixty-three flowers of _Corydalis cava_, borne on distinct plants, were fertilised by Dr. Hildebrand[305] with pollen from other plants of the same species; and fifty-eight capsules were obtained, including on an average {133} 4. 5 seed in each. He then fertilised sixteen flowers produced by the same raceme, one with another, but obtained only three capsules, one of which alone contained any good seeds, namely, two in number. Lastly, he fertilised twenty-seven flowers, each with its own pollen; he left also fifty-seven flowers to be spontaneously fertilised, and this would certainly have ensued if it had been possible, for the anthers not only touch the stigma, but the pollen-tubes were seen by Dr. Hildebrand to penetrate it; nevertheless these eighty-four flowers did not produce a single seed-capsule! This whole case is highly instructive, as it shows how widely different the action of the same pollen is, according as it is placed on the stigma of the same flower, or on that of another flower on the same raceme, or on that of a distinct plant. With exotic Orchids several analogous cases have been observed, chiefly by Mr. John Scott. [306] _Oncidium sphacelatum_ has effective pollen, for with it Mr. Scott fertilised two distinct species; its ovules are likewise capable of impregnation, for they were readily fertilised by the pollen of _O. Divaricatum_; nevertheless, between one and two hundred flowers fertilised by their own pollen did not produce a single capsule, though the stigmas were penetrated by the pollen-tubes. Mr. Robinson Munro, of the Royal Botanic Gardens of Edinburgh, also informs me (1864) that a hundred and twenty flowers of this same species were fertilised by him with their own pollen, and did not produce a capsule, but eight flowers fertilised by the pollen of _O. Divaricatum_ produced four fine capsules: again, between two and three hundred flowers of _O. Divaricatum_, fertilised by their own pollen, did not set a capsule, but twelve flowers fertilised by _O. Flexuosum_ produced eight fine capsules: so that here we have three utterly self-impotent species, with their male and female organs perfect, as shown by their mutual fertilisation. In these cases fertilisation was effected only by the aid of a distinct species. But, as we shall presently see, distinct plants, raised from seed, of _Oncidium flexuosum_, and probably of the other species, would have been perfectly capable of fertilising each other, for this is the natural process. Again, Mr. Scott found that the pollen of a plant of _O. Microchilum_ was good, for with it he fertilised two distinct species; he found its ovules good, for they could be fertilised by the pollen of one of these species, and by the pollen of a distinct plant of _O. Microchilum_; but they could not be fertilised by pollen of the same plant, though the pollen-tubes penetrated the stigma. An analogous case has been recorded by M. Rivière, [307] with two plants of _O. Cavendishianum_, which were both self-sterile, but reciprocally fertilised each other. All these cases refer to the genus Oncidium, but Mr. Scott found that _Maxillaria atro-rubens_ was "totally insusceptible of fertilisation with its own pollen, " but fertilised, and was fertilised by, a widely distinct species, viz. _M. Squalens_. As these orchids had grown under unnatural conditions, in {134} hot-houses, I concluded without hesitation that their self-sterility was due to this cause. But Fritz Müller informs me that at Desterro, in Brazil, he fertilised above one hundred flowers of the above-mentioned _Oncidium flexuosum_, which is there endemic, with its own pollen, and with that taken from distinct plants; all the former were sterile, whilst those fertilised by pollen from any _other plant_ of the same species were fertile. During the first three days there was no difference in the action of the two kinds of pollen: that placed on the stigma of the same plant separated in the usual manner into grains, and emitted tubes which penetrated the column, and the stigmatic chamber shut itself; but the flowers alone which had been fertilised by pollen taken from a distinct plant produced seed-capsules. On a subsequent occasion these experiments were repeated on a large scale with the same result. Fritz Müller found that four other endemic species of Oncidium were in like manner utterly sterile with their own pollen, but fertile with that from any other plant: some of them likewise produced seed-capsules when impregnated with pollen of widely distinct genera, such as Leptotes, Cyrtopodium, and Rodriguezia! _Oncidium crispum_, however, differs from the foregoing species in varying much in its self-sterility; some plants producing fine pods with their own pollen, others failing to do so; in two or three instances, Fritz Müller observed that the pods produced by pollen taken from a distinct flower on the same plant, were larger than those produced by the flower's own pollen. In _Epidendrum cinnabarinum_, an orchid belonging to another division of the family, fine pods were produced by the plant's own pollen, but they contained by weight only about half as much seed as the capsules which had been fertilized by pollen from a distinct plant, and in one instance from a distinct species; moreover, a very large proportion, and in some cases nearly all the seed produced by the plant's own pollen, was embryonless and worthless. Some self-fertilized capsules of a Maxillaria were in a similar state. Another observation made by Fritz Müller is highly remarkable, namely, that with various orchids the plant's own pollen not only fails to impregnate the flower, but acts on the stigma, and is acted on, in an injurious or poisonous manner. This is shown by the surface of the stigma in contact with the pollen, and by the pollen itself, becoming in from three to five days dark brown, and then decaying. The discolouration and decay are not caused by parasitic cryptogams, which were observed by Fritz Müller in only a single instance. These changes are well shown by placing on the same stigma, at the same time, the plant's own pollen and that from a distinct plant of the same species, or of another species, or even of another and widely remote genus. Thus, on the stigma of _Oncidium flexuosum_, the plant's own pollen and that from a distinct plant were placed side by side, and in five days' time the latter was perfectly fresh, whilst the plant's own pollen was brown. On the other hand, when the pollen of a distinct plant of the _Oncidium flexuosum_, and of the _Epidendrum zebra_ (_nov. Spec. ?_), were placed together on the same stigma, they behaved in exactly the same manner, the grains separating, emitting tubes, and penetrating the stigma, so that the two {135} pollen-masses, after an interval of eleven days, could not be distinguished except by the difference of their caudicles, which, of course, undergo no change. Fritz Müller has, moreover, made a large number of crosses between orchids belonging to distinct species and genera, and he finds that in all cases when the flowers are not fertilised their footstalks first begin to wither; and the withering slowly spreads upwards until the germens fall off, after an interval of one or two weeks, and in one instance of between six and seven weeks; but even in this latter case, and in most other cases, the pollen and stigma remained in appearance fresh. Occasionally, however, the pollen becomes brownish, generally on the external surface, and not in contact with the stigma, as is invariably the case when the plant's own pollen is applied. Fritz Müller observed the poisonous action of the plant's own pollen in the above-mentioned _Oncidium flexuosum_, _O. Unicorne, pubes_ (_?_), and in two other unnamed species. Also in two species of Rodriguezia, in two of Notylia, in one of Burlingtonia, and of a fourth genus in the same group. In all these cases, except the last, it was proved that the flowers were, as might have been expected, fertile with pollen from a distinct plant of the same species. Numerous flowers of one species of Notylia were fertilized with pollen from the same raceme; in two days' time they all withered, the germens began to shrink, the pollen-masses became dark brown, and not one pollen-grain emitted a tube. So that in this orchid the injurious action of the plant's own pollen is more rapid than with _Oncidium flexuosum_. Eight other flowers on the same raceme were fertilized with pollen from a distinct plant of the same species: two of these were dissected, and their stigmas were found to be penetrated by numberless pollen-tubes; and the germens of the other six flowers became well developed. On a subsequent occasion many other flowers were fertilized with their own pollen, and all fell off dead in a few days; whilst some flowers on the same raceme which had been left simply unfertilised adhered and long remained fresh. We have seen that in cross-unions between extremely distinct orchids the pollen long remains undecayed; but Notylia behaved in this respect differently; for when its pollen was placed on the stigma of _Oncidium flexuosum_, both the stigma and pollen quickly became dark brown, in the same manner as if the plant's own pollen had been applied. Fritz Müller suggests that, as in all these cases the plant's own pollen is not only impotent (thus effectually preventing self-fertilization), but likewise prevents, as was ascertained in the case of the Notylia and _Oncidium flexuosum_, the action of subsequently applied pollen from a distinct individual, it would be an advantage to the plant to have its own pollen rendered more and more deleterious; for the germens would thus quickly be killed, and, dropping off, there would be no further waste in nourishing a part which ultimately could be of no avail. Fritz Müller's discovery that a plant's own pollen and stigma in some cases act on each other as if mutually poisonous, is certainly most remarkable. We now come to cases closely analogous with those just {136} given, butdifferent, inasmuch as individual plants alone of the species areself-impotent. This self-impotence does not depend on the pollen or ovulesbeing in a state unfit for fertilisation, for both have been foundeffective in union with other plants of the same or of a distinct species. The fact of these plants having spontaneously acquired so peculiar aconstitution, that they can be fertilised more readily by the pollen of adistinct species than by their own, is remarkable. These abnormal cases, aswell as the foregoing normal cases, in which certain orchids, for instance, can be much more easily fertilised by the pollen of a distinct species thanby their own, are exactly the reverse of what occurs with all ordinaryspecies. For in these latter the two sexual elements of the same individualplant are capable of freely acting on each other; but are so constitutedthat they are more or less impotent when brought into union with the sexualelements of a distinct species, and produce more or less sterile hybrids. It would appear that the pollen or ovules, or both, of the individualplants which are in this abnormal state, have been affected in some strangemanner by the conditions to which they themselves or their parents havebeen exposed; but whilst thus rendered self-sterile, they have retained thecapacity common to most species of partially fertilizing and beingpartially fertilized by allied forms. However this may be, the subject, toa certain extent, is related to our general conclusion that good is derivedfrom the act of crossing. Gärtner experimented on two plants of _Lobelia fulgens_, brought from separate places, and found[308] that their pollen was good, for he fertilised with it _L. Cardinalis_ and _syphilitica_; their ovules were likewise good, for they were fertilised by the pollen of these same two species; but these two plants of _L. Fulgens_ could not be fertilised by their own pollen, as can generally be effected with perfect ease with this species. Again, the pollen of a plant of _Verbascum nigrum_ grown in a pot was found by Gärtner[309] capable of fertilising _V. Lychnitis_ and _V. Austriacum_; the ovules could be fertilised by the pollen of _V. Thapsus_; but the flowers could not be fertilised by their own pollen. Kölreuter, also, [310] gives the case of three {137} garden plants of _Verbascum phoeniceum_, which bore during two years many flowers; these he successfully fertilised by the pollen of no less than four distinct species, but they produced not a seed with their own apparently good pollen; subsequently these same plants, and others raised from seed, assumed a strangely fluctuating condition, being temporarily sterile on the male or female side, or on both sides, and sometimes fertile on both sides; but two of the plants were perfectly fertile throughout the summer. It appears[311] that certain flowers on certain plants of _Lilium candidum_ can be fertilised more easily by pollen from a distinct individual than by their own. So, again, with the varieties of the potato. Tinzmann, [312] who made many trials with this plant, says that pollen from another variety sometimes "exerts a powerful influence, and I have found sorts of potatoes which would not bear seed from impregnation with the pollen of their own flowers, would bear it when impregnated with other pollen. " It does not, however, appear to have been proved that the pollen which failed to act on the flower's own stigma was in itself good. In the genus Passiflora it has long been known that several species do not produce fruit, unless fertilised by pollen taken from distinct species: thus, Mr. Mowbray[313] found that he could not get fruit from _P. Alata_ and _racemosa_ except by reciprocally fertilising them with each other's pollen. Similar facts have been observed in Germany and France;[314] and I have received two authentic accounts of _P. Quadrangularis_, which never produced fruit with its own pollen, but would do so freely when fertilised in one case with the pollen of _P. Coerulea_, and in another case with that of _P. Edulis_. So again, with respect to _P. Laurifolia_, a cultivator of much experience has recently remarked[315] that the flowers "must be fertilised with the pollen of _P. Coerulea_, or of some other common kind, as their own pollen will not fertilise them. " But the fullest details on this subject have been given by Mr. Scott:[316] plants of _Passiflora racemosa_, _coerulea_, and _alata_ flowered profusely during many years in the Botanic Gardens of Edinburgh, and, though repeatedly fertilised by Mr. Scott and by others with their own pollen, never produced any seed; yet this occurred at once with all three species when they were crossed together in various ways. But in the case of _P. Coerulea_, three plants, two of which grew in the Botanic Gardens, were all rendered fertile, merely by impregnating the one with pollen of the other. The same result was attained in the same manner with _P. Alata_, but only with one plant out of three. As so many self-sterile species have been mentioned, it may be stated that in the case of _P. Gracilis_, which is an annual, the flowers are nearly as fertile with their own pollen as with that from a distinct plant; thus sixteen flowers {138} spontaneously self-fertilised produced fruit, each containing on an average 21. 3 seed, whilst fruit from fourteen crossed flowers contained 24. 1 seed. Returning to _P. Alata_, I have received (1866) some interesting details from Mr. Robinson Munro. Three plants, including one in England, have already been mentioned which were inveterately self-sterile, and Mr. Munro informs me of several others which, after repeated trials during many years, have been found in the same predicament. At some other places, however, this species fruits readily when fertilised with its own pollen. At Taymouth Castle there is a plant which was formerly grafted by Mr. Donaldson on a distinct species, name unknown, and ever since the operation it has produced fruit in abundance by its own pollen; so that this small and unnatural change in the state of this plant has restored its self-fertility! Some of the seedlings from the Taymouth Castle plant were found to be not only sterile with their own pollen, but with each other's pollen, and with the pollen of distinct species. Pollen from the Taymouth plant failed to fertilise certain plants of the same species, but was successful on one plant in the Edinburgh Botanic Gardens. Seedlings were raised from this latter union, and some of their flowers were fertilised by Mr. Munro with their own pollen; but they were found to be as self-impotent as the mother-plant had always proved, except when fertilised by the grafted Taymouth plant, and except, as we shall see, when fertilised by her own seedlings. For Mr. Munro fertilised eighteen flowers on the self-impotent mother-plant with pollen from these her own self-impotent seedlings, and obtained, remarkable as the fact is, eighteen fine capsules full of excellent seed! I have met with no case in regard to plants which shows so well as this of _P. Alata_, on what small and mysterious causes complete fertility or complete sterility depends. The facts hitherto given relate to the much-lessened or completelydestroyed fertility of pure species when impregnated with their own pollen, in comparison with their fertility when impregnated by distinct individualsor distinct species; but closely analogous facts have been observed withhybrids. Herbert states[317] that having in flower at the same time nine hybrid Hippeastrums, of complicated origin, descended from several species, he found that "almost every flower touched with pollen from another cross produced seed abundantly, and those which were touched with their own pollen either failed entirely, or formed slowly a pod of inferior size, with fewer seeds. " In the 'Horticultural Journal' he adds that, "the admission of the pollen of another cross-bred Hippeastrum (however complicated the cross) to any _one_ flower of the number, is almost sure to check the fructification of the others. " In a letter written to me in 1839, Dr. Herbert says that he had already tried these experiments during five consecutive years, and he subsequently repeated them, with the same invariable result. {139} He was thus led to make an analogous trial on a pure species, namely, on the _Hippeastrum aulicum_, which he had lately imported from Brazil: this bulb produced four flowers, three of which were fertilised by their own pollen, and the fourth by the pollen of a triple cross between _H. Bulbulosum_, _reginæ_, and _vittatum_; the result was, that "the ovaries of the three first flowers soon ceased to grow, and after a few days perished entirely: whereas the pod impregnated by the hybrid made vigorous and rapid progress to maturity, and bore good seed, which vegetated freely. " This is, indeed, as Herbert remarks, "a strange truth, " but not so strange as it then appeared. As a confirmation of these statements, I may add that Mr. M. Mayes, [318] after much experience in crossing the species of Amaryllis (Hippeastrum), says, "neither the species nor the hybrids will, we are well aware, produce seed so abundantly from their own pollen as from that of others. " So, again, Mr. Bidwell, in New South Wales, [319] asserts that _Amaryllis belladonna_ bears many more seeds when fertilised by the pollen of _Brunswigia_ (_Amaryllis_ of some authors) _Josephinæ_ or of _B. Multiflora_, than when fertilised by its own pollen. Mr. Beaton dusted four flowers of a Cyrtanthus with their own pollen, and four with the pollen of _Vallota_ (_Amaryllis_) _purpurea_; on the seventh day "those which received their own pollen slackened their growth, and ultimately perished; those which were crossed with the Vallota held on. "[320] These latter cases, however, relate to uncrossed species, like those before given with respect to Passiflora, Orchids, &c. , and are here referred to only because the plants belong to the same group of Amaryllidaceæ. In the experiments on the hybrid Hippeastrums, if Herbert had found that the pollen of two or three kinds alone had been more efficient on certain kinds than their own pollen, it might have been argued that these, from their mixed parentage, had a closer mutual affinity than the others; but this explanation is inadmissible, for the trials were made reciprocally backwards and forwards on nine different hybrids; and a cross, whichever way taken, always proved highly beneficial. I can add a striking and analogous case from experiments made by the Rev. A. Rawson, of Bromley Common, with some complex hybrids of Gladiolus. This skilful horticulturist possessed a number of French varieties, differing from each other only in the colour and size of the flowers, all descended from Gandavensis, a well-known old hybrid, said to be descended from _G. Natalensis_ by the pollen of _G. Oppositiflorus_. [321] Mr. Rawson, after repeated trials, found that none of the varieties would set seed with their own pollen, although {140} taken from distinct plants of the same variety, which had, of course, been propagated by bulbs, but that they all seeded freely with pollen from any other variety. To give two examples: Ophir did not produce a capsule with its own pollen, but when fertilised with that of Janire, Brenchleyensis, Vulcain, and Linné, it produced ten fine capsules; but the pollen of Ophir was good, for when Linné was fertilised by it seven capsules were produced. This later variety, on the other hand, was utterly barren with its own pollen, which we have seen was perfectly efficient on Ophir. Altogether, Mr. Rawson, in the year 1861, fertilised twenty-six flowers borne by four varieties with pollen taken from other varieties, and every single flower produced a fine seed-capsule; whereas fifty-two flowers on the same plants, fertilised at the same time with their own pollen, did not yield a single seed-capsule. Mr. Rawson fertilised, in some cases, the alternate flowers, and in other cases all those down one side of the spike, with pollen of other varieties, and the remaining flowers with their own pollen; I saw these plants when the capsules were nearly mature, and their curious arrangement at once brought full conviction to the mind that an immense advantage had been derived from crossing these hybrids. Lastly, I have heard from Dr. E. Bornet, of Antibes, who has made numerous experiments in crossing the species of Cistus, but as not yet published the results, that, when any of these hybrids are fertile, they may be said to be, in regard to function, dioecious; "for the flowers are always sterile when the pistil is fertilised by pollen taken from the same flower or from flowers on the same plant. But they are often fertile if pollen be employed from a distinct individual of the same hybrid nature, or from a hybrid made by a reciprocal cross. " _Conclusion. _--The facts just given, which show that certain plants areself-sterile, although both sexual elements are in a fit state forreproduction when united with distinct individuals of the same or otherspecies, appear at first sight opposed to all analogy. The sexual elementsof the same flower have become, as already remarked, differentiated inrelation to each other, almost like those of two distinct species. With respect to the species which, whilst living under their naturalconditions, have their reproductive organs in this peculiar state, we mayconclude that it has been naturally acquired for the sake of effectuallypreventing self-fertilisation. The case is closely analous with dimorphicand trimorphic plants, which can be fully fertilised only by plants belongto the opposite form, and not, as in the foregoing cases, in differently byany other plant. Some of these dimorphic plants are completely sterile withpollen taken from the same plant or from the same {141} form. It isinteresting to observe the graduated series from plants which, whenfertilised by their own pollen, yield the full number of seed, but with theseedlings a little dwarfed in stature--to plants which when self-fertilisedyield few seeds--to those with yield none--and, lastly, to those in whichthe plant's own pollen and stigma act on each other like poison. Thispeculiar state of the reproductive organs, when occurring in certainindividuals alone, is evidently abnormal; and as it chiefly affects exoticplants, or indigenous plants cultivated in pots, we may attribute it tosome change in the conditions of life, acting on the plants themselves oron their parents. The self-impotent _Passiflora alata_, which recovered itsself-fertility after having been grafted on a distinct stock, shows howsmall a change is sufficient to act powerfully on the reproductive system. The possibility of a plant becoming under culture self-impotent isinteresting as throwing light on the occurrence of this same condition innatural species. A cultivated plant in this state generally remains soduring its whole life; and from this fact we may infer that the state isprobably congenital. Kölreuter, however, has described some plants of Verbascum which varied inthis respect even during the same season. As in all the normal cases, andin many, probably in most, of the abnormal cases, any two self-impotentplants can reciprocally fertilize each other, we may infer that a veryslight difference in the nature of their sexual elements suffices to givefertility; but in other instances, as with some Passifloras and the hybridGladioli, a greater degree of differentiation appears to be necessary, forwith these plants fertility is gained only by the union of distinctspecies, or of hybrids of distinct parentage. These facts all point to thesame general conclusion, namely, that good is derived from a cross betweenindividuals, which either innately, or from exposure to dissimilarconditions, have come to differ in sexual constitution. Exotic animals confined in menageries are sometimes in nearly the samestate as the above-described self-impotent plants; for, as we shall see inthe following chapter, certain monkeys, the larger carnivora, severalfinches, geese, and pheasants, cross together, quite as freely as, or evenmore freely than, the individuals of the same species breed together. Caseswill, {142} also, be given of sexual incompatibility between certain maleand female domesticated animals, which, nevertheless, are fertile whenmatched with any other individual of the same kind. In the early part of this chapter it was shown that the crossing ofdistinct forms, whether closely or distantly allied, gives increased sizeand constitutional vigour, and, except in the case of crossed species, increased fertility, to the offspring. The evidence rests on the universaltestimony of breeders (for it should be observed that I am not herespeaking of the evil results of close interbreeding), and is practicallyexemplified in the higher value of cross-bred animals for immediateconsumption. The good results of crossing have also been demonstrated, inthe case of some animals and of numerous plants, by actual weight andmeasurement. Although animals of pure blood will obviously be deterioratedby crossing, as far as their characteristic qualities are concerned, thereseems to be no exception to the rule that advantages of the kind justmentioned are thus gained, even when there has not been any previous closeinterbreeding. The rule applies to all animals, even to cattle and sheep, which can long resist breeding in-and-in between the nearestblood-relations. It applies to individuals of the same sub-variety but ofdistinct families, to varieties or races, to sub-species, as well as toquite distinct species. In this latter case, however, whilst size, vigour, precocity, and hardinessare, with rare exceptions, gained, fertility, in a greater or less degree, is lost; but the gain cannot be exclusively attributed to the principle ofcompensation; for there is no close parallelism between the increased sizeand vigour of the offspring and their sterility. Moreover it has beenclearly proved that mongrels which are perfectly fertile gain these sameadvantages as well as sterile hybrids. The evil consequences of long-continued close interbreeding are not soeasily recognised as the good effects from crossing, for the deteriorationis gradual. Nevertheless it is the general opinion of those who have hadmost experience, especially with animals which propagate quickly, that evildoes inevitably follow sooner or later, but at different rates withdifferent animals. No doubt a false belief may widely prevail like asuperstition; yet it is difficult to suppose that so many acute andoriginal {143} observers have all been deceived at the expense of much costand trouble. A male animal may sometimes be paired with his daughter, granddaughter, and so on, even for seven generations, without any manifestbad result; but the experiment has never been tried of matching brothersand sisters, which is considered the closest form of interbreeding, for anequal number of generations. There is good reason to believe that bykeeping the members of the same family in distinct bodies, especially ifexposed to somewhat different conditions of life, and by occasionallycrossing these families, the evil results may be much diminished, or quiteeliminated. These results are loss of constitutional vigour, size, andfertility; but there is no necessary deterioration in the general form ofthe body, or in other good qualities. We have seen that with pigsfirst-rate animals have been produced after long-continued closeinterbreeding, though they had become extremely infertile when paired withtheir near relations. The loss of fertility, when it occurs, seems never tobe absolute, but only relative to animals of the same blood; so that thissterility is to a certain extent analogous with that of self-impotentplants which cannot be fertilised by their own pollen, but are perfectlyfertile with pollen of any other plant of the same species. The fact ofinfertility of this peculiar nature being one of the results oflong-continued interbreeding, shows that interbreeding does not act merelyby combining and augmenting various morbid tendencies common to bothparents; for animals with such tendencies, if not at the time actually ill, can generally propagate their kind. Although offspring descended from thenearest blood-relations are not necessarily deteriorated in structure, yetsome authors[322] believe that they are eminently liable to malformations;and this is not improbable, as everything which lessens the vital powersacts in this manner. Instances of this kind have been recorded in the caseof pigs, bloodhounds, and some other animals. Finally, when we consider the various facts now given which plainly showthat good follows from crossing, and less plainly {144} that evil followsfrom close interbreeding, and when we bear in mind that throughout thewhole organic world elaborate provision has been made for the occasionalunion of distinct individuals, the existence of a great law of nature is, if not proved, at least rendered in the highest degree probable; namely, that the crossing of animals and plants which are not closely related tobeach other is highly beneficial or even necessary, and that interbreedingprolonged during many generations is highly injurious. * * * * * {145} CHAPTER XVIII. ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE:STERILITY FROM VARIOUS CAUSES. ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE--STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE COUNTRY AND IN MENAGERIES--MAMMALS, BIRDS, AND INSECTS--LOSS OF SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS--CAUSES OF STERILITY--STERILITY OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS--SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS--STERILITY OF PLANTS FROM CHANGED CONDITIONS OF LIFE--CONTABESCENCE OF THE ANTHERS--MONSTROSITIES AS A CAUSE OF STERILITY--DOUBLE FLOWERS--SEEDLESS FRUIT--STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF VEGETATION--FROM LONG-CONTINUED PROPAGATION BY BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESS FRUIT. _On the Good derived from slight Changes in the Conditions of Life. _--Inconsidering whether any facts were known which might throw light on theconclusion arrived at in the last chapter, namely, that benefits ensue fromcrossing, and that it is a law of nature that all organic beings shouldoccasionally cross, it appeared to me probable that the good derived fromslight changes in the conditions of life, from being an analogousphenomenon, might serve this purpose. No two individuals, and still less notwo varieties, are absolutely alike in constitution and structure; and whenthe germ of one is fertilised by the male element of another, we maybelieve that it is acted on in a somewhat similar manner as an individualwhen exposed to slightly changed conditions. Now, every one must haveobserved the remarkable influence on convalescents of a change ofresidence, and no medical man doubts the truth of this fact. Small farmerswho hold but little land are convinced that their cattle derive greatbenefit from a change of pasture. In the case of plants, the evidence isstrong that a great advantage is derived from exchanging seeds, tubers, bulbs, and cuttings from one soil or place to another as different aspossible. {146} The belief that plants are thus benefited, whether or not well founded, has been firmly maintained from the time of Columella, who wrote shortly after the Christian era, to the present day; and it now prevails in England, France, and Germany. [323] A sagacious observer, Bradley, writing in 1724, [324] says, "When we once become Masters of a good Sort of Seed, we should at least put it into Two or Three Hands, where the Soils and Situations are as different as possible; and every Year the Parties should change with one another; by which Means, I find the Goodness of the Seed will be maintained for several Years. For Want of this Use many Farmers have failed in their Crops and been great Losers. " He then gives his own practical experience on this head. A modern writer[325] asserts, "Nothing can be more clearly established in agriculture than that the continual growth of any one variety in the same district makes it liable to deterioration either in quality or quantity. " Another writer states that he sowed close together in the same field two lots of wheat-seed, the product of the same original stock, one of which had been grown on the same land, and the other at a distance, and the difference in favour of the crop from the latter seed was remarkable. A gentleman in Surrey who has long made it his business to raise wheat to sell for seed, and who has constantly realised in the market higher prices than others, assures me that he finds it indispensable continually to change his seed; and that for this purpose he keeps two farms differing much in soil and elevation. With respect to the tubers of the potato, I find that at the present day the practice of exchanging sets is almost everywhere followed. The great growers of potatoes in Lancashire formerly used to get tubers from Scotland, but they found that "a change from the moss-lands, and _vice versâ_, was generally sufficient. " In former times in France the crop of potatoes in the Vosges had become reduced in the course of fifty or sixty years in the proportion from 120-150 to 30-40 bushels; and the famous Oberlin attributed the surprising good which he effected in large part to changing the sets. [326] A well-known practical gardener, Mr. Robson[327] positively states that he has himself witnessed decided advantage from obtaining bulbs of the onion, tubers of the potato, and various seeds, all of the same kind, from different soils and distant parts of England. He further states that with {147} plants propagated by cuttings, as with the Pelargonium, and especially the Dahlia, manifest advantage is derived from getting plans of the same variety, which have been cultivated in another place; or, "where the extent of the place allows, to take cuttings from one description of soil to plant on another, so as to afford the change that seems so necessary to the well-being of the plants. " He maintains that after a time an exchange of this nature is "forced on the grower, whether he be prepared for it or not. " Similar remarks have been made by another excellent gardener, Mr. Fish, namely, that cuttings of the same variety of Calceolaria, which he obtained from a neighbour, "showed much greater vigour than some of his own that were treated in exactly the same manner, " and he attributed this solely to his own plants having become "to a certain extent worn out or tired of their quarters. " Something of this kind apparently occurs in grafting and budding fruit-trees; for, according to Mr. Abbey, grafts or buds generally take on a distinct variety or even species, or on a stock previously grafted, with greater facility than on stocks raised from seeds of the variety which is to be grafted; and he believes this cannot be altogether explained by the stocks in question being better adapted to the soil and climate of the place. It should, however, be added, that varieties grafted or budded on very distinct kinds, though they may take more readily and grow at first more vigorously than when grafted on closely allied stocks, afterwards often become unhealthy. I have studied M. Tessier's careful and elaborate experiments, [328] made to disprove the common belief that good is derived from a change of seed; and he certainly shows that the same seed may with care be cultivated on the same farm (it is not stated whether on exactly the same soil) for ten consecutive years without loss. Another excellent observer, Colonel Le Couteur, [329] has come to the same conclusion; but then he expressly adds, if the same seed be used, "that which is grown on land manured from the mixen one year becomes seed for land prepared with lime, and that again becomes seed for land dressed with ashes, then for land dressed with mixed manure, and so on. " But this in effect is a systematic exchange of seed, within the limits of the same farm. On the whole the belief, which has long been held by many skilfulcultivators, that good follows from exchanging seed, tubers, &c. , seems tobe fairly well founded. Considering the small size of most seeds, it seemshardly credible that the advantage thus derived can be due to the seedsobtaining in one soil some chemical element deficient in the other soil. Asplants after once germinating naturally become fixed to the same spot, itmight have been anticipated that they would show the good effects of achange more plainly than animals, which continually wander about; and thisapparently is the {148} case. Life depending on, or consisting in, anincessant play of the most complex forces, it would appear that theiraction is in some way stimulated by slight changes in the circumstances towhich each organism is exposed. All forces throughout nature, as Mr. Herbert Spencer[330] remarks, tend towards an equilibrium, and for the lifeof each being it is necessary that this tendency should be checked. Ifthese views and the foregoing facts can be trusted, they probably throwlight, on the one hand, on the good effects of crossing the breed, for thegerm will be thus slightly modified or acted on by new forces; and on theother hand, on the evil effects of close interbreeding prolonged duringmany generations, during which the germ will be acted on by a male havingalmost identically the same constitution. _Sterility from changed Conditions of Life. _ I will now attempt to show that animals and plants, when removed from theirnatural conditions, are often rendered in some degree infertile orcompletely barren; and this occurs even when the conditions have not beengreatly changed. This conclusion is not necessarily opposed to that atwhich we have just arrived, namely, that lesser changes of other kinds areadvantageous to organic beings. Our present subject is of some importance, from having an intimate connexion with the causes of variability. Indirectly it perhaps bears on the sterility of species when crossed: foras, on the one hand, slight changes in the conditions of life arefavourable to plants and animals, and the crossing of varieties adds to thesize, vigour, and fertility of their offspring; so, on the other hand, certain other changes in the conditions of life cause sterility; and asthis likewise ensues from crossing much-modified forms or species, we havea parallel and double series of facts, which apparently stand in closerelation to each other. It is notorious that many animals, though perfectly tamed, {149} refuse tobreed in captivity. Isidore Geoffroy St. Hilaire[331] consequently hasdrawn a broad distinction between tamed animals which will not breed undercaptivity, and truly domesticated animals which breed freely--generallymore freely, as shown in the sixteenth chapter, than in a state of nature. It is possible and generally easy to tame most animals; but experience hasshown that it is difficult to get them to breed regularly, or even at all. I shall discuss this subject in detail; but will give only those caseswhich seem most illustrative. My materials are derived from noticesscattered through various works, and especially from a Report, drawn up forme by the kindness of the officers of the Zoological Society of London, which has especial value, as it records all the cases, during nine yearsfrom 1838-46, in which the animals were seen to couple but produced nooffspring, as well as the cases in which they never, as far as known, coupled. This MS. Report I have corrected by the annual Reportssubsequently published. Many facts are given on the breeding of the animalsin that magnificent work, 'Gleanings from the Menageries of Knowsley Hall, 'by Dr. Gray. I made, also, particular inquiries from the experienced keeperof the birds in the old Surrey Zoological Gardens. I should premise that aslight change in the treatment of animals sometimes makes a greatdifference in their fertility; and it is probable that the results observedin different menageries would differ. Indeed some animals in our ZoologicalGardens have become more productive since the year 1846. It is, also, manifest from F. Cuvier's account of the Jardin des Plantes, [332] that theanimals formerly bred much less freely there than with us; for instance, inthe Duck tribe, which is highly prolific, only one species had at thatperiod produced young. The most remarkable cases, however, are afforded by animals kept in their native country, which, though perfectly tamed, quite healthy, and allowed some freedom, are absolutely incapable of breeding. Rengger, [333] who in Paraguay particularly attended to this subject, specifies six quadrupeds in this condition; and he mentions two or three others which most rarely {150} breed. Mr. Bates, in his admirable work on the Amazons, strongly insists on similar cases;[334] and he remarks, that the fact of thoroughly tamed native mammals and birds not breeding when kept by the Indians, cannot be wholly accounted for by their negligence or indifference, for the turkey is valued by them, and the fowl has been adopted by the remotest tribes. In almost every part of the world--for instance, in the interior of Africa, and in several of the Polynesian islands--the natives are extremely fond of taming the indigenous quadrupeds and birds; but they rarely or never succeed in getting them to breed. The most notorious case of an animal not breeding in captivity is that of the elephant. Elephants are kept in large numbers in their native Indian home, live to old age, and are vigorous enough for the severest labour; yet, with one or two exceptions, they have never been known even to couple, though both males and females have their proper periodical seasons. If, however, we proceed a little eastward to Ava, we hear from Mr. Crawfurd[335] that their "breeding in the domestic state, or at least in the half-domestic state in which the female elephants are generally kept, is of every-day occurrence;" and Mr. Crawfurd informs me that he believes that the difference must be attributed solely to the females being allowed to roam the forests with some degree of freedom. The captive rhinoceros, on the other hand, seems from Bishop Heber's account[336] to breed in India far more readily than the elephant. Four wild species of the horse genus have bred in Europe, though here exposed to a great change in their natural habits of life; but the species have generally been crossed one with another. Most of the members of the pig family breed readily in our menageries: even the Red River hog (_Potamochoerus penicillatus_), from the sweltering plains of West Africa, has bred twice in the Zoological Gardens. Here also the Peccary (_Dicotyles torquatus_) has bred several times; but another species, the _D. Labiatus_, though rendered so tame as to be half-domesticated, breeds so rarely in its native country of Paraguay, that according to Rengger[337] the fact requires confirmation. Mr. Bates remarks that the tapir, though often kept tame in Amazonia by the Indians, never breeds. Ruminants generally breed quite freely in England, though brought from widely different climates, as may be seen in the Annual Reports of the Zoological Gardens, and in the Gleanings from Lord Derby's menagerie. The Carnivora, with the exception of the Plantigrade division, generally breed (though with capricious exceptions) almost as freely as ruminants. Many species of Felidæ have bred in various menageries, although imported from various climates and closely confined. Mr. Bartlett, the present superintendent of the Zoological Gardens, [338] remarks that the lion appears to breed more frequently and to bring forth more young at a birth than any other species of the family. He adds that the tiger has rarely bred; {151} "but there are several well-authenticated instances of the female tiger breeding with the lion. " Strange as the fact may appear, many animals under confinement unite with distinct species and produce hybrids quite as freely as, or even more freely than, with their own species. On inquiring from Dr. Falconer and others, it appears that the tiger when confined in India does not breed, though it has been known to couple. The cheetah (_Felis jubata_) has never been known by Mr. Bartlett to breed in England, but it has bred at Frankfort; nor does it breed in India, where it is kept in large numbers for hunting; but no pains would be taken to make them breed, as only those animals which have hunted for themselves in a state of nature are serviceable and worth training. [339] According to Rengger, two species of wild cats in Paraguay, though thoroughly tamed, have never bred. Although so many of the Felidæ breed readily in the Zoological Gardens, yet conception by no means always follows union: in the nine-year Report, various species are specified which were observed to couple seventy-three times, and no doubt this must have passed many times unnoticed; yet from the seventy-three unions only fifteen births ensued. The Carnivora in the Zoological Gardens were formerly less freely exposed to the air and cold than at present, and this change of treatment, as I was assured by the former superintendent, Mr. Miller, greatly increased their fertility. Mr. Bartlett, and there cannot be a more capable judge, says, "it is remarkable that lions breed more freely in travelling collections than in the Zoological Gardens; probably the constant excitement and irritation produced by moving from place to place, or change of air, may have considerable influence in the matter. " Many members of the Dog family breed readily when confined. The Dhole is one of the most untameable animals in India, yet a pair kept there by Dr. Falconer produced young. Foxes, on the other hand, rarely breed, and I have never heard of such an occurrence with the European fox: the silver fox of North America (_Canis argentatus_), however, has bred several times in the Zoological Gardens. Even the otter has bred there. Every one knows how readily the semi-domesticated ferret breeds, though shut up in miserably small cages; but other species of Viverra and Paradoxurus absolutely refuse to breed in the Zoological Gardens. The Genetta has bred both here and in the Jardin des Plantes, and produced hybrids. The _Herpestes fasciatus_ has likewise bred; but I was formerly assured that the _H. Griseus_, though many were kept in the Gardens, never bred. The Plantigrade Carnivora breed under confinement much less freely, without our being able to assign any reason, than other members of the group. In the nine-year Report it is stated that the bears had been seen in the Zoological Gardens to couple freely, but previously to 1848 had most rarely conceived. In the Reports published since this date three species have produced young (hybrids in one case), and, wonderful to relate, the white Polar bear has produced young. The badger (_Meles taxus_) has bred several times in the Gardens; but I have not heard of this {152} occurring elsewhere in England, and the event must be very rare, for an instance in Germany has been thought worth recording. [340] In Paraguay the native Nasua, though kept in pairs during many years and perfectly tamed, has never been known, according to Rengger, to breed or show any sexual passion; nor, as I hear from Mr. Bates, does this animal, or the Cercoleptes, breed in the region of the Amazons. Two other plantigrade genera, Procyon and Gulo, though often kept tame in Paraguay, never breed there. In the Zoological Gardens species of Nasua and Procyon have been seen to couple; but they did not produce young. As domesticated rabbits, guinea-pigs, and white mice breed so abundantly when closely confined under various climates, it might have been thought that most other members of the Rodent order would have bred in captivity, but this is not the case. It deserves notice, as showing how the capacity to breed sometimes goes by affinity, that the one native rodent of Paraguay, which there breeds _freely_ and has yielded successive generations, is the _Cavia aperea_; and this animal is so closely allied to the guinea-pig, that it has been erroneously thought to be the parent-form. [341] In the Zoological Gardens, some rodents have coupled, but have never produced young; some have neither coupled nor bred; but a few have bred, as the porcupine more than once, the Barbary mouse, lemming, chinchilla, and the agouti (_Dasyprocta aguti_), several times. This latter animal has also produced young in Paraguay, though they were born dead and ill-formed; but in Amazonia, according to Mr. Bates, it never breeds, though often kept tame about the houses. Nor does the paca (_Coelogenys paca_) breed there. The common hare when confined has, I believe, never bred in Europe;[342] though, according to a recent statement, it has crossed with the rabbit. I have never heard of the dormouse breeding in confinement. But squirrels offer a more curious case: with one exception, no species has ever bred in the Zoological Gardens, yet as many as fourteen individuals of _S. Palmarum_ were kept together during several years. The _S. Cinerea_ has been seen to couple, but it did not produce young; nor has this species, when rendered extremely tame in its native country, North America, been ever known to breed. [343] At Lord Derby's menagerie squirrels of many kinds were kept in numbers, but Mr. Thompson, the superintendent, told me that none had ever bred there, or elsewhere as far as he knew. I have never heard of the English squirrel breeding in confinement. But the species which has bred more than once in the Zoological Gardens is the one which perhaps might have been least expected, namely, the flying squirrel (_Sciuropterus volucella_): it has, also, bred several times {153} near Birmingham; but the female never produced more than two young at a birth, whereas in its native American home she bears from three to six young. [344] Monkeys, in the nine-year Report from the Zoological Gardens, are stated to unite most freely, but during this period, though many individuals were kept, there were only seven births. I have heard of one American monkey alone, the Ouistiti, breeding in Europe. [345] A Macacus, according to Flourens, bred in Paris; and more than one species of this genus has produced young in London, especially the _Macacus rhesus_, which everywhere shows a special capacity to breed under confinement. Hybrids have been produced both in Paris and London from this same genus. The Arabian baboon, or _Cynocephalus hamadryas_, [346] and a Cercopithecus have bred in the Zoological Gardens, and the latter species at the Duke of Northumberland's. Several members of the family of Lemurs have produced hybrids in the Zoological Gardens. It is much more remarkable that monkeys very rarely breed when confined in their native country; thus the Cay (_Cebus azaræ_) is frequently and completely tamed in Paraguay, but Rengger[347] says that it breeds so rarely, that he never saw more than two females which had produced young. A similar observation has been made with respect to the monkeys which are frequently tamed by the aborigines in Brazil. [348] In the region of the Amazons, these animals are so often kept in a tame state, that Mr. Bates in walking through the streets of Parà counted thirteen species; but, as he asserts, they have never been known to breed in captivity. [349] _Birds. _ Birds offer in some respects better evidence than quadrupeds, from their breeding more rapidly and being kept in greater numbers. We have seen that carnivorous animals are more fertile under confinement than most other mammals. The reverse holds good with carnivorous birds. It is said[350] that as many as eighteen species have been used in Europe for hawking, and several others in Persia and India;[351] they have been kept in their native country in the finest condition, and have been flown during six, eight, or nine years;[352] yet there is no record of their having ever produced young. As these birds were formerly caught whilst young, at great expense, being imported from Iceland, Norway, and Sweden, there can {154} be little doubt that, if possible, they would have been propagated. In the Jardin des Plantes, no bird of prey has been known to couple. [353] No hawk, vulture, or owl has ever produced fertile eggs in the Zoological Gardens, or in the old Surrey Gardens, with the exception, in the former place on one occasion, of a condor and a kite (_Milvus niger_). Yet several species, namely, the _Aquila fusca_, _Haliætus leucocephalus_, _Falco tinnunculus_, _F. Subbuteo_, and _Buteo vulgaris_, have been seen to couple in the Zoological Gardens. Mr. Morris[354] mentions as a unique fact that a kestrel (_Falco tinnunculus_) bred in an aviary. The one kind of owl which has been known to couple in the Zoological Gardens was the Eagle Owl (_Bubo maximus_); and this species shows a special inclination to breed in captivity; for a pair at Arundel Castle, kept more nearly in a state of nature "than ever fell to the lot of an animal deprived of its liberty, "[355] actually reared their young. Mr. Gurney has given another instance of this same owl breeding in confinement; and he records the case of a second species of owl, the _Strix passerina_, breeding in captivity. [356] Of the smaller graminivorous birds, many kinds have been kept tame in their native countries, and have lived long; yet, as the highest authority on cage-birds[357] remarks, their propagation is "uncommonly difficult. " The canary-bird shows that there is no inherent difficulty in these birds breeding freely in confinement; and Audubon says[358] that the _Fringilla_ (_Spiza_) _ciris_ of North America breeds as perfectly as the canary. The difficulty with the many finches which have been kept in confinement is all the more remarkable as more than a dozen species could be named which have yielded hybrids with the canary; but hardly any of these, with the exception of the siskin (_Fringilla spinus_), have reproduced their own kind. Even the bullfinch (_Loxia pyrrhula_) has bred as frequently with the canary, though belonging to a distinct genus, as with its own species. [359] With respect to the skylark (_Alauda arvensis_), I have heard of birds living for seven years in an aviary, which never produced young; and a great London bird-fancier assured me that he had never known an instance of their breeding; nevertheless one case has been recorded. [360] In the nine-year Report from the Zoological Society, twenty-four incessorial species are enumerated which had not bred, and of these only four were known to have coupled. Parrots are singularly long-lived birds; and Humboldt mentions the curious fact of a parrot in South America, which spoke the language of {155} an extinct Indian tribe, so that this bird preserved the sole relic of a lost language. Even in this country there is reason to believe[361] that parrots have lived to the age of nearly one hundred years; yet, though many have been kept in Europe, they breed so rarely that the event has been thought worth recording in the gravest publications. [362] According to Bechstein[363] the African _Psittacus erithacus_ breeds oftener than any other species: the _P. Macoa_ occasionally lays fertile eggs, but rarely succeeds in hatching them; this bird, however, has the instinct of incubation sometimes so strongly developed, that it will hatch the eggs of fowls or pigeons. In the Zoological Gardens and in the old Surrey Gardens some few species have coupled, but, with the exception of three species of parrakeets, none have bred. It is a much more remarkable fact that in Guiana parrots of two kinds, as I am informed by Sir E. Schomburgk, are often taken from the nests by the Indians and reared in large numbers; they are so tame that they fly freely about the houses, and come when called to be fed, like pigeons; yet he has never heard of a single instance of their breeding. [364] In Jamaica, a resident naturalist, Mr. R. Hill, [365] says, "no birds more readily submit to human dependence than the parrot-tribe, but no instance of a parrot breeding in this tame life has been known yet. " Mr. Hill specifies a number of other native birds kept tame in the West Indies, which never breed in this state. The great pigeon family offers a striking contrast with parrots: in the nine-year Report thirteen species are recorded as having bred, and, what is more noticeable, only two were seen to couple without any result. Since the above date every annual Report gives many cases of various pigeons breeding. The two magnificent crowned pigeons (_Goura coronata_ and _Victoriæ_) produced hybrids; nevertheless, of the former species more than a dozen birds were kept, as I am informed by Mr. Crawfurd, in a park at Penang, under a perfectly well-adapted climate, but never once bred. The _Columba migratoria_ in its native country, North America, invariably lays two eggs, but in Lord Derby's menagerie never more than one. The same fact has been observed with the _C. Leucocephala_. [366] Gallinaceous birds of many genera likewise show an eminent capacity for breeding under captivity. This is particularly the case with pheasants; yet our English species seldom lays more than ten eggs in confinement; whilst from eighteen to twenty is the usual number in the wild state. [367] With the Gallinaceæ, as with all other orders, there are marked and {156} inexplicable exceptions in regard to the fertility of certain species and genera under confinement. Although many trials have been made with the common partridge, it has rarely bred, even when reared in large aviaries; and the hen will never hatch her own eggs. [368] The American tribe of Guans or Cracidæ are tamed with remarkable ease, but are very shy breeders in this country;[369] but with care various species were formerly made to breed rather freely in Holland. [370] Birds of this tribe are often kept in a perfectly tamed condition in their native country by the Indians, but they never breed. [371] It might have been expected that grouse from their habits of life would not have bred in captivity, more especially as they are said soon to languish and die. [372] But many cases are recorded of their breeding: the capercailzie (_Tetrao urogallus_) has bred in the Zoological Gardens; it breeds without much difficulty when confined in Norway, and in Russia five successive generations have been reared: _Tetrao tetrix_ has likewise bred in Norway; _T. Scoticus_ in Ireland; _T. Umbellus_ at Lord Derby's; and _T. Cupido_ in North America. It is scarcely possible to imagine a greater change in habits than that which the members of the ostrich family must suffer, when cooped up in small enclosures under a temperate climate, after freely roaming over desert and tropical plains or entangled forests. Yet almost all the kinds, even the mooruk (_Casuarius Bennettii_) from New Ireland, has frequently produced young in the various European menageries. The African ostrich, though perfectly healthy and living long in the South of France, never lays more than from twelve to fifteen eggs, though in its native country it lays from twenty-five to thirty. [373] Here we have another instance of fertility impaired, but not lost, under confinement, as with the flying squirrel, the hen-pheasant, and two species of American pigeons. Most Waders can be tamed, as the Rev. E. S. Dixon informs me, with remarkable facility; but several of them are short-lived under confinement, so that their sterility in this state is not surprising. The cranes breed more readily than other genera: _Grus montigresia_ has bred several times in Paris and in the Zoological Gardens, as has _G. Cinerea_ at the latter place, and _G. Antigone_ at Calcutta. Of other members of this great order, _Tetrapteryx paradisea_ has bred at Knowsley, a Porphyrio in Sicily, and the _Gallinula chloropus_ in the Zoological Gardens. On the other hand, several {157} birds belonging to this order will not breed in their native country, Jamaica; and the Psophia, though often kept by the Indians of Guiana about their houses, "is seldom or never known to breed. "[374] No birds breed with such complete facility under confinement as the members of the great Duck family; yet, considering their aquatic and wandering habits, and the nature of their food, this could not have been anticipated. Even some time ago above two dozen species had bred in the Zoological Gardens; and M. Selys-Longchamps has recorded the production of hybrids from forty-four different members of the family; and to these Professor Newton has added a few more cases. [375] "There is not, " says Mr. Dixon, [376] "in the wide world, a goose which is not in the strict sense of the word domesticable;" that is, capable of breeding under confinement; but this statement is probably too bold. The capacity to breed sometimes varies in individuals of the same species; thus Audubon[377] kept for more than eight years some wild geese (_Anser Canadensis_), but they would not mate; whilst other individuals of the same species produced young during the second year. I know of but one instance in the whole family of a species which absolutely refuses to breed in captivity, namely, the _Dendrocygna viduata_, although, according to Sir R. Schomburgk, [378] it is easily tamed, and is frequently kept by the Indians of Guiana. Lastly, with respect to Gulls, though many have been kept in the Zoological Gardens and in the old Surrey Gardens, no instance was known before the year 1848 of their coupling or breeding; but since that period the herring gull (_Larus argentatus_) has bred many times in the Zoological Gardens and at Knowsley. There is reason to believe that insects are affected by confinement like the higher animals. It is well known that the Sphingidæ rarely breed when thus treated. An entomologist[379] in Paris kept twenty-five specimens of _Saturnia pyri_, but did not succeed in getting a single fertile egg. A number of females of _Orthosia munda_ and of _Mamestra suasa_ reared in confinement were unattractive to the males. [380] Mr. Newport kept nearly a hundred individuals of two species of Vanessa, but not one paired; this, however, might have been due to their habit of coupling on the wing. [381] Mr. Atkinson could never succeed in India in making the Tarroo silk-moth breed in confinement. [382] It appears that a number of moths, especially the Sphingidæ, when hatched in the autumn out of their proper season, {158} are completely barren; but this latter case is still involved in some obscurity. [383] Independently of the fact of many animals under confinement not coupling, or, if they couple, not producing young, there is evidence of another kind, that their sexual functions are thus disturbed. For many cases have beenrecorded of the loss by male birds when confined of their characteristicplumage. Thus the common linnet (_Linota cannabina_) when caged does notacquire the fine crimson colour on its breast, and one of the buntings(_Emberiza passerina_) loses the black on its head. A Pyrrhula and anOriolus have been observed to assume the quiet plumage of the hen-bird; andthe _Falco albidus_ returned to the dress of an earlier age. [384] Mr. Thomson, the superintendent of the Knowsley menagerie, informed me that hehad often observed analogous facts. The horns of a male deer (_CervusCanadensis_) during the voyage from America were badly developed; butsubsequently in Paris perfect horns were produced. When conception takes place under confinement, the young are often borndead, or die soon, or are ill-formed. This frequently occurs in theZoological Gardens, and, according to Rengger, with native animals confinedin Paraguay. The mother's milk often fails. We may also attribute to thedisturbance of the sexual functions the frequent occurrence of thatmonstrous instinct which leads the mother to devour her own offspring, --amysterious case of perversion, as it at first appears. Sufficient evidence has now been advanced to prove that animals when firstconfined are eminently liable to suffer in their reproductive systems. Wefeel at first naturally inclined to attribute the result to loss of health, or at least to loss of vigour; but this view can hardly be admitted when wereflect how healthy, long-lived, and vigorous many animals are under {159}captivity, such as parrots, and hawks when used for hawking, chetahs whenused for hunting, and elephants. The reproductive organs themselves are notdiseased; and the diseases, from which animals in menageries usuallyperish, are not those which in any way affect their fertility. No domesticanimal is more subject too disease than the sheep, yet it is remarkablyprolific. The failure of animals to breed under confinement has beensometimes attributed exclusively to a failure in their sexual instincts:this may occasionally come into play, but there is no obvious reason whythis instinct should be especially liable to be affected with perfectlytamed animals, except indeed indirectly through the reproductive systemitself being disturbed. Moreover, numerous cases have been given of variousanimals which couple freely under confinement, but never conceive; or, ifthey conceive and produce young, these are fewer in number than is naturalto the species. In the vegetable kingdom instinct of course can play nopart; and we shall presently see that plants when removed from theirnatural conditions are affected in nearly the same manner as animals. Change of climate cannot be the cause of the loss of fertility, for, whilstmany animals imported into Europe from extremely different climates breedfreely, many others when confined in their native land are completelysterile. Change of food cannot be the chief cause; for ostriches, ducks, and many other animals, which must have undergone a great change in thisrespect, breed freely. Carnivorous birds when confined are extremelysterile; whilst most carnivorous mammals, except plantigrades, aremoderately fertile. Nor can the amount of food be the cause; for asufficient supply will certainly be given to valuable animals; and there isno reason to suppose that much more food would be given to them, than toour choice domestic productions which retain their full fertility. Lastly, we may infer from the case of the elephant, chetah, various hawks, and ofmany animals which are allowed to lead an almost free life in their nativeland, that want of exercise is not the sole cause. It would appear that any change in the habits of life, whatever thesehabits may be, if great enough, tends to affect in an inexplicable mannerthe powers of reproduction. The result {160} depends more on theconstitution of the species than on the nature of the change; for certainwhole groups are affected more than others; but exceptions always occur, for some species in the most fertile groups refuse to breed, and some inthe most sterile groups breed freely. Those animals which usually breedfreely under confinement, rarely breed, as I was assured, in the ZoologicalGardens, within a year or two after their first importation. When an animalwhich is generally sterile under confinement happens to breed, the youngapparently do not inherit this power; for had this been the case, variousquadrupeds and birds, which are valuable for exhibition, would have becomecommon. Dr. Broca even affirms[385] that many animals in the Jardin desPlantes, after having produced young for three or four successivegenerations, become sterile; but this may be the result of too closeinterbreeding. It is a remarkable circumstance that many mammals and birdshave produced hybrids under confinement quite as readily as, or even morereadily than, they have procreated their own kind. Of this fact manyinstances have been given;[386] and we are thus reminded of those plantswhich when cultivated refuse to be fertilised by their own pollen, but caneasily be fertilised by that of a distinct species. Finally, we mustconclude, limited as the conclusion is, that changed conditions of lifehave an especial power of acting injuriously on the reproductive system. The whole case is quite peculiar, for these organs, though not diseased, are thus rendered incapable of performing their proper functions, orperform them imperfectly. _Sterility of Domesticated Animals from changed conditions. _--With respect to domesticated animals, as their domestication mainly depends on the accident of their breeding freely under captivity, we ought not to expect that their reproductive system would be affected by any moderate degree of change. Those orders of quadrupeds and birds, of which the wild species breed most readily in our menageries, have afforded us the greatest number of domesticated productions. Savages in most parts of the world are fond of taming animals;[387] and if any of these regularly produced {161} young, and were at the same time useful, they would be at once domesticated. If, when their masters migrated into other countries, they were in addition found capable of withstanding various climates, they would be still more valuable; and it appears that the animals which breed readily in captivity can generally withstand different climates. Some few domesticated animals, such as the reindeer and camel, offer an exception to this rule. Many of our domesticated animals can bear with undiminished fertility the most unnatural conditions; for instance, rabbits, guinea-pigs, and ferrets breed in miserably confined hutches. Few European dogs of any kind withstand without degeneration the climate of India; but as long as they survive, they retain, as I hear from Mr. Falconer, their fertility; so it is, according to Dr. Daniell, with English dogs taken to Sierra Leone. The fowl, a native of the hot jungles of India, becomes more fertile than its parent-stock in every quarter of the world, until we advance as far north as Greenland and Northern Siberia, where this bird will not breed. Both fowls and pigeons, which I received during the autumn direct from Sierra Leone, were at once ready to couple. [388] I have, also, seen pigeons breeding as freely as the common kinds within a year after their importation from the Upper Nile. The guinea-fowl, an aboriginal of the hot and dry deserts of Africa, whilst living under our damp and cool climate, produces a large supply of eggs. Nevertheless, our domesticated animals under new conditions occasionally show signs of lessened fertility. Roulin asserts that in the hot valleys of the equatorial Cordillera sheep are not fully fecund;[389] and according to Lord Somerville, [390] the merino-sheep which he imported from Spain were not at first perfectly fertile. It is said[391] that mares brought up on dry food in the stable, and turned out to grass, do not at first breed. The peahen, as we have seen, is said not to lay so many eggs in England as in India. It was long before the canary-bird was fully fertile, and even now first-rate breeding birds are not common. [392] In the hot and dry province of Delhi, the eggs of the turkey, as I hear from Dr. Falconer, though placed under a hen, are extremely liable to fail. According to Roulin, geese taken within a recent period to the lofty plateau of Bogota, at first laid seldom, and then only a few eggs; of these scarcely a fourth were hatched, and half the young birds died: in the second generation they were more fertile; and when Roulin wrote they were becoming as {162} fertile as our geese in Europe. In the Philippine Archipelago the goose, it is asserted, will not breed or even lay eggs. [393] A more curious case is that of the fowl, which, according to Roulin, when first introduced would not breed at Cusco in Bolivia, but subsequently became quite fertile; and the English Game fowl, lately introduced, had not as yet arrived a its full fertility, for to raise two or three chickens from a nest of eggs was thought fortunate. In Europe close confinement has a marked effect on the fertility of the fowl: it has been found in France that with fowls allowed considerable freedom only twenty per cent. Of the eggs failed; when allowed less freedom forty per cent. Failed; and in close confinement sixty out of the hundred were not hatched. [394] So we see that unnatural and changed conditions of life produce some effect on the fertility of our most thoroughly domesticated animals, in the same manner, though in a far less degree, as with captive wild animals. It is by no means rare to find certain males and females which will not breed together, though both are known to be perfectly fertile with other males and females. We have no reason to suppose that this is caused by these animals having been subjected to any change in their habits of life; therefore such cases are hardly related to our present subject. The cause apparently lies in an innate sexual incompatibility of the pair which are matched. Several instances have been communicated to me by Mr. W. C. Spooner (well known for his essay on Cross-breeding), by Mr. Eyton of Eyton, by Mr. Wicksted and othe breeders, and especially by Mr. Waring of Chelsfield, in relation to horses, cattle, pigs, foxhounds, other dogs, and pigeons. [395] In these cases, females, which either previously or subsequently were proved to be fertile, failed to breed with certain males, with whom it was particularly desired to match them. A change in the constitution of the female may sometimes have occurred before she was put to the second male; but in other cases this explanation is hardly tenable, for a female, known not to be barren, has been unsuccessfully paired seven or eight times with the same male likewise known to be perfectly fertile. With cart-mares, which sometimes will not breed with stallions of pure blood, but subsequently have bred with cart-stallions, Mr. Spooner is inclined to attribute the failure to the lesser sexual power of the race-horse. But I have heard from the greatest breeder of race-horses at the present day, through Mr. Waring, that "it frequently occurs with a mare to be put several times during one or two seasons to a particular stallion of acknowledged power, and yet prove barren; the mare afterwards breeding at once with some other horse. " These facts are worth recording, as they show, like so many previous facts, on what slight constitutional differences the fertility of an animal often depends. {163} _Sterility of Plants from changed Conditions of Life, and from othercauses. _ In the vegetable kingdom cases of sterility frequently occur, analogouswith those previously given in the animal kingdom. But the subject isobscured by several circumstances, presently to be discussed, namely, thecontabescence of the anthers, as Gärtner has named a certainaffection--monstrosities--doubleness of the flower--much-enlargedfruit--and long-continued or excessive propagation by buds. It is notorious that many plants in our gardens and hot-houses, though preserved in the most perfect health, rarely or never produce seed. I do not allude to plants which run to leaves, from being kept too damp, or too warm, or too much manured; for these do not produce the reproductive individual or flower, and the case may be wholly different. Nor do I allude to fruit not ripening from want of heat, or rotting from too much moisture. But many exotic plants, with their ovules and pollen appearing perfectly sound, will not set any seed. The sterility in many cases, as I know from my own observation, is simply due to the absence of the proper insects for carrying the pollen to the stigma. But after excluding the several cases just specified, there are many plants in which the reproductive system has been seriously affected by the altered conditions of life to which they have been subjected. It would be tedious to enter on many details. Linnæus long ago observed[396] that Alpine plants, although naturally laded with seed, produce either few or none when cultivated in gardens. But exceptions often occur: the _Draba sylvestris_, one of our most thoroughly Alpine plants, multiplies itself by seed in Mr. H. C. Watson's garden, near London; and Kerner, who has particularly attended to the cultivation of Alpine plants, found that various kinds, when cultivated, spontaneously sowed themselves. [397] Many plants which naturally grow in peat-earth are entirely sterile in our gardens. I have noticed the same fact with several liliaceous plants, which nevertheless grew vigorously. Too much manure renders some kinds utterly sterile, as I have myself observed. The tendency to sterility from this cause runs in families; thus, according to Gärtner, [398] it is hardly possible to give too much manure to most Gramineæ, Cruciferæ, and Leguminosæ, whilst succulent and bulbous-rooted plants are easily affected. Extreme poverty of soil is less {164} apt to induce sterility; but dwarfed plants of _Trifolium minus_ and _repens_, growing on a lawn often mown and never manured, did not produce any seed. The temperature of the soil, and the season at which plants are watered, often have a marked effect on their fertility, as was observed by Kölreuter in the case of Mirabilis. [399] Mr. Scott in the Botanic Gardens of Edinburgh observed that _Oncidium divaricatum_ would not set seed when grown in a basket in which it throve, but was capable of fertilisation in a pot where it was a little damper. _Pelargonium fulgidum_, for many years after its introduction, seeded freely; it then became sterile; now it is fertile[400] if kept in a dry stove during the winter. Other varieties of pelargonium are sterile and others fertile without our being able to assign any cause. Very slight changes in the position of a plant, whether planted on a bank or at its base, sometimes make all the difference in its producing seed. Temperature apparently has a much more powerful influence on the fertility of plants than on that of animals. Nevertheless it is wonderful what changes some few plants will withstand with undiminished fertility: thus the _Zephyranthes candida_, a native of the moderately warm banks of the Plata, sows itself in the hot dry country near Lima, and in Yorkshire resists the severest frosts, and I have seen seeds gathered from pods which had been covered with snow during three weeks. [401] _Berberis Wallichii_, from the hot Khasia range in India, is uninjured by our sharpest frosts, and ripens its fruit under our cool summers. Nevertheless I presume we must attribute to change of climate the sterility of many foreign plants; thus the Persian and Chinese lilacs (_Syringa Persica_ and _Chinensis_), though perfectly hardly, never here produce a seed; the common lilac (_S. Vulgaris_) seeds with us moderately well, but in parts of Germany the capsules never contain seed. [402] Some of the cases, given in the last chapter, of self-impotent plants, which are fertile both on the male and female side when united with distinct individuals or species, might have been here introduced; for as this peculiar form of sterility generally occurs with exotic plants or with endemic plants cultivated in pots, and as it disappeared in the _Passiflora alata_ when grafted, we may conclude that in these cases it is the result of the treatment to which the plants or their parents have been exposed. The liability of plants to be affected in their fertility by slightly changed conditions is the more remarkable, as the pollen when once in process of formation is not easily injured; a plant may be transplanted, or a branch with flower-buds be cut off and placed in water, and the pollen will be matured. Pollen, also, when once mature, may be kept for weeks or even months. [403] The female organs are more sensitive, for Gärtner[404] found that dicotyledonous plants, when carefully removed so that they did not in the least flag, could seldom be fertilised; this occurred even with potted {165} plants if the roots had grown out of the hole at the bottom. In some few cases, however, as with Digitalis, transplantation did not prevent fertilisation; and according to the testimony of Mawz, _Brassica rapa_, when pulled up by its roots and placed in water, ripened its seed. Flower-stems of several monocotyledonous plants when cut off and placed in water likewise produce seed. But in these cases I presume that the flowers had been already fertilised, for Herbert[405] found with the Crocus that the plants might be removed or mutilated after the act of fertilisation, and would still perfect their seeds; but that, if transplanted before being fertilised, the application of pollen was powerless. Plants which have been long cultivated can generally endure with undiminished fertility various and great changes; but not in most cases so great a change of climate as domesticated animals. It is remarkable that many plants under these circumstances are so much affected that the proportions and the nature of their chemical ingredients are modified, yet their fertility is unimpaired. Thus, as Dr. Falconer informs me, there is a great difference in the character of the fibre in hemp, in the quantity of oil in the seed of the Linum, in the proportion of narcotin to morphine in the poppy, in gluten to starch in wheat, when these plants are cultivated on the plains and on the mountains of India; nevertheless, they all remain fully fertile. _Contabescence. _--Gärtner has designated by this term a peculiar condition of the anthers in certain plants, in which they are shrivelled, or become brown and tough, and contain no good pollen. When in this state they exactly resemble the anthers of the most sterile hybrids. Gärtner, [406] in his discussion on this subject, has shown that plants of many orders are occasionally thus affected; but the Caryophyllaceæ and Liliaceæ suffer most, and to these orders, I think, the Ericaceæ may be added. Contabescence varies in degree, but on the same plant all the flowers are generally affected to nearly the same extent. The anthers are affected at a very early period in the flower-bud, and remain in the same state (with one recorded exception) during the life of the plant. The affection cannot be cured by any change of treatment, and is propagated by layers, cuttings, &c. , and perhaps even by seed. In contabescent plants the female organs are seldom affected, or merely become precocious in their development. The cause of this affection is doubtful, and is different in different cases. Until I read Gärtner's discussion I attributed it, as apparently did Herbert, to the unnatural treatment of the plants; but its permanence under changed conditions, and the female organs not being affected, seem incompatible with this view. The fact of several endemic plants becoming contabescent in our gardens seems, at first sight, equally incompatible with this view; but Kölreuter believes that this is the result of their transplantation. The contabescent plants of Dianthus and Verbascum, found wild by Wiegmann, grew on a dry and sterile bank. The fact that exotic {166} plants are eminently liable to this affection also seems to show that it is in some manner caused by their unnatural treatment. In some instances, as with Silene, Gärtner's view seems the most probable, namely, that it is caused by an inherent tendency in the species to become dioecious. I can add another cause, namely, the illegitimate unions of reciprocally dimorphic or trimorphic plants, for I have observed seedlings of three species of Primula and of _Lythrum salicaria_, which had been raised from plants illegitimately fertilised by their own-form pollen, with some or all their anthers in a contabescent state. There is perhaps an additional cause, namely, self-fertilisation; for many plants of Dianthus and Lobelia, which had been raised from self-fertilised seeds, had their anthers in this state; but these instances are not conclusive, as both genera are liable from other causes to this affection. Cases of an opposite nature likewise occur, namely, plants with the female organs struck with sterility, whilst the male organs remain perfect. _Dianthus Japonicus_, a Passiflora, and Nicotiana, have been described by Gärtner[407] as being in this unusual condition. _Monstrosities as a cause of Sterility. _--Great deviations of structure, even when the reproductive organs themselves are not seriously affected, sometimes cause plants to become sterile. But in other cases plants may become monstrous to an extreme degree and yet retain their full fertility. Gallesio, who certainly had great experience, [408] often attributes sterility to this cause; but it may be suspected that in some of his cases sterility was the cause, and not the result, of the monstrous growths. The curious St. Valery apple, although it bears fruit, rarely produces seed. The wonderfully anomalous flowers of _Begonia frigida_, formerly described, though they appear fit for fructification, are sterile. [409] Species of Primulæ, in which the calyx is brightly coloured, are said[410] to be often sterile, though I have known them to be fertile. On the other hand, Verlot gives several cases of proliferous flowers which can be propagated by seed. This was the case with a poppy, which had become monopetalous by the union of its petals. [411] Another extraordinary poppy, with the stamens replaced by numerous small supplementary capsules, likewise reproduces itself by seed. This has also occurred with a plant of _Saxifraga geum_, in which a series of adventitious carpels, bearing ovules on their margins, had been developed between the stamens and the normal carpels. [412] Lastly, with respect to peloric flowers, which depart wonderfully from the natural structure, --those of _Linaria vulgaris_ seem generally to be more or less sterile, whilst those before described of _Antirrhinum majus_, when artificially fertilised with their own pollen, are perfectly {167} fertile, though sterile when left to themselves, for bees are unable to crawl into the narrow tubular flower. The peloric flowers of _Corydalis solida_, according to Godron, [413] are barren; whilst those of Gloxinia are well known to yield plenty of seed. In our greenhouse Pelargoniums, the central flower of the truss is often peloric, and Mr. Masters informs me that he tried in vain during several years to get seed from these flowers. I likewise made many vain attempts, but sometimes succeeded in fertilising them with pollen from a normal flower of another variety; and conversely I several times fertilised ordinary flowers with peloric pollen. Only once I succeeded in raising a plant from a peloric flower fertilised by pollen from a peloric flower borne by another variety; but the plant, it may be added, presented nothing particular in its structure. Hence we may conclude that no general rule can be laid down; but any great deviation from the normal structure, even when the reproductive organs themselves are not seriously affected, certainly often leads to sexual impotence. _Double Flowers. _--When the stamens are converted into petals, the plant becomes on the male side sterile; when both stamens and pistils are thus changed, the plant becomes completely barren. Symmetrical flowers having numerous stamens and petals are the most liable to become double, as perhaps follows from all multiple organs being the most subject to variability. But flowers furnished with only a few stamens, and others which are asymmetrical in structure, sometimes become double, as we see with the double gorse or Ulex, Petunia, and Antirrhinum. The Compositæ bear what are called double flowers by the abnormal development of the corolla of their central florets. Doubleness is sometimes connected with prolification, [414] or the continued growth of the axis of the flower. Doubleness is strongly inherited. No one has produced, as Lindley remarks, [415] double flowers by promoting the perfect health of the plant. On the contrary, unnatural conditions of life favour their production. There is some reason to believe that seeds kept during many years, and seeds believed to be imperfectly fertilised, yield double flowers more freely than fresh and perfectly fertilised seed. [416] Long-continued cultivation in rich soil seems to be the commonest exciting cause. A double narcissus and a double _Anthemis nobilis_, transplanted into very poor soil, have been observed to become single;[417] and I have seen a completely double white primrose rendered permanently single by being divided and transplanted whilst in full flower. It has been observed by Professor Morren that doubleness of the flowers and variegation of the leaves are antagonistic states; but so many exceptions to the rule have lately been recorded, [418] that, though general, it cannot be looked at as invariable. {168} Variegation seems generally to result from a feeble or atrophied condition of the plant, and a large proportion of the seedlings raised from parents both of which are variegated usually perish at an early age; hence we may perhaps infer that doubleness, which is the antagonistic state, commonly arises from a plethoric condition. On the other hand, extremely poor soil sometimes, though rarely, appears to cause doubleness: I formerly described[419] some completely double, bud-like, flowers produced in large numbers by stunted wild plants of _Gentiana amarella_ growing on a poor chalky bank. I have also noticed a distinct tendency to doubleness in the flowers of a Ranunculus, Horse-chesnut, and Bladder-nut (_Ranunculus repens_, _Æsculus pavia_, and _Staphylea_), growing under very unfavourable conditions. Professor Lehman[420] found several wild plants growing near a hot spring with double flowers. With respect to the cause of doubleness, which arises, as we see, under widely different circumstances, I shall presently attempt to show that the most probable view is that unnatural conditions first give a tendency to sterility, and that then, on the principle of compensation, as the reproductive organs do not perform their proper functions, they either become developed into petals, or additional petals are formed. This view has lately been supported by Mr. Laxton, [421] who advances the case of some common peas, which, after long-continued heavy rain, flowered a second time, and produced double flowers. _Seedless Fruit. _--Many of our most valuable fruits, although consisting in a homological sense of widely different organs, are either quite sterile, or produce extremely few seeds. This is notoriously the case with our best pears, grapes, and figs, with the pine-apple, banana, bread-fruit, pomegranate, azarole, date-palms, and some members of the orange-tribe. Poorer varieties of these same fruits either habitually or occasionally yield seed. [422] Most horticulturists look at the great size and anomalous development of the fruit as the cause, and sterility as the result; but the opposite view, as we shall presently see, is more probable. _Sterility from the excessive development of the Organs of Growth or Vegetation. _--Plants which from any cause grow too luxuriantly, and produce leaves, stems, runners, suckers, tubers, bulbs, &c. , in excess, sometimes do not flower, or if they flower do not yield seed. To make European vegetables under the hot climate of India yield seed, it is necessary to check their growth; and, when one-third grown, they are taken up, and their stems and {169} tap-roots are cut or mutilated. [423] So it is with hybrids; for instance, Prof. Lecoq[424] had three plants of Mirabilis, which, though they grew luxuriantly and flowered, were quite sterile; but after beating one with a stick until a few branches alone were left, these at once yielded good seed. The sugar-cane, which grows vigorously and produces a large supply of succulent stems, never, according to various observers, bears seed in the West Indies, Malaga, India, Cochin China, or the Malay Archipelago. [425] Plants which produce a large number of tubers are apt to be sterile, as occurs, to a certain extent, with the common potato; and Mr. Fortune informs me that the sweet potato (_Convolvulus batatas_) in China never, as far as he has seen, yields seed. Dr. Royle remarks[426] that in India the _Agave vivipara_, when grown in rich soil, invariably produces bulbs, but no seeds; whilst a poor soil and dry climate leads to an opposite result. In China, according to Mr. Fortune, an extraordinary number of little bulbs are developed in the axils of the leaves of the yam, and this plant does not bear seed. Whether in these cases, as in those of double flowers and seedless fruit, sexual sterility from changed conditions of life is the primary cause which leads to the excessive development of the organs of vegetation, is doubtful; though some evidence might be advanced in favour of this view. It is perhaps a more probable view that plants which propagate themselves largely by one method, namely by buds, have not sufficient vital power or organised matter for the other method of sexual generation. Several distinguished botanists and good practical judges believe that long-continued propagation by cuttings, runners, tubers, bulbs, &c. , independently of any excessive development of these parts, is the cause of many plants failing to produce flowers and of others failing to produce fertile flowers, --it is as if they had lost the habit of sexual generation. [427] That many plants when thus propagated are sterile there can be no doubt, but whether the long continuance of this form of propagation is the actual cause of their sterility, I will not venture, from the want of sufficient evidence, to express an opinion. That plants may be propagated for long periods by buds, without the aid of sexual generation, we may safely infer from this being the case with many plants which must have long survived in a state of nature. As I have had occasion before to allude to this subject, I will here give such cases as I have collected. Many alpine plants ascend mountains beyond the height at which they can produce seed. [428] Certain species of {170} Poa and Festuca, when growing on mountain-pastures, propagate themselves, as I hear from Mr. Bentham, almost exclusively by bulblets. Kalm gives a more curious instance[429] of several American trees, which grow so plentifully in marshes or in thick woods, that they are certainly well adapted for these stations, yet scarcely ever produce seeds; but when accidentally growing on the outside of the marsh or wood, are loaded with seed. The common ivy is found in Northern Sweden and Russia, but flowers and fruits only in the southern provinces. The _Acorus calamus_ extends over a large portion of the globe, but so rarely perfects its fruit that this has been seen but by few botanists. [430] The _Hypericum calycinum_, which propagates itself so freely in our shrubberies by rhizomas and is naturalised in Ireland, blossoms profusely, but sets no seed; nor did it set any when fertilised in my garden by pollen from plants growing at a distance. The _Lysimachia nummularia_, which is furnished with long runners, so seldom produces seed-capsules, that Prof. Decaisne, [431] who has especially attended to this plant, has never seen it in fruit. The _Carex rigida_ often fails to perfect its seed in Scotland, Lapland, Greenland, Germany, and New Hampshire in the United States. [432] The periwinkle (_Vinca minor_), which spreads largely by runners, is said scarcely ever to produce fruit in England;[433] but this plant requires insect-aid for its fertilisation, and the proper insects may be absent or rare. The _Jussiæa grandiflora_ has become naturalised in Southern France, and has spread by its rhizomas so extensively as to impede the navigation of the waters, but never produces fertile seed. [434] The horse-radish (_Cochlearia armoracia_) spreads pertinaciously and is naturalised in various parts of Europe; though it bears flowers, these rarely produce capsules: Professor Caspary also informs me that he has watched this plant since 1851, but has never seen its fruit; nor is this surprising, as he finds scarcely a grain of good pollen. The common little _Ranunculus ficaria_ rarely, and some say never, bears seed in England, France, or Switzerland; but in 1863 I observed seeds on several plants growing near my house. According to M. Chatin, there are two forms of this Ranunculus; and it is the bulbiferous form which does not yield seed from producing no pollen. [435] Other cases {171} analogous with the foregoing could be given; for instance, some kinds of mosses and lichens have never been seen to fructify in France. Some of these endemic and naturalised plants are probably rendered sterile from excessive multiplication by buds, and their consequent incapacity to produce and nourish seed. But the sterility of others more probably depends on the peculiar conditions under which they live, as in the case of the ivy in the northern parts of Europe, and of the trees in the swamps of the United States; yet these plants must be in some respects eminently well adapted for the stations which they occupy, for they hold their places against a host of competitors. Finally, when we reflect on the sterility which accompanies the doubling offlowers, --the excessive development of fruit, --and a great increase in theorgans of vegetation, we must bear in mind that the whole effect has seldombeen caused at once. An incipient tendency is observed, and continuedselection completes the work, as is known to be the case with our doubleflowers and best fruits. The view which seems the most probable, and whichconnects together all the foregoing facts and brings them within ourpresent subject, is, that changed and unnatural conditions of life firstgive a tendency to sterility; and in consequence of this, the organs ofreproduction being no longer able fully to perform their proper functions, a supply of organised matter, not required for the development of the seed, flows either into these same organs and renders them foliaceous, or intothe fruit, stems, tubers, &c. , increasing their size and succulency. But Iam far from wishing to deny that there exists, independently of anyincipient sterility, an antagonism between the two forms of reproduction, namely, by seed and by buds, when either is carried to an extreme degree. That incipient sterility plays an important part in the doubling offlowers, and in the other cases just specified, I infer chiefly from thefollowing facts. When fertility is lost from a wholly different cause, namely, from hybridism, there is a strong tendency, as Gärtner[436]affirms, for flowers to become double, and this tendency is inherited. Moreover it is notorious that with hybrids the male organs become sterilebefore the female organs, and with double flowers the stamens first become{172} foliaceous. This latter fact is well shown by the male flowers ofdioecious plants, which, according to Gallesio, [437] first become double. Again, Gärtner[438] often insists that the flowers of even utterly sterilehybrids, which do not produce any seed, generally yield perfect capsules orfruit, --a fact which has likewise been repeatedly observed by Naudin withthe Cucurbitaceæ; so that the production of fruit by plants renderedsterile through any other and distinct cause is intelligible. Kölreuter hasalso expressed his unbounded astonishment at the size and development ofthe tubers in certain hybrids; and all experimentalists[439] have remarkedon the strong tendency in hybrids to increase by roots, runners, andsuckers. Seeing that hybrid plants, which from their nature are more orless sterile, thus tend to produce double flowers; that they have the partsincluding the seed, that is the fruit, perfectly developed, even whencontaining no seed; that they sometimes yield gigantic roots; that theyalmost invariably tend to increase largely by suckers and other suchmeans;--seeing this, and knowing, from the many facts given in the earlierparts of this chapter, that almost all organic beings when exposed tounnatural conditions tend to become more or less sterile, it seems much themost probable view that with cultivated plants sterility is the excitingcause, and double flowers, rich seedless fruit, and in some caseslargely-developed organs of vegetation, &c. , are the indirectresults--these results having been in most cases largely increased throughcontinued selection by man. * * * * * {173} CHAPTER XIX. SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM. ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON FERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED CONDITIONS OF LIFE--VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONS WITH RESPECT TO HYBRIDISM--LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE PROGENY OF DIMORPHIC AND TRIMORPHIC PLANTS--STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE SYSTEM--NOT ACCUMULATED THROUGH NATURAL SELECTION--REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE--TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES--CONCLUSION. It was shown in the fifteenth chapter that when individuals of the samevariety, or even of a distinct variety, are allowed freely to intercross, uniformity of character is ultimately acquired. Some few characters, however, are incapable of fusion, but these are unimportant, as they arealmost always of a semi-monstrous nature, and have suddenly appeared. Hence, to preserve our domesticated breeds true, or to improve them bymethodical selection, it is obviously necessary that they should be keptseparate. Nevertheless, through unconscious selection, a whole body ofindividuals may be slowly modified, as we shall see in a future chapter, without separating them into distinct lots. Domestic races have often beenintentionally modified by one or two crosses, made with some allied race, and occasionally even by repeated crosses with very distinct races; but inalmost all such cases, long-continued and careful selection has beenabsolutely necessary, owing to the excessive variability of the crossedoffspring, due to the principle of reversion. In a few instances, however, mongrels have retained a uniform character from their first production. When two varieties are allowed to cross freely, and one is {174} much morenumerous than the other, the former will ultimately absorb the latter. Should both varieties exist in nearly equal numbers, it is probable that aconsiderable period would elapse before the acquirement of a uniformcharacter; and the character ultimately acquired would largely depend onprepotency of transmission, and on the conditions of life; for the natureof these conditions would generally favour one variety more than another, so that a kind of natural selection would come into play. Unless thecrossed offspring were slaughtered by man without the least discrimination, some degree of unmethodical selection would likewise come into action. Fromthese several considerations we may infer, that when two or more closelyallied species first came into the possession of the same tribe, theircrossing will not have influenced, in so great a degree as has often beensupposed, the character of the offspring in future times; although in somecases it probably has had a considerable effect. Domestication, as a general rule, increases the prolificness of animals andplants. It eliminates the tendency to sterility which is common to specieswhen first taken from a state of nature and crossed. On this latter head wehave no direct evidence; but as our races of dogs, cattle, pigs, &c. , arealmost certainly descended from aboriginally distinct stocks, and as theseraces are now fully fertile together, or at least incomparably more fertilethan most species when crossed, we may with much confidence accept thisconclusion. Abundant evidence has been given that crossing adds to the size, vigour, and fertility of the offspring. This holds good when there has been noprevious close interbreeding. It applies to the individuals of the samevariety but belonging to different families, to distinct varieties, sub-species, and partially even to species. In the latter case, though sizeis often gained, fertility is lost; but the increased size, vigour, andhardiness of many hybrids cannot be accounted for solely on the principleof compensation from the inaction of the reproductive system. Certainplants, both of pure and hybrid origin, though perfectly healthy, havebecome self-impotent, apparently from the unnatural conditions to whichthey have been exposed; and such plants, as well as others in their normalstate, can be stimulated to {175} fertility only by crossing them withother individuals of the same species or even of a distinct species. On the other hand, long-continued close interbreeding between the nearestrelations diminishes the constitutional vigour, size, and fertility of theoffspring; and occasionally leads to malformations, but not necessarily togeneral deterioration of form or structure. This failure of fertility showsthat the evil results of interbreeding are independent of the augmentationof morbid tendencies common to both parents, though this augmentation nodoubt is often highly injurious. Our belief that evil follows from closeinterbreeding rests to a large extent on the experience of practicalbreeders, especially of those who have reared many animals of the kindswhich can be propagated quickly; but it likewise rests on several carefullyrecorded experiments. With some animals close interbreeding may be carriedon for a long period with impunity by the selection of the most vigorousand healthy individuals; but sooner or later evil follows. The evil, however, comes on so slowly and gradually that it easily escapesobservation, but can be recognised by the almost instantaneous manner inwhich size, constitutional vigour, and fertility are regained when animalsthat have long been interbred are crossed with a distinct family. These two great classes of facts, namely, the good derived from crossing, and the evil from close interbreeding, with the consideration of theinnumerable adaptations throughout nature for compelling, or favouring, orat least permitting, the occasional union of distinct individuals, takentogether, lead to the conclusion that it is a law of nature that organicbeings shall not fertilise themselves for perpetuity. This law was firstplainly hinted at in 1799, with respect to plants, by Andrew Knight, [440]and, not long afterwards, that sagacious observer Kölreuter, after showinghow well the Malvaceæ are adapted for {176} crossing, asks, "an id aliquidin recessu habeat, quod hujuscemodi flores nunquam proprio suo pulvere, sedsemper eo aliarum suæ speciei impregnentur, merito quæritur? Certe naturanil facit frustra. " Although we may demur to Kölreuter's saying that naturedoes nothing in vain, seeing how many organic beings retain rudimentary anduseless organs, yet undoubtedly the argument from the innumerablecontrivances, which favour the crossing of distinct individuals of the samespecies, is of the greatest weight. The most important result of this lawis that it leads to uniformity of character in the individuals of the samespecies. In the case of certain hermaphrodites, which probably intercrossonly at long intervals of time, and with unisexual animals inhabitingsomewhat separated localities, which can only occasionally come intocontact and pair, the greater vigour and fertility of the crossed offspringwill ultimately prevail in giving uniformity of character to theindividuals of the same species. But when we go beyond the limits of thesame species, free intercrossing is barred by the law of sterility. In searching for facts which might throw light on the cause of the goodeffects from crossing, and of the evil effects from close interbreeding, wehave seen that, on the one hand, it is a widely prevalent and ancientbelief that animals and plants profit from slight changes in theircondition of life; and it would appear that the germ, in a somewhatanalogous manner, is more effectually stimulated by the male element, whentaken from a distinct individual, and therefore slightly modified innature, than when taken from a male having the same identical constitution. On the other hand, numerous facts have been given, showing that whenanimals are first subjected to captivity, even in their native land, andalthough allowed much liberty, their reproductive functions are oftengreatly impaired or quite annulled. Some groups of animals are moreaffected than others, but with apparently capricious exceptions in everygroup. Some animals never or rarely couple: some couple freely, but neveror rarely conceive. The secondary male characters, the maternal functionsand instincts, are occasionally affected. With plants, when first subjectedto cultivation, analogous facts have been observed. We probably owe ourdouble flowers, rich seedless {177} fruits, and in some cases greatlydeveloped tubers, &c. , to incipient sterility of the above nature combinedwith a copious supply of nutriment. Animals which have long beendomesticated, and plants which have long been cultivated, can generallywithstand with unimpaired fertility great changes in their conditions oflife; though both are sometimes slightly affected. With animals thesomewhat rare capacity of breeding freely under confinement has mainlydetermined, together with their utility, the kinds which have beendomesticated. We can in no case precisely say what is the cause of the diminishedfertility of an animal when first captured, or of a plant when firstcultivated; we can only infer that it is caused by a change of some kind inthe natural conditions of life. The remarkable susceptibility of thereproductive system to such changes, --a susceptibility not common to anyother organ, --apparently has an important bearing on Variability, as weshall see in a future chapter. It is impossible not to be struck with the double parallelism between thetwo classes of facts just alluded to. On the one hand, slight changes inthe conditions of life, and crosses between slightly modified forms orvarieties, are beneficial as far as prolificness and constitutional vigourare concerned. On the other hand, changes in the conditions greater indegree, or of a different nature, and crosses between forms which have beenslowly and greatly modified by natural means, --in other words, betweenspecies, --are highly injurious, as far as the reproductive system isconcerned, and in some few instances as far as constitutional vigour isconcerned. Can this parallelism be accidental? Does it not rather indicatesome real bond of connection? As a fire goes out unless it be stirred up, so the vital forces are always tending, according to Mr. Herbert Spencer, to a state of equilibrium, unless disturbed and renovated through theaction of other forces. In some few cases varieties tend to keep distinct, by breeding at differentperiods, by great differences in size, or by sexual preference, --in thislatter respect more especially resembling species in a state of nature. Butthe actual crossing of varieties, far from diminishing, generally adds tothe fertility of both the first union and the mongrel offspring. Whetherall {178} the most widely distinct domestic varieties are invariably quitefertile when crossed, we do not positively know; much time and troublewould be requisite for the necessary experiments, and many difficultiesoccur, such as the descent of the various races from aboriginally distinctspecies, and the doubts whether certain forms ought to be ranked as speciesor varieties. Nevertheless, the wide experience of practical breedersproves that the great majority of varieties, even if some should hereafterprove not to be indefinitely fertile _inter se_, are far more fertile whencrossed, than the vast majority of closely allied natural species. A fewremarkable cases have, however, been given on the authority of excellentobservers, showing that with plants certain forms, which undoubtedly mustbe ranked as varieties, yield fewer seeds when crossed than is natural tothe parent-species. Other varieties have had their reproductive powers sofar modified that they are either more or less fertile than are theirparents, when crossed with a distinct species. Nevertheless, the fact remains indisputable that domesticated varieties ofanimals and of plants, which differ greatly from each other in structure, but which are certainly descended from the same aboriginal species, such asthe races of the fowl, pigeon, many vegetables, and a host of otherproductions, are extremely fertile when crossed; and this seems to make abroad and impassable barrier between domestic varieties and naturalspecies. But, as I will now attempt to show, the distinction is not sogreat and overwhelmingly important as it at first appears. _On the Difference in Fertility between Varieties and Species whencrossed. _ This work is not the proper place for fully treating the subject ofhybridism, and I have already given in my 'Origin of Species' a moderatelyfull abstract. I will here merely enumerate the general conclusions whichmay be relied on, and which bear on our present point. _Firstly_, the laws governing the production of hybrids are identical, ornearly identical, in the animal and vegetable kingdoms. _Secondly_, the sterility of distinct species when first united, {179} andthat of their hybrid offspring, graduates, by an almost infinite number ofsteps, from zero, when the ovule is never impregnated and a seed-capsule isnever formed, up to complete fertility. We can only escape the conclusionthat some species are fully fertile when crossed, by determining todesignate as varieties all the forms which are quite fertile. This highdegree of fertility is, however, rare. Nevertheless plants, which have beenexposed to unnatural conditions, sometimes become modified in so peculiar amanner, that they are much more fertile when crossed by a distinct speciesthan when fertilised by their own pollen. Success in effecting a firstunion between two species, and the fertility of their hybrids, depends inan eminent degree on the conditions of life being favourable. The innatesterility of hybrids of the same parentage and raised from the sameseed-capsule often differs much in degree. _Thirdly_, the degree of sterility of a first cross between two speciesdoes not always run strictly parallel with that of their hybrid offspring. Many cases are known of species which can be crossed with ease, but yieldhybrids excessively sterile; and conversely some which can be crossed withgreat difficulty, but produce fairly fertile hybrids. This is aninexplicable fact, on the view that species have been specially endowedwith mutual sterility in order to keep them distinct. _Fourthly_, the degree of sterility often differs greatly in two specieswhen reciprocally crossed; for the first will readily fertilise the second;but the latter is incapable, after hundreds of trials, of fertilising theformer. Hybrids produced from reciprocal crosses between the same twospecies, likewise sometimes differ in their degree of sterility. Thesecases also are utterly inexplicable on the view of sterility being aspecial endowment. _Fifthly_, the degree of sterility of first crosses and of hybrids runs, toa certain extent, parallel with the general or systematic affinity of theforms which are united. For species belonging to distinct genera canrarely, and those belonging to distinct families can never, be crossed. Theparallelism, however, is far from complete; for a multitude of closelyallied species will not unite, or unite with extreme difficulty, whilstother species, widely different from each other, can be crossed withperfect facility. Nor does the difficulty depend on ordinary {180}constitutional differences, for annual and perennial plants, deciduous andevergreen trees, plants flowering at different seasons, inhabitingdifferent stations, and naturally living under the most opposite climates, can often be crossed with ease. The difficulty or facility apparentlydepends exclusively on the sexual constitution of the species which arecrossed; or on their sexual elective affinity, _i. E. _ _Wahlverwandtschaft_of Gärtner. As species rarely or never become modified in one character, without being at the same time modified in many, and as systematic affinityincludes all visible resemblances and dissimilarities, any difference insexual constitution between two species would naturally stand in more orless close relation with their systematic position. _Sixthly_, the sterility of species when first crossed, and that ofhybrids, may possibly depend to a certain extent on distinct causes. Withpure species the reproductive organs are in a perfect condition, whilstwith hybrids they are often plainly deteriorated. A hybrid embryo whichpartakes of the constitution of its father and mother is exposed tounnatural conditions, as long as it is nourished within the womb, or egg, or seed of the mother-form; and as we know that unnatural conditions ofteninduce sterility, the reproductive organs of the hybrid might at this earlyage be permanently affected. But this cause has no bearing on theinfertility of first unions. The diminished number of the offspring fromfirst unions may often result, as is certainly sometimes the case, from thepremature death of most of the hybrid embryos. But we shall immediately seethat a law of an unknown nature apparently exists, which causes theoffspring from unions, which are infertile, to be themselves more or lessinfertile; and this at present is all that can be said. _Seventhly_, hybrids and mongrels present, with the one great exception offertility, the most striking accordance in all other respects; namely, inthe laws of their resemblance to their two parents, in their tendency toreversion, in their variability, and in being absorbed through repeatedcrosses by either parent-form. Since arriving at the foregoing conclusions, condensed from my former work, I have been led to investigate a subject which throws considerable light onhybridism, namely, the fertility of {181} reciprocally dimorphic andtrimorphic plants, when illegitimately united. I have had occasion severaltimes to allude to these plants, and I may here give a brief abstract[441]of my observations. Several plants belonging to distinct orders present twoforms, which exist in about equal numbers, and which differ in no respectexcept in their reproductive organs; one form having a long pistil withshort stamens, the other a short pistil with long stamens; both withdifferently sized pollen-grains. With trimorphic plants there are threeforms likewise differing in the lengths of their pistils and stamens, inthe size and colour of the pollen-grains, and in some other respects; andas in each of the three forms there are two sets of stamens, there arealtogether six sets of stamens and three kinds of pistils. These organs areso proportioned in length to each other that, in any two of the forms, halfthe stamens in each stand on a level with the stigma of the third form. NowI have shown, and the result has been confirmed by other observers, that, in order to obtain full fertility with these plants, it is necessary thatthe stigma of the one form should be fertilised by pollen taken from thestamens of corresponding height in the other form. So that with dimorphicspecies two unions, which may be called legitimate, are fully fertile, andtwo, which may be called illegitimate, are more or less infertile. Withtrimorphic species six unions are legitimate or fully fertile, and twelveare illegitimate or more or less infertile. The infertility which may be observed in various dimorphic and trimorphicplants, when they are illegitimately fertilised, that is, by pollen takenfrom stamens not corresponding in height with the pistil, differs much indegree, up to absolute and utter sterility; just in the same manner asoccurs in crossing distinct species. As the degree of sterility in thelatter case depends in an eminent degree on the conditions of life beingmore or less favourable, so I have found it with illegitimate unions. It iswell known that if pollen of a distinct species be placed on the stigma ofa flower, and its own pollen be afterwards, even {182} after a considerableinterval of time, placed on the same stigma, its action is so stronglyprepotent that it generally annihilates the effect of the foreign pollen;so it is with the pollen of the several forms of the same species, forlegitimate pollen is strongly prepotent over illegitimate pollen, when bothare placed on the same stigma. I ascertained this by fertilising severalflowers, first illegitimately, and twenty-four hours afterwardslegitimately, with pollen taken from a peculiarly coloured variety, and allthe seedlings were similarly coloured; this shows that the legitimatepollen, though applied twenty-four hours subsequently, had wholly destroyedor prevented the action of the previously applied illegitimate pollen. Again, as, in making reciprocal crosses between the same two species, thereis occasionally a great difference in the result, so something analogousoccurs with dimorphic plants; for a short-styled cowslip (_P. Veris_)yields more seed when fertilised by the long-styled form, and less seedwhen fertilised by its own form, compared with a long-styled cowslip whenfertilised in the two corresponding methods. In all these respects the forms of the same undoubted species, whenillegitimately united, behave in exactly the same manner as do two distinctspecies when crossed. This led me carefully to observe during four yearsmany seedlings, raised from several illegitimate unions. The chief resultis that these illegitimate plants, as they may be called, are not fullyfertile. It is possible to raise from dimorphic species, both long-styledand short-styled illegitimate plants, and from trimorphic plants all threeillegitimate forms. These can then be properly united in a legitimatemanner. When this is done, there is no apparent reason why they should notyield as many seeds as did their parents when legitimately fertilised. Butsuch is not the case; they are all infertile, but in various degrees; somebeing so utterly and incurably sterile that they did not yield during fourseasons a single seed or even seed-capsule. These illegitimate plants, which are so sterile, although united with each other in a legitimatemanner, may be strictly compared with hybrids when crossed _inter se_, andit is well known how sterile these latter generally are. When, on the otherhand, a hybrid is crossed with either pure parent-species, the sterility isusually much lessened: and so it is when an illegitimate plant isfertilised by {183} a legitimate plant. In the same manner as the sterilityof hybrids does not always run parallel with the difficulty of making thefirst cross between the two parent species, so the sterility of certainillegitimate plants was unusually great, whilst the sterility of the unionfrom which they were derived was by no means great. With hybrids raisedfrom the same seed-capsule the degree of sterility is innately variable, soit is in a marked manner with illegitimate plants. Lastly, many hybrids areprofuse and persistent flowerers, whilst other and more sterile hybridsproduce few flowers, and are weak, miserable dwarfs; exactly similar casesoccur with the illegitimate offspring of various dimorphic and trimorphicplants. Altogether there is the closest identity in character and behaviour betweenillegitimate plants and hybrids. It is hardly an exaggeration to maintainthat the former are hybrids, but produced within the limits of the samespecies by the improper union of certain forms, whilst ordinary hybrids areproduced from an improper union between so-called distinct species. We havealready seen that there is the closest similarity in all respects betweenfirst illegitimate unions, and first crosses between distinct species. Thiswill perhaps be made more fully apparent by an illustration: we may supposethat a botanist found two well-marked varieties (and such occur) of thelong-styled form of the trimorphic _Lythrum salicaria_, and that hedetermined to try by crossing whether they were specifically distinct. Hewould find that they yielded only about one-fifth of the proper number ofseed, and that they behaved in all the other above-specified respects as ifthey had been two distinct species. But to make the case sure, he wouldraise plants from his supposed hybridised seed, and he would find that theseedlings were miserably dwarfed and utterly sterile, and that they behavedin all other respects like ordinary hybrids. He might then maintain that hehad actually proved, in accordance with the common view, that his twovarieties were as good and as distinct species as any in the world; but hewould be completely mistaken. The facts now given on dimorphic and trimorphic plants are important, because they show us, firstly, that the physiological {184} test oflessened fertility, both in first crosses and in hybrids, is no safecriterion of specific distinction; secondly, because we may conclude thatthere must be some unknown law or bond connecting the infertility ofillegitimate unions with that of their illegitimate offspring, and we arethus led to extend this view to first crosses and hybrids; thirdly, becausewe find, and this seems to me of especial importance, that with trimorphicplants three forms of the same species exist, which when crossed in aparticular manner are infertile, and yet these forms differ in no respectfrom each other, except in their reproductive organs, --as in the relativelength of the stamens and pistils, in the size, form, and colour of thepollen-grains, in the structure of the stigma, and in, the number and sizeof the seeds. With these differences and no others, either in organisationor constitution, we find that the illegitimate unions and the illegitimateprogeny of these three forms are more or less sterile, and closely resemblein a whole series of relations the first unions and hybrid offspring ofdistinct species. From this we may infer that the sterility of species whencrossed and of their hybrid progeny is likewise in all probabilityexclusively due to differences confined to the reproductive system. We haveindeed been brought to a similar conclusion by observing that the sterilityof crossed species does not strictly coincide with their systematicaffinity, that is, with the sum of their external resemblances; nor does itcoincide with their similarity in general constitution. But we are moreespecially led to this same conclusion by considering reciprocal crosses, in which the male of one species cannot be united, or can be united withextreme difficulty, with the female of a second species, whilst theconverse cross can be effected with perfect facility; for this differencein the facility of making reciprocal crosses, and in the fertility of theiroffspring, must be attributed either to the male or female element in thefirst species having been differentiated with reference to the sexualelement of the second species in a higher degree than in the converse case. In so complex a subject as Hybridism it is of considerable importance thusto arrive at a definitive conclusion, namely, that the sterility whichalmost invariably follows the union of distinct {185} species dependsexclusively on differences in their sexual constitution. * * * * * On the principle which makes it necessary for man, whilst he is selectingand improving his domestic varieties, to keep them separate, it wouldclearly be advantageous to varieties in a state of nature, that is toincipient species, if they could be kept from blending, either throughsexual aversion, or by becoming mutually sterile. Hence it at one timeappeared to me probable, as it has to others, that this sterility mighthave been acquired through natural selection. On this view we must supposethat a shade of lessened fertility first spontaneously appeared, like anyother modification, in certain individuals of a species when crossed withother individuals of the same species; and that successive slight degreesof infertility, from being advantageous, were slowly accumulated. Thisappears all the more probable, if we admit that the structural differencesbetween the forms of dimorphic and trimorphic plants, as the length andcurvature of the pistil, &c. , have been co-adapted through naturalselection; for if this be admitted, we can hardly avoid extending the sameconclusion to their mutual infertility. Sterility moreover has beenacquired through natural selection for other and widely different purposes, as with neuter insects in reference to their social economy. In the case ofplants, the flowers on the circumference of the truss in the guelder-rose(_Viburnum opulus_) and those on the summit of the spike in thefeather-hyacinth (_Muscari comosum_) have been rendered conspicuous, andapparently in consequence sterile, in order that insects might easilydiscover and visit the other flowers. But when we endeavour to apply theprinciple of natural selection to the acquirement by distinct species ofmutual sterility, we meet with great difficulties. In the first place, itmay be remarked that separate regions are often inhabited by groups ofspecies or by single species, which when brought together and crossed arefound to be more or less sterile; now it could clearly have been of noadvantage to such separated species to have been rendered mutually sterile, and consequently this could not have been effected through naturalselection; but it may perhaps be argued, that, if a species were renderedsterile with {186} some one compatriot, sterility with other species wouldfollow as a necessary consequence. In the second place, it is as muchopposed to the theory of natural selection, as to the theory of specialcreation, that in reciprocal crosses the male element of one form shouldhave been rendered utterly impotent on a second form, whilst at the sametime the male element of this second form is enabled freely to fertilisethe first form; for this peculiar state of the reproductive system couldnot possibly be advantageous to either species. In considering the probability of natural selection having come into actionin rendering species mutually sterile, one great difficulty will be foundto lie in the existence of many graduated steps from slightly lessenedfertility to absolute sterility. It may be admitted, on the principle aboveexplained, that it would profit an incipient species if it were rendered insome slight degree sterile when crossed with its parent-form or with someother variety; for thus fewer bastardised and deteriorated offspring wouldbe produced to commingle their blood with the new species in process offormation. But he who will take the trouble to reflect on the steps bywhich this first degree of sterility could be increased through naturalselection to that higher degree which is common to so many species, andwhich is universal with species which have been differentiated to a genericor family rank, will find the subject extraordinarily complex. After maturereflection it seems to me that this could not have been effected throughnatural selection; for it could have been of no direct advantage to anindividual animal to breed badly with another individual of a differentvariety, and thus leave few offspring; consequently such individuals couldnot have been preserved or selected. Or take the case of two species whichin their present state, when crossed, produce few and sterile offspring;now, what is there which could favour the survival of those individualswhich happened to be endowed in a slightly higher degree with mutualinfertility and which thus approached by one small step towards absolutesterility? yet an advance of this kind, if the theory of natural selectionbe brought to bear, must have incessantly occurred with many species, for amultitude are mutually quite barren. With sterile neuter insects we havereason to {187} believe that modifications in their structure have beenslowly accumulated by natural selection, from an advantage having been thusindirectly given to the community to which they belonged over othercommunities of the same species; but an individual animal, if renderedslightly sterile when crossed with some other variety, would not thus initself gain any advantage, or indirectly give any advantage to its nearestrelatives or to other individuals of the same variety, leading to theirpreservation. I infer from these considerations that, as far as animals areconcerned, the various degrees of lessened fertility which occur withspecies when crossed cannot have been slowly accumulated by means ofnatural selection. With plants, it is possible that the case may be somewhat different. Withmany kinds, insects constantly carry pollen from neighbouring plants to thestigmas of each flower; and with some species this is effected by the wind. Now, if the pollen of a variety, when deposited on the stigma of the samevariety, should become by spontaneous variation in ever so slight a degreeprepotent over the pollen of other varieties, this would certainly be anadvantage to the variety; for its own pollen would thus obliterate theeffects of the pollen of other varieties, and prevent deterioration ofcharacter. And the more prepotent the variety's own pollen could berendered through natural selection, the greater the advantage would be. Weknow from the researches of Gärtner that, with species which are mutuallysterile, the pollen of each is always prepotent on its own stigma over thatof the other species; but we do not know whether this prepotency is aconsequence of the mutual sterility, or the sterility a consequence of theprepotency. If the latter view be correct, as the prepotency becamestronger through natural selection, from being advantageous to a species inprocess of formation, so the sterility consequent on prepotency would atthe same time be augmented; and the final result would be various degreesof sterility, such as occurs with existing species. This view might beextended to animals, if the female before each birth received severalmales, so that the sexual element of the prepotent male of her own varietyobliterated the effects of the access of previous males belonging to othervarieties; but we have no reason to believe, at least {188} withterrestrial animals, that this is the ease; as most males and females pairfor each birth, and some few for life. On the whole we may conclude that with animals the sterility of crossedspecies has not been slowly augmented through natural selection; and asthis sterility follows the same general laws in the vegetable as in theanimal kingdom, it is improbable, though apparently possible, that withplants crossed species should have been rendered sterile by a differentprocess. From this consideration, and remembering that species which havenever co-existed in the same country, and which therefore could not havereceived any advantage from having been rendered mutually infertile, yetare generally sterile when crossed; and bearing in mind that in reciprocalcrosses between the same two species there is sometimes the widestdifference in their sterility, we must give up the belief that naturalselection has come into play. As species have not been rendered mutually infertile through theaccumulative action of natural selection, and as we may safely conclude, from the previous as well as from other and more general considerations, that they have not been endowed through an act of creation with thisquality, we must infer that it has arisen incidentally during their slowformation in connection with other and unknown changes in theirorganisation. By a quality arising incidentally, I refer to such cases asdifferent species of animals and plants being differently affected bypoisons to which they are not naturally exposed; and this difference insusceptibility is clearly incidental on other and unknown differences intheir organisation. So again the capacity in different kinds of trees to begrafted on each other, or on a third species, differs much, and is of noadvantage to these trees, but is incidental on structural or functionaldifferences in their woody tissues. We need not feel surprise at sterilityincidentally resulting from crosses between distinct species, --the modifieddescendants of a common progenitor, --when we bear in mind how easily thereproductive system is affected by various causes--often by extremelyslight changes in the conditions of life, by too close interbreeding, andby other agencies. It is well to bear in mind such cases, as that of the_Passiflora alata_, which recovered its self-fertility from {189} beinggrafted on a distinct species--the cases of plants which normally orabnormally are self-impotent, but can readily be fertilised by the pollenof a distinct species--and lastly the cases of individual domesticatedanimals which evince towards each other sexual incompatibility. * * * * * We now at last come to the immediate point under discussion: how is itthat, with some few exceptions in the case of plants, domesticatedvarieties, such as those of the dog, fowl, pigeon, several fruit-trees, andculinary vegetables, which differ from each other in external charactersmore than many species, are perfectly fertile when crossed, or even fertilein excess, whilst closely allied species are almost invariably in somedegree sterile? We can, to a certain extent, give a satisfactory answer tothis question. Passing over the fact that the amount of external differencebetween two species is no sure guide to their degree of mutual sterility, so that similar differences in the case of varieties would be no sureguide, we know that with species the cause lies exclusively in differencesin their sexual constitution. Now the conditions to which domesticatedanimals and cultivated plants have been subjected, have had so littletendency towards modifying the reproductive system in a manner leading tomutual sterility, that we have good grounds for admitting the directlyopposite doctrine of Pallas, namely, that such conditions generallyeliminate this tendency; so that the domesticated descendants of species, which in their natural state would have been in some degree sterile whencrossed, become perfectly fertile together. With plants, so far iscultivation from giving a tendency towards mutual sterility, that inseveral well-authenticated cases, already often alluded to, certain specieshave been affected in a very different manner, for they have becomeself-impotent, whilst still retaining the capacity of fertilising, andbeing fertilised by, distinct species. If the Pallasian doctrine of theelimination of sterility through long-continued domestication be admitted, and it can hardly be rejected, it becomes in the highest degree improbablethat similar circumstances should commonly both induce and eliminate thesame tendency; though in certain cases, with species having a peculiarconstitution, sterility might occasionally be thus {190} induced. Thus, asI believe, we can understand why with domesticated animals varieties havenot been produced which are mutually sterile; and why with plants only afew such cases have been observed, namely, by Gärtner, with certainvarieties of maize and verbascum, by other experimentalists with varietiesof the gourd and melon, and by Kölreuter with one kind of tobacco. With respect to varieties which have originated in a state of nature, it isalmost hopeless to expect to prove by direct evidence that they have beenrendered mutually sterile; for if even a trace of sterility could bedetected, such varieties would at once be raised by almost every naturalistto the rank of distinct species. If, for instance, Gärtner's statement werefully confirmed, that the blue and red-flowered forms of the pimpernel(_Anagallis arvensis_) are sterile when crossed, I presume that all thebotanists who now maintain on various grounds that these two forms aremerely fleeting varieties, would at once admit that they were specificallydistinct. The real difficulty in our present subject is not, as it appears to me, whydomestic varieties have not become mutually infertile when crossed, but whythis has so generally occurred with natural varieties as soon as they havebeen modified in a sufficient and permanent degree to take rank as species. We are far from precisely knowing the cause; nor is this surprising, seeinghow profoundly ignorant we are in regard to the normal and abnormal actionof the reproductive system. But we can see that species, owing to theirstruggle for life with numerous competitors, must have been exposed to moreuniform conditions during long periods of time, than have been domesticvarieties; and this may well make a wide difference in the result. For weknow how commonly wild animals and plants, when taken from their naturalconditions and subjected to captivity, are rendered sterile; and thereproductive functions of organic beings which have always lived and beenslowly modified under natural conditions would probably in like manner beeminently sensitive to the influence of an unnatural cross. Domesticatedproductions, on the other hand, which, as shown by the mere fact of theirdomestication, were not originally highly sensitive to changes in theirconditions of life, and which can now generally resist {191} withundiminished fertility repeated changes of conditions, might be expected toproduce varieties, which would be little liable to have their reproductivepowers injuriously affected by the act of crossing with other varietieswhich had originated in a like manner. Certain naturalists have recently laid too great stress, as it appears tome, on the difference in fertility between varieties and species whencrossed. Some allied species of trees cannot be grafted on each other, --allvarieties can be so grafted. Some allied animals are affected in a verydifferent manner by the same poison, but with varieties no such case untilrecently was known, but now it has been proved that immunity from certainpoisons stands in some cases in correlation with the colour of the hair. The period of gestation generally differs much with distinct species, butwith varieties until lately no such difference had been observed. The timerequired for the germination of seeds differs in an analogous manner, and Iam not aware that any difference in this respect has as yet been detectedwith varieties. Here we have various physiological differences, and nodoubt others could be added, between one species and another of the samegenus, which do not occur, or occur with extreme rarity, in the case ofvarieties; and these differences are apparently wholly or in chief partincidental on other constitutional differences, just in the same manner asthe sterility of crossed species is incidental on differences confined tothe sexual system. Why, then, should these latter differences, howeverserviceable they may indirectly be in keeping the inhabitants of the samecountry distinct, be thought of such paramount importance, in comparisonwith other incidental and functional differences? No sufficient answer tothis question can be given. Hence the fact that the most distinct domesticvarieties are, with rare exceptions, perfectly fertile when crossed, andproduce fertile offspring, whilst closely allied species are, with rareexceptions, more or less sterile, is not nearly so formidable an objectionas it appears at first to the theory of the common descent of alliedspecies. * * * * * {192} CHAPTER XX. SELECTION BY MAN. SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL SELECTION--RESULTS OF METHODICAL SELECTION--CARE TAKEN IN SELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS, AND BY SEMI-CIVILIZED PEOPLE--UNIMPORTANT CHARACTERS OFTEN ATTENDED TO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS SELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB-VARIETY--PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN. The power of Selection, whether exercised by man, or brought into playunder nature through the struggle for existence and the consequent survivalof the fittest, absolutely depends on the variability of organic beings. Without variability nothing can be effected; slight individual differences, however, suffice for the work, and are probably the sole differences whichare effective in the production of new species. Hence our discussion on thecauses and laws of variability ought in strict order to have preceded ourpresent subject, as well as the previous subjects of inheritance, crossing, &c. ; but practically the present arrangement has been found the mostconvenient. Man does not attempt to cause variability; though heunintentionally effects this by exposing organisms to new conditions oflife, and by crossing breeds already formed. But variability being granted, he works wonders. Unless some degree of selection be exercised, the freecommingling of the individuals of the same variety soon obliterates, as wehave previously seen, the slight differences which may arise, and gives tothe whole body of individuals uniformity of character. In separateddistricts, long-continued exposure to different conditions of life mayperhaps produce new races without the aid of selection; but to thisdifficult subject {193} of the direct action of the conditions of life weshall in a future chapter recur. When animals or plants are born with some conspicuous and firmly inheritednew character, selection is reduced to the preservation of suchindividuals, and to the subsequent prevention of crosses; so that nothingmore need be said on the subject. But in the great majority of cases a newcharacter, or some superiority in an old character, is at first faintlypronounced, and is not strongly inherited; and then the full difficulty ofselection is experienced. Indomitable patience, the finest powers ofdiscrimination, and sound judgment must be exercised during many years. Aclearly predetermined object must be kept steadily in view. Few men areendowed with all these qualities, especially with that of discriminatingvery slight differences; judgment can be acquired only by long experience;but if any of these qualities be wanting, the labour of a life may bethrown away. I have been astonished when celebrated breeders, whose skilland judgment have been proved by their success at exhibitions, have shownme their animals, which appeared all alike, and have assigned their reasonsfor matching this and that individual. The importance of the greatprinciple of Selection mainly lies in this power of selecting scarcelyappreciable differences, which nevertheless are found to be transmissible, and which can be accumulated until the result is made manifest to the eyesof every beholder. The principle of selection may be conveniently divided into three kinds. _Methodical selection_ is that which guides a man who systematicallyendeavours to modify a breed according to some predetermined standard. _Unconscious selection_ is that which follows from men naturally preservingthe most valued and destroying the less valued individuals, without anythought of altering the breed; and undoubtedly this process slowly worksgreat changes. Unconscious selection graduates into methodical, and onlyextreme cases can be distinctly separated; for he who preserves a useful orperfect animal will generally breed from it with the hope of gettingoffspring of the same character; but as long as he has not a predeterminedpurpose to improve the breed, he may be said to be selecting {194}unconsciously. [442] Lastly, we have _Natural selection_, which implies thatthe individuals which are best fitted for the complex, and in the course ofages changing conditions to which they are exposed, generally survive andprocreate their kind. With domestic productions, with which alone we arehere strictly concerned, natural selection comes to a certain extent intoaction, independently of, and even in opposition to, the will of man. * * * * * _Methodical Selection. _--What man has effected within recent times inEngland by methodical selection is clearly shown by our exhibitions ofimproved quadrupeds and fancy birds. With respect to cattle, sheep, andpigs, we owe their great improvement to a long series of well-knownnames--Bakewell, Colling, Ellman, Bates, Jonas Webb, Lords Leicester andWestern, Fisher Hobbs, and others. Agricultural writers are unanimous onthe power of selection: any number of statements to this effect could bequoted; a few will suffice. Youatt, a sagacious and experienced observer, writes, [443] the principle of selection is "that which enables theagriculturist, not only to modify the character of his flock, but to changeit altogether. " A great breeder of shorthorns[444] says, "In the anatomy ofthe shoulder modern breeders have made great improvements on the Kettonshorthorns by correcting the defect in the knuckle or shoulder-joint, andby laying the top of the shoulder more snugly into the crop, and therebyfilling up the hollow behind it.... The eye has its fashion at differentperiods: at one time the eye high and outstanding from the head, and atanother time the sleepy eye sunk into the head; but these extremes havemerged into the medium of a full, clear, and prominent eye with a placidlook. " Again, hear what an excellent judge of pigs[445] says: "The legs {195}should be no longer than just to prevent the animal's belly from trailingon the ground. The leg is the least profitable portion of the hog, and wetherefore require no more of it than is absolutely necessary for thesupport of the rest. " Let any one compare the wild-boar with any improvedbreed, and he will see how effectually the legs have been shortened. Few persons, except breeders, are aware of the systematic care taken inselecting animals, and of the necessity of having a clear and almostprophetic vision into futurity. Lord Spencer's skill and judgment were wellknown; and he writes, [446] "It is therefore very desirable, before any mancommences to breed either cattle or sheep, that he should make up his mindto the shape and qualities he wishes to obtain, and steadily pursue thisobject. " Lord Somerville, in speaking of the marvellous improvement of theNew Leicester sheep, effected by Bakewell and his successors, says, "Itwould seem as if they had first drawn a perfect form, and then given itlife. " Youatt[447] urges the necessity of annually drafting each flock, asmany animals will certainly degenerate "from the standard of excellence, which the breeder has established in his own mind. " Even with a bird ofsuch little importance as the canary, long ago (1780-1790) rules wereestablished, and a standard of perfection was fixed, according to which theLondon fanciers tried to breed the several sub-varieties. [448] A greatwinner of prizes at the Pigeon-shows, [449] in describing the Short-facedAlmond Tumbler, says, "There are many first-rate fanciers who areparticularly partial to what is called the goldfinch-beak, which is verybeautiful; others say, take a full-size round cherry, then take abarley-corn, and judiciously placing and thrusting it into the cherry, formas it were your beak; and that is not all, for it will form a good head andbeak, provided, as I said before, it is judiciously done; others take anoat; but as I think the goldfinch-beak the handsomest, I would advise theinexperienced fancier to get the head of a goldfinch, and keep it by himfor his observation. " Wonderfully different as is the beak of therock-pigeon and goldfinch, undoubtedly, as far as {196} external shape andproportions are concerned, the end has been nearly gained. Not only should our animals be examined with the greatest care whilstalive, but, as Anderson remarks, [450] their carcases should be scrutinised, "so as to breed from the descendants of such only as, in the language ofthe butcher, cut up well. " The "grain of the meat" in cattle, and its beingwell marbled with fat, [451] and the greater or less accumulation of fat inthe abdomen of our sheep, have been attended to with success. So withpoultry, a writer, [452] speaking of Cochin-China fowls, which are said todiffer much in the quality of their flesh, says, "the best mode is topurchase two young brother-cocks, kill, dress, and serve up one; if he beindifferent, similarly dispose of the other, and try again; if, however, hebe fine and well-flavoured, his brother will not be amiss for breedingpurposes for the table. " The great principle of the division of labour has been brought to bear onselection. In certain districts[453] "the breeding of bulls is confined toa very limited number of persons, who by devoting their whole attention tothis department, are able from year to year to furnish a class of bullswhich are steadily improving the general breed of the district. " Therearing and letting of choice rams has long been, as is well known, a chiefsource of profit to several eminent breeders. In parts of Germany thisprinciple is carried with merino sheep to an extreme point. [454] "Soimportant is the proper selection of breeding animals considered, that thebest flock-masters do not trust to their own judgment, or to that of theirshepherds, but employ persons called 'sheep-classifiers, ' who make it theirspecial business to attend to this part of the management of severalflocks, and thus to preserve, or if possible to improve, the best qualitiesof both parents in the lambs. " In Saxony, "when the lambs are weaned, eachin his turn is placed upon a table that his wool and form may be minutelyobserved. {197} The finest are selected for breeding and receive a firstmark. When they are one year old, and prior to shearing them, another closeexamination of those previously marked takes place: those in which nodefect can be found receive a second mark, and the rest are condemned. Afew months afterwards a third and last scrutiny is made; the prime rams andewes receive a third and final mark, but the slightest blemish issufficient to cause the rejection of the animal. " These sheep are bred andvalued almost exclusively for the fineness of their wool; and the resultcorresponds with the labour bestowed on their selection. Instruments havebeen invented to measure accurately the thickness of the fibres; and "anAustrian fleece has been produced of which twelve hairs equalled inthickness one from a Leicester sheep. " Throughout the world, wherever silk is produced, the greatest care isbestowed on selecting the cocoons from which the moths for breeding are tobe reared. A careful cultivator[455] likewise examines the mothsthemselves, and destroys those that are not perfect. But what moreimmediately concerns us is that certain families in France devotethemselves to raising eggs for sale. [456] In China, near Shanghai, theinhabitants of two small districts have the privilege of raising eggs forthe whole surrounding country, and that they may give up their whole timeto this business, they are interdicted by law from producing silk. [457] The care which successful breeders take in matching their birds issurprising. Sir John Sebright, whose fame is perpetuated by the "SebrightBantam, " used to spend "two and three days in examining, consulting, anddisputing with a friend which were the best of five or six birds. "[458] Mr. Bult, whose pouter-pigeons won so many prizes and were exported to NorthAmerica under the charge of a man sent on purpose, told me that he alwaysdeliberated for several days before he matched each pair. Hence we canunderstand the advice of an eminent fancier, who writes, [459] "I would hereparticularly guard {198} you against having too great a variety of pigeons, otherwise you will know a little of all, but nothing about one as it oughtto be known. " Apparently it transcends the power of the human intellect tobreed all kinds: "it is possible that there may be a few fanciers that havea good general knowledge of fancy pigeons; but there are many more wholabour under the delusion of supposing they know what they do not. " Theexcellence of one sub-variety, the Almond Tumbler, lies in the plumage, carriage, head, beak, and eye; but it is too presumptuous in the beginnerto try for all these points. The great judge above quoted says, "there aresome young fanciers who are over-covetous, who go for all the above fiveproperties at once; they have their reward by getting nothing. " We thus seethat breeding even fancy pigeons is no simple art: we may smile at thesolemnity of these precepts, but he who laughs will win no prizes. What methodical selection has effected for our animals is sufficientlyproved, as already remarked, by our Exhibitions. So greatly were the sheepbelonging to some of the earlier breeders, such as Bakewell and LordWestern, changed, that many persons could not be persuaded that they hadnot been crossed. Our pigs, as Mr. Corringham remarks, [460] during the lasttwenty years have undergone, through rigorous selection together withcrossing, a complete metamorphosis. The first exhibition for poultry washeld in the Zoological Gardens in 1845; and the improvement effected sincethat time has been great. As Mr. Baily, the great judge, remarked to me, itwas formerly ordered that the comb of the Spanish cock should be upright, and in four or five years all good birds had upright combs; it was orderedthat the Polish cock should have no comb or wattles, and now a bird thusfurnished would be at once disqualified; beards were ordered, and out offifty-seven pens lately (1860) exhibited at the Crystal Palace, all hadbeards. So it has been in many other cases. But in all cases the judgesorder only what is occasionally produced and what can be improved andrendered constant by selection. The steady increase of weight during thelast few years in our {199} fowls, turkeys, ducks, and geese is notorious;"six-pound ducks are now common, whereas four pounds was formerly theaverage. " As the actual time required to make a change has not often beenrecorded, it may be worth mentioning that it took Mr. Wicking thirteenyears to put a clean white head on an almond tumbler's body, "a triumph, "says another fancier, "of which he may be justly proud. "[461] Mr. Tollet, of Betley Hall, selected cows, and especially bulls, descendedfrom good milkers, for the sole purpose of improving his cattle for theproduction of cheese; he steadily tested the milk with the lactometer, andin eight years he increased, as I was informed by him, the product in theproportion of four to three. Here is a curious case[462] of steady but slowprogress, with the end not as yet fully attained: in 1784 a race ofsilkworms was introduced into France, in which one hundred out of thethousand failed to produce white cocoons; but now, after careful selectionduring sixty-five generations, the proportion of yellow cocoons has beenreduced to thirty-five in the thousand. With plants selection has been followed with the same good results as withanimals. But the process is simpler, for plants in the great majority ofcases bear both sexes. Nevertheless, with most kinds it is necessary totake as much care to prevent crosses as with animals or unisexual plants;but with some plants, such as peas, this care does not seem to benecessary. With all improved plants, excepting of course those which arepropagated by buds, cuttings, &c. , it is almost indispensable to examinethe seedlings and destroy those which depart from the proper type. This iscalled "roguing, " and is, in fact, a form of selection, like the rejectionof inferior animals. Experienced horticulturists and agriculturistsincessantly urge every one to preserve the finest plants for the productionof seed. Although plants often present much more conspicuous variations thananimals, yet the closest attention is generally requisite to detect eachslight and favourable change. Mr. Masters relates[463] how "many a patienthour was devoted, " whilst he was {200} young, to the detection ofdifferences in peas intended for seed. Mr. Barnet[464] remarks that the oldscarlet American strawberry was cultivated for more than a century withoutproducing a single variety; and another writer observes how singular it wasthat when gardeners first began to attend to this fruit it began to vary;the truth no doubt being that it had always varied, but that, until slightvarieties were selected and propagated by seed, no conspicuous result wasobtained. The finest shades of difference in wheat have been discriminatedand selected with almost as much care, as we see in Colonel Le Couteur'sworks, as in the case of the higher animals; but with our cereals theprocess of selection has seldom or never been long continued. It may be worth while to give a few examples of methodical selection withplants; but in fact the great improvement of all our anciently cultivatedplants may be attributed to selection long carried on, in partmethodically, and in part unconsciously. I have shown in a former chapterhow the weight of the gooseberry has been increased by systematic selectionand culture. The flowers of the Heartsease have been similarly increased insize and regularity of outline. With the Cineraria, Mr. Glenny[465] "wasbold enough, when the flowers were ragged and starry and ill defined incolour, to fix a standard which was then considered outrageously high andimpossible, and which, even if reached, it was said, we should be nogainers by, as it would spoil the beauty of the flowers. He maintained thathe was right; and the event has proved it to be so. " The doubling offlowers has several times been effected by careful selection: the Rev. W. Williamson, [466] after sowing during several years seed of _Anemonecoronaria_, found a plant with one additional petal; he sowed the seed ofthis, and by perseverance in the same course obtained several varietieswith six or seven rows of petals. The single Scotch rose was doubled, andyielded eight good varieties in nine or ten years. [467] The Canterbury bell(_Campanula medium_) was doubled by careful selection in fourgenerations. [468] In four years Mr. Buckman, [469] by culture and {201}careful selection, converted parsnips, raised from wild seed, into a newand good variety. By selection during a long course of years, the earlymaturity of peas has been hastened from ten to twenty-one days. [470] A morecurious case is offered by the beet-plant, which, since its cultivation inFrance, has almost exactly doubled its yield of sugar. This has beeneffected by the most careful selection; the specific gravity of the rootsbeing regularly tested, and the best roots saved for the production ofseed. [471] _Selection by Ancient and Semi-civilised People. _ In attributing so much importance to the selection of animals and plants, it may be objected that methodical selection would not have been carried onduring ancient times. A distinguished naturalist considers it as absurd tosuppose that semi-civilised people should have practised selection of anykind. Undoubtedly the principle has been systematically acknowledged andfollowed to a far greater extent within the last hundred years than at anyformer period, and a corresponding result has been gained; but it would bea great error to suppose, as we shall immediately see, that its importancewas not recognised and acted on during the most ancient times, and bysemi-civilised people. I should premise that many facts now to be givenonly show that care was taken in breeding; but when this is the case, selection is almost sure to be practised to a certain extent. We shallhereafter be enabled better to judge how far selection, when onlyoccasionally carried on, by a few of the inhabitants of a country, willslowly produce a great effect. In a well-known passage in the thirtieth chapter of Genesis, rules aregiven for influencing, as was then thought possible, the colour of sheep;and speckled and dark breeds are spoken of as being kept separate. By thetime of David the fleece was likened to snow. Youatt, [472] who hasdiscussed all the passages in relation to breeding in the Old Testament, concludes that {202} at this early period "some of the best principles ofbreeding must have been steadily and long pursued. " It was ordered, according to Moses, that "Thou shalt not let thy cattle gender with adiverse kind;" but mules were purchased, [473] so that at this early periodother nations must have crossed the horse and ass. It is said[474] thatErichthonius, some generations before the Trojan war, had many brood-mares, "which by his care and judgment in the choice of stallions produced a breedof horses superior to any in the surrounding countries. " Homer (Book v. )speaks of Æneas's horses as bred from mares which were put to the steeds ofLaomedon. Plato, in his 'Republic, ' says to Glaucus, "I see that you raiseat your house a great many dogs for the chase. Do you take care aboutbreeding and pairing them? Among animals of good blood, are there notalways some which are superior to the rest?" To which Glaucus answers inthe affirmative. [475] Alexander the Great selected the finest Indian cattleto send to Macedonia to improve the breed. [476] According to Pliny, [477]King Pyrrhus had an especially valuable breed of oxen; and he did notsuffer the bulls and cows to come together till four years old, that thebreed might not degenerate. Virgil, in his Georgics (lib. Iii. ), gives asstrong advice as any modern agriculturist could do, carefully to select thebreeding stock; "to note the tribe, the lineage, and the sire; whom toreserve for husband of the herd;"--to brand the progeny;--to select sheepof the purest white, and to examine if their tongues are swarthy. We haveseen that the Romans kept pedigrees of their pigeons, and this would havebeen a senseless proceeding had not great care been taken in breeding them. Columella gives detailed instructions about breeding fowls: "Let thebreeding hens therefore be of a choice colour, a robust body, square-built, full-breasted, with large heads, with upright and bright-red combs. Thoseare believed to be the best bred which have five toes. "[478] According toTacitus, the Celts attended to the races of their domestic animals; {203}and Cæsar states that they paid high prices to merchants for fine importedhorses. [479] In regard to plants, Virgil speaks of yearly culling thelargest seeds; and Celsus says, "where the corn and crop is but small, wemust pick out the best ears of corn, and of them lay up our seed separatelyby itself. "[480] Coming down the stream of time, we may be brief. At about the beginning ofthe ninth century Charlemagne expressly ordered his officers to take greatcare of his stallions; and if any proved bad or old, to forewarn him ingood time before they were put to the mares. [481] Even in a country solittle civilised as Ireland during the ninth century, it would appear fromsome ancient verses, [482] describing a ransom demanded by Cormac, thatanimals from particular places, or having a particular character, werevalued. Thus it is said, -- Two pigs of the pigs of Mac Lir, A ram and ewe both round and red, I brought with me from Aengus. I brought with me a stallion and a mare From the beautiful stud of Manannan, A bull and a white cow from Druim Cain. Athelstan, in 930, received as a present from Germany, running-horses; andhe prohibited the exportation of English horses. King John imported "onehundred chosen stallions from Flanders. "[483] On June 16th, 1305, thePrince of Wales wrote to the Archbishop of Canterbury, begging for the loanof any choice stallion, and promising its return at the end of theseason. [484] There are numerous records at ancient periods in Englishhistory of the importation of choice animals of various kinds, and offoolish laws against their exportation. In the reigns of Henry VII. AndVIII. It was ordered that the magistrates, at Michaelmas, should scour theheaths and commons, and destroy all mares beneath a certain size. [485] Someof our earlier kings passed laws against the slaughtering rams of any goodbreed before they were seven years old, so that they {204} might have timeto breed. In Spain Cardinal Ximenes issued, in 1509, regulations on the_selection_ of good rams for breeding. [486] The Emperor Akbar Khan before the year 1600 is said to have "wonderfullyimproved" his pigeons by crossing the breeds; and this necessarily impliescareful selection. About the same period the Dutch attended with thegreatest care to the breeding of these birds. Belon in 1555 says that goodmanagers in France examined the colour of their goslings in order to getgeese of a white colour and better kinds. Markham in 1631 tells the breeder"to elect the largest and goodliest conies, " and enters into minutedetails. Even with respect to seeds of plants for the flower-garden, Sir J. Hanmer writing about the year 1660[487] says, in "choosing seed, the bestseed is the most weighty, and is had from the lustiest and most vigorousstems;" and he then gives rules about leaving only a few flowers on plantsfor seed; so that even such details were attended to in our flower-gardenstwo hundred years ago. In order to show that selection has been silentlycarried on in places where it would not have been expected, I may add thatin the middle of the last century, in a remote part of North America, Mr. Cooper improved by careful selection all his vegetables, "so that they weregreatly superior to those of any other person. When his radishes, forinstance, are fit for use, he takes ten or twelve that he most approves, and plants them at least 100 yards from others that blossom at the sametime. In the same manner he treats all his other plants, varying thecircumstances according to their nature. "[488] In the great work on China published in the last century by the Jesuits, and which is chiefly compiled from ancient Chinese encyclopædias, it issaid that with sheep "improving the breed consists in choosing withparticular care the lambs which are destined for propagation, in nourishingthem well, and in keeping the flocks separate. " The same principles wereapplied by the Chinese to various plants and fruit-trees. [489] An {205}imperial edict recommends the choice of seed of remarkable size; andselection was practised even by imperial hands, for it is said that theYa-mi, or imperial rice, was noticed at an ancient period in a field by theEmperor Khang-hi, was saved and cultivated in his garden, and has sincebecome valuable from being the only kind which will grow north of the GreatWall. [490] Even with flowers, the tree pæony (_P. Moutan_) has beencultivated, according to Chinese traditions, for 1400 years; between 200and 300 varieties have been raised, which are cherished like tulipsformerly were by the Dutch. [491] Turning now to semi-civilised people and to savages: it occurred to me, from what I had seen of several parts of South America, where fences do notexist, and where the animals are of little value, that there would beabsolutely no care in breeding or selecting them; and this to a largeextent is true. Roulin, [492] however, describes in Colombia a naked race ofcattle, which are not allowed to increase, on account of their delicateconstitution. According to Azara[493] horses are often born in Paraguaywith curly hair; but, as the natives do not like them, they are destroyed. On the other hand, Azara states that a hornless bull, born in 1770, waspreserved and propagated its race. I was informed of the existence in BandaOriental of a breed with reversed hair; and the extraordinary niata cattlefirst appeared and have since been kept distinct in La Plata. Hence certainconspicuous variations have been preserved, and others have been habituallydestroyed, in these countries, which are so little favourable for carefulselection. We have also seen that the inhabitants sometimes introducecattle on their estates to prevent the evil effects of close interbreeding. On the other hand, I have heard on reliable authority that the Gauchos ofthe Pampas never take any pains in selecting the best bulls or stallionsfor breeding; and this probably accounts for the cattle and horses beingremarkably uniform in character throughout the immense range of theArgentine republic. Looking to the Old World, in the Sahara Desert "The Touareg is as carefulin the selection of his breeding Mahari {206} (a fine race of thedromedary) as the Arab is in that of his horse. The pedigrees are handeddown, and many a dromedary can boast a genealogy far longer than thedescendants of the Darley Arabian. "[494] According to Pallas the Mongoliansendeavour to breed the Yaks or horse-tailed buffaloes with white tails, forthese are sold to the Chinese mandarins as fly-flappers; and Moorcroft, about seventy years after Pallas, found that white-tailed animals werestill selected for breeding. [495] We have seen in the chapter on the Dog that savages in different parts ofNorth America and in Guiana cross their dogs with wild Canidæ, as did theancient Gauls, according to Pliny. This was done to give their dogsstrength and vigour, in the same way as the keepers in large warrens nowsometimes cross their ferrets (as I have been informed by Mr. Yarrell) withthe wild polecat, "to give them more devil. " According to Varro, the wildass was formerly caught and crossed with the tame animal to improve thebreed, in the same manner as at the present day the natives of Javasometimes drive their cattle into the forests to cross with the wildBanteng (_Bos sondaicus_). [496] In Northern Siberia, among the Ostyaks thedogs vary in markings in different districts, but in each place they arespotted black and white in a remarkably uniform manner;[497] and from thisfact alone we may infer careful breeding, more especially as the dogs ofone locality are famed throughout the country for their superiority. I haveheard of certain tribes of Esquimaux who take pride in their teams of dogsbeing uniformly coloured. In Guiana, as Sir R. Schomburgk informs me, [498]the dogs of the Turuma Indians are highly valued and extensively bartered:the price of a good one is the same as that given for a wife: they are keptin a sort of cage, and the Indians "take great care when the female is inseason to prevent her uniting with a dog of an inferior description. " TheIndians told Sir Robert that, if a dog proved bad or useless, {207} he wasnot killed, but was left to die from sheer neglect. Hardly any nation ismore barbarous than the Fuegians, but I hear from Mr. Bridges, theCatechist to the Mission, that, "when these savages have a large, strong, and active bitch, they take care to put her to a fine dog, and even takecare to feed her well, that her young may be strong and well favoured. " In the interior of Africa, negroes, who have not associated with white men, show great anxiety to improve their animals: they "always choose the largerand stronger males for stock:" the Malakolo were much pleased atLivingstone's promise to send them a bull, and some Bakalolo carried a livecock all the way from Loanda into the interior. [499] Further south on thesame continent, Andersson states that he has known a Damara give two fineoxen for a dog which struck his fancy. The Damaras take great delight inhaving whole droves of cattle of the same colour, and they prize their oxenin proportion to the size of their horns. "The Namaquas have a perfectmania for a uniform team; and almost all the people of Southern Africavalue their cattle next to their women, and take a pride in possessinganimals that look high-bred. " "They rarely or never make use of a handsomeanimal as a beast of burden. "[500] The power of discrimination which thesesavages possess is wonderful, and they can recognise to which tribe anycattle belong. Mr. Andersson further informs me that the natives frequentlymatch a particular bull with a particular cow. The most curious case of selection by semi-civilised people, or indeed byany people, which I have found recorded, is that given by Garcilazo de laVega, a descendant of the Incas, as having been practised in Peru beforethe country was subjugated by the Spaniards. [501] The Incas annually heldgreat hunts, when all the wild animals were driven from an immense circuitto a central point. The beasts of prey were first destroyed as injurious. The wild Guanacos and Vicunas were sheared; the old males and femaleskilled, and the others set at liberty. The various kinds of deer wereexamined; the old males and females {208} were likewise killed; "but theyoung females, with a certain number of males, selected from the mostbeautiful and strong, " were given their freedom. Here, then, we haveselection by man aiding natural selection. So that the Incas followedexactly the reverse system of that which our Scottish sportsmen are accusedof following, namely, of steadily killing the finest stags, thus causingthe whole race to degenerate. [502] In regard to the domesticated llamas andalpacas, they were separated in the time of the Incas according to colour;and if by chance one in a flock was born of the wrong colour, it waseventually put into another flock. In the genus Auchenia there are four forms, --the Guanaco and Vicuna, foundwild and undoubtedly distinct species; the Llama and Alpaca, known only ina domesticated condition. These four animals appear so different, that mostprofessed naturalists, especially those who have studied these animals intheir native country, maintain that they are specifically distinct, notwithstanding that no one pretends to have seen a wild llama or alpaca. Mr. Ledger, however, who has closely studied these animals both in Peru andduring their exportation to Australia, and who has made many experiments ontheir propagation, adduces arguments[503] which seem to me conclusive, thatthe llama is the domesticated descendant of the guanaco, and the alpaca ofthe vicuna. And now that we know that these animals many centuries ago weresystematically bred and selected, there is nothing surprising in the greatamount of change which they have undergone. It appeared to me at one time probable that, though ancient andsemi-civilised people might have attended to the improvement of their moreuseful animals in essential points, yet that they would have disregardedunimportant characters. But human nature is the same throughout the world:fashion everywhere reigns supreme, and man is apt to value whatever he maychance to possess. We have seen that in South America the niata cattle, which certainly are not made useful by their shortened faces and upturnednostrils, have been preserved. The Damaras of South Africa value theircattle for uniformity {209} of colour and enormously long horns. TheMongolians value their yaks for their white tails. And I shall now showthat there is hardly any peculiarity in our most useful animals which, fromfashion, superstition, or some other motive, has not been valued, andconsequently preserved. With respect to cattle, "an early record, "according to Youatt, [504] "speaks of a hundred white cows with red earsbeing demanded as a compensation by the princes of North and South Wales. If the cattle were of a dark or black colour, 150 were to be presented. " Sothat colour was attended to in Wales before its subjugation by England. InCentral Africa, an ox that beats the ground with its tail is killed; and inSouth Africa some of the Damaras will not eat the flesh of a spotted ox. The Kaffirs value an animal with a musical voice; and "at a sale in BritishKaffraria the low of a heifer excited so much admiration that a sharpcompetition sprung up for her possession, and she realised a considerableprice. "[505] With respect to sheep, the Chinese prefer rams without horns;the Tartars prefer them with spirally wound horns, because the hornless arethought to lose courage. [506] Some of the Damaras will not eat the flesh ofhornless sheep. In regard to horses, at the end of the fifteenth centuryanimals of the colour described as _liart pommé_ were most valued inFrance. The Arabs have a proverb, "Never buy a horse with four white feet, for he carries his shroud with him;"[507] the Arabs also, as we have seen, despise dun-coloured horses. So with dogs, Xenophon and others at anancient period were prejudiced in favour of certain colours; and "white orslate-coloured hunting dogs were not esteemed. "[508] Turning to poultry, the old Roman gourmands thought that the liver of awhite goose was the most savoury. In Paraguay black-skinned fowls are keptbecause they are thought to be more productive, and their flesh the mostproper for invalids. [509] In Guiana, as I am informed by Sir R. Schomburgk, the aborigines will not eat the flesh or eggs of the fowl, but two {210}races are kept distinct merely for ornament. In the Philippines, no lessthan nine sub-varieties of the game cock are kept and named, so that theymust be separately bred. At the present time in Europe, the smallest peculiarities are carefullyattended to in our most useful animals, either from fashion, or as a markof purity of blood. Many examples could be given, two will suffice. "In theWestern counties of England the prejudice against a white pig is nearly asstrong as against a black one in Yorkshire. " In one of the Berkshiresub-breeds, it is said, "the white should be confined to four white feet, awhite spot between the eyes, and a few white hairs behind each shoulder. "Mr. Saddler possessed "three hundred pigs, every one of which was marked inthis manner. "[510] Marshall, towards the close of the last century, inspeaking of a change in one of the Yorkshire breeds of cattle, says thehorns have been considerably modified, as "a clean, small, sharp horn hasbeen _fashionable_ for the last twenty years. "[511] In a part of Germanythe cattle of the Race de Gfoehl are valued for many good qualities, butthey must have horns of a particular curvature and tint, so much so thatmechanical means are applied if they take a wrong direction; but theinhabitants "consider it of the highest importance that the nostrils of thebull should be flesh-coloured, and the eyelashes light; this is anindispensable condition. A calf with blue nostrils would not be purchased, or purchased at a very low price. "[512] Therefore let no man say that anypoint or character is too trifling to be methodically attended to andselected by breeders. * * * * * _Unconscious Selection. _--By this term I mean, as already more than onceexplained, the preservation by man of the most valued, and the destructionof the least valued individuals, without any conscious intention on hispart of altering the breed. It is difficult to offer direct proofs of theresults which follow from this kind of selection; but the indirect evidenceis abundant. In fact, except that in the one case man acts intentionally, and in the other unintentionally, there is little difference between {211}methodical and unconscious selection. In both cases man preserves theanimals which are most useful or pleasing to him, and destroys or neglectsthe others. But no doubt a far more rapid result follows from methodicalthan from unconscious selection. The "roguing" of plants by gardeners, andthe destruction by law in Henry VIII. 's reign of all under-sized mares, areinstances of a process the reverse of selection in the ordinary sense ofthe word, but leading to the same general result. The influence of thedestruction of individuals having a particular character is well shown bythe necessity of killing every lamb with a trace of black about it, inorder to keep the flock white; or again, by the effects on the averageheight of the men of France of the destructive wars of Napoleon, by whichmany tall men were killed, the short ones being left to be the fathers offamilies. This at least is the conclusion of those who have closely studiedthe subject of the conscription; and it is certain that since Napoleon'stime the standard for the army has been lowered two or three times. Unconscious selection so blends into methodical that it is scarcelypossible to separate them. When a fancier long ago first happened to noticea pigeon with an unusually short beak, or one with the tail-feathersunusually developed, although he bred from these birds with the distinctintention of propagating the variety, yet he could not have intended tomake a short-faced tumbler or a fantail, and was far from knowing that hehad made the first step towards this end. If he could have seen the finalresult, he would have been struck with astonishment, but, from what we knowof the habits of fanciers, probably not with admiration. Our Englishcarriers, barbs, and short-faced tumblers have been greatly modified in thesame manner, as we may infer both from the historical evidence given in thechapters on the Pigeon, and from the comparison of birds brought fromdistant countries. So it has been with dogs; our present fox-hounds differ from the oldEnglish hound; our greyhounds have become lighter; the wolf-dog, whichbelonged to the greyhound class, has become extinct; the Scotch deer-houndhas been modified, and is now rare. Our bulldogs differ from those whichwere formerly used for baiting bulls. Our pointers and Newfoundlands do not{212} closely resemble any native dog now found in the countries whencethey were brought, These changes have been effected partly by crosses; butin every case the result has been governed by the strictest selection. Nevertheless there is no reason to suppose that man intentionally andmethodically made the breeds exactly what they now are. As our horsesbecame fleeter, and the country more cultivated and smoother, fleeterfox-hounds were desired and produced, but probably without any onedistinctly foreseeing what they would become. Our pointers and setters, thelatter almost certainly descended from large spaniels, have been greatlymodified in accordance with fashion and the desire for increased speed. Wolves have become extinct, deer have become rarer, bulls are no longerbaited, and the corresponding breeds of the dog have answered to thechange. But we may feel almost sure that when, for instance, bulls were nolonger baited, no man said to himself, I will now breed my dogs of smallersize, and thus create the present race. As circumstances changed, menunconsciously and slowly modified their course of selection. With race-horses selection for swiftness has been followed methodically, and our horses can now easily beat their progenitors. The increased sizeand different appearance of the English race-horse led a good observer inIndia to ask, "Could any one in this year of 1856, looking at ourrace-horses, conceive that they were the result of the union of the Arabhorse and the African mare?"[513] This change has, it is probable, beenlargely effected through unconscious selection, that is, by the generalwish to breed as fine horses as possible in each generation, combined withtraining and high feeding, but without any intention to give to them theirpresent appearance. According to Youatt, [514] the introduction in OliverCromwell's time of three celebrated Eastern stallions speedily affected theEnglish breed; "so that Lord Harleigh, one of the old school, complainedthat the great horse was fast disappearing. " This is an excellent proof howcarefully selection must have been attended to; for without such care, alltraces of so small an infusion of Eastern blood would soon have beenabsorbed and {213} lost. Notwithstanding that the climate of England hasnever been esteemed particularly favourable to the horse, yetlong-continued selection, both methodical and unconscious, together withthat practised by the Arabs during a still longer and earlier period, hasended in giving us the best breed of horses in the world. Macaulay[515]remarks, "Two men whose authority on such subjects was held in greatesteem, the Duke of Newcastle and Sir John Fenwick, pronounced that themeanest hack ever imported from Tangier would produce a finer progeny thancould be expected from the best sire of our native breed. They would notreadily have believed that a time would come when the princes and nobles ofneighbouring lands would be as eager to obtain horses from England as everthe English had been to obtain horses from Barbary. " The London dray-horse, which differs so much in appearance from any naturalspecies, and which from its size has so astonished many Eastern princes, was probably formed by the heaviest and most powerful animals having beenselected during many generations in Flanders and England, but without theleast intention or expectation of creating a horse such as we now see. Ifwe go back to an early period of history, we behold in the antique Greekstatues, as Schaaffhausen has remarked, [516] a horse equally unlike a raceor dray horse, and differing from any existing breed. The results of unconscious selection, in an early stage, are well shown inthe difference between the flocks descended from the same stock, butseparately reared by careful breeders. Youatt gives an excellent instanceof this fact in the sheep belonging to Messrs. Buckley and Burgess, which"have been purely bred from the original stock of Mr. Bakewell for upwardsof fifty years. There is not a suspicion existing in the mind of any one atall acquainted with the subject that the owner of either flock has deviatedin any one instance from the pure blood of Mr. Bakewell's flock; yet thedifference between the sheep possessed by these two gentlemen is so great, that they have the appearance of being quite different varieties. "[517] Ihave seen several analogous and {214} well-marked cases with pigeons: forinstance, I had a family of barbs, descended from those long bred by Sir J. Sebright, and another family long bred by another fancier, and the twofamilies plainly differed from each other. Nathusius--and a more competentwitness could not be cited--observes that, though the Shorthorns areremarkably uniform inn appearance (except in colouring), yet that theindividual character and wishes of each breeder become impressed on hiscattle, so that different herds differ slightly from each other. [518] TheHereford cattle assumed their present well-marked character soon after theyear 1769, through careful selection by Mr. Tomkins, [519] and the breed haslately split into two strains--one strain having a white face, anddiffering slightly, it is said, [520] in some other points; but there is noreason to believe that this split, the origin of which is unknown, wasintentionally made; it may with much more probability be attributed todifferent breeders having attended to different points. So again, theBerkshire breed of swine in the year 1810 had greatly changed from what ithad been in 1780; and since 1810 at least two distinct sub-breeds haveborne this same name. [521] When we bear in mind how rapidly all animalsincrease, and that some must be annually slaughtered and some saved forbreeding, then, if the same breeder during a long course of yearsdeliberately settles which shall be saved and which shall be killed, it isalmost inevitable that his individual frame of mind will influence thecharacter of his stock, without his having had any intention to modify thebreed or form a new strain. Unconscious selection in the strictest sense of the word, that is, thesaving of the more useful animals and the neglect or slaughter of the lessuseful, without any thought of the future, must have gone on occasionallyfrom the remotest period and amongst the most barbarous nations. Savagesoften suffer from famines, and are sometimes expelled by war from their ownhomes. In such cases it can hardly be doubted that they would save theirmost useful animals. When the Fuegians {215} are hard pressed by want, theykill their old women for food rather than their dogs; for, as we wereassured, "old women no use--dogs catch otters. " The same sound sense wouldsurely lead them to preserve their more useful dogs when still harderpressed by famine. Mr. Oldfield, who has seen so much of the aborigines ofAustralia, informs me that "they are all very glad to get a Europeankangaroo dog, and several instances have been known of the father killinghis own infant that the mother might suckle the much-prized puppy. "Different kinds of dogs would be useful to the Australian for huntingopossums and kangaroos, and to the Fuegian for catching fish and otters;and the occasional preservation in the two countries of the most usefulanimals would ultimately lead to the formation of two widely distinctbreeds. * * * * * With plants, from the earliest dawn of civilisation, the best variety whichat each period was known would generally have been cultivated and its seedsoccasionally sown; so that there will have been some selection from anextremely remote period, but without any prefixed standard of excellence orthought of the future. We at the present day profit by a course ofselection occasionally and unconsciously carried on during thousands ofyears. This is proved in an interesting manner by Oswald Heer's researcheson the lake-inhabitants of Switzerland, as given in a former chapter; forhe shows that the grain and seed of our present varieties of wheat, barley, oats, peas, beans, lentils, and poppy, exceed in size those which werecultivated in Switzerland during the Neolithic and Bronze periods. Theseancient people, during the Neolithic period, possessed also a crabconsiderably larger than that now growing wild on the Jura. [522] The pearsdescribed by Pliny were evidently extremely inferior in quality to ourpresent pears. We can realise the effects of long-continued selection andcultivation in another way, for would any one in his senses expect to raisea first-rate apple from the seed of a truly wild crab, or a lusciousmelting pear from the wild pear? Alphonse De Candolle informs me that hehas lately seen on an ancient mosaic at Rome a representation of {216} themelon; and as the Romans, who were such gourmands, are silent on thisfruit, he infers that the melon has been greatly ameliorated since theclassical period. Coming to later times, Buffon, [523] on comparing the flowers, fruit, andvegetables which were then cultivated, with some excellent drawings made ahundred and fifty years previously, was struck with surprise at the greatimprovement which had been effected; and remarks that these ancient flowersand vegetables would now be rejected, not only by a florist but by avillage gardener. Since the time of Buffon the work of improvement hassteadily and rapidly gone on. Every florist who compares our presentflowers with those figured in books published not long since, is astonishedat the change. A well-known amateur, [524] in speaking of the varieties ofPelargonium raised by Mr. Garth only twenty-two years before, remarks, "what a rage they excited: surely we had attained perfection, it was said;and now not one of the flowers of those days will be looked at. But nonethe less is the debt of gratitude which we owe to those who saw what was tobe done, and did it. " Mr. Paul, the well-known horticulturist, in writingof the same flower, [525] says he remembers when young being delighted withthe portraits in Sweet's work; "but what are they in point of beautycompared with the Pelargoniums of this day? Here again nature did notadvance by leaps; the improvement was gradual, and, if we had neglectedthose very gradual advances, we must have foregone the present grandresults. " How well this practical horticulturist appreciates andillustrates the gradual and accumulative force of selection! The Dahlia hasadvanced in beauty in a like manner; the line of improvement being guidedby fashion, and by the successive modifications which the flower slowlyunderwent. [526] A steady and gradual change has been noticed in many otherflowers: thus an old florist, [527] after describing the leading varietiesof the Pink which were grown in 1813, adds, "the pinks of those days wouldnow be scarcely grown as border-flowers. " The improvement of {217} so manyflowers and the number of the varieties which have been raised is all themore striking when we hear that the earliest known flower-garden in Europe, namely at Padua, dates only from the year 1545. [528] * * * * * _Effects of Selection, as shown by the parts most valued by man presentingthe greatest amount of Difference. _--The power of long-continued selection, whether methodical or unconscious, or both combined, is well shown in ageneral way, namely, by the comparison of the differences between thevarieties of distinct species, which are valued for different parts, suchas for the leaves, or stems, or tubers, the seed, or fruit, or flowers. Whatever part man values most, that part will be found to present thegreatest amount of difference. With trees cultivated for their fruit, Sageret remarks that the fruit is larger than in the parent-species, whilstwith those cultivated for the seed, as with nuts, walnuts, almonds, chesnuts, &c. , it is the seed itself which is larger; and he accounts forthis fact by the fruit in the one case, and by the seed in the other, having been carefully attended to and selected during many ages. Gallesiohas made the same observation. Godron insists on the diversity of the tuberin the potato, of the bulb in the onion, and of the fruit in the melon; andon the close similarity in these same plants of the other parts. [529] In order to judge how far my own impression on this subject was correct, Icultivated numerous varieties of the same species close to each other. Thecomparison of the amount of difference between widely different organs isnecessarily vague; I will therefore give the results in only a few cases. We have previously seen in the ninth chapter how greatly the varieties ofthe cabbage differ in their foliage and stems, which are the selectedparts, and how closely they resembled each other in their flowers, capsules, and seeds. In seven varieties of the radish, the roots differedgreatly in colour and shape, but no difference {218} whatever could bedetected in their foliage, flowers, or seeds. Now what a contrast ispresented, if we compare the flowers of the varieties of these two plantswith those of any species cultivated in our flower-gardens for ornament; orif we compare their seeds with those of the varieties of maize, peas, beans, &c. , which are valued and cultivated for their seeds. In the ninthchapter it was shown that the varieties of the pea differ but little exceptin the tallness of the plant, moderately in the shape of the pod, andgreatly in the pea itself, and these are all selected points. Thevarieties, however, of the _Pois sans parchemin_ differ much more in theirpods, and these are eaten and valued. I cultivated twelve varieties of thecommon bean; one alone, the Dwarf Fan, differed considerably in generalappearance; two differed in the colour of their flowers, one being analbino, and the other being wholly instead of partially purple; severaldiffered considerably in the shape and size of the pod, but far more in thebean itself, and this is the valued and selected part. Toker's bean, forinstance, is twice-and-a-half as long and broad as the horse-bean, and ismuch thinner and of a different shape. The varieties of the gooseberry, as formerly described, differ much intheir fruit, but hardly perceptibly in their flowers or organs ofvegetation. With the plum, the differences likewise appear to be greater inthe fruit than in the flowers or leaves. On the other hand, the seed of thestrawberry, which corresponds with the fruit of the plum, differs hardly atall; whilst every one knows how greatly the fruit--that is, the enlargedreceptacle--differs in the several varieties. In apples, pears, and peachesthe flowers and leaves differ considerably, but not, as far as I can judge, in proportion with the fruit. The Chinese double-flowering peaches, on theother hand, show that varieties of this tree have been formed, which differmore in the flower than in fruit. If, as is highly probable, the peach isthe modified descendant of the almond, a surprising amount of change hasbeen effected in the same species, in the fleshy covering of the former andin the kernels of the latter. When parts stand in such close relation to each other as the fleshycovering of the fruit (whatever its homological nature may be) and theseed, when one part is modified, so generally is the other, but by no meansnecessarily in the same degree. With {219} the plum-tree, for instance, some varieties produce plums which are nearly alike, but include stonesextremely dissimilar in shape; whilst conversely other varieties producedissimilar fruit with barely distinguishable stones; and generally thestones, though they have never been subjected to selection, differ greatlyin the several varieties of the plum. In other cases organs which are notmanifestly related, through some unknown bond vary together, and areconsequently liable, without any intention on man's part, to besimultaneously acted on by selection. Thus the varieties of the stock(Matthiola) have been selected solely for the beauty of their flowers, butthe seeds differ greatly in colour and somewhat in size. Varieties of thelettuce have been selected solely on account of their leaves, yet produceseeds which likewise differ in colour. Generally, through the law ofcorrelation, when a variety differs greatly from its fellow-varieties inany one character, it differs to a certain extent in several othercharacters. I observed this fact when I cultivated together many varietiesof the same species, for I used first to make a list of the varieties whichdiffered most from each other in their foliage and manner of growth, afterwards of those that differed most in their flowers, then in theirseed-capsules, and lastly in their mature seed; and I found that the samenames generally occurred in two, three, or four of the successive lists. Nevertheless the greatest amount of difference between the varieties wasalways exhibited, as far as I could judge, by that part or organ for whichthe plant was cultivated. When we bear in mind that each plant was at first cultivated because usefulto man, and that its variation was a subsequent, often a long subsequent, event, we cannot explain the greater amount of diversity in the valuableparts by supposing that species endowed with an especial tendency to varyin any particular manner, were originally chosen. We must attribute theresult to the variations in these parts having been successively preserved, and thus continually augmented; whilst other variations, excepting such asinevitably appeared through correlation, were neglected and lost. Hence wemay infer that most plants might be made, through long-continued selection, to yield races as different from each other in any character {220} as theynow are in those parts for which they are valued and cultivated. With animals we see something of the same kind; but they have not beendomesticated in sufficient number or yielded sufficient varieties for afair comparison. Sheep are valued for their wool, and the wool differs muchmore in the several races than the hair in cattle. Neither sheep, goats, European cattle, nor pigs are valued for their fleetness or strength; andwe do not possess breeds differing in these respects like the race-horseand dray-horse. But fleetness and strength are valued in camels and dogs;and we have with the former the swift dromedary and heavy camel; with thelatter the greyhound and mastiff. But dogs are valued even in a higherdegree for their mental qualities and senses; and every one knows howgreatly the races differ in these respects. On the other hand, where thedog is valued solely to serve for food, as in the Polynesian islands andChina, it is described as an extremely stupid animal. [530] Blumenbachremarks that "many dogs, such as the badger-dog, have a build so marked andso appropriate for particular purposes, that I should find it verydifficult to persuade myself that this astonishing figure was an accidentalconsequence of degeneration. "[531] But had Blumenbach reflected on thegreat principle of selection, he would not have used the term degeneration, and he would not have been astonished that dogs and other animals shouldbecome excellently adapted for the service of man. On the whole we may conclude that whatever part or character is mostvalued--whether the leaves, stems, tubers, bulbs, flowers, fruit, or seedof plants, or the size, strength, fleetness, hairy covering, or intellectof animals--that character will almost invariably be found to present thegreatest amount of difference both in kind and degree. And this result maybe safely attributed to man having preserved during a long course ofgenerations the variations which were useful to him, and neglected theothers. I will conclude this chapter by some remarks on an important subject. Withanimals such as the giraffe, of which {221} the whole structure isadmirably co-ordinated for certain purposes, it has been supposed that allthe parts must have been simultaneously modified; and it has been arguedthat, on the principle of natural selection, this is scarcely possible. Butin thus arguing, it has been tacitly assumed that the variations must havebeen abrupt and great. No doubt, if the neck of a ruminant were suddenly tobecome greatly elongated, the fore limbs and back would have to besimultaneously strengthened and modified; but it cannot be denied that ananimal might have its neck, or head, or tongue, or fore-limbs elongated avery little without any corresponding modification in other parts of thebody; and animals thus slightly modified would, during a dearth, have aslight advantage, and be enabled to browse on higher twigs, and thussurvive. A few mouthfuls more or less every day would make all thedifference between life and death. By the repetition of the same process, and by the occasional intercrossing of the survivors, there would be someprogress, slow and fluctuating though it would be, towards the admirablyco-ordinated structure of the giraffe. If the short-faced tumbler-pigeon, with its small conical beak, globular head, rounded body, short wings, andsmall feet--characters which appear all in harmony--had been a naturalspecies, its whole structure would have been viewed as well fitted for itslife; but in this case we know that inexperienced breeders are urged toattend to point after point, and not to attempt improving the wholestructure at the same time. Look at the greyhound, that perfect image ofgrace, symmetry, and vigour; no natural species can boast of a moreadmirably co-ordinated structure, with its tapering head, slim body, deepchest, tucked-up abdomen, rat-like tail, and long muscular limbs, alladapted for extreme fleetness, and for running down weak prey. Now, fromwhat we see of the variability of animals, and from what we know of themethod which different men follow in improving their stock--some chieflyattending to one point, others to another point, others again correctingdefects by crosses, and so forth--we may feel assured that if we could seethe long line of ancestors of a first-rate greyhound, up to its wildwolf-like progenitor, we should behold an infinite number of the finestgradations, sometimes in one character and sometimes in another, but allleading towards our {222} present perfect type. By small and doubtful stepssuch as these, nature, as we may confidently believe, has progressed on hergrand march of improvement and development. A similar line of reasoning is as applicable to separate organs as to thewhole organisation. A writer[532] has recently maintained that "it isprobably no exaggeration to suppose that, in order to improve such an organas the eye at all, it must be improved in ten different ways at once. Andthe improbability of any complex organ being produced and brought toperfection in any such way is an improbability of the same kind and degreeas that of producing a poem or a mathematical demonstration by throwingletters at random on a table. " If the eye were abruptly and greatlymodified, no doubt many parts would have to be simultaneously altered, inorder that the organ should remain serviceable. But is this the case with smaller changes? There are persons who can seedistinctly only in a dull light, and this condition depends, I believe, onthe abnormal sensitiveness of the retina, and is known to be inherited. Now, if a bird, for instance, received some great advantage from seeingwell in the twilight, all the individuals with the most sensitive retinawould succeed best and be the most likely to survive; and why should notall those which happened to have the eye itself a little larger, or thepupil capable of greater dilatation, be likewise preserved, whether or notthese modifications were strictly simultaneous? These individuals wouldsubsequently intercross and blend their respective advantages. By suchslight successive changes, the eye of a diurnal bird would be brought intothe condition of that of an owl, which has often been advanced as anexcellent instance of adaptation. Short-sight, which is often inherited, permits a person to see distinctly a minute object at so near a distancethat it would be indistinct to ordinary eyes; and here we have a capacitywhich might be serviceable under certain conditions, abruptly gained. TheFuegians on board the {223} Beagle could certainly see distant objects moredistinctly than our sailors with all their long practice; I do not knowwhether this depends on nervous sensitiveness or on the power of adjustmentin the focus; but this capacity for distant vision might, it is probable, be slightly augmented by successive modifications of either kind. Amphibious animals, which are enabled to see both in the water and in theair, require and possess, as M. Plateau has shown, [533] eyes constructed onthe following plan: "the cornea is always flat, or at least much flattenedin front of the crystalline and over a space equal to the diameter of thatlens, whilst the lateral portions may be much curved. " The crystalline isvery nearly a sphere, and the humours have nearly the same density aswater. Now, as a terrestrial animal slowly became more and more aquatic inits habits, very slight changes, first in the curvature of the cornea orcrystalline, and then in the density of the humours, or conversely, mightsuccessively occur, and would be advantageous to the animal whilst underwater, without serious detriment to its power of vision in the air. It isof course impossible to conjecture by what steps the fundamental structureof the eye in the Vertebrata was originally acquired, for we knowabsolutely nothing about this organ in the first progenitors of the class. With respect to the lowest animals in the scale, the transitional statesthrough which the eye at first probably passed, can by the aid of analogybe indicated, as I have attempted to show in my 'Origin of Species. '[534] * * * * * {224} CHAPTER XXI. SELECTION, _continued_. NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE--THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE--WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO DEGENERATION--TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE--CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE ALREADY VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT TO THE POWER OF SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH DOMESTIC RACES HAVE ORIGINATED--SUMMARY. _Natural Selection, or the Survival of the Fittest, as affecting domesticproductions. _--We know little on this head. But as animals kept by savageshave to provide their own food, either entirely or to a large extent, throughout the year, it can hardly be doubted that, in different countries, varieties differing in constitution and in various characters would succeedbest, and so be naturally selected. Hence perhaps it is that the fewdomesticated animals kept by savages partake, as has been remarked by morethan one writer, of the wild appearance of their masters, and likewiseresemble natural species. Even in long-civilised countries, at least in thewilder parts, natural selection must act on our domestic races. It isobvious that varieties, having very different habits, constitution, andstructure, would succeed best on mountains and on rich lowland pastures. For example, the improved Leicester sheep were formerly taken to theLammermuir Hills; but an intelligent sheep-master reported that "our coarselean pastures were unequal to the task of supporting such heavy-bodiedsheep; and they gradually dwindled away into less and less bulk: {225} eachgeneration was inferior to the preceding one; and when the spring wassevere, seldom more than two-thirds of the lambs survived the ravages ofthe storms. "[535] So with the mountain cattle of North Wales and theHebrides, it has been found that they could not withstand being crossedwith the larger and more delicate lowland breeds. Two French naturalists, in describing the horses of Circassia, remark that, subjected as they areto extreme vicissitudes of climate, having to search for scanty pasture, and exposed to constant danger from wolves, the strongest and most vigorousalone survive. [536] Every one must have been struck with the surpassing grace, strength, andvigour of the Game-cock, with its bold and confident air, its long, yetfirm neck, compact body, powerful and closely pressed wings, muscularthighs, strong beak massive at the base, dense and sharp spurs set low onthe legs for delivering the fatal blow, and its compact, glossy, andmail-like plumage serving as a defence. Now the English game-cock has notonly been improved during many years by man's careful selection, but inaddition, as Mr. Tegetmeier has remarked, [537] by a kind of naturalselection, for the strongest, most active and courageous birds havestricken down their antagonists in the cockpit, generation aftergeneration, and have subsequently served as the progenitors of their kind. In Great Britain, in former times, almost every district had its own breedof cattle and sheep; "they were indigenous to the soil, climate, andpasturage of the locality on which they grazed: they seemed to have beenformed for it and by it. "[538] But in this case we are quite unable todisentangle the effects of the direct action of the conditions of life, --ofuse or habit--of natural selection--and of that kind of selection which wehave seen is occasionally and unconsciously followed by man even during therudest periods of history. Let us now look to the action of natural selection on special characters. Although nature is difficult to resist, yet man often strives against herpower, and sometimes, as we shall see, with {226} success. From the factsto be given, it will also be seen that natural selection would powerfullyaffect many of our domestic productions if left unprotected. This is apoint of much interest, for we thus learn that differences apparently ofvery slight importance would certainly determine the survival of a formwhen forced to struggle for its own existence. It may have occurred to somenaturalists, as it formerly did to me, that, though selection acting undernatural conditions would determine the structure of all important organs, yet that it could not affect characters which are esteemed by us of littleimportance; but this is an error to which we are eminently liable, from ourignorance of what characters are of real value to each living creature. When man attempts to breed an animal with some serious defect in structure, or in the mutual relation of parts, he will either partially or completelyfail, or encounter much difficulty; and this is in fact a form of naturalselection. We have seen that the attempt was once made in Yorkshire tobreed cattle with enormous buttocks, but the cows perished so often inbringing forth their calves, that the attempt had to be given up. Inrearing short-faced tumblers, Mr. Eaton says, [539] "I am convinced thatbetter head and beak birds have perished in the shell than ever werehatched; the reason being that the amazingly short-faced bird cannot reachand break the shell with its beak, and so perishes. " Here is a more curiouscase, in which natural selection comes into play only at long intervals oftime: during ordinary seasons the Niata cattle can graze as well as others, but occasionally, as from 1827 to 1830, the plains of La Plata suffer fromlong-continued droughts and the pasture is burnt up; at such times commoncattle and horses perish by the thousand, but many survive by browsing ontwigs, reeds, &c. ; this the Niata cattle cannot so well effect from theirupturned jaws and the shape of their lips; consequently, if not attendedto, they perish before the other cattle. In Colombia, according to Roulin, there is a breed of nearly hairless cattle, called Pelones; these succeedin their native hot district, but are found too tender for the Cordillera;in this case, natural selection {227} determines only the range of thevariety. It is obvious that a host of artificial races could never survivein a state of nature;--such as Italian greyhounds, --hairless and almosttoothless Turkish dogs, --fantail pigeons, which cannot fly well against astrong wind, --barbs with their vision impeded by their eye-wattle, --Polishfowls with their vision impeded by their great topknots, --hornless bullsand rams which consequently cannot cope with other males, and thus have apoor chance of leaving offspring, --seedless plants, and many other suchcases. Colour is generally esteemed by the systematic naturalist as unimportant:let us, therefore, see how far it indirectly affects our domesticproductions, and how far it would affect them if they were left exposed tothe full force of natural selection. In a future chapter I shall have toshow that constitutional peculiarities of the strangest kind, entailingliability to the action of certain poisons, are correlated with the colourof the skin. I will here give a single case, on the high authority ofProfessor Wyman; he informs me that, being surprised at all the pigs in apart of Virginia being black, he made inquiries, and ascertained that theseanimals feed on the roots of the _Lachnanthes tinctoria_, which colourstheir bones pink, and, excepting in the case of the black varieties, causesthe hoofs to drop off. Hence, as one of the squatters remarked, "we selectthe black members of the litter for raising, as they alone have a goodchance of living. " So that here we have artificial and natural selectionworking hand in hand. I may add that in the Tarentino the inhabitants keepblack sheep alone, because the _Hypericum crispum_ abounds there; and thisplant does not injure black sheep, but kills the white ones in about afortnight's time. [540] Complexion, and liability to certain diseases, are believed to run togetherin man and the lower animals. Thus white terriers suffer more than terriersof any other colour from the fatal Distemper. [541] In North Americaplum-trees are liable to a disease which Downing[542] believes is notcaused by insects; the kinds bearing purple fruit are most affected, "andwe have never known the green or yellow fruited varieties infected {228}until the other sorts had first become filled with the knots. " On the otherhand, peaches in North America suffer much from a disease called the_yellows_, which seems to be peculiar to that continent, and "more thannine-tenths of the victims, when the disease first appeared, were theyellow-fleshed peaches. The white-fleshed kinds are much more rarelyattacked; in some parts of the country never. " In Mauritius, the whitesugar-canes have of late years been so severely attacked by a disease, thatmany planters have been compelled to give up growing this variety (althoughfresh plants were imported from China for trial), and cultivate only redcanes. [543] Now, if these plants had been forced to struggle with othercompeting plants and enemies, there cannot be a doubt that the colour ofthe flesh or skin of the fruit, unimportant as these characters areconsidered, would have rigorously determined their existence. Liability to the attacks of parasites is also connected with colour. Itappears that white chickens are certainly more subject than dark-colouredchickens to the _gapes_, which is caused by a parasitic worm in thetrachea. [544] On the other hand, experience has shown that in France thecaterpillars which produce white cocoons resist the deadly fungus betterthan those producing yellow cocoons. [545] Analogous facts have beenobserved with plants: a new and beautiful white onion, imported fromFrance, though planted close to other kinds, was alone attacked by aparasitic fungus. [546] White verbenas are especially liable to mildew. [547]Near Malaga, during an early period of the vine-disease, the green sortssuffered most; "and red and black grapes, even when interwoven with thesick plants, suffered not at all. " In France whole groups of varieties werecomparatively free, and others, such as the Chasselas, did not afford asingle fortunate exception; but I do not know whether any correlationbetween colour and liability to disease was here observed. [548] In a formerchapter it was shown how curiously liable one variety of the strawberry isto mildew. {229} It is certain that insects regulate in many cases the range and even theexistence of the higher animals, whilst living under their naturalconditions. Under domestication light-coloured animals suffer most: inThuringia[549] the inhabitants do not like grey, white, or pale cattle, because they are much more troubled by various kinds of flies than thebrown, red, or black cattle. An Albino negro, it has been remarked, [550]was peculiarly sensitive to the bites of insects. In the West Indies[551]it is said that "the only horned cattle fit for work are those which have agood deal of black in them. The white are terribly tormented by theinsects; and they are weak and sluggish in proportion to the white. " In Devonshire there is a prejudice against white pigs, because it isbelieved that the sun blisters them when turned out;[552] and I knew a manwho would not keep white pigs in Kent, for the same reason. The scorchingof flowers by the sun seems likewise to depend much on colour; thus, darkpelargoniums suffer most; and from various accounts it is clear that thecloth-of-gold variety will not withstand a degree of exposure to sunshinewhich other varieties enjoy. Another amateur asserts that not only alldark-coloured verbenas, but likewise scarlets, suffer from the sun; "thepaler kinds stand better, and pale blue is perhaps the best of all. " Soagain with the heartsease (_Viola tricolor_); hot weather suits theblotched sorts, whilst it destroys the beautiful markings of some otherkinds. [553] During one extremely cold season in Holland all red-floweredhyacinths were observed to be very inferior in quality. It is believed bymany agriculturists that red wheat is hardier in northern climates thanwhite wheat. [554] With animals, white varieties from being conspicuous are the most liable tobe attacked by beasts and birds of prey. In parts of France and Germanywhere hawks abound, persons are advised not to keep white pigeons; for, asParmentier says, "it {230} is certain that in a flock the white alwaysfirst fall victims to the kite. " In Belgium, where so many societies havebeen established for the flight of carrier-pigeons, white is the one colourwhich for the same reason is disliked. [555] On the other hand, it is saidthat the sea-eagle (_Falco ossifragus_, Linn. ) on the west coast of Irelandpicks out the black fowls, so that "the villagers avoid as much as possiblerearing birds of that colour. " M. Daudin, [556] speaking of white rabbitskept in warrens in Russia, remarks that their colour is a greatdisadvantage, as they are thus more exposed to attack, and can be seenduring bright nights from a distance. A gentleman in Kent, who failed tostock his woods with a nearly white and hardy kind of rabbit, accounted inthe same manner for their early disappearance. Any one who will watch awhite cat prowling after her prey will soon perceive under what adisadvantage she lies. The white Tartarian cherry, "owing either to its colour being so much likethat of the leaves, or to the fruit always appearing from a distanceunripe, " is not so readily attacked by birds as other sorts. Theyellow-fruited raspberry, which generally comes nearly true by seed, "isvery little molested by birds, who evidently are not fond of it; so thatnets may be dispensed with in places where nothing else will protect thered fruit. "[557] This immunity, though a benefit to the gardener, would bea disadvantage in a state of nature both to the cherry and raspberry, astheir dissemination depends on birds. I noticed during several winters thatsome trees of the yellow-berried holly, which were raised from seed from awild tree found by my father, remained covered with fruit, whilst not ascarlet berry could be seen on the adjoining trees of the common kind. Afriend informs me that a mountain-ash (_Pyrus aucuparia_) growing in hisgarden bears berries which, though not differently coloured, are alwaysdevoured by birds before those on the other trees. This variety of themountain-ash would thus be more freely disseminated, and the yellow-berriedvariety of the holly less freely, than the common varieties of these twotrees. {231} Independently of colour, other trifling differences are sometimes found tobe of importance to plants under cultivation, and would be of paramountimportance if they had to fight their own battle and to struggle with manycompetitors. The thin-shelled peas, called _pois sans parchemin_, areattacked by birds[558] much more than common peas. On the other hand, thepurple-podded pea, which has a hard shell, escaped the attacks of tomtits(_Parus major_) in my garden far better than any other kind. Thethin-shelled walnut likewise suffers greatly from the tomtit. [559] Thesesame birds have been observed to pass over and thus favour the filbert, destroying only the other kinds of nuts which grew in the sameorchard. [560] Certain varieties of the pear have soft bark, and these suffer severelyfrom boring wood-beetles; whilst other varieties are known to resist theirattacks much better. [561] In North America the smoothness, or absence ofdown on the fruit, makes a great difference in the attacks of the weevil, "which is the uncompromising foe of all smooth stone-fruits;" and thecultivator "has the frequent mortification of seeing nearly all, or indeedoften the whole crop, fall from the trees when half or two-thirds grown. "Hence the nectarine suffers more than the peach. A particular variety ofthe Morello cherry, raised in North America, is without any assignablecause more liable to be injured by this same insect than othercherry-trees. [562] From some unknown cause, the Winter Majetin apple enjoysthe great advantage of not being infested by the coccus. On the other hand, a particular case has been recorded in which aphides confined themselves tothe Winter Nelis pear, and touched no other kind in an extensiveorchard. [563] The existence of minute glands on the leaves of peaches, nectarines, and apricots, would not be esteemed by botanists as a characterof the least importance, for they are present or absent in closely relatedsub-varieties, descended from the same parent-tree; yet there is goodevidence[564] that the {232} absence of glands leads to mildew, which ishighly injurious to these trees. A difference either in flavour or in the amount of nutriment in certainvarieties causes them to be more eagerly attacked by various enemies thanother varieties of the same species. Bullfinches (_Pyrrhula vulgaris_)injure our fruit-trees by devouring the flower-buds, and a pair of thesebirds have been seen "to denude a large plum-tree in a couple of days ofalmost every bud;" but certain varieties[565] of the apple and thorn(_Cratægus oxyacantha_) are more especially liable to be attacked. Astriking instance of this was observed in Mr. Rivers's garden, in which tworows of a particular variety of plum[566] had to be carefully protected, asthey were usually stripped of all their buds during the winter, whilstother sorts growing near them escaped. The root (or enlarged stem) ofLaing's Swedish turnip is preferred by hares, and therefore suffers morethan other varieties. Hares and rabbits eat down common rye before St. John's-day-rye, when both grow together. [567] In the South of France, whenan orchard of almond-trees is formed, the nuts of the bitter variety aresown, "in order that they may not be devoured by field-mice;"[568] so wesee the use of the bitter principle in almonds. Other slight differences, which would be thought quite unimportant, are nodoubt sometimes of great service both to plants and animals. TheWhitesmith's gooseberry, as formerly stated, produces its leaves later thanother varieties, and, as the flowers are thus left unprotected, the fruitoften fails. In one variety of the cherry, according to Mr. Rivers, [569]the petals are much curled backwards, and in consequence of this thestigmas were observed to be killed by a severe frost; whilst at the sametime, in another variety with incurved petals, the stigmas were not in theleast injured. The straw of the Fenton wheat is remarkably unequal inheight; and a competent observer believes that this variety is highlyproductive, partly because the ears, from being distributed at variousheights above the ground, {233} are less crowded together. The sameobserver maintains that in the upright varieties the divergent awns areserviceable by breaking the shocks when the ears are dashed together by thewind. [570] If several varieties of a plant are grown together, and the seedis indiscriminately harvested, it is clear that the hardier and moreproductive kinds will, by a sort of natural selection, gradually prevailover the others; this takes place, as Colonel Le Couteur believes, [571] inour wheat-fields, for, as formerly shown, no variety is quite uniform incharacter. The same thing, as I am assured by nurserymen, would take placein our flower-gardens, if the seed of the different varieties were notseparately saved. When the eggs of the wild and tame duck are hatchedtogether, the young wild ducks almost invariably perish, from being ofsmaller size and not getting their fair share of food. [572] Facts in sufficient number have now been given showing that naturalselection often checks, but occasionally favours, man's power of selection. These facts teach us, in addition, a valuable lesson, namely, that we oughtto be extremely cautious in judging what characters are of importance in astate of nature to animals and plants, which have to struggle from the hourof their birth to that of their death for existence, --their existencedepending on conditions, about which we are profoundly ignorant. _Circumstances favourable to Selection by Man. _ The possibility of selection rests on variability, and this, as we shallsee in the following chapters, mainly depends on changed conditions oflife, but is governed by infinitely complex, and, to a great extent, unknown laws. Domestication, even when long continued, occasionally causesbut a small amount of variability, as in the case of the goose and turkey. The slight differences, however, which characterise each individual animaland plant would in most, probably in all cases, suffice for the productionof distinct races through careful and prolonged selection. We see whatselection, though acting on mere individual differences, can effect whenfamilies of cattle, sheep, {234} pigeons, &c. , of the same race, have beenseparately bred during a number of years by different men without any wishon their part to modify the breed. We see the same fact in the differencebetween hounds bred for hunting in different districts, [573] and in manyother such cases. In order that selection should produce any result, it is manifest that thecrossing of distinct races must be prevented; hence facility in pairing, aswith the pigeon, is highly favourable for the work; and difficulty inpairing, as with cats, prevents the formation of distinct breeds. On nearlythe same principle the cattle of the small island of Jersey have beenimproved in their milking qualities "with a rapidity that could not havebeen obtained in a widely extended country like France. "[574] Although freecrossing is a danger on the one side which every one can see, too closeinterbreeding is a hidden danger on the other side. Unfavourable conditionsof life overrule the power of selection. Our improved heavy breeds ofcattle and sheep could not have been formed on mountainous pastures; norcould dray-horses have been raised on a barren and inhospitable land, suchas the Falkland islands, where even the light horses of La Plata rapidlydecrease in size. Nor could the wool of sheep have been much increased inlength within the Tropics; yet selection has kept Merino sheep nearly trueunder diversified and unfavourable conditions of life. The power ofselection is so great, that breeds of the dog, sheep, and poultry, of thelargest and least size, long and short beaked pigeons, and other breedswith opposite characters, have had their characteristic qualitiesaugmented, though treated in every way alike, being exposed to the sameclimate and fed on the same food. Selection, however, is either checked orfavoured by the effects of use or habit. Our wonderfully-improved pigscould never have been formed if they had been forced to search for theirown food; the English racehorse and greyhound could not have been improvedup to their present high standard of excellence without constant training. As conspicuous deviations of structure occur rarely, the improvement ofeach breed is generally the result, as already {235} remarked, of theselection of slight individual differences. Hence the closest attention, the sharpest powers of observation, and indomitable perseverance, areindispensable. It is, also, highly important that many individuals of thebreed which is to be improved should be raised; for thus there will be abetter chance of the appearance of variations in the right direction, andindividuals varying in an unfavourable manner may be freely rejected ordestroyed. But that a large number of individuals should be raised, it isnecessary that the conditions of life should favour the propagation of thespecies. Had the peacock been bred as easily as the fowl, we shouldprobably ere this have had many distinct races. We see the importance of alarge number of plants, from the fact of nursery gardeners almost alwaysbeating amateurs in the exhibition of new varieties. In 1845 it wasestimated[575] that between 4000 and 5000 pelargoniums were annually raisedfrom seed in England, yet a decidedly improved variety is rarely obtained. At Messrs. Carter's grounds, in Essex, where such flowers as the Lobelia, Nemophila, Mignonette, &c. , are grown by the acre for seed, "scarcely aseason passes without some new kinds being raised, or some improvementaffected on old kinds. "[576] At Kew, as Mr. Beaton remarks, where manyseedlings of common plants are raised, "you see new forms of Laburnums, Spiræas, and other shrubs. "[577] So with animals: Marshall, [578] inspeaking of the sheep in one part of Yorkshire, remarks, "as they belong topoor people, and are mostly in small lots, they never can be improved. "Lord Rivers, when asked how he succeeded in always having first-rategreyhounds, answered, "I breed many, and hang many. " This, as another manremarks, "was the secret of his success; and the same will be found inexhibiting fowls, --successful competitors breed largely, and keep thebest. "[579] It follows from this that the capacity of breeding at an early age and atshort successive intervals, as with pigeons, rabbits, &c. , facilitatesselection; for the result is thus soon made visible, and perseverance inthe work is encouraged. It can hardly be {236} accidental that the greatmajority of the culinary and agricultural plants which have yieldednumerous races are annuals or biennials, which therefore are capable ofrapid propagation and thus of improvement. Sea-kale, asparagus, common andJerusalem artichokes, potatoes, and onions, alone are perennials. Onionsare propagated like annuals, and of the other plants just specified, none, with the exception of the potato, have yielded more than one or twovarieties. No doubt fruit-trees, which cannot be propagated quickly byseed, have yielded a host of varieties, though not permanent races; butthese, judging from pre-historic remains, were produced at a later and morecivilised epoch than the races of culinary and agricultural plants. A species may be highly variable, but distinct races will not be formed, iffrom any cause selection be not applied. The carp is highly variable, butit would be extremely difficult to select slight variations in fisheswhilst living in their natural state, and distinct races have not beenformed;[580] on the other hand, a closely allied species, the gold-fish, from being reared in glass or open vessels, and from having been carefullyattended to by the Chinese, has yielded many races. Neither the bee, whichhas been semi-domesticated from an extremely remote period, nor thecochineal insect, which was cultivated by the aboriginal Mexicans, hasyielded races; and it would be impossible to match the queen-bee with anyparticular drone, and most difficult to match cochineal insects. Silk-moths, on the other hand, have been subjected to rigorous selection, and have produced a host of races. Cats, which from their nocturnal habitscannot be selected for breeding, do not, as formerly remarked, yielddistinct races in the same country. The ass in England varies much incolour and size; but it is an animal of little value, bred by poor people;consequently there has been no selection, and distinct races have not beenformed. We must not attribute the inferiority of our asses to climate, forin India they are of even smaller size than in Europe. But when selectionis brought to bear on the ass, all is changed. Near Cordova, as I aminformed (Feb. 1860) by Mr. W. E. Webb, C. E. , they are carefully bred, asmuch as 200l. Having been paid for a stallion ass, {237} and they have beenimmensely improved. In Kentucky, asses have been imported (for breedingmules) from Spain, Malta, and France; these "seldom averaged more thanfourteen hands high; but the Kentuckians, by great care, have raised themup to fifteen hands, and sometimes even to sixteen. The prices paid forthese splendid animals, for such they really are, will prove how much theyare in request. One male, of great celebrity, was sold for upwards of onethousand pounds sterling. " These choice asses are sent to cattle-shows, oneday being given to their exhibition. [581] Analogous facts have been observed with plants: the nutmeg-tree in theMalay archipelago is highly variable, but there has been no selection, andthere are no distinct races. [582] The common mignonette (_Reseda odorata_), from bearing inconspicuous flowers, valued solely for their fragrance, "remains in the same unimproved condition as when first introduced. "[583]Our common forest-trees are very variable, as may be seen in everyextensive nursery-ground; but as they are not valued like fruit-trees, andas they seed late in life, no selection has been applied to them;consequently, as Mr. Patrick Matthews remarks, [584] they have not yieldeddistinct races, leafing at different periods, growing to different sizes, and producing timber fit for different purposes. We have gained only somefanciful and semi-monstrous varieties, which no doubt appeared suddenly aswe now see them. Some botanists have argued that plants cannot have so strong a tendency tovary as is generally supposed, because many species long grown in botanicgardens, or unintentionally cultivated year after year mingled with ourcorn crops, have not produced distinct races; but this is accounted for byslight variations not having been selected and propagated. Let a plantwhich is now grown in a botanic garden, or any common weed, be cultivatedon a large scale, and let a sharp-sighted gardener look out for each slightvariety and sow the seed, and then, if distinct races are not produced, theargument will be valid. {238} The importance of selection is likewise shown by considering specialcharacters. For instance, with most breeds of fowls the form of the comband the colour of the plumage have been attended to, and are eminentlycharacteristic of each race; but in Dorkings, fashion has never demandeduniformity of comb or colour; and the utmost diversity in these respectsprevails. Rose-combs, double-combs, cup-combs, &c. , and colours of allkinds, may be seen in purely-bred and closely related Dorking fowls, whilstother points, such as the general form of body, and the presence of anadditional toe, have been attended to, and are invariably present. It hasalso been ascertained that colour can be fixed in this breed, as well as inany other. [585] * * * * * During the formation or improvement of a breed, its members will always befound to vary much in those characters to which especial attention isdirected, and of which each slight improvement is eagerly sought andselected. Thus with short-faced tumbler-pigeons, the shortness of the beak, shape of head and plumage, --with carriers, the length of the beak andwattle, --with fantails, the tail and carriage, --with Spanish fowls, thewhite face and comb, --with long-eared rabbits, the length of ear, are allpoints which are eminently variable. So it is in every case, and the largeprice paid for first-rate animals proves the difficulty of breeding them upto the highest standard of excellence. This subject has been discussed byfanciers, [586] and the greater prizes given for highly improved breeds, incomparison with those given for old breeds which are not now undergoingrapid improvement, has been fully justified. Nathusius makes[587] a similarremark when discussing the less uniform character of improved Shorthorncattle and of the English horse, in comparison, for example, with theunennobled cattle of Hungary, or with the horses of the Asiatic steppes. This want of uniformity in the parts which at the time are undergoingselection, chiefly depends on the strength of the principle of reversionbut it likewise depends to a certain extent on the continued {239}variability of the parts which have recently varied. That the same parts docontinue varying in the same manner we must admit, for, if it were not so, there could be no improvement beyond an early standard of excellence, andwe know that such improvement is not only possible, but is of generaloccurrence. As a consequence of continued variability, and more especially ofreversion, all highly improved races, if neglected or not subjected toincessant selection, soon degenerate. Youatt gives a curious instance ofthis in some cattle formerly kept in Glamorganshire; but in this case thecattle were not fed with sufficient care. Mr. Baker, in his memoir on theHorse, sums up: "It must have been observed in the preceding pages that, whenever there has been neglect, the breed has proportionallydeteriorated. "[588] If a considerable number of improved cattle, sheep, orother animals of the same race, were allowed to breed freely together, withno selection, but with no change in their condition of life, there can beno doubt that after a score or hundred generations they would be very farfrom excellent of their kind; but, from what we see of the many commonraces of dogs, cattle, fowls, pigeons, &c. , which without any particularcare have long retained nearly the same character, we have no grounds forbelieving that they would altogether depart from their type. It is a general belief amongst breeders that characters of all kinds becomefixed by long-continued inheritance. But I have attempted to show in thefourteenth chapter that this belief apparently resolves itself into thefollowing proposition, namely, that all characters whatever, whetherrecently acquired or ancient, tend to be transmitted, but that those whichhave already long withstood all counteracting influences, will, as ageneral rule, continue to withstand them, and consequently be faithfullytransmitted. _Tendency in Man to carry the practice of Selection to an extreme point. _ It is an important principle that in the process of selection man almostinvariably wishes to go to an extreme point. Thus, in useful qualities, there is no limit to his desire to breed certain {240} horses and dogs asfleet as possible, and others as strong as possible; certain kinds of sheepfor extreme fineness, and others for extreme length of wool; and he wishesto produce fruit, grain, tubers, and other useful parts of plants, as largeand excellent as possible. With animals bred for amusement, the sameprinciple is even more powerful; for fashion, as we see even in our dress, always runs to extremes. This view has been expressly admitted by fanciers. Instances were given in the chapters on the pigeon, but here is another:Mr. Eaton, after describing a comparatively new variety, namely, theArchangel, remarks, "What fanciers intend doing with this bird I am at aloss to know, whether they intend to breed it down to the tumbler's headand beak, or carry it out to the carrier's head and beak; leaving it asthey found it, is not progressing. " Ferguson, speaking of fowls, says, "their peculiarities, whatever they may be, must necessarily be fullydeveloped: a little peculiarity forms nought but ugliness, seeing itviolates the existing laws of symmetry. " So Mr. Brent, in discussing themerits of the sub-varieties of the Belgian canary-bird, remarks, "Fanciersalways go to extremes; they do not admire indefinite properties. "[589] This principle, which necessarily leads to divergence of character, explains the present state of various domestic races. We can thus see howit is that race-horses and dray-horses, greyhounds and mastiffs, which areopposed to each other in every character, --how varieties so distinct asCochin-China fowls and bantams, or carrier-pigeons with very long beaks, and tumblers with excessively short beaks, have been derived from the samestock. As each breed is slowly improved, the inferior varieties are firstneglected and finally lost. In a few cases, by the aid of old records, orfrom intermediate varieties still existing in countries where otherfashions have prevailed, we are enabled partially to trace the graduatedchanges through which certain breeds have passed. Selection, whethermethodical or unconscious, always tending towards an extreme point, together with the neglect and slow extinction of the intermediate andless-valued forms, is the key which unlocks the mystery how man hasproduced such wonderful results. {241} In a few instances selection, guided by utility for a single purpose, hasled to convergence of character. All the improved and different races ofthe pig, as Nathusius has well shown, [590] closely approach each other incharacter, in their shortened legs and muzzles, their almost hairless, large, rounded bodies, and small tusks. We see some degree of convergencein the similar outline of the body in well-bred cattle belonging todistinct races. [591] I know of no other such cases. Continued divergence of character depends on, and is indeed a clear proof, as previously remarked, of the same parts continuing to vary in the samedirection. The tendency to mere general variability or plasticity oforganisation can certainly be inherited, even from one parent, as has beenshown by Gärtner and Kölreuter, in the production of varying hybrids fromtwo species, of which one alone was variable. It is in itself probablethat, when an organ has varied in any manner, it will again vary in thesame manner, if the conditions which first caused the being to vary remain, as far as can be judged, the same. This is either tacitly or expresslyadmitted by all horticulturists: if a gardener observes one or twoadditional petals in a flower, he feels confident that in a few generationshe will be able to raise a double flower, crowded with petals. Some of theseedlings from the weeping Moccas oak were so prostrate that they onlycrawled along the ground. A seedling from the fastigate or upright Irishyew is described as differing greatly from the parent-form "by theexaggeration of the fastigate habit of its branches. "[592] Mr. Sheriff, whohas been more successful than any other man in raising new kinds of wheat, remarks, "A good variety may safely be regarded as the forerunner of abetter one. "[593] A great rose-grower, Mr. Rivers, has made the same remarkwith respect to roses. Sageret, [594] who had large experience, in speakingof the future progress of fruit-trees, observes that the most importantprinciple is "that the more plants have departed from their original type, the more they tend to depart from it. " There is apparently much truth inthis {242} remark; for we can in no other way understand the surprisingamount of difference between varieties in the parts or qualities which arevalued, whilst other parts retain nearly their original character. The foregoing discussion naturally leads to the question, what is the limitto the possible amount of variation in any part or quality, and, consequently, is there any limit to what selection can effect? Will arace-horse ever be reared fleeter than Eclipse? Can our prize-cattle andsheep be still further improved? Will a gooseberry ever weigh more thanthat produced by "London" in 1852? Will the beet-root in France yield agreater percentage of sugar? Will future varieties of wheat and other grainproduce heavier crops than our present varieties? These questions cannot bepositively answered; but it is certain that we ought to be cautious inanswering by a negative. In some lines of variation the limit has probablybeen reached. Youatt believes that the reduction of bone in some of oursheep has already been carried so far that it entails great delicacy ofconstitution. [595] But seeing the great improvement within recent times inour cattle and sheep, and especially in our pigs; seeing the wonderfulincrease in weight in our poultry of all kinds during the last few years;he would be a bold man who would assert that perfection has been reached. Eclipse perhaps may never be beaten until all our race-horses have beenrendered swifter, through the selection of the best horses during manygenerations; and then the old Eclipse may possibly be eclipsed; but, as Mr. Wallace has remarked, there must be an ultimate limit to the fleetness ofevery animal, whether under nature or domestication; and with the horsethis limit has perhaps been reached. Until our fields are better manured, it may be impossible for a new variety of wheat to yield a heavier crop. But in many cases those who are best qualified to judge do not believe thatthe extreme point has as yet been reached even with respect to characterswhich have already been carried to a high standard of perfection. Forinstance, the short-faced tumbler-pigeon has been greatly modified;nevertheless, according to Mr. Eaton, [596] "the field is still as open forfresh competitors as it was one hundred years ago. " Over and over again ithas been said that {243} perfection had been attained with our flowers, buta higher standard has soon been reached. Hardly any fruit has been moreimproved than the strawberry, yet a great authority remarks, [597] "it mustnot be concealed that we are far from the extreme limits at which we mayarrive. " Time is an important element in the formation of our domestic races, as itpermits innumerable individuals to be born, and these when exposed todiversified conditions are rendered variable. Methodical selection has beenoccasionally practised from an ancient period to the present day, even bysemi-civilised people, and during former times will have produced someeffect. Unconscious selection will have been still more effective; forduring a lengthened period the more valuable individual animals willoccasionally have been saved, and the less valuable neglected. In thecourse, also, of time, different varieties, especially in the lesscivilised countries, will have been more or less modified through naturalselection. It is generally believed, though on this head we have little orno evidence, that new characters in time become fixed; and after havinglong remained fixed it seems possible that under new conditions they mightagain be rendered variable. How great the lapse of time has been since man first domesticated animalsand cultivated plants, we begin dimly to see. When the lake-buildings ofSwitzerland were inhabited during the Neolithic period, several animalswere already domesticated and various plants cultivated. If we may judgefrom what we now see of the habits of savages, it is probable that the menof the earlier Stone period--when many great quadrupeds were living whichare now extinct, and when the face of the country was widely different fromwhat it now is--possessed at least some few domesticated animals, althoughtheir remains have not as yet been discovered. If the science of languagecan be trusted, the art of ploughing and sowing the land was followed, andthe chief animals had been already domesticated, at an epoch so immenselyremote, that the Sanskrit, Greek, Latin, Gothic, Celtic, and Sclavoniclanguages had not as yet diverged from their common parent-tongue. [598] {244} It is scarcely possible to overrate the effects of selection occasionallycarried on in various ways and places during thousands of generations. Allthat we know, and, in a still stronger degree, all that we do notknow, [599] of the history of the great majority of our breeds, even of ourmore modern breeds, agrees with the view that their production, through theaction of unconscious and methodical selection, has been almost insensiblyslow. When a man attends rather more closely than is usual to the breedingof his animals, he is almost sure to improve them to a slight extent. Theyare in consequence valued in his immediate neighbourhood, and are bred byothers; and their characteristic features, whatever these may be, will thenslowly but steadily be increased, sometimes by methodical and almost alwaysby unconscious selection. At last a strain, deserving to be called asub-variety, becomes a little more widely known, receives a local name, andspreads. The spreading will have been extremely slow during ancient andless civilised times, but now is rapid. By the time that the new breed hadassumed a somewhat distinct character, its history, hardly noticed at thetime, will have been completely forgotten; for, as Low remarks, [600] "weknow how quickly the memory of such events is effaced. " As soon as a new breed is thus formed, it is liable through the sameprocess to break up into new strains and sub-varieties. For differentvarieties are suited for, and are valued under, different circumstances. Fashion changes, but, should a fashion last for even a moderate length oftime, so strong is the principle of inheritance, that some effect willprobably be impressed on the breed. Thus varieties go on increasing innumber, and history shows us how wonderfully they have increased since theearliest records. [601] As each new variety is produced, the earlier, intermediate, and less valuable forms will be neglected, and perish. When abreed, from not being valued, is kept in small numbers, its extinctionalmost inevitably follows sooner or later, either from accidental causes ofdestruction or from close interbreeding; and this is an event which, in thecase of well-marked breeds, excites attention. The birth or production of anew domestic race is so slow a process that it {245} escapes notice; itsdeath or destruction is comparatively sudden, is often recorded, and whentoo late sometimes regretted. Several authors have drawn a wide distinction between artificial andnatural races. The latter are more uniform in character, possessing in ahigh degree the character of natural species, and are of ancient origin. They are generally found in less civilised countries, and have probablybeen largely modified by natural selection, and only to a small extent byman's unconscious and methodical selection. They have, also, during a longperiod, been directly acted on by the physical conditions of the countrieswhich they inhabit. The so-called artificial races, on the other hand, arenot so uniform in character; some have a semi-monstrous character, such as"the wry-legged terriers so useful in rabbit-shooting, "[602] turnspit dogs, ancon sheep, niata oxen, Polish fowls, fantail-pigeons, &c. ; theircharacteristic features have generally been acquired suddenly, thoughsubsequently increased in many cases by careful selection. Other races, which certainly must be called artificial, for they have been largelymodified by methodical selection and by crossing, as the Englishrace-horse, terrier-dogs, the English game-cock, Antwerp carrier-pigeons, &c. , nevertheless cannot be said to have an unnatural appearance; and nodistinct line, as it seems to me, can be drawn between natural andartificial races. It is not surprising that domestic races should generally present adifferent aspect from natural species. Man selects and propagatesmodifications solely for his own use or fancy, and not for the creature'sown good. His attention is struck by strongly marked modifications, whichhave appeared suddenly, due to some great disturbing cause in theorganisation. He attends almost exclusively to external characters; andwhen he succeeds in modifying internal organs, --when for instance hereduces the bones and offal, or loads the viscera with fat, or gives earlymaturity, &c. , --the chances are strong that he will at the same time weakenthe constitution. On the other hand, when an animal has to strugglethroughout its life with many competitors and enemies, under circumstancesinconceivably complex and liable to change, modifications of the mostvaried nature--in the internal organs as well as in external characters, inthe {246} functions and mutual relations of parts--will be rigorouslytested, preserved, or rejected. Natural selection often checks man'scomparatively feeble and capricious attempts at improvement; and if thiswere not so, the result of his work, and of nature's work, would be evenstill more different. Nevertheless, we must not overrate the amount ofdifference between natural species and domestic races; the most experiencednaturalists have often disputed whether the latter are descended from oneor from several aboriginal stocks, and this clearly shows that there is nopalpable difference between species and races. Domestic races propagate their kind far more truly, and endure for muchlonger periods, than most naturalists are willing to admit. Breeders feelno doubt on this head; ask a man who has long reared Shorthorn or Herefordcattle, Leicester or Southdown sheep, Spanish or Game poultry, tumbler orcarrier-pigeons, whether these races may not have been derived from commonprogenitors, and he will probably laugh you to scorn. The breeder admitsthat he may hope to produce sheep with finer or longer wool and with bettercarcases, or handsomer fowls, or carrier-pigeons with beaks justperceptibly longer to the practised eye, and thus be successful at anexhibition. Thus far he will go, but no farther. He does not reflect onwhat follows from adding up during a long course of time many, slight, successive modifications; nor does he reflect on the former existence ofnumerous varieties, connecting the links in each divergent line of descent. He concludes, as was shown in the earlier chapters, that all the chiefbreeds to which he has long attended are aboriginal productions. Thesystematic naturalist, on the other hand, who generally knows nothing ofthe art of breeding, who does not pretend to know how and when the severaldomestic races were formed, who cannot have seen the intermediategradations, for they do not now exist, nevertheless feels no doubt thatthese races are sprung from a single source. But ask him whether theclosely allied natural species which he has studied may not have descendedfrom a common progenitor, and he in his turn will perhaps reject the notionwith scorn. Thus the naturalist and breeder may mutually learn a usefullesson from each other. * * * * * _Summary on Selection by Man. _--There can be no doubt that {247} methodicalselection has effected and will effect wonderful results. It wasoccasionally practised in ancient times, and is still practised bysemi-civilised people. Characters of the highest importance, and others oftrifling value, have been attended to, and modified. I need not here repeatwhat has been so often said on the part which unconscious selection hasplayed: we see its power in the difference between flocks which have beenseparately bred, and in the slow changes, as circumstances have slowlychanged, which many animals have undergone in the same country, or whentransported into a foreign land. We see the combined effects of methodicaland unconscious selection in the great amount of difference betweenvarieties in those parts or qualities which are valued by man, incomparison with those which are not valued, and consequently have not beenattended to. Natural selection often determines man's power of selection. We sometimes err in imagining that characters, which are considered asunimportant by the systematic naturalist, could not be affected by thestruggle for existence, and therefore be acted on by natural selection; butstriking cases have been given, showing how great an error this is. The possibility of selection coming into action rests on variability; andthis is mainly caused, as we shall hereafter see, by changes in theconditions of life. Selection is sometimes rendered difficult, or evenimpossible, by the conditions being opposed to the desired character orquality. It is sometimes checked by the lessened fertility and weakenedconstitution which follow from long-continued close interbreeding. Thatmethodical selection may be successful, the closest attention anddiscernment, combined with unwearied patience, are absolutely necessary;and these same qualities, though not indispensable, are highly serviceablein the case of unconscious selection. It is almost necessary that a largenumber of individuals should be reared; for thus there will be a fairchance of variations of the desired nature arising, and every individualwith the slightest blemish or in any degree inferior may be freelyrejected. Hence length of time is an important element of success. Thus, also, propagation at an early age and at short intervals favours the work. Facility in pairing animals, or their inhabiting a confined area, isadvantageous as a check to free crossing. Whenever and {248} whereverselection is not practised, distinct races are not formed. When any onepart of the body or quality is not attended to, it remains either unchangedor varies in a fluctuating manner, whilst at the same time other parts andother qualities may become permanently and greatly modified. But from thetendency to reversion and to continued variability, those parts or organswhich are now undergoing rapid improvement through selection, are likewisefound to vary much. Consequently highly-bred animals, when neglected, soondegenerate; but we have no reason to believe that the effects oflong-continued selection would, if the conditions of life remained thesame, be soon and completely lost. Man always tends to go to an extreme point in the selection, whethermethodical or unconscious, of all useful and pleasing qualities. This is animportant principle, as it leads to continued divergence, and in some rarecases to convergence of character. The possibility of continued divergencerests on the tendency in each part or organ to go on varying in the samemanner in which it has already varied; and that this occurs, is proved bythe steady and gradual improvement of many animals and plants duringlengthened periods. The principle of divergence of character, combined withthe neglect and final extinction of all previous, less-valued, andintermediate varieties, explains the amount of difference and thedistinctness of our several races. Although we may have reached the utmostlimit to which certain characters can be modified, yet we are far fromhaving reached, as we have good reason to believe, the limit in themajority of cases. Finally, from the difference between selection ascarried on by man and by nature, we can understand how it is that domesticraces often, though by no means always, differ in general aspect fromclosely allied natural species. Throughout this chapter and elsewhere I have spoken of selection as theparamount power, yet its action absolutely depends on what we in ourignorance call spontaneous or accidental variability. Let an architect becompelled to build an edifice with uncut stones, fallen from a precipice. The shape of each fragment may be called accidental; yet the shape of eachhas been determined by the force of gravity, the nature {249} of the rock, and the slope of the precipice, --events and circumstances, all of whichdepend on natural laws; but there is no relation between these laws and thepurpose for which each fragment is used by the builder. In the same mannerthe variations of each creature are determined by fixed and immutable laws;but these bear no relation to the living structure which is slowly built upthrough the power of selection, whether this be natural or artificialselection. If our architect succeeded in rearing a noble edifice, using the roughwedge-shaped fragments for the arches, the longer stones for the lintels, and so forth, we should admire his skill even in a higher degree than if hehad used stones shaped for the purpose. So it is with selection, whetherapplied by man or by nature; for though variability is indispensablynecessary, yet, when we look at some highly complex and excellently adaptedorganism, variability sinks to a quite subordinate position in importancein comparison with selection, in the same manner as the shape of eachfragment used by our supposed architect is unimportant in comparison withhis skill. * * * * * {250} CHAPTER XXII. CAUSES OF VARIABILITY. VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES ASSIGNED BY VARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF EVERY KIND DUE TO CHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH CHANGES--CLIMATE, FOOD, EXCESS OF NUTRIMENT--SLIGHT CHANGES SUFFICIENT--EFFECTS OF GRAFTING ON THE VARIABILITY OF SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TO CHANGED CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSE INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE VARIABILITY--CROSSING AS A CAUSE OF THE APPEARANCE OF NEW CHARACTERS--VARIABILITY FROM THE COMMINGLING OF CHARACTERS AND FROM REVERSION--ON THE MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH EITHER DIRECTLY, OR INDIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE VARIABILITY. We will now consider, as far as we can, the causes of the almost universalvariability of our domesticated productions. The subject is an obscure one;but it may be useful to probe our ignorance. Some authors, for instance Dr. Prosper Lucas, look at variability as a necessary contingent onreproduction, and as much an aboriginal law, as growth or inheritance. Others have of late encouraged, perhaps unintentionally, this view byspeaking of inheritance and variability as equal and antagonisticprinciples. Pallas maintained, and he has had some followers, thatvariability depends exclusively on the crossing of primordially distinctforms. Other authors attribute the tendency to variability to an excess offood, and with animals to an excess relatively to the amount of exercisetaken, or again to the effects of a more genial climate. That these causesare all effective is highly probable. But we must, I think, take a broaderview, and conclude that organic beings, when subjected during severalgenerations to any change whatever in their conditions, tend to vary; thekind of variation which ensues depending in a far higher degree on thenature or constitution of the being, than on the nature of the changedconditions. {251} Those authors who believe that it is a law of nature that each individualshould differ in some slight degree from every other, may maintain, apparently with truth, that this is the fact, not only with alldomesticated animals and cultivated plants, but likewise with all organicbeings in a state of nature. The Laplander by long practice knows and givesa name to each reindeer, though, as Linnæus remarks, "to distinguish onefrom another among such multitudes was beyond my comprehension, for theywere like ants on an ant-hill. " In Germany shepherds have won wagers byrecognising each sheep in a flock of a hundred, which they had never seenuntil the previous fortnight. This power of discrimination, however, is asnothing compared to that which some florists have acquired. Verlot mentionsa gardener who could distinguish 150 kinds of camellia, when not in flower;and it has been positively asserted that the famous old Dutch floristVoorhelm, who kept above 1200 varieties of the hyacinth, was hardly everdeceived in knowing each variety by the bulb alone. Hence we must concludethat the bulbs of the hyacinth and the branches and leaves of the camellia, though appearing to an unpractised eye absolutely undistinguishable, yetreally differ. [603] As Linnæus has compared the reindeer in number to ants, I may add that eachant knows its fellow of the same community. Several times I carried ants ofthe same species (_Formica rufa_) from one ant-hill to another, inhabitedapparently by tens of thousands of ants; but the strangers were instantlydetected and killed. I then put some ants taken from a very large nest intoa bottle strongly perfumed with assafoetida, and after an interval oftwenty-four hours returned them to their home; they were at firstthreatened by their fellows, but were soon recognised and allowed to pass. Hence each ant certainly recognises, independently of odour, its fellow;and if all the ants of the same community have not some countersign orwatchword, they must present to each other's senses some distinguishablecharacter. {252} The dissimilarity of brothers or sisters of the same family, and ofseedlings from the same capsule, may be in part accounted for by theunequal blending of the characters of the two parents, and by the more orless complete recovery through reversion of ancestral characters on eitherside; but we thus only push the difficulty further back in time, for whatmade the parents or their progenitors different? Hence the belief[604] thatan innate tendency to vary exists, independently of external conditions, seems at first sight probable. But even the seeds nurtured in the samecapsule are not subjected to absolutely uniform conditions, as they drawtheir nourishment from different points; and we shall see in a futurechapter that this difference sometimes suffices greatly to affect thecharacter of the future plant. The less close similarity of the successivechildren of the same family in comparison with human twins, which oftenresemble each other in external appearance, mental disposition, andconstitution, in so extraordinary a manner, apparently proves that thestate of the parents at the exact period of conception, or the nature ofthe subsequent embryonic development, has a direct and powerful influenceon the character of the offspring. Nevertheless, when we reflect on the{253} individual differences between organic beings in a state of nature, as shown by every wild animal knowing its mate; and when we reflect on theinfinite diversity of the many varieties of our domesticated productions, we may well be inclined to exclaim, though falsely as I believe, thatVariability must be looked at as an ultimate fact, necessarily contingenton reproduction. Those authors who adopt this latter view would probably deny that eachseparate variation has its own proper exciting cause. Although we canseldom trace the precise relation between cause and effect, yet theconsiderations presently to be given lead to the conclusion that eachmodification must have its own distinct cause. When we hear of an infantborn, for instance, with a crooked finger, a misplaced tooth, or otherslight deviation of structure, it is difficult to bring the conviction hometo the mind that such abnormal cases are the result of fixed laws, and notof what we blindly call accident. Under this point of view the followingcase, which has been carefully examined and communicated to me by Dr. William Ogle, is highly instructive. Two girls, born as twins, and in allrespects extremely alike, had their little fingers on both hands crooked;and in both children the second bicuspid tooth in the upper jaw, of thesecond dentition, was misplaced; for these teeth, instead of standing in aline with the others, grew from the roof of the mouth behind the firstbicuspids. Neither the parents nor any other member of the family hadexhibited any similar peculiarity. Now, as both these children wereaffected in exactly the same manner by both deviations of structure, theidea of accident is at once excluded; and we are compelled to admit thatthere must have existed some precise and sufficient cause which, if it hadoccurred a hundred times, would have affected a hundred children. We will now consider the general arguments, which appear to me to havegreat weight, in favour of the view that variations of all kinds anddegrees are directly or indirectly caused by the conditions of life towhich each being, and more especially its ancestors, have been exposed. No one doubts that domesticated productions are more variable than organicbeings which have never been removed from their {254} natural conditions. Monstrosities graduate so insensibly into mere variations that it isimpossible to separate them; and all those who have studied monstrositiesbelieve that they are far commoner with domesticated than with wild animalsand plants;[605] and in the case of plants, monstrosities would be equallynoticeable in the natural as in the cultivated state. Under nature, theindividuals of the same species are exposed to nearly uniform conditions, for they are rigorously kept to their proper places by a host of competinganimals and plants; they have, also, long been habituated to theirconditions of life; but it cannot be said that they are subject to quiteuniform conditions, and they are liable to a certain amount of variation. The circumstances under which our domestic productions are reared arewidely different: they are protected from competition; they have not onlybeen removed from their natural conditions and often from their nativeland, but they are frequently carried from district to district, where theyare treated differently, so that they never remain during a considerablelength of time exposed to closely similar conditions. In conformity withthis, all our domesticated productions, with the rarest exceptions, varyfar more than natural species. The hive-bee, which feeds itself and followsin most respects its natural habits of life, is the least variable of alldomesticated animals, and probably the goose is the next least variable;but even the goose varies more than almost any wild bird, so that it cannotbe affiliated with perfect certainty to any natural species. Hardly asingle plant can be named, which has long been cultivated and propagated byseed, that is not highly variable; common rye (_Secale cereale_) hasafforded fewer and less marked varieties than almost any other cultivatedplant;[606] but it may be doubted whether the variations of this, the leastvaluable of all our cereals, have been closely observed. Bud-variation, which was fully discussed in a former chapter, shows us thatvariability may be quite independent of seminal reproduction, and likewiseof reversion to long-lost ancestral characters. No one will maintain thatthe sudden appearance {255} of a moss-rose on a Provence-rose is a returnto a former state, for mossiness of the calyx has been observed in nonatural species; the same argument is applicable to variegated andlaciniated leaves; nor can the appearance of nectarines on peach-trees beaccounted for with any probability on the principle of reversion. Butbud-variations more immediately concern us, as they occur far morefrequently on plants which have been highly cultivated during a length oftime, than on other and less highly cultivated plants; and very fewwell-marked instances have been observed with plants growing under strictlynatural conditions. I have given one instance of an ash-tree growing in agentleman's pleasure-grounds; and occasionally there may be seen, on beechand other trees, twigs leafing at a different period from the otherbranches. But our forest trees in England can hardly be considered asliving under strictly natural conditions; the seedlings are raised andprotected in nursery-grounds, and must often be transplanted into placeswhere wild trees of the kind would not naturally grow. It would be esteemeda prodigy if a dog-rose growing in a hedge produced by bud-variation amoss-rose, or a wild bullace or wild cherry-tree yielded a branch bearingfruit of a different shape and colour from the ordinary fruit. The prodigywould be enhanced if these varying branches were found capable ofpropagation, not only by grafts, but sometimes by seed; yet analogous caseshave occurred with many of our highly cultivated trees and herbs. These several considerations alone render it probable that variability ofevery kind is directly or indirectly caused by changed conditions of life. Or, to put the case under another point of view, if it were possible toexpose all the individuals of a species during many generations toabsolutely uniform conditions of life, there would be no variability. _On the Nature of the Changes in the Conditions of Life which induceVariability. _ From a remote period to the present day, under climates and circumstancesas different as it is possible to conceive, organic beings of all kinds, when domesticated or cultivated, have {256} varied. We see this with themany domestic races of quadrupeds and birds belonging to different orders, with gold-fish and silkworms, with plants of many kinds, raised in variousquarters of the world. In the deserts of northern Africa the date-palm hasyielded thirty-eight varieties; in the fertile plains of India it isnotorious how many varieties of rice and of a host of other plants exist;in a single Polynesian island, twenty-four varieties of the bread-fruit, the same number of the banana, and twenty-two varieties of the arum, arecultivated by the natives; the mulberry-tree in India and Europe hasyielded many varieties serving as food for the silkworm; and in Chinasixty-three varieties of the bamboo are used for various domesticpurposes. [607] These facts alone, and innumerable others could be added, indicate that a change of almost any kind in the conditions of lifesuffices to cause variability--different changes acting on differentorganisms. Andrew Knight[608] attributed the variation of both animals and plants to amore abundant supply of nourishment, or to a more favourable climate, thanthat natural to the species. A more genial climate, however, is far fromnecessary; the kidney-bean, which is often injured by our spring frosts, and peaches, which require the protection of a wall, have varied much inEngland, as has the orange-tree in northern Italy, where it is barely ableto exist. [609] Nor can we overlook the fact, though not immediatelyconnected with our present subject, that the plants and shells of thearctic regions are eminently variable. [610] Moreover, it does not appearthat a change of climate, whether more or less genial, is one of the mostpotent causes of variability; for in regard to plants Alph. De Candolle, inhis 'Géographie {257} Botanique, ' repeatedly shows that the native countryof a plant, where in most cases it has been longest cultivated, is thatwhere it has yielded the greatest number of varieties. It is doubtful whether a change in the nature of the food is a potent causeof variability. Scarcely any domesticated animal has varied more than thepigeon or the fowl, but their food, especially that of highly-bred pigeons, is generally the same. Nor can our cattle and sheep have been subjected toany great change in this respect. But in all these cases the food probablyis much less varied in kind than that which was consumed by the species inits natural state. [611] Of all the causes which induce variability, excess of food, whether or notchanged in nature, is probably the most powerful. This view was held withregard to plants by Andrew Knight, and is now held by Schleiden, moreespecially in reference to the inorganic elements of the food. [612] Inorder to give a plant more food it suffices in most cases to grow itseparately, and thus prevent other plants robbing its roots. It issurprising, as I have often seen, how vigorously our common wild plantsflourish when planted by themselves, though not in highly manured land. Growing plants separately is, in fact, the first step in cultivation. Wesee the converse of the belief that excess of food induces variability inthe following statement by a great raiser of seeds of all kinds. [613] "Itis a rule invariably with us, when we desire to keep a true stock of anyone kind of seed, to grow it on poor land without dung; but when we growfor quantity, we act contrary, and sometimes have dearly to repent of it. " In the case of animals the want of a proper amount of exercise, asBechstein has remarked, has perhaps played, independently of the directeffects of the disuse of any particular organ, an important part in causingvariability. We can see in a vague manner that, when the organised andnutrient fluids of the body are not used during growth, or by the wear andtear of the tissues, {258} they will be in excess; and as growth, nutrition, and reproduction are intimately allied processes, thissuperfluity might disturb the due and proper action of the reproductiveorgans, and consequently affect the character of the future offspring. Butit may be argued that neither an excess of food nor a superfluity in theorganised fluids of the body necessarily induces variability. The goose andthe turkey have been well fed for many generations, yet have varied verylittle. Our fruit-trees and culinary plants, which are so variable, havebeen cultivated from an ancient period, and, though they probably stillreceive more nutriment than in their natural state, yet they must havereceived during many generations nearly the same amount; and it might bethought that they would have become habituated to the excess. Nevertheless, on the whole, Knight's view, that excess of food is one of the most potentcauses of variability, appears, as far as I can judge, probable. Whether or not our various cultivated plants have received nutriment inexcess, all have been exposed to changes of various kinds. Fruit-trees aregrafted on different stocks, and grown in various soils. The seeds ofculinary and agricultural plants are carried from place to place; andduring the last century the rotation of our crops and the manures used havebeen greatly changed. Slight changes of treatment often suffice to induce variability. The simplefact of almost all our cultivated plants and domesticated animals havingvaried in all places and at all times, leads to this conclusion. Seedstaken from common English forest-trees, grown under their native climate, not highly manured or otherwise artificially treated, yield seedlings whichvary much, as may be seen in every extensive seed-bed. I have shown in aformer chapter what a number of well marked and singular varieties thethorn (_Cratægus oxyacantha_) has produced; yet this tree has beensubjected to hardly any cultivation. In Staffordshire I carefully examineda large number of two British plants, namely, _Geranium phæum_ and_Pyrenaicum_, which have never been highly cultivated. These plants hadspread spontaneously by seed from a common garden into an open plantation;and the seedlings varied in almost every single character, both in theirflowers and foliage, to a degree which {259} I have never seen exceeded;yet they could not have been exposed to any great change in theirconditions. With respect to animals, Azara has remarked with much surprise, [614] that, whilst the feral horses on the Pampas are always of one of three colours, and the cattle always of a uniform colour, yet these animals, when bred onthe unenclosed estancias, though kept in a state which can hardly be calleddomesticated, and apparently exposed to almost identically the sameconditions as when they are feral, nevertheless display a great diversityof colour. So again in India several species of fresh-water fish are onlyso far treated artificially, that they are reared in great tanks; but thissmall change is sufficient to induce much variability. [615] Some facts on the effects of grafting, in regard to the variability oftrees, deserve attention. Cabanis asserts that when certain pears aregrafted on the quince, their seeds yield more varieties than do the seedsof the same variety of pear when grafted on the wild pear. [616] But as thepear and quince are distinct species, though so closely related that theone can be readily grafted and succeeds admirably on the other, the fact ofvariability being thus caused is not surprising; we are, however, hereenabled to see the cause, namely, the different nature of the stock withits roots and the rest of the tree. Several North American varieties of theplum and peach are well known to reproduce themselves truly by seed; butDowning asserts, [617] "that when a graft is taken from one of these treesand placed upon another stock, this grafted tree is found to lose itssingular property of producing the same variety by seed, and becomes likeall other worked trees;"--that is, its seedlings become highly variable. Another case is worth giving: the Lalande variety of the walnut-tree leafsbetween April 20th and May 15th, and its seedlings invariably inherit thesame habit; whilst several other varieties of the walnut leaf in June. Now, if seedlings are raised from the May-leafing Lalande variety, grafted onanother May-leafing variety, though both stock and graft have the sameearly habit of leafing, yet the seedlings leaf at various times, {260} evenas late as the 5th of June. [618] Such facts as these are well fitted toshow, on what obscure and slight causes variability rests. I may here just allude to the appearance of new and valuable varieties of fruit-trees and of wheat in woods and waste places, which at first sight seems a most anomalous circumstance. In France a considerable number of the best pears have been discovered in woods; and this has occurred so frequently, that Poiteau asserts that "improved varieties of our cultivated fruits rarely originate with nurserymen. "[619] In England, on the other hand, no instance of a good pear having been found wild has been recorded; and Mr. Rivers informs me that he knows of only one instance with apples, namely, the Bess Poole, which was discovered in a wood in Nottinghamshire. This difference between the two countries may be in part accounted for by the more favourable climate of France, but chiefly from the great number of seedlings which spring up there in the woods. I infer that this is the case from a remark made by a French gardener, [620] who regards it as a national calamity that such a number of pear-trees are periodically cut down for firewood, before they have borne fruit. The new varieties which thus spring up in the woods, though they cannot have received any excess of nutriment, will have been exposed to abruptly changed conditions, but whether this is the cause of their production is very doubtful. These varieties, however, are probably all descended[621] from old cultivated kinds growing in adjoining orchards, --a circumstance which will account for their variability; and out of a vast number of varying trees there will always be a good chance of the appearance of a valuable kind. In North America, where fruit-trees frequently spring up in waste places, the Washington pear was found in a hedge, and the Emperor peach in a wood. [622] With respect to wheat, some writers have spoken[623] as if it were an ordinary event for new varieties to be found in waste places; the Fenton wheat was certainly discovered growing on a pile of basaltic detritus in a quarry, but in such a situation the plant would probably receive a sufficient amount {261} of nutriment. The Chidham wheat was raised from an ear found _on_ a hedge; and Hunter's wheat was discovered _by_ the roadside in Scotland, but it is not said that this latter variety grew where it was found. [624] Whether our domestic productions would ever become so completely habituatedto the conditions under which they now live, as to cease varying, we haveno sufficient means for judging. But, in fact, our domestic productions arenever exposed for a great length of time to uniform conditions, and it iscertain that our most anciently cultivated plants, as well as animals, still go on varying, for all have recently undergone marked improvement. Insome few cases, however, plants have become habituated to new conditions. Thus Metzger, who cultivated in Germany during many years numerousvarieties of wheat, brought from different countries, [625] states that somekinds were at first extremely variable, but gradually, in one instanceafter an interval of twenty-five years, became constant; and it does notappear that this resulted from the selection of the more constant forms. * * * * * _On the Accumulative Action of changed Conditions of Life. _--We have goodgrounds for believing that the influence of changed conditions accumulates, so that no effect is produced on a species until it has been exposed duringseveral generations to continued cultivation or domestication. Universalexperience shows us that when new flowers are first introduced into ourgardens they do not vary; but ultimately all, with the rarest exceptions, vary to a greater or less extent. In a few cases the requisite number ofgenerations, as well as the successive steps in the progress of variation, have been recorded, as in the often-quoted instance of the Dahlia. [626]After several years' culture the Zinnia has only lately (1860) begun tovary in any great degree. "In the first seven or eight years of highcultivation the Swan River daisy (_Brachycome iberidifolia_) kept to itsoriginal colour; it then varied into lilac and purple and other minorshades. "[627] Analogous facts have been recorded with the Scotch rose. Indiscussing the variability of plants several experienced horticulturistshave spoken to the {262} same general effect. Mr. Salter[628] remarks, "Every one knows that the chief difficulty is in breaking through theoriginal form and colour of the species, and every one will be on thelook-out for any natural sport, either from seed or branch; that being onceobtained, however trifling the change may be, the result depends uponhimself. " M. De Jonghe, who has had so much success in raising newvarieties of pears and strawberries, [629] remarks with respect to theformer, "There is another principle, namely, that the more a type hasentered into a state of variation, the greater is its tendency to continuedoing so; and the more it has varied from the original type, the more it isdisposed to vary still farther. " We have, indeed, already discussed thislatter point when treating of the power which man possesses, throughselection, of continually augmenting in the same direction eachmodification; for this power depends on continued variability of the samegeneral kind. The most celebrated horticulturist in France, namely, Vilmorin, [630] even maintains that, when any particular variation isdesired, the first step is to get the plant to vary in any manner whatever, and to go on selecting the most variable individuals, even though they varyin the wrong direction; for the fixed character of the species being oncebroken, the desired variation will sooner or later appear. As nearly all our animals were domesticated at an extremely remote epoch, we cannot, of course, say whether they varied quickly or slowly when firstsubjected to new conditions. But Dr. Bachman[631] states that he has seenturkeys raised from the eggs of the wild species lose their metallic tintsand become spotted with white in the third generation. Mr. Yarrell manyyears ago informed me that the wild ducks bred on the ponds in St. James'sPark, which had never been crossed, as it is believed, with domestic ducks, lost their true plumage after a few generations. An excellentobserver, [632] who has often reared birds from the eggs of the wild duck, and who took precautions {263} that there should be no crossing withdomestic breeds, has given, as previously stated, full details on thechanges which they gradually undergo. He found that he could not breedthese wild ducks true for more than five or six generations, "as they thenproved so much less beautiful. The white collar round the neck of themallard became much broader and more irregular, and white feathers appearedin the ducklings' wings. " They increased also in size of body; their legsbecame less fine, and they lost their elegant carriage. Fresh eggs werethen procured from wild birds; but again the same result followed. In thesecases of the duck and turkey we see that animals, like plants, do notdepart from their primitive type until they have been subjected duringseveral generations to domestication. On the other hand, Mr. Yarrellinformed me that the Australian dingos, bred in the Zoological Gardens, almost invariably produced in the first generation puppies marked withwhite and other colours; but these introduced dingos had probably beenprocured from the natives, who keep them in a semi-domesticated state. Itis certainly a remarkable fact that changed conditions should at firstproduce, as far as we can see, absolutely no effect; but that they shouldsubsequently cause the character of the species to change. In the chapteron pangenesis I shall attempt to throw a little light on this fact. * * * * * Returning now to the causes which are supposed to induce variability. Someauthors[633] believe that close interbreeding gives this tendency, andleads to the production of monstrosities. In the seventeenth chapter somefew facts were advanced, showing that monstrosities are, as it appears, occasionally thus caused; and there can be no doubt that closeinterbreeding induces lessened fertility and a weakened constitution; henceit may lead to variability: but I have not sufficient evidence on thishead. On the other hand, close interbreeding, if not carried to aninjurious extreme, far from causing variability, tends to fix the characterof each breed. It was formerly a common belief, still held by some persons, that theimagination of the mother affects the child in {264} the womb. [634] Thisview is evidently not applicable to the lower animals, which layunimpregnated eggs, or to plants. Dr. William Hunter, in the last century, told my father that during many years every woman in a large LondonLying-in Hospital was asked before her confinement whether anything hadspecially affected her mind, and the answer was written down; and it sohappened that in no one instance could a coincidence be detected betweenthe woman's answer and any abnormal structure; but when she knew the natureof the structure, she frequently suggested some fresh cause. The belief inthe power of the mother's imagination may perhaps have arisen from thechildren of a second marriage resembling the previous father, as certainlysometimes occurs, in accordance with the facts given in the eleventhchapter. * * * * * _Crossing as a Cause of Variability. _--In an early part of this chapter itwas stated that Pallas[635] and a few other naturalists maintain thatvariability is wholly due to crossing. If this means that new charactersnever spontaneously appear in our domestic races, but that they are alldirectly derived from certain aboriginal species, the doctrine is littleless than absurd; for it implies that animals like Italian greyhounds, pug-dogs, bull-dogs, pouter and fantail pigeons, &c. , were able to exist ina state of nature. But the doctrine may mean something widely different, namely, that the crossing of distinct species is the sole cause of thefirst appearance of new characters, and that without this aid man could nothave formed his various breeds. As, however, new characters have appearedin certain cases by bud-variation, we may conclude with certainty thatcrossing is not necessary for variability. It is, moreover, almost certainthat the breeds of various animals, such as of the rabbit, pigeon, duck, &c. , and the varieties of several plants, are the modified descendants of asingle wild species. Nevertheless, it is probable that the crossing of twoforms, when one or both have long been domesticated or cultivated, adds tothe variability of the offspring, independently of the commingling of thecharacters derived from the two parent-forms; and this implies {265} thatnew characters actually arise. But we must not forget the facts advanced inthe thirteenth chapter, which clearly prove that the act of crossing oftenleads to the reappearance or reversion of long-lost characters; and in mostcases it would be impossible to distinguish between the reappearance ofancient characters and the first appearance of new characters. Practically, whether new or old, they would be new to the breed in which theyreappeared. Gärtner declares, [636] and his experience is of the highest value on such a point, that, when he crossed native plants which had not been cultivated, he never once saw in the offspring any new character; but that from the odd manner in which the characters derived from the parents were combined, they sometimes appeared as if new. When, on the other hand, he crossed cultivated plants, he admits that new characters occasionally appeared, but he is strongly inclined to attribute their appearance to ordinary variability, not in any way to the cross. An opposite conclusion, however, appears to me the more probable. According to Kölreuter, hybrids in the genus Mirabilis vary almost infinitely, and he describes new and singular characters in the form of the seeds, in the colour of the anthers, in the cotyledons being of immense size, in new and highly peculiar odours, in the flowers expanding early in the season, and in their closing at night. With respect to one lot of these hybrids, he remarks that they presented characters exactly the reverse of what might have been expected from their parentage. [637] Prof. Lecoq[638] speaks strongly to the same effect in regard to this same genus, and asserts that many of the hybrids from _Mirabilis jalapa_ and _multiflora_ might easily be mistaken for distinct species, and adds that they differed in a greater degree, than the other species of the genus, from _M. Jalapa_. Herbert, also, has described[639] the offspring from a hybrid Rhododendron as being "as _unlike all others_ in foliage, as if they had been a separate species. " The common experience of floriculturists proves that the crossing and recrossing of distinct but allied plants, such as the species of Petunia, Calceolaria, Fuchsia, Verbena, &c. , induces excessive variability; hence the appearance of quite new characters is probable. M. Carrière[640] has lately discussed this subject: he states that _Erythrina cristagalli_ had been multiplied by seed for many years, but had not yielded any varieties: it was then crossed with the allied _E. Herbacea_, and "the resistance was now overcome, and varieties were produced with flowers of extremely different size, form, and colour. " From the general and apparently well-founded belief that the crossing {266} of distinct species, besides commingling their characters, adds greatly to their variability, it has probably arisen that some botanists have gone so far as to maintain[641] that, when a genus includes only a single species, this when cultivated never varies. The proposition made so broadly cannot be admitted; but it is probably true that the variability of cultivated monotypic genera is much less than that of genera including numerous species, and this quite independently of the effects of crossing. I have stated in my 'Origin of Species, ' and in a future work shall more fully show, that the species belonging to small genera generally yield a less number of varieties in a state of nature than those belonging to large genera. Hence the species of small genera would, it is probable, produce fewer varieties under cultivation than the already variable species of larger genera. Although we have not at present sufficient evidence that the crossing of species, which have never been cultivated, leads to the appearance of new characters, this apparently does occur with species which have been already rendered in some degree variable through cultivation. Hence crossing, like any other change in the conditions of life, seems to be an element, probably a potent one, in causing variability. But we seldom have the means of distinguishing, as previously remarked, between the appearance of really new characters and the reappearance of long-lost characters, evoked through the act of crossing. I will give an instance of the difficulty in distinguishing such cases. The species of Datura may be divided into two sections, those having white flowers with green stems, and those having purple flowers with brown stems: now Naudin[642] crossed _Datura lævis_ and _ferox_, both of which belong to the white section, and raised from them 205 hybrids. Of these hybrids, every one had brown stems and bore purple flowers; so that they resembled the species of the other section of the genus, and not their own two parents. Naudin was so much astonished at this fact, that he was led carefully to observe both parent-species, and he discovered that the pure seedlings of _D. Ferox_, immediately after germination, had dark purple stems, extending from the young roots up to the cotyledons, and that this tint remained ever afterwards as a ring round the base of the stem of the plant when old. Now I have shown in the thirteenth chapter that the retention or exaggeration of an early character is so intimately related to reversion, that it evidently comes under the same principle. Hence probably we ought to look at the purple flowers and brown stems of these hybrids, not as new characters due to variability, but as a return to the former state of some ancient progenitor. Independently of the appearance of new characters from crossing, a few words may be added to what has been said in former chapters on the unequal combination and transmission of the characters proper to the two parent-forms. When two species or races are crossed, the offspring of {267} the first generation are generally uniform, but subsequently they display an almost infinite diversity of character. He who wishes, says Kölreuter, [643] to obtain an endless number of varieties from hybrids should cross and recross them. There is also much variability when hybrids or mongrels are reduced or absorbed by repeated crosses with either pure parent-form; and a still higher degree of variability when three distinct species, and most of all when four species, are blended together by successive crosses. Beyond this point Gärtner, [644] on whose authority the foregoing statements are made, never succeeded in effecting a union; but Max Wichura[645] united six distinct species of willows into a single hybrid. The sex of the parent-species affects in an inexplicable manner the degree of variability of hybrids; for Gärtner[646] repeatedly found that when a hybrid was used as the father, and either one of the pure parent-species, or a third species, was used as the mother, the offspring were more variable than when the same hybrid was used as the mother, and either pure parent or the same third species as the father: thus seedlings from _Dianthus barbatus_ crossed by the hybrid _D. Chinensi-barbatus_ were more variable than those raised from this latter hybrid fertilised by the pure _D. Barbatus_. Max Wichura[647] insists strongly on an analogous result with his hybrid willows. Again Gärtner[648] asserts that the degree of variability sometimes differs in hybrids raised from reciprocal crosses between the same two species; and here the sole difference is, that the one species is first used as the father and then as the mother. On the whole we see that, independently of the appearance of new characters, the variability of successive crossed generations is extremely complex, partly from the offspring partaking unequally of the characters of the two parent-forms, and more especially from their unequal tendency to revert to these same characters or to those of more ancient progenitors. * * * * * _On the Manner and on the Period of Action of the Causes which induceVariability. _--This is an extremely obscure subject, and we need here onlybriefly consider, firstly, whether inherited variations are caused by theorganisation being directly acted on, or indirectly through thereproductive system; and secondly, at what period of life or growth theyare primarily caused. We shall see in the two following chapters thatvarious agencies, such as an abundant supply of food, exposure to adifferent climate, increased use or disuse of parts, &c. , prolonged duringseveral generations, certainly modify either the whole organisation orcertain organs. This direct action of changed conditions perhaps comes intoplay much more frequently than can be proved, and it is at least clear thatin all cases of {268} bud-variation the action cannot have been through thereproductive system. With respect to the part which the reproductive system takes in causing variability, we have seen in the eighteenth chapter that even slight changes in the conditions of life have a remarkable power in causing a greater or less degree of sterility. Hence it seems not improbable that being generated though a system so easily affected should themselves be affected, or should fail to inherit, or inherit in excess, characters proper to their parents. We know that certain groups of organic beings, but with exceptions in each group, have their reproductive systems much more easily affected by changed conditions than other groups; for instance, carnivorous birds more readily than carnivorous mammals, and parrots more readily than pigeons; and this fact harmonizes with the apparently capricious manner and degree in which various groups of animals and plants vary under domestication. Kölreuter[649] was struck with the parallelism between the excessive variability of hybrids when crossed and recrossed in various ways, --these hybrids having their reproductive powers more or less affected, --and the variability of anciently cultivated plants. Max Wichura[650] has gone one step farther, and shows that with many of our highly cultivated plants, such as the hyacinth, tulip, auricula, snapdragon, potato, cabbage, &c. , which there is no reason to believe have been hybridized, the anthers contain many irregular pollen-grains, in the same state as in hybrids. He finds also in certain wild forms, the same coincidence between the state of the pollen and a high degree of variability, as in many species of Rubus; but in _R. Cæsius_ and _idæus_, which are not highly variable species, the pollen is sound. It is also notorious that many cultivated plants, such as the banana, pine-apple, breadfruit, and others previously mentioned, have their reproductive organs so seriously affected as to be generally quite sterile; and when they do yield seed, the seedlings, judging from the large number of cultivated races which exist, must be variable in an extreme degree. These facts indicate that there is some relation between the state of the reproductive organs and a tendency to variability; but we must not conclude that the relation is strict. Although many of our highly cultivated plants may have their pollen in a deteriorated condition, yet, as we have previously seen, they yield more seed, and our anciently domesticated animals are more prolific, than the corresponding species in a state of nature. The peacock is almost the only bird which is believed to be less fertile under domestication than in its native state, and it has varied in a remarkably small degree. From these considerations it would seem that changes in the conditions of life lead either to sterility or to variability, or to both; and not that sterility induces variability. On the whole it is probable that any cause affecting the organs of reproduction would likewise affect their product, --that is, the offspring thus generated. {269} The period of life at which the causes that induce variability act, is another obscure subject, which has been discussed by various authors. [651] In some of the cases, to be given in the following chapter, of modifications from the direct action of changed conditions, which are inherited, there can be no doubt that the causes have acted on the mature or nearly mature animal. On the other hand, monstrosities, which cannot be distinctly separated from lesser variations, are often caused by the embryo being injured whilst in the mother's womb or in the egg. Thus I. Geoffroy St. Hilaire[652] asserts that poor women who work hard during their pregnancy, and the mothers of illegitimate children troubled in their minds and forced to conceal their state, are far more liable to give birth to monsters than women in easy circumstances. The eggs of the fowl when placed upright or otherwise treated unnaturally frequently produce monstrous chickens. It would, however, appear that complex monstrosities are induced more frequently during a rather late than during a very early period of embryonic life; but this may partly result from some one part, which has been injured during an early period, affecting by its abnormal growth other parts subsequently developed; and this would be less likely to occur with parts injured at a later period. [653] When any part or organ becomes monstrous through abortion, a rudiment is generally left, and this likewise indicates that its development had already commenced. Insects sometimes have their antennæ or legs in a monstrous condition, and yet the larvæ from which they are metamorphosed do not possess either antennæ or legs; and in those cases, as Quatrefages[654] believes, we are enabled to see the precise period at which the normal progress of development has been troubled. But the nature of the food given to a caterpillar sometimes affects the colours of the moth, without the caterpillar itself being affected; therefore it seems possible that other characters in the mature insect might be indirectly modified through the larvæ. There is no reason to suppose that organs which have been rendered monstrous have always been acted on during their development; the cause may have acted on the organisation at a much earlier stage. It is even probable that either the male or female sexual elements, or both, before their union, may be affected in such a manner as to lead to modifications in organs developed at a late period of life; in nearly the same manner as a child may inherit from his father a disease which does not appear until old age. In accordance with the facts above given, which prove that in many cases a close relation exists between variability and the sterility following from changed conditions, we may conclude that the exciting cause often acts at the earliest possible period, namely, on the sexual elements, before impregnation has taken place. That an affection of the female sexual element may induce variability we may likewise infer as probable from the occurrence of bud-variations; for a bud seems to be the analogue of an ovule. But the male element is apparently much oftener affected by changed {270} conditions, at least in a visible manner, than the female element or ovule; and we know from Gärtner's and Wichura's statements that a hybrid used as the father and crossed with a pure species gives a greater degree of variability to the offspring, than does the same hybrid when used as the mother. Lastly, it is certain that variability may be transmitted through either sexual element, whether or not originally excited in them, for Kölreuter and Gärtner[655] found that when two species were crossed, if either one was variable, the offspring were rendered variable. * * * * * _Summary. _--From the facts given in this chapter, we may conclude that thevariability of organic beings under domestication, although so general, isnot an inevitable contingent on growth and reproduction, but results fromthe conditions to which the parents have been exposed. Changes of any kindin the conditions of life, even extremely slight changes, often suffice tocause variability. Excess of nutriment is perhaps the most efficient singleexciting cause. Animals and plants continue to be variable for an immenseperiod after their first domestication; but the conditions to which theyare exposed never long remain quite constant. In the course of time theycan be habituated to certain changes, so as to become less variable; and itis possible that when first domesticated they may have been even morevariable than at present. There is good evidence that the power of changedconditions accumulates; so that two, three, or more generations must beexposed to new conditions before any effect is visible. The crossing ofdistinct forms, which have already become variable, increases in theoffspring the tendency to further variability, by the unequal comminglingof the characters of the two parents, by the reappearance of long-lostcharacters, and by the appearance of absolutely new characters. Somevariations are induced by the direct action of the surrounding conditionson the whole organisation, or on certain parts alone, and other variationsare induced indirectly through the reproductive system being affected inthe same manner as is so common with organic beings when removed from theirnatural conditions. The causes which induce variability act on the matureorganism, on the embryo, and, as we have good reason to believe, on bothsexual elements before impregnation has been effected. * * * * * {271} CHAPTER XXIII. DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF LIFE. SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED CONDITIONS IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE TISSUES--LOCAL DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR FOOD, ETC. --PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE INOCULATION OF POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL CONDITIONS--COMPARISON OF AMERICAN AND EUROPEAN TREES--GALLS--EFFECTS OF PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL SERIES OF VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF CHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BY UNNATURAL TREATMENT--SUMMARY. If we ask ourselves why this or that character has been modified underdomestication, we are, in most cases lost in utter darkness. Manynaturalists, especially of the French school, attribute every modificationto the "monde ambiant, " that is, to changed climate, with all itsdiversities of heat and cold, dampness and dryness, light and electricity, to the nature of the soil, and to varied kinds and amount of food. By theterm definite action, as used in this chapter, I mean an action of such anature that, when many individuals of the same variety are exposed duringseveral generations to any change in their physical conditions of life, all, or nearly all the individuals, are modified in the same manner. A newsub-variety would thus be produced without the aid of selection. I do not include under the term of definite action the effects of habit orof the increased use and disuse of various organs. Modifications of thisnature, no doubt, are definitely caused by the conditions to which thebeings are subjected; but they depend much less on the nature of theconditions than on the laws of growth; hence they are included under adistinct head in the {272} following chapter. We know, however, far toolittle of the causes and laws of variation to make a sound classification. The direct action of the conditions of life, whether leading to definite orindefinite results, is a totally distinct consideration from the effects ofnatural selection; for natural selection depends on the survival undervarious and complex circumstances of the best-fitted individuals, but hasno relation whatever to the primary cause of any modification of structure. I will first give in detail all the facts which I have been able tocollect, rendering it probable that climate, food, &c. , have acted sodefinitely and powerfully on the organisation of our domesticatedproductions, that they have sufficed to form new sub-varieties or races, without the aid of selection by man or of natural selection. I will thengive the facts and considerations opposed to this conclusion, and finallywe will weigh, as fairly as we can, the evidence on both sides. When we reflect that distinct races of almost all our domesticated animalsexist in each kingdom of Europe, and formerly even in each district ofEngland, we are at first strongly inclined to attribute their origin to thedefinite action of the physical conditions of each country; and this hasbeen the conclusion of many authors. But we should bear in mind that manannually has to choose which animals shall be preserved for breeding, andwhich shall be slaughtered. We have also seen that both methodical andunconscious selection were formerly practised, and are now occasionallypractised by the most barbarous races, to a much greater extent than mighthave been anticipated. Hence it is very difficult to judge how far thedifference in conditions between, for instance, the several districts inEngland, could have sufficed without the aid of selection to modify thebreeds which have been reared in each. It may be argued that, as numerouswild animals and plants have ranged during many ages throughout GreatBritain, and still retain the same character, the difference in conditionsbetween the several districts could not have modified in so marked a mannerthe various native races of cattle, sheep, pigs, and horses. The samedifficulty of distinguishing between selection and the definite effects ofthe conditions of life, is encountered in a still higher degree when wecompare closely allied natural {273} forms, inhabiting two countries, suchas North America and Europe, which do not differ greatly in climate, natureof soil, &c. , for in this case natural selection will inevitably andrigorously have acted during a long succession of ages. From the importance of the difficulty just alluded to, it will be advisable to give as large a body of facts as possible, showing that extremely slight differences in treatment, either in different parts of the same country, or during different seasons, certainly cause an appreciable effect, at least on varieties which are already in an unstable condition. Ornamental flowers are good for this purpose, as they are highly variable, and are carefully observed. All floriculturists are unanimous that certain varieties are affected by very slight differences in the nature of the artificial compost in which they are grown, and by the natural soil of the district, and by the season. Thus, a skilful judge, in writing on Carnations and Picotees, [656] asks "where can Admiral Curzon be seen possessing the colour, size, and strength which it has in Derbyshire? Where can Flora's Garland be found equal to those at Slough? Where do high-coloured flowers revel better than at Woolwich and Birmingham? Yet in no two of these districts do the same varieties attain an equal degree of excellence, although each may be receiving the attention of the most skilful cultivators. " The same writer then recommends every cultivator to keep five different kinds of soil and manure, "and to endeavour to suit the respective appetites of the plants you are dealing with, for without such attention all hope of general success will be vain. " So it is with the Dahlia:[657] the Lady Cooper rarely succeeds near London, but does admirably in other districts; the reverse holds good with other varieties; and again, there are others which succeed equally well in various situations. A skilful gardener[658] states that he procured cuttings of an old and well-known variety (pulchella) of Verbena, which from having been propagated in a different situation presented a slightly different shade of colour; the two varieties were afterwards multiplied by cuttings, being carefully kept distinct; but in the second year they could hardly be distinguished, and in the third year no one could distinguish them. The nature of the season has an especial influence on certain varieties of the Dahlia: in 1841 two varieties were pre-eminently good, and the next year these same two were pre-eminently bad. A famous amateur[659] asserts that in 1861 many varieties of the Rose came so untrue in character, "that it was hardly possible to recognise them, and the thought was not seldom entertained that the grower had lost his tally. " The same amateur[660] states that in 1862 two-thirds of his Auriculas produced central trusses of flowers, and these are remarkable from not keeping true; {274} and he adds that in some seasons certain varieties of this plant all prove good, and the next season all prove bad; whilst exactly the reverse happens with other varieties. In 1845 the editor of the 'Gardener's Chronicle'[661] remarked how singular it was that this year many Calceolarias tended to assume a tubular form. With Heartsease[662] the blotched sorts do not acquire their proper character until hot weather sets in; whilst other varieties lose their beautiful marks as soon as this occurs. Analogous facts have been observed with leaves: Mr. Beaton asserts[663] that he raised at Shrubland, during six years, twenty thousand seedlings from the Punch Pelargonium, and not one had variegated leaves; but at Surbiton, in Surrey, one-third, or even a greater proportion, of the seedlings from this same variety were more or less variegated. The soil of another district in Surrey has a strong tendency to cause variegation, as appears from information given me by Sir F. Pollock. Verlot[664] states that the variegated strawberry retains its character as long as grown in a dryish soil, but soon loses it when planted in fresh and humid soil. Mr. Salter, who is well known for his success in cultivating variegated plants, informs me that rows of strawberries were planted in his garden in 1859, in the usual way; and at various distances in one row, several plants simultaneously became variegated, and what made the case more extraordinary, all were variegated in precisely the same manner. These plants were removed, but during the three succeeding years other plants in the same row became variegated, and in no instance were the plants in any adjoining row affected. The chemical qualities, odours, and tissues of plants are often modified by a change which seems to us slight. The Hemlock is said not to yield conicine in Scotland. The root of the _Aconitum napellus_ becomes innocuous in frigid climates. The medicinal properties of the Digitalis are easily affected by culture. The Rhubarb flourishes in England, but does not produce the medicinal substance which makes the plant so valuable in Chinese Tartary. As the _Pistacia lentiscus_ grows abundantly in the South of France, the climate must suit it, but it yields no mastic. The _Laurus sassafras_ in Europe loses the odour proper to it in North America. [665] Many similar facts could be given, and they are remarkable because it might have been thought that definite chemical compounds would have been little liable to change either in quality or quantity. The wood of the American Locust-tree (_Robinia_) when grown in England is nearly worthless, as is that of the Oak-tree when grown at the Cape of Good Hope. [666] Hemp and flax, as I hear from Dr. Falconer, flourish and yield plenty of seed on the plains of India, but their fibres are brittle {275} and useless. Hemp, on the other hand, fails to produce in England that resinous matter which is so largely used in India as an intoxicating drug. The fruit of the Melon is greatly influenced by slight differences in culture and climate. Hence it is generally a better plan, according to Naudin, to improve an old kind than to introduce a new one into any locality. The seed of the Persian Melon produces near Paris fruit inferior to the poorest market kinds, but at Bordeaux yields delicious fruit. [667] Seed is annually brought from Thibet to Kashmir, [668] and produces fruit weighing from four to ten pounds, but plants raised from seed saved in Kashmir next year give fruit weighing only from two to three pounds. It is well known that American varieties of the Apple produce in their native land magnificent and brightly-coloured fruit, but in England of poor quality and a dull colour. In Hungary there are many varieties of the Kidney-bean, remarkable for the beauty of their seeds, but the Rev. M. J. Berkeley[669] found that their beauty could hardly ever be preserved in England, and in some cases the colour was greatly changed. We have seen in the ninth chapter, with respect to wheat, what a remarkable effect transportal from the North to the South of France, and reversely, produced on the weight of the grain. When man can perceive no change in plants or animals which have beenexposed to a new climate or to different treatment, insects can sometimesperceive a marked change. The same species of cactus has been carried toIndia from Canton, Manilla, Mauritius, and from the hot-houses of Kew, andthere is likewise a so-called native kind, formerly introduced from SouthAmerica; all these plants are alike in appearance, but the cochineal insectflourishes only on the native kind, on which it thrives prodigiously. [670]Humboldt remarks[671] that white men "born in the torrid zone walk barefootwith impunity in the same apartment where a European, recently landed, isexposed to the attacks of the _Pulex penetrans_. " This insect, the toowell-known chigoe, must therefore be able to distinguish what the mostdelicate chemical analysis fails to distinguish, namely, a differencebetween the blood or tissues of a European and those of a white man born inthe country. But the discernment of the chigoe is not so surprising as itat first appears; for {276} according to Liebig[672] the blood of men withdifferent complexions, though inhabiting the same country, emits adifferent odour. Diseases peculiar to certain localities, heights, or climates, may be here briefly noticed, as showing the influence of external circumstances on the human body. Diseases confined to certain races of man do not concern us, for the constitution of the race may play the more important part, and this may have been determined by unknown causes. The Plica Polonica stands, in this respect, in a nearly intermediate position; for it rarely affects Germans, who inhabit the neighbourhood of the Vistula, where so many Poles are grievously affected; and on the other hand, it does not affect Russians, who are said to belong to the same original stock with the Poles. [673] The elevation of a district often governs the appearance of diseases; in Mexico the yellow fever does not extend above 924 mètres; and in Peru, people are affected with the _verugas_ only between 600 and 1600 mètres above the sea; many other such cases could be given. A peculiar cutaneous complaint, called the _Bouton d'Alep_, affects in Aleppo and some neighbouring districts almost every native infant, and some few strangers; and it seems fairly well established that this singular complaint depends on drinking certain waters. In the healthy little island of St. Helena the scarlet-fever is dreaded like the Plague; analogous facts have been observed in Chili and Mexico. [674] Even in the different departments of France it is found that the various infirmities which render the conscript unfit for serving in the army, prevail with remarkable inequality, revealing, as Boudin observes, that many of them are endemic, which otherwise would never have been suspected. [675] Any one who will study the distribution of disease will be struck with surprise at what slight differences in the surrounding circumstances govern the nature and severity of the complaints by which man is at least temporarily affected. The modifications as yet referred to have been extremely slight, and inmost cases have been caused, as far as we can judge, by equally slightchanges in the conditions. But can it be safely maintained that suchchanged conditions, if acting during a long series of generations, wouldnot produce a marked effect? It is commonly believed that the people of theUnited States differ in appearance from the parent Anglo-Saxon race; andselection cannot have come into action within so short a period. A goodobserver[676] states that a general absence of fat, {277} a thin andelongated neck, stiff and lank hair, are the chief characteristics. Thechange in the nature of the hair is supposed to be caused by the dryness ofthe atmosphere. If immigration into the United States were now stopped, whocan say that the character of the whole people would not be greatlymodified in the course of two or three thousand years? The direct and definite action of changed conditions, in contradistinction to the accumulation of indefinite variations, seems to me so important that I will give a large additional body of miscellaneous facts. With plants, a considerable change of climate sometimes produces a conspicuous result. I have given in detail in the ninth chapter the most remarkable case known to me, namely, that in Germany several varieties of maize brought from the hotter parts of America were transformed in the course of only two or three generations. Dr. Falconer informs me that he has seen the English Ribston-pippin apple, a Himalayan oak, Prunus and Pyrus, all assume in the hotter parts of India a fastigate or pyramidal habit; and this fact is the more interesting, as a Chinese tropical species of Pyrus naturally has this habit of growth. Although in these cases the changed manner of growth seems to have been directly caused by the great heat, we know that many fastigate trees have originated in their temperate homes. In the Botanic Gardens of Ceylon the apple-tree[677] "sends out numerous runners under ground, which continually rise into small stems, and form a growth around the parent-tree. " The varieties of the cabbage which produce heads in Europe fail to do so in certain tropical countries. [678] The _Rhododendron ciliatum_ produced at Kew flowers so much larger and paler-coloured than those which it bears on its native Himalayan mountain, that Dr. Hooker[679] would hardly have recognised the species by the flowers alone. Many similar facts with respect to the colour and size of flowers could be given. The experiments of Vilmorin and Buckman on carrots and parsnips prove that abundant nutriment produces a definite and inheritable effect on the so-called roots, with scarcely any change in other parts of the plant. Alum directly influences the colour of the flowers of the Hydrangea. [680] Dryness seems generally to favour the hairyness or villosity of plants. Gärtner found that hybrid Verbascums became extremely woolly when grown in pots. Mr. Masters, on the other hand, states that the _Opuntia leucotricha_ "is well clothed with beautiful white hairs when grown in a damp heat; but in a dry heat exhibits none of this peculiarity. "[681] Slight variations of many kinds, not worth specifying in detail, are retained only as {278} long as plants are grown in certain soils, of which Sageret[682] gives from his own experience some instances. Odart, who insists strongly on the permanence of the varieties of the grape, admits[683] that some varieties, when grown under a different climate or treated differently, vary in an extremely slight degree, as in the tint of the fruit and in the period of ripening. Some authors have denied that grafting causes even the slightest difference in the scion; but there is sufficient evidence that the fruit is sometimes slightly affected in size and flavour, the leaves in duration, and the flowers in appearance. [684] With animals there can be no doubt, from the facts given in the first chapter, that European dogs deteriorate in India, not only in their instincts but in structure; but the changes which they undergo are of such a nature, that they may be partly due to reversion to a primitive form, as in the case of feral animals. In parts of India the turkey becomes reduced in size, "with the pendulous appendage over the beak enormously developed. "[685] We have seen how soon the wild duck, when domesticated, loses its true character, from the effects of abundant or changed food, or from taking little exercise. From the direct action of a humid climate and poor pasture the horse rapidly decreases in size in the Falkland Islands. From information which I have received, this seems likewise to be the case to a certain extent with sheep in Australia. Climate definitely influences the hairy covering of animals; in the West Indies a great change is produced in the fleece of sheep, in about three generations. Dr. Falconer states[686] that the Thibet mastiff and goat, when brought down from the Himalaya to Kashmir, lose their fine wool. At Angora not only goats, but shepherd-dogs and cats, have fine fleecy hair, and Mr. Ainsworth[687] attributes the thickness of the fleece to the severe winters, and its silky lustre to the hot summers. Burnes states positively[688] that the Karakool sheep lose their peculiar black curled fleeces when removed into any other country. Even within the limits of England, I have been assured that with two breeds of sheep the wool was slightly changed by the flocks being pastured in different localities. [689] It has been asserted on good authority[690] that horses kept during several years in the deep coal-mines of Belgium become covered with velvety hair, almost like that on the mole. These cases probably stand in close relation to the natural change of coat in winter and summer. Naked varieties of several domestic animals have occasionally appeared; but there is no reason to {279} believe that this is in any way related to the nature of the climate to which they have been exposed. [691] It appears at first sight probable that the increased size, the tendency to fatten, the early maturity and altered forms of our improved cattle, sheep, and pigs, have directly resulted from their abundant supply of food. This is the opinion of many competent judges, and probably is to a great extent true. But as far as form is concerned, we must not overlook the equal or more potent influence of lessened use on the limbs and lungs. We see, moreover, as far as size is concerned, that selection is apparently a more powerful agent than a large supply of food, for we can thus only account for the existence, as remarked to me by Mr. Blyth, of the largest and smallest breeds of sheep in the same country, of Cochin-China fowls and Bantams, of small Tumbler and large Runt pigeons, all kept together and supplied with abundant nourishment. Nevertheless there can be little doubt that our domesticated animals have been modified, independently of the increased or lessened use of parts, by the conditions to which they have been subjected, without the aid of selection. For instance, Prof. Rütimeyer[692] shows that the bones of all domesticated quadrupeds can be distinguished from those of wild animals by the state of their surface and general appearance. It is scarcely possible to read Nathusius's excellent 'Vorstudien, '[693] and doubt that, with the highly improved races of the pig, abundant food has produced a conspicuous effect on the general form of the body, on the breadth of the head and face, and even on the teeth. Nathusius rests much on the case of a purely bred Berkshire pig, which when two months old became diseased in its digestive organs, and was preserved for observation until nineteen months old; at this age it had lost several characteristic features of the breed, and had acquired a long, narrow head, of large size relatively to its small body, and elongated legs. But in this case and in some others we ought not to assume that, because certain characters are lost, perhaps through reversion, under one course of treatment, therefore that they had been at first directly produced by an opposite course. In the case of the rabbit, which has become feral on the island of Porto Santo, we are at first strongly tempted to attribute the whole change--the greatly reduced size, the altered tints of the fur, and the loss of certain characteristic marks--to the definite action of the new conditions to which it has been exposed. But in all such cases we have to consider in addition the tendency to reversion to progenitors more or less remote, and the natural selection of the finest shades of difference. The nature of the food sometimes either definitely induces certain peculiarities, or stands in some close relation with them. Pallas long ago asserted that the fat-tailed sheep of Siberia degenerated and lost their enormous tails when removed from certain saline pastures; and recently {280} Erman[694] states that this occurs with the Kirgisian sheep when brought to Orenburgh. It is well known that hemp-seed causes bullfinches and certain other birds to become black. Mr. Wallace has communicated to me some much more remarkable facts of the same nature. The natives of the Amazonian region feed the common green parrot (_Chrysotis festiva_, Linn. ) with the fat of large Siluroid fishes, and the birds thus treated become beautifully variegated with red and yellow feathers. In the Malayan archipelago, the natives of Gilolo alter in an analogous manner the colours of another parrot, namely, the _Lorius garrulus_, Linn. , and thus produce the _Lori rajah_ or King-Lory. These parrots in the Malay Islands and South America, when fed by the natives on natural vegetable food, such as rice and plantains, retain their proper colours. Mr. Wallace has, also, recorded[695] a still more singular fact. "The Indians (of S. America) have a curious art by which they change the colours of the feathers of many birds. They pluck out those from the part they wish to paint, and inoculate the fresh wound with the milky secretion from the skin of a small toad. The feathers grow of a brilliant yellow colour, and on being plucked out, it is said, grow again of the same colour without any fresh operation. " Bechstein[696] does not entertain any doubt that seclusion from light affects, at least temporarily, the colours of cage-birds. It is well known that the shells of land-mollusca are affected by the abundance of lime in different districts. Isidore Geoffroy St. Hilaire[697] gives the case of _Helix lactea_, which has recently been carried from Spain to the South of France and to the Rio Plata, and in both these countries now presents a distinct appearance, but whether this has resulted from food or climate is not known. With respect to the common oyster, Mr. F. Buckland informs me that he can generally distinguish the shells from different districts; young oysters brought from Wales and laid down in beds where "_natives_" are indigenous, in the short space of two months begin to assume the "native" character. M. Costa[698] has recorded a much more remarkable case of the same nature, namely, that young shells taken from the shores of England and placed in the Mediterranean, at once altered their manner of growth and formed prominent diverging rays, like those on the shells of the proper Mediterranean oyster. The same individual shell, showing both forms of growth, was exhibited before a society in Paris. Lastly, it is well known that caterpillars fed on different food sometimes either themselves acquire a different colour or produce moths different in colour. [699] {281} It would be travelling beyond my proper limits here to discuss how far organic beings in a state of nature are definitely modified by changed conditions. In my 'Origin of Species' I have given a brief abstract of the facts bearing on this point, and have shown the influence of light on the colours of birds, and of residence near the sea on the lurid tints of insects, and on the succulency of plants. Mr. Herbert Spencer[700] has recently discussed with much ability this whole subject on broad and general grounds. He argues, for instance, that with all animals the external and internal tissues are differently acted on by the surrounding conditions, and they invariably differ in intimate structure. So again the upper and lower surfaces of true leaves, as well as of stems and petioles, when these assume the function and occupy the position of leaves, are differently circumstanced with respect to light, &c. , and apparently in consequence differ in structure. But, as Mr. Herbert Spencer admits, it is most difficult in all such cases to distinguish between the effects of the definite action of physical conditions and the accumulation through natural selection of inherited variations which are serviceable to the organism, and which have arisen independently of the definite action of these conditions. Although we are not here concerned with organic beings in a state ofnature, yet I may call attention to one case. Mr. Meehan, [701] in aremarkable paper, compares twenty-nine kinds of American trees, belongingto various orders, with their nearest European allies, all grown in closeproximity in the same garden and under as nearly as possible the sameconditions. In the American species Mr. Meehan finds, with the rarestexceptions, that the leaves fall earlier in the season, and assume beforefalling a brighter tint; that they are less deeply toothed or serrated;that the buds are smaller; that the trees are more diffuse in growth andhave fewer branchlets; and, lastly, that the seeds are smaller--all incomparison with the corresponding European species. Now, considering thatthese trees belong to distinct orders, it is out of the question that thepeculiarities just specified should have been inherited in the onecontinent from one progenitor, and in the other from another progenitor;and considering that the trees inhabit widely different stations, thesepeculiarities can hardly be supposed to be of any special {282} service tothe two series in the Old and New Worlds; therefore these peculiaritiescannot have been naturally selected. Hence we are led to infer that theyhave been definitely caused by the long-continued action of the differentclimate of the two continents on the trees. _Galls. _--Another class of facts, not relating to cultivated plants, deserves attention. I allude to the production of galls. Every one knowsthe curious, bright-red, hairy productions on the wild rose-tree, and thevarious different galls produced by the oak. Some of the latter resemblefruit, with one face as rosy as the rosiest apple. These bright colours canbe of no service either to the gall-forming insect or to the tree, andprobably are the direct result of the action of the light, in the samemanner as the apples of Nova Scotia or Canada are brighter coloured thanEnglish apples. The strongest upholder of the doctrine that organic beingsare created beautiful to please mankind would not, I presume, extend thisview to galls. According to Osten Sacken's latest revision, no less thanfifty-eight kinds of galls are produced on the several species of oak, byCynips with its sub-genera; and Mr. B. D. Walsh[702] states that he can addmany others to the list. One American species of willow, the _Salixhumilis_, bears ten distinct kinds of galls. The leaves which spring fromthe galls of various English willows differ completely in shape from thenatural leaves. The young shoots of junipers and firs, when punctured bycertain insects, yield monstrous growths like flowers and cones; and theflowers of some plants become from the same cause wholly changed inappearance. Galls are produced in every quarter of the world; of severalsent to me by Mr. Thwaites from Ceylon, some were as symmetrical as acomposite flower when in bud, others smooth and spherical like a berry;some protected by long spines, others clothed with yellow wool formed oflong cellular hairs, others with regularly tufted hairs. In some galls theinternal structure is simple, but in others it is highly complex; thus M. Lucaze-Duthiers[703] has figured in the common ink-gall no less than sevenconcentric layers, composed of distinct tissue, {283} namely, theepidermic, sub-epidermic, spongy, intermediate, and the hard protectivelayer formed of curiously thickened woody cells, and, lastly, the centralmass abounding with starch-granules on which the larvæ feed. Galls are produced by insects of various orders, but the greater number byspecies of Cynips. It is impossible to read M. Lucaze-Duthier's discussionand doubt that the poisonous secretion of the insect causes the growth ofthe gall, and every one knows how virulent is the poison secreted by waspsand bees, which belong to the same order with Cynips. Galls grow withextraordinary rapidity, and it is said that they attain their full size ina few days;[704] it is certain that they are almost completely developedbefore the larvæ are hatched. Considering that many gall-insects areextremely small, the drop of secreted poison must be excessively minute; itprobably acts on one or two cells alone, which, being abnormallystimulated, rapidly increase by a process of self-division. Galls, as Mr. Walsh[705] remarks, afford good, constant, and definite characters, eachkind keeping as true to form as does any independent organic being. Thisfact becomes still more remarkable when we hear that, for instance, sevenout of the ten different kinds of galls produced on _Salix humilis_ areformed by gall-gnats (_Cecidomyidæ_) which, "though essentially distinctspecies, yet resemble one another so closely that in almost all cases it isdifficult, and in some cases impossible, to distinguish the full-growninsects one from the other. "[706] For in accordance with a wide-spreadanalogy we may safely infer that the poison secreted by insects so closelyallied would not differ much in nature; yet this slight difference issufficient to induce widely different results. In some few cases the samespecies of gall-gnat produces on distinct species of willows galls whichcannot be distinguished; the _Cynips fecundatrix_, also, has been known toproduce on the Turkish oak, to which it is not properly attached, exactlythe same kind of gall as on the European oak. [707] These latter factsapparently prove that the nature of the poison is a much more powerful{284} agent in determining the form of the gall than the specific characterof the tree which is acted on. As the poisonous secretion of insects belonging to various orders has thespecial power of affecting the growth of various plants;--as a slightdifference in the nature of the poison suffices to produce widely differentresults;--and lastly, as we know that the chemical compounds secreted byplants are eminently liable to be modified by changed conditions of life, we may believe it possible that various parts of a plant might be modifiedthrough the agency of its own altered secretions. Compare, for instance, the mossy and viscid calyx of a moss-rose, which suddenly appears throughbud-variation on a Provence-rose, with the gall of red moss growing fromthe inoculated leaf of a wild rose, with each filament symmetricallybranched like a microscopical spruce-fir, bearing a glandular tip andsecreting odoriferous gummy matter. [708] Or compare, on the one hand, thefruit of the peach, with its hairy skin, fleshy covering, hard shell andkernel, and on the other hand one of the more complex galls with itsepidermic, spongy, and woody layers, surrounding tissue loaded with starchgranules. These normal and abnormal structures manifestly present a certaindegree of resemblance. Or, again, reflect on the cases above given ofparrots which have had their plumage brightly decorated through some changein their blood, caused by having been fed on certain fishes, or locallyinoculated with the poison of a toad. I am far from wishing to maintainthat the moss-rose or the hard shell of the peach-stone or the brightcolours of birds are actually due to any chemical change in the sap orblood; but these cases of galls and of parrots are excellently adapted toshow us how powerfully and singularly external agencies may affectstructure. With such facts before us, we need feel no surprise at theappearance of any modification in any organic being. I may, also, here allude to the remarkable effects which parasitic fungi sometimes produce on plants. Reissek[709] has described a Thesium, affected by an Oecidium, which was greatly modified, and assumed some of the {285} characteristic features of certain allied species, or even genera. Suppose, says Reissek, "the condition originally caused by the fungus to become constant in the course of time, the plant would, if found growing wild, be considered as a distinct species or even as belonging to a new genus. " I quote this remark to show how profoundly, yet in how natural a manner, this plant must have been modified by the parasitic fungus. _Facts and Considerations opposed to the belief that the Conditions of Lifeact in a potent manner in causing definite Modifications of Structure. _ I have alluded to the slight differences in species when naturally livingin distinct countries under different conditions; and such differences wefeel at first inclined, probably to a limited extent with justice, toattribute to the definite action of the surrounding conditions. But it mustbe borne in mind that there are a far greater number of animals and plantswhich range widely and have been exposed to great diversities ofconditions, yet remain nearly uniform in character. Some authors, aspreviously remarked, account for the varieties of our culinary andagricultural plants by the definite action of the conditions to which theyhave been exposed in the different parts of Great Britain; but there areabout 200 plants[710] which are found in every single English county; theseplants must have been exposed for an immense period to considerabledifferences of climate and soil, yet do not differ. So, again, some birds, insects, other animals, and plants range over large portions of the world, yet retain the same character. Notwithstanding the facts previously given on the occurrence of highly peculiar local diseases and on the strange modifications of structure in plants caused by the inoculated poison of insects, and other analogous cases; still there are a multitude of variations--such as the modified skull of the niata ox and bulldog, the long horns of Caffre cattle, the conjoined toes of the solid-hoofed swine, the immense crest and protuberant skull of Polish fowls, the crop of the pouter-pigeon, and a host of other such cases--which we can hardly attribute to the definite action, in the sense before specified, of the external conditions of life. No doubt in every case there must have been some exciting cause; but as we see innumerable individuals exposed to nearly the same conditions, and one alone is affected, we may conclude that the constitution of the individual is of far higher {286} importance than the conditions to which it has been exposed. It seems, indeed, to be a general rule that conspicuous variations occur rarely, and in one individual alone out of many thousands, though all may have been exposed, as far as we can judge, to nearly the same conditions. As the most strongly marked variations graduate insensibly into the most trifling, we are led by the same train of thought to attribute each slight variation much more to innate differences of constitution, however caused, than to the definite action of the surrounding conditions. We are led to the same conclusion by considering the cases, formerly alluded to, of fowls and pigeons, which have varied and will no doubt go on varying in directly opposite ways, though kept during many generations under nearly the same conditions. Some, for instance, are born with their beaks, wings, tails, legs, &c. , a little longer, and others with these same parts a little shorter. By the long-continued selection of such slight individual differences, which occur in birds kept in the same aviary, widely different races could certainly be formed; and long-continued selection, important as is the result, does nothing but preserve the variations which appear to us to arise spontaneously. In these cases we see that domesticated animals vary in an indefinite number of particulars, though treated as uniformly as is possible. On the other hand, there are instances of animals and plants, which, though exposed to very different conditions, both under nature and domestication, have varied in nearly the same manner. Mr. Layard informs me that he has observed amongst the Caffres of South Africa a dog singularly like an arctic Esquimaux dog. Pigeons in India present nearly the same wide diversities of colour as in Europe; and I have seen chequered and simply barred pigeons, and pigeons with blue and white loins, from Sierra Leone, Madeira, England, and India. New varieties of flowers are continually raised in different parts of Great Britain, but many of these are found by the judges at our exhibitions to be almost identical with old varieties. A vast number of new fruit-trees and culinary vegetables have been produced in North America: these differ from European varieties in the same general manner as the several varieties raised in Europe differ from each other; and no one has ever pretended that the climate of America has given to the many American varieties any general character by which they can be recognised. Nevertheless, from the facts previously advanced on the authority of Mr. Meehan with respect to American and European forest-trees, it would be rash to affirm that varieties raised in the two countries would not in the course of ages assume a distinctive character. Mr. Masters has recorded a striking fact[711] bearing on this subject: he raised numerous plants of _Hybiscus Syriacus_ from seed collected in South Carolina and the Holy Land, where the parent-plants must have been exposed to considerably different conditions; yet the seedlings from both localities broke into two similar strains, one with obtuse leaves and purple or crimson flowers, and the other with elongated leaves and more or less pink flowers. {287} We may, also, infer the prepotent influence of the constitution of the organism over the definite action of the conditions of life, from the several cases given in the earlier chapters of parallel series of varieties, --an important subject, hereafter to be more fully discussed. Sub-varieties of the several kinds of wheat, gourds, peaches, and other plants, and to a certain limited extent sub-varieties of the fowl, pigeon, and dog, have been shown either to resemble or to differ from each other in a closely corresponding and parallel manner. In other cases, a variety of one species resembles a distinct species; or the varieties of two distinct species resemble each other. Although these parallel resemblances no doubt often result from reversion to the former characters of a common progenitor; yet in other cases, when new characters first appear, the resemblance must be attributed to the inheritance of a similar constitution, and consequently to a tendency to vary in the same manner. We see something of a similar kind in the same monstrosity appearing and reappearing many times in the same animal, and, as Dr. Maxwell Masters has remarked to me, in the same plant. We may at least conclude thus far, that the amount of modification whichanimals and plants have undergone under domestication, does not correspondwith the degree to which they have been subjected to changed circumstances. As we know the parentage of domesticated birds far better than of mostquadrupeds, we will glance through the list. The pigeon has varied inEurope more than almost any other bird; yet it is a native species, and hasnot been exposed to any extraordinary change of conditions. The fowl hasvaried equally, or almost equally, with the pigeon, and is a native of thehot jungles of India. Neither the peacock, a native of the same country, nor the guinea-fowl, an inhabitant of the dry deserts of Africa, has variedat all, or only in colour. The turkey, from Mexico, has varied but little. The duck, on the other hand, a native of Europe, has yielded somewell-marked races; and as this is an aquatic bird, it must have beensubjected to a far more serious change in its habits than the pigeon oreven the fowl, which nevertheless have varied in a much higher degree. Thegoose, a native of Europe and aquatic like the duck, has varied less thanany other domesticated bird, except the peacock. Bud-variation is, also, important under our present point of view. In somefew cases, as when all the eyes or buds on the same tuber of the potato, orall the fruit on the same plum-tree, or all the flowers on the same plant, have suddenly varied in the same manner, it might be argued that the {288}variation had been definitely caused by some change in the conditions towhich the plants had been exposed; yet, in other cases, such an admissionis extremely difficult. As new characters sometimes appear bybud-variation, which do not occur in the parent-species or in any alliedspecies, we may reject, at least in these cases, the idea that they are dueto reversion. Now it is well worth while to reflect maturely on somestriking case of bud-variation, for instance that of the peach. This treehas been cultivated by the million in various parts of the world, has beentreated differently, grown on its own roots and grafted on various stocks, planted as a standard, against a wall, and under glass; yet each bud ofeach sub-variety keeps true to its kind. But occasionally, at longintervals of time, a tree in England, or under the widely-different climateof Virginia, produces a single bud, and this yields a branch which everafterwards bears nectarines. Nectarines differ, as every one knows, frompeaches in their smoothness, size, and flavour; and the difference is sogreat, that some botanists have maintained that they are specificallydistinct. So permanent are the characters thus suddenly acquired, that anectarine produced by bud-variation has propagated itself by seed. To guardagainst the supposition that there is some fundamental distinction betweenbud and seminal variation, it is well to bear in mind that nectarines havelikewise been produced from the stone of the peach; and, reversely, peachesfrom the stone of the nectarine. Now is it possible to conceive externalconditions more closely alike than those to which the buds on the same treeare exposed? Yet one bud alone, out of the many thousands borne by the sametree, has suddenly without any apparent cause produced a nectarine. But thecase is even stronger than this, for the same flower-bud has yielded afruit, one-half or one-quarter a nectarine, and the other half orthree-quarters a peach. Again, seven or eight varieties of the peach haveyielded by bud-variation nectarines: the nectarines thus produced, nodoubt, differ a little from each other; but still they are nectarines. Ofcourse there must be some cause, internal or external, to excite thepeach-bud to change its nature; but I cannot imagine a class of factsbetter adapted to force on our minds the conviction that what we call theexternal conditions of life are quite insignificant in {289} relation toany particular variation, in comparison with the organisation orconstitution of the being which varies. It is known from the labours of Geoffroy St. Hilaire, and recently fromthose of Dareste and others, that eggs of the fowl, if shaken, placedupright, perforated, covered in part with varnish, &c. , produce monstrouschickens. Now these monstrosities may be said to be directly caused by suchunnatural conditions, but the modifications thus induced are not of adefinite nature. An excellent observer, M. Camille Dareste, [712] remarks"that the various species of monstrosities are not determined by specificcauses; the external agencies which modify the development of the embryoact solely in causing a perturbation--a perversion in the normal course ofdevelopment. " He compares the result to what we see in illness: a suddenchill, for instance, affects one individual alone out of many, causingeither a cold, or sore-throat, rheumatism, or inflammation of the lungs orpleura. Contagious matter acts in an analogous manner. [713] We may take astill more specific instance: seven pigeons were struck byrattle-snakes;[714] some suffered from convulsions; some had their bloodcoagulated, in others it was perfectly fluid; some showed ecchymosed spotson the heart, others on the intestines, &c. ; others again showed no visiblelesion in any organ. It is well known that excess in drinking causesdifferent diseases in different men; but men living under a cold andtropical climate are differently affected:[715] and in this case we see thedefinite influence of opposite conditions. The foregoing facts apparentlygive us as good an idea as we are likely for a long time to obtain, how inmany cases external conditions act directly, though not definitely, incausing modifications of structure. * * * * * _Summary. _--There can be no doubt, from the facts given in the early partof this chapter, that extremely slight changes in {290} the conditions oflife sometimes act in a definite manner on our already variabledomesticated productions; and, as the action of changed conditions incausing general or indefinite variability is accumulative, so it may bewith their definite action. Hence it is possible that great and definitemodifications of structure may result from altered conditions acting duringa long series of generations. In some few instances a marked effect hasbeen produced quickly on all, or nearly all, the individuals which havebeen exposed to some considerable change of climate, food, or othercircumstance. This has occurred, and is now occurring, with European men inthe United States, with European dogs in India, with horses in the FalklandIslands, apparently with various animals at Angora, with foreign oysters inthe Mediterranean, and with maize grown in Europe from tropical seed. Wehave seen that the chemical compounds secreted by plants and the state oftheir tissues are readily affected by changed conditions. In some cases arelation apparently exists between certain characters and certainconditions, so that if the latter be changed the character is lost--as withcultivated flowers, with some few culinary plants, with the fruit of themelon, with fat-tailed sheep, and other sheep having peculiar fleeces. The production of galls, and the change of plumage in parrots when fed onpeculiar food or when inoculated by the poison of a toad, prove to us whatgreat and mysterious changes in structure and colour may be the definiteresult of chemical changes in the nutrient fluids or tissues. We have also reason to believe that organic beings in a state of nature maybe modified in various definite ways by the conditions to which they havebeen long exposed, as in the case of American trees in comparison withtheir representatives in Europe. But in all such cases it is most difficultto distinguish between the definite results of changed conditions, and theaccumulation through natural selection of serviceable variations which havearisen independently of the nature of the conditions. If, for instance, aplant had to be modified so as to become fitted to inhabit a humid insteadof an arid station, we have no reason to believe that variations of theright kind would occur more frequently if the parent-plant inhabited astation a little more {291} humid than usual. Whether the station wasunusually dry or humid, variations adapting the plant in a slight degreefor directly opposite habits of life would occasionally arise, as we havereason to believe from what we know in other cases. In most, perhaps in all cases, the organisation or constitution of thebeing which is acted on, is a much more important element than the natureof the changed conditions, in determining the nature of the variation. Wehave evidence of this in the appearance of nearly similar modificationsunder different conditions, and of different modifications under apparentlynearly the same conditions. We have still better evidence of this inclosely parallel varieties being frequently produced from distinct races, or even distinct species, and in the frequent recurrence of the samemonstrosity in the same species. We have also seen that the degree to whichdomesticated birds have varied, does not stand in any close relation withthe amount of change to which they have been subjected. To recur once again to bud-variations. When we reflect on the millions ofbuds which many trees have produced, before some one bud has varied, we arelost in wonder what the precise cause of each variation can be. Let usrecall the case given by Andrew Knight of the forty-year-old tree of theyellow magnum bonum plum, an old variety which has been propagated bygrafts on various stocks for a very long period throughout Europe and NorthAmerica, and on which a single bud suddenly produced the red magnum bonum. We should also bear in mind that distinct varieties, and even distinctspecies, --as in the case of peaches, nectarines, and apricots, --of certainroses and camellias, --although separated by a vast number of generationsfrom any progenitor in common, and although cultivated under diversifiedconditions, have yielded by bud-variation closely analogous varieties. Whenwe reflect on these facts we become deeply impressed with the convictionthat in such cases the nature of the variation depends but little on theconditions to which the plant has been exposed, and not in any especialmanner on its individual character, but much more on the general nature orconstitution, inherited from some remote progenitor, of the whole group ofallied beings to which the plant belongs. We are thus driven to concludethat in most {292} cases the conditions of life play a subordinate part incausing any particular modification; like that which a spark plays, when amass of combustibles bursts into flame--the nature of the flame dependingon the combustible matter, and not on the spark. No doubt each slight variation must have its efficient cause; but it is ashopeless an attempt to discover the cause of each as to say why a chill ora poison affects one man differently from another. Even with modificationsresulting from the definite action of the conditions of life, when all ornearly all the individuals, which have been similarly exposed, aresimilarly affected, we can rarely see the precise relation between causeand effect. In the next chapter it will be shown that the increased use ordisuse of various organs, produces an inherited effect. It will further beseen that certain variations are bound together by correlation and otherlaws. Beyond this we cannot at present explain either the causes or mannerof action of Variation. Finally, as indefinite and almost illimitable variability is the usualresult of domestication and cultivation, with the same part or organvarying in different individuals in different or even in directly oppositeways; and as the same variation, if strongly pronounced, usually recursonly after long intervals of time, any particular variation would generallybe lost by crossing, reversion, and the accidental destruction of thevarying individuals, unless carefully preserved by man. Hence, although itmust be admitted that new conditions of life do sometimes definitely affectorganic beings, it may be doubted whether well-marked races have often beenproduced by the direct action of changed conditions without the aid ofselection either by man or nature. * * * * * {293} CHAPTER XXIV. LAWS OF VARIATION--USE AND DISUSE, ETC. NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON THE EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS OF LIFE--ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY WHICH THIS CAN BE EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS. In this and the two following chapters I shall discuss, as well as thedifficulty of the subject permits, the several laws which governVariability. These may be grouped under the effects of use and disuse, including changed habits and acclimatisation--arrests ofdevelopment--correlated variation--the cohesion of homologous parts--thevariability of multiple parts--compensation of growth--the position of budswith respect to the axis of the plant--and lastly, analogous variation. These several subjects so graduate into each other that their distinctionis often arbitrary. It may be convenient first briefly to discuss that co-ordinating andreparative power which is common, in a higher or lower degree, to allorganic beings, and which was formerly designated by physiologists as the_nisus formativus_. Blumenbach and others[716] have insisted that the principle which permits a Hydra, when cut into fragments, to develop itself into two or more perfect animals, is the same with that which causes a wound in the higher animals to heal by a cicatrice. Such cases as that of the Hydra are evidently analogous with the spontaneous division or fissiparous generation of the lowest animals, and likewise with the budding of plants. Between these extreme cases and that of a mere cicatrice we have every gradation. Spallanzani, [717] by cutting off the legs and tail of a Salamander, got in the course of three months six crops of these members; so that 687 perfect bones were reproduced by one animal during one season. At whatever {294} point the limb was cut off, the deficient part, and no more, was exactly reproduced. Even with man, as we have seen in the twelfth chapter, when treating of polydactylism, the entire limb whilst in an embryonic state, and supernumerary digits, are occasionally, though imperfectly, reproduced after amputation. When a diseased bone has been removed, a new one sometimes "gradually assumes the regular form, and all the attachments of muscles, ligaments, &c. , become as complete as before. "[718] This power of regrowth does not, however, always act perfectly: the reproduced tail of a lizard differs in the forms of the scales from the normal tail: with certain Orthopterous insects the large hind legs are reproduced of smaller size:[719] the white cicatrice which in the higher animals unites the edges of a deep wound is not formed of perfect skin, for elastic tissue is not produced till long afterwards. [720] "The activity of the _nisus formativus_, " says Blumenbach, "is in an inverse ratio to the age of the organised body. " To this may be added that its power is greater in animals the lower they are in the scale of organisation; and animals low in the scale correspond with the embryos of higher animals belonging to the same class. Newport's observations[721] afford a good illustration of this fact, for he found that "myriapods, whose highest development scarcely carries them beyond the larvæ of perfect insects, can regenerate limbs and antennæ up to the time of their last moult;" and so can the larvæ of true insects, but not the mature insect. Salamanders correspond in development with the tadpoles or larvæ of the tailless Batrachians, and both possess to a large extent the power of regrowth; but not so the mature tailless Batrachians. Absorption often plays an important part in the repairs of injuries. When a bone is broken, and does not unite, the ends are absorbed and rounded, so that a false joint is formed; or if the ends unite, but overlap, the projecting parts are removed. [722] But absorption comes into action, as Virchow remarks, during the normal growth of bones; parts which are solid during youth become hollowed out for the medullary tissue as the bone increases in size. In trying to understand the many well-adapted cases of regrowth when aided by absorption, we should remember that most parts of the organisation, even whilst retaining the same form, undergo constant renewal; so that a part which was not renewed would naturally be liable to complete absorption. Some cases, usually classed under the so-called _nisus formativus_, at first appear to come under a distinct head; for not only are old structures reproduced, but structures which appear new are formed. Thus, after inflammation "false membranes, " furnished with blood-vessels, lymphatics, and nerves, are developed; or a foetus escapes from the Fallopian tubes, and falls into the abdomen, "nature pours out a quantity of plastic lymph, which forms itself into organised membrane, richly supplied with blood-vessels, " and the foetus is nourished for a time. In certain cases of {295} hydrocephalus the open and dangerous spaces in the skull are filled up with new bones, which interlock by perfect serrated sutures. [723] But most physiologists, especially on the Continent, have now given up the belief in plastic lymph or blastema, and Virchow[724] maintains that every structure, new or old, is formed by the proliferation of pre-existing cells. On this view false membranes, like cancerous or other tumours, are merely abnormal developments of normal growths; and we can thus understand how it is that they resemble adjoining structures; for instance, that "false membrane in the serous cavities acquires a covering of epithelium exactly like that which covers the original serous membrane; adhesions of the iris may become black apparently from the production of pigment-cells like those of the uvea. "[725] No doubt the power of reparation, though not always quite perfect, is an admirable provision, ready for various emergencies, even for those which occur only at long intervals of time. [726] Yet this power is not more wonderful than the growth and development of every single creature, more especially of those which are propagated by fissiparous generation. This subject has been here noticed, because we may infer that, when any part or organ is either greatly increased in size or wholly suppressed through variation and continued selection, the co-ordinating power of the organisation will continually tend to bring all the parts again into harmony with each other. _On the Effects of the Increased Use and Disuse of Organs. _ It is notorious, and we shall immediately adduce proofs, that increased useor action strengthens muscles, glands, sense-organs, &c. ; and that disuse, on the other hand, weakens them. I have not met with any clear explanationof this fact in works on Physiology. Mr. Herbert Spencer[727] maintainsthat when muscles are much used, or when intermittent pressure is appliedto the epidermis, an excess of nutritive matter exudes from the vessels, and that this gives additional development to the adjoining parts. That anincreased flow of blood towards an organ leads to its greater developmentis probable, if not certain. Mr. Paget[728] thus accounts for the long, thick, and dark-coloured hair which occasionally grows, even in youngchildren, near old-standing inflamed surfaces or fractured bones. WhenHunter {296} inserted the spur of a cock into the comb, which is wellsupplied with blood-vessels, it grew in one case in a spiral direction to alength of six inches, and in another case forward, like a horn, so that thebird could not touch the ground with its beak. But whether Mr. HerbertSpencer's view of the exudation of nutritive matter due to increasedmovement and pressure, will fully account for the augmented size of bones, ligaments, and especially of internal glands and nerves, seems doubtful. According to the interesting observations of M. Sedillot, [729] when aportion of one bone of the leg or fore-arm of an animal is removed and isnot replaced by growth, the associated bone enlarges till it attains a bulkequal to that of the two bones, of which it has to perform the functions. This is best exhibited in dogs in which the tibia has been removed; thecompanion bone, which is naturally almost filiform and not one-fifth thesize of the other, soon acquires a size equal to or greater than the tibia. Now, it is at first difficult to believe that increased weight acting on astraight bone could, by alternately increased and diminished pressure, cause nutritive matter to exude from the vessels which permeate theperiosteum. Nevertheless, the observations adduced by Mr. Spencer, [730] onthe strengthening of the bowed bones of rickety children, along theirconcave sides, leads to the belief that this is possible. Mr. H. Spencer has also shown that the ascent of the sap in trees is aidedby the rocking movement caused by the wind; and the sap strengthens thetrunk "in proportion to the stress to be borne; since the more severe andthe more repeated the strains, the greater must be the exudation from thevessels into the surrounding tissue, and the greater the thickening of thistissue by secondary deposits. "[731] But woody trunks may be formed of hardtissue without their having been subjected to any movement, as we see withivy closely attached to old walls. In all these cases, it is very difficultto disentangle the effects of long-continued selection from thoseconsequent on the increased action or movement of the part. Mr. H. Spencer[732] acknowledges this difficulty, and gives as an instance thespines {297} or thorns of trees, and the shells of nuts. Here we haveextremely hard woody tissue without the possibility of any movement tocause exudation, and without, as far as we can see, any other directlyexciting cause; and as the hardness of these parts is of manifest serviceto the plant, we may look at the result as probably due to the selection ofso-called spontaneous variations. Every one knows that hard work thickensthe epidermis on the hands; and when we hear that with infants long beforetheir birth the epidermis is thicker on the palms and soles of the feetthan on any other part of the body, as was observed with admiration byAlbinus, [733] we are naturally inclined to attribute this to the inheritedeffects of long-continued use or pressure. We are tempted to extend thesame view even to the hoofs of quadrupeds; but who will pretend todetermine how far natural selection may have aided in the formation ofstructures of such obvious importance to the animal? That use strengthens the muscles may be seen in the limbs of artisans who follow different trades; and when a muscle is strengthened, the tendons, and the crests of bone to which they are attached, become enlarged; and this must likewise be the case with the blood-vessels and nerves. On the other hand, when a limb is not used, as by Eastern fanatics, or when the nerve supplying it with nervous power is effectually destroyed, the muscles wither. So again, when the eye is destroyed the optic nerve becomes atrophied, sometimes even in the course of a few months. [734] The Proteus is furnished with branchiæ as well as with lungs: and Schreibers[735] found that when the animal was compelled to live in deep water the branchiæ were developed to thrice their ordinary size, and the lungs were partially atrophied. When, on the other hand, the animal was compelled to live in shallow water, the lungs became larger and more vascular, whilst the branchiæ disappeared in a more or less complete degree. Such modifications as these are, however, of comparatively little value for us, as we do not actually know that they tend to be inherited. In many cases there is reason to believe that the lessened use of various organs has affected the corresponding parts in the offspring. But there is no good evidence that this ever follows in the course of a single generation. It appears, as in the case of general or indefinite variability, that several generations must be subjected to changed habits for any appreciable result. Our domestic fowls, ducks, and geese have almost lost, not {298} only in the individual but in the race, their power of flight; for we do not see a chicken, when frightened, take flight like a young pheasant. Hence I was led carefully to compare the limb-bones of fowls, ducks, pigeons, and rabbits, with the same bones in the wild parent-species. As the measurements and weights were fully given in the earlier chapters, I need here only recapitulate the results. With domestic pigeons, the length of the sternum, the prominence of its crest, the length of the scapulæ and furcula, the length of the wings as measured from tip to tip of the radius, are all reduced relatively to the same parts in the wild pigeon. The wing and tail feathers, however, are increased in length, but this may have as little connection with the use of the wings or tail, as the lengthened hair on a dog with the amount of exercise which the breed has habitually taken. The feet of pigeons, except in the long-beaked races, are reduced in size. With fowls the crest of the sternum is less prominent, and is often distorted or monstrous; the wing-bones have become lighter relatively to the leg-bones, and are apparently a little shorter in comparison with those of the parent-form, the _Gallus bankiva_. With ducks, the crest of the sternum is affected in the same manner as in the foregoing cases: the furcula, coracoids, and scapulæ are all reduced in weight relatively to the whole skeleton: the bones of the wings are shorter and lighter, and the bones of the legs longer and heavier, relatively to each other, and relatively to the whole skeleton, in comparison with the same bones in the wild-duck. The decreased weight and size of the bones, in the foregoing cases, is probably the indirect result of the reaction of the weakened muscles on the bones. I failed to compare the feathers of the wings of the tame and wild duck; but Gloger[736] asserts that in the wild duck the tips of the wing-feathers reach almost to the end of the tail, whilst in the domestic duck they often hardly reach to its base. He remarks, also, on the greater thickness of the legs, and says that the swimming membrane between the toes is reduced; but I was not able to detect this latter difference. With the domesticated rabbit the body, together with the whole skeleton, is generally larger and heavier than in the wild animal, and the leg-bones are heavier in due proportion; but whatever standard of comparison be taken, neither the leg-bones nor the scapulæ have increased in length proportionally with the increased dimensions of the rest of the skeleton. The skull has become in a marked manner narrower, and, from the measurements of its capacity formerly given, we may conclude, that this narrowness results from the decreased size of the brain, consequent on the mentally inactive life led by these closely-confined animals. We have seen in the eighth chapter that silk-moths, which have been kept during many centuries closely confined, emerge from their cocoons with their wings distorted, incapable of flight, often greatly reduced in size, or even, according to Quatrefages, quite rudimentary. This condition of the wings may be largely owing to the same kind of monstrosity which often affects wild Lepidoptera when artificially reared from the cocoon; or it may {299} be in part due to an inherent tendency, which is common to the females of many Bombycidæ, to have their wings in a more or less rudimentary state; but part of the effect may probably be attributed to long-continued disuse. From the foregoing facts there can be no doubt that certain parts of theskeleton in our anciently domesticated animals, have been modified inlength and weight by the effects of decreased or increased use; but theyhave not been modified, as shown in the earlier chapters, in shape orstructure. We must, however, be cautious in extending this latterconclusion to animals living a free life; for these will occasionally beexposed during successive generations to the severest competition. Withwild animals it would be an advantage in the struggle for life that everysuperfluous and useless detail of structure should be removed or absorbed;and thus the reduced bones might ultimately become changed in structure. With highly-fed domesticated animals, on the other hand, there is noeconomy of growth; nor any tendency to the elimination of trifling andsuperfluous details of structure. Turning now to more general observations, Nathusius has shown that, withthe improved races of the pig, the shortened legs and snout, the form ofthe articular condyles of the occiput, and the position of the jaws withthe upper canine teeth projecting in a most anomalous manner in front ofthe lower canines, may be attributed to these parts not having been fullyexercised. For the highly-cultivated races do not travel in search of food, nor root up the ground with their ringed muzzles. These modifications ofstructure, which are all strictly inherited, characterise several improvedbreeds, so that they cannot have been derived from any single domestic orwild stock. [737] With respect to cattle, Professor Tanner has remarked thatthe lungs and liver in the improved breeds "are found to be considerablyreduced in size when compared with those possessed by animals havingperfect liberty;"[738] and the reduction of these organs affects thegeneral shape of the body. The cause of the reduced lungs in highly-bredanimals which take little exercise is {300} obvious; and perhaps the livermay be affected by the nutritious and artificial food on which they largelysubsist. It is well known that, when an artery is tied, the anastomosing branches, from being forced to transmit more blood, increase in diameter; and this increase cannot be accounted for by mere extension, as their coats gain in strength. Mr. Herbert Spencer[739] has argued that with plants the flow of sap from the point of supply to the growing part first elongates the cells in this line; and that the cells then become confluent, thus forming the ducts; so that, on this view, the vessels in plants are formed by the mutual reaction of the flowing sap and cellular tissue. Dr. W. Turner has remarked, [740] with respect to the branches of arteries, and likewise to a certain extent with nerves, that the great principle of compensation frequently comes into play; for "when two nerves pass to adjacent cutaneous areas, an inverse relation as regards size may subsist between them; a deficiency in one may be supplied by an increase in the other, and thus the area of the former may be trespassed on by the latter nerve. " But how far in these cases the difference in size in the nerves and arteries is due to original variation, and how far to increased use or action, is not clear. In reference to glands, Mr. Paget observes that "when one kidney is destroyed the other often becomes much larger, and does double work. "[741] If we compare the size of the udders and their power of secretion in cows which have been long domesticated, and in certain goats in which the udders nearly touch the ground, with the size and power of secretion of these organs in wild or half-domesticated animals, the difference is great. A good cow with us daily yields more than five gallons, or forty pints of milk, whilst a first-rate animal, kept, for instance, by the Damaras of South Africa, [742] "rarely gives more than two or three pints of milk daily, and, should her calf be taken from her, she absolutely refuses to give any. " We may attribute the excellence of our cows, and of certain goats, partly to the continued selection of the best milking animals, and partly to the inherited effects of the increased action, through man's art, of the secreting glands. It is notorious, as was remarked in the twelfth chapter, that short-sight is inherited; and if we compare watchmakers or engravers with, for instance, sailors, we can hardly doubt that vision continually directed towards a near object permanently affects the structure of the eye. Veterinarians are unanimous that horses become affected with spavins, splints, ringbones, &c. , from being shod, and from travelling on hard roads, and they are almost equally unanimous that these injuries are transmitted. Formerly horses were not shod in North Carolina, and it has been asserted that they did not then suffer from these diseases of the legs and feet. [743] {301} Our domesticated quadrupeds are all descended, as far as is known, fromspecies having erect ears; yet few kinds can be named, of which at leastone race has not drooping ears. Cats in China, horses in parts of Russia, sheep in Italy and elsewhere, the guinea-pig in Germany, goats and cattlein India, rabbits, pigs, and dogs in all long-civilised countries, havedependent ears. With wild animals, which constantly use their ears likefunnels to catch every passing sound, and especially to ascertain thedirection whence it comes, there is not, as Mr. Blyth has remarked, anyspecies with drooping ears except the elephant. Hence the incapacity toerect the ears is certainly in some manner the result of domestication; andthis incapacity has been attributed by various authors[744] to disuse, foranimals protected by man are not compelled habitually to use their ears. Col. Hamilton Smith[745] states that in ancient effigies of the dog, "withthe exception of one Egyptian instance, no sculpture of the earlier Grecianera produces representations of hounds with completely drooping ears; thosewith them half pendulous are missing in the most ancient; and thischaracter increases, by degrees, in the works of the Roman period. " Godronalso has remarked that "the pigs of the ancient Egyptians had not theirears enlarged and pendent. "[746] But it is remarkable that the drooping ofthe ears, though probably the effect of disuse, is not accompanied by anydecrease in size; on the contrary, when we remember that animals sodifferent as fancy rabbits, certain Indian breeds of the goat, our pettedspaniels, bloodhounds, and other dogs, have enormously elongated ears, itwould appear as if disuse actually caused an increase in length. Withrabbits, the drooping of the much elongated ears has affected even thestructure of the skull. The tail of no wild animal, as remarked to me by Mr. Blyth, is curled;whereas pigs and some races of dogs have their tails much curled. Thisdeformity, therefore, appears to be the result of domestication, butwhether in any way connected with the lessened use of the tail is doubtful. {302} The epidermis on our hands is easily thickened, as every one knows, by hardwork. In a district of Ceylon the sheep have "horny callosities that defendtheir knees, and which arise from their habit of kneeling down to crop theshort herbage, and this distinguishes the Jaffna flocks from those of otherportions of the island;" but it is not stated whether this peculiarity isinherited. [747] The mucous membrane which lines the stomach is continuous with the externalskin of the body; therefore it is not surprising that its texture should beaffected by the nature of the food consumed, but other and more interestingchanges likewise follow. Hunter long ago observed that the muscular coat ofthe stomach of a gull (_Larus tridactylus_) which had been fed for a yearchiefly on grain was thickened; and, according to Dr. Edmondston, a similarchange periodically occurs in the Shetland Islands in the stomach of the_Larus argentatus_, which in the spring frequents the corn-fields and feedson the seed. The same careful observer has noticed a great change in thestomach of a raven which had been long fed on vegetable food. In the caseof an owl (_Strix grallaria_) similarly treated, Menetries states that theform of the stomach was changed, the inner coat became leathery, and theliver increased in size. Whether these modifications in the digestiveorgans would in the course of generations become inherited is notknown. [748] The increased or diminished length of the intestines, which apparentlyresults from changed diet, is a more remarkable case, because it ischaracteristic of certain animals in their domesticated condition, andtherefore must be inherited. The complex absorbent system, theblood-vessels, nerves, and muscles, are necessarily all modified togetherwith the intestines. According to Daubenton, the intestines of the domesticcat are one-third longer than those of the wild cat of Europe; and althoughthis species is not the parent-stock of the domestic animal, yet, asIsidore Geoffroy has remarked, the several species {303} of cats are soclosely allied that the comparison is probably a fair one. The increasedlength appears to be due to the domestic cat being less strictlycarnivorous in its diet than any wild feline species; I have seen a Frenchkitten eating vegetables as readily as meat. According to Cuvier, theintestines of the domesticated pig exceed greatly in proportionate lengththose of the wild boar. In the tame and wild rabbit the change is of anopposite nature, and probably results from the nutritious food given to thetame rabbit. [749] * * * * * _Changed Habits of Life, independently of the Use or Disuse of particularOrgans. _--This subject, as far as the mental powers of animals areconcerned, so blends into instinct, on which I shall treat in a futurework, that I will here only remind the reader of the many cases which occurunder domestication, and which are familiar to every one--for instance thetameness of our animals--the pointing or retrieving of dogs--their notattacking the smaller animals kept by man--and so forth. How much of thesechanges ought to be attributed to inherited habit, and how much to theselection of individuals which have varied in the desired manner, irrespectively of the special circumstances under which they have beenkept, can seldom be told. We have already seen that animals may behabituated to a changed diet; but a few additional instances may here begiven. In the Polynesian Islands and in China the dog is fed exclusively onvegetable matter, and the taste for this kind of food is to a certainextent inherited. [750] Our sporting dogs will not touch the bones of gamebirds, whilst other dogs devour them with greediness. In some parts of theworld sheep have been largely fed on fish. The domestic hog is fond ofbarley, the wild boar is said to disdain it; and the disdain is partiallyinherited, for some young wild pigs bred in captivity showed an aversionfor this grain, whilst others of the same brood relished it. [751] One of myrelations bred some young pigs from {304} a Chinese sow by a wild Alpineboar; they lived free in the park, and were so tame that they came to thehouse to be fed; but they would not touch swill, which was devoured by theother pigs. An animal when once accustomed to an unnatural diet, which cangenerally be effected only during youth, dislikes its proper food, asSpallanzani found to be the case with a pigeon which had been long fed onmeat. Individuals of the same species take to new food with differentdegrees of readiness; one horse, it is stated, soon learned to eat meat, whilst another would have perished from hunger rather than have partaken ofit. [752] The caterpillars of the _Bombyx hesperus_ feed in a state of nature on theleaves of the _Café diable_, but, after having been reared on theAilanthus, they would not touch the _Café diable_, and actually died ofhunger. [753] It has been found possible to accustom marine fish to live in fresh water;but as such changes in fish, and other marine animals, have been chieflyobserved in a state of nature, they do not properly belong to our presentsubject. The period of gestation and of maturity, as shown in the earlierchapters, --the season and the frequency of the act of breeding, --have allbeen greatly modified under domestication. With the Egyptian goose the rateof change in the season has been recorded. [754] The wild drake pairs withone female, the domestic drake is polygamous. Certain breeds of fowls havelost the habit of incubation. The paces of the horse, and the manner offlight in certain breeds of the pigeon, have been modified, and areinherited. The voice differs much in certain fowls and pigeons. Some breedsare clamorous and others silent, as in the Call and common duck, or in theSpitz and pointer dog. Every one knows how dogs differ from each other intheir manner of hunting, and in their ardour after different kinds of gameor vermin. With plants the period of vegetation is easily changed and is inherited, asin the case of summer and winter wheat, barley, {305} and vetches; but tothis subject we shall immediately return under acclimatisation. Annualplants sometimes become perennial under a new climate, as I hear from Dr. Hooker is the case with the stock and mignonette in Tasmania. On the otherhand, perennials sometimes become annuals, as with the Ricinus in England, and as, according to Captain Mangles, with many varieties of theheartsease. Von Berg[755] raised from seed of _Verbascum phoenicium_, whichis usually a biennial, both annual and perennial varieties. Some deciduousbushes become evergreen in hot countries. [756] Rice requires much water, but there is one variety in India which can be grown withoutirrigation. [757] Certain varieties of the oat and of our other cereals arebest fitted for certain soils. [758] Endless similar facts could be given inthe animal and vegetable kingdoms. They are noticed here because theyillustrate analogous differences in closely allied natural species, andbecause such changed habits of life, whether due to use and disuse, or tothe direct action of external conditions, or to so-called spontaneousvariation, would be apt to lead to modifications of structure. * * * * * _Acclimatisation. _--From the previous remarks we are naturally led to themuch disputed subject of acclimatisation. There are two distinct questions:Do varieties descended from the same species differ in their power ofliving under different climates? And secondly, if they so differ, how havethey become thus adapted? We have seen that European dogs do not succeedwell in India, and it is asserted, [759] that no one has succeeded in therekeeping the Newfoundland long alive; but then it may be argued, probablywith truth, that these northern breeds are specifically distinct from thenative dogs which flourish in India. The same remark may be made withrespect to different breeds of sheep, of which, according to Youatt, [760]not one brought "from a torrid climate lasts out the second year, " in theZoological Gardens. But sheep are capable of some degree ofacclimatisation, for Merino sheep bred at the Cape of Good Hope have beenfound {306} far better adapted for India than those imported fromEngland. [761] It is almost certain that the breeds of the fowl aredescended from the same species; but the Spanish breed, which there is goodreason to believe originated near the Mediterranean, [762] though so fineand vigorous in England, suffers more from frost than any other breed. TheArrindy silk-moth introduced from Bengal, and the Ailanthus moth from thetemperate province of Shan Tung, in China, belong to the same species, aswe may infer from their identity in the caterpillar, cocoon, and maturestates;[763] yet they differ much in constitution: the Indian form "willflourish only in warm latitudes, " the other is quite hardy and withstandscold and rain. Plants are more strictly adapted to climate than are animals. The latter when domesticated withstand such great diversities of climate, that we find nearly the same species in tropical and temperate countries; whilst the cultivated plants are widely dissimilar. Hence a larger field is open for inquiry in regard to the acclimatisation of plants than of animals. It is no exaggeration to say that with almost every plant which has long been cultivated varieties exist, which are endowed with constitutions fitted for very different climates; I will select only a few of the more striking cases, as it would be tedious to give all. In North America numerous fruit-trees have been raised, and in horticultural publications, --for instance, in Downing, --lists are given of the varieties which are best able to withstand the severe climate of the northern States and Canada. Many American varieties of the pear, plum, and peach are excellent in their own country, but until recently hardly one was known that succeeded in England; and with apples, [764] not one succeeds. Though the American varieties can withstand a severer winter than ours, the summer here is not hot enough. Fruit-trees have originated in Europe as in America with different constitutions, but they are not here much noticed, as the same nurserymen do not supply a wide area. The Forelle pear flowers early, and when the flowers have just set, and this is the critical period, they have been observed, both in France and England, to withstand with complete impunity a frost of 18° and even 14° Fahr. , which killed the flowers, whether fully expanded or in bud, of all other kinds of pears. [765] This power in the flower of resisting cold and afterwards producing fruit does not invariably depend, as we know on good authority, [766] on general constitutional vigour. {307} In proceeding northward, the number of varieties which are enabled to resist the climate rapidly decreases, as may be seen in the list of the varieties of the cherry, apple, and pear, which can be cultivated in the neighbourhood of Stockholm. [767] Near Moscow, Prince Troubetzkoy planted for experiment in the open ground several varieties of the pear, but one alone, the _Poire sans Pepins_, withstood the cold of winter. [768] We thus see that our fruit-trees, like distinct species of the same genus, certainly differ from each other in their constitutional adaptation to different climates. With the varieties of many plants, the adaptation to climate is often very close. Thus it has been proved by repeated trials "that few if any of the English varieties of wheat are adapted for cultivation in Scotland;"[769] but the failure in this case is at first only in the quantity, though ultimately in the quality, of the grain produced. The Rev. J. M. Berkeley sowed wheat-seed from India, and got "the most meagre ears, " on land which would certainly have yielded a good crop from English wheat. [770] In these cases varieties have been carried from a warmer to a cooler climate; in the reverse case, as "when wheat was imported directly from France into the West Indian Islands, it produced either wholly barren spikes or furnished with only two or three miserable seeds, while West Indian seed by its side yielded an enormous harvest. "[771] Here is another case of close adaptation to a slightly cooler climate; a kind of wheat which in England may be used indifferently either as a winter or summer variety, when sown under the warmer climate of Grignan, in France, behaved exactly as if it had been a true winter wheat. [772] Botanists believe that all the varieties of maize belong to the same species; and we have seen that in North America, in proceeding northward, the varieties cultivated in each zone produce their flowers and ripen their seed within shorter and shorter periods. So that the tall, slowly maturing southern varieties do not succeed in New England, and the New English varieties do not succeed in Canada. I have not met with any statement that the southern varieties are actually injured or killed by a degree of cold which the northern varieties withstand with impunity, though this is probable; but the production of early flowering and early seeding varieties deserves to be considered as one form of acclimatisation. Hence it has been found possible, according to Kalm, to cultivate maize further and further northwards in America. In Europe, also, as we learn from the evidence given by Alph. De Candolle, the culture of maize has extended since the end of the last century thirty leagues north of its former boundary. [773] On the authority of the great Linnæus, [774] I may quote an {308} analogous case, namely, that in Sweden tobacco raised from home-grown seed ripens its seed a month sooner and is less liable to miscarry than plants raised from foreign seed. With the Vine, differently from the maize, the line of practical culture has retreated a little southward since the middle ages;[775] but this seems due to commerce, including that of wine, being now freer or more easy. Nevertheless the fact of the vine not having spread northward shows that acclimatisation has made no progress during several centuries. There is, however, a marked difference in the constitution of the several varieties, --some being hardy, whilst others, like the muscat of Alexandria, require a very high temperature to come to perfection. According to Labat, [776] vines taken from France to the West Indies succeed with extreme difficulty, whilst those imported from Madeira, or the Canary Islands, thrive admirably. Gallesio gives a curious account of the naturalisation of the Orange in Italy. Daring many centuries the sweet orange was propagated exclusively by grafts, and so often suffered from frosts that it required protection. After the severe frost of 1709, and more especially after that of 1763, so many trees were destroyed that seedlings from the sweet orange were raised, and, to the surprise of the inhabitants, their fruit was found to be sweet. The trees thus raised were larger, more productive, and hardier than the former kinds; and seedlings are now continually raised. Hence Gallesio concludes that much more was effected for the naturalisation of the orange in Italy by the accidental production of new kinds during a period of about sixty years, than had been effected by grafting old varieties during many ages. [777] I may add that Risso[778] describes some Portuguese varieties of the orange as extremely sensitive to cold, and as much tenderer than certain other varieties. The peach was known to Theophrastus, 322 B. C. [779] According to the authorities quoted by Dr. F. Rolle, [780] it was tender when first introduced into Greece, and even in the island of Rhodes only occasionally bore fruit. If this be correct, the peach, in spreading during the last two thousand years over the middle parts of Europe, must have become much hardier. At the present day different varieties differ much in hardiness: some French varieties will not succeed in England; and near Paris, the _Pavie de Bonneuil_ does not ripen its fruit till very late, even when grown on a wall; "it is, therefore, only fit for a very hot southern climate. "[781] I will briefly give a few other cases. A variety of _Magnolia grandiflora_, raised by M. Roy, withstands cold several degrees lower than that which any other variety can resist. With camellias there is much difference in hardiness. One particular variety of Noisette rose withstood the severe frost of 1860 "untouched and hale amidst a universal destruction of other {309} Noisettes. " In New York the "Irish yew is quite hardy, but the common yew is liable to be cut down. " I may add that there are varieties of the sweet potato (_Convolvulus batatas_) which are suited for warmer, as well as for colder, climates. [782] The plants as yet mentioned have been found capable of resisting an unusualdegree of cold or heat, when fully grown. The following cases refer toplants whilst young. In a large bed of young Araucarias of the same age, growing close together and equally exposed, it was observed, [783] after theunusually severe winter of 1860-61, that, "in the midst of the dying, numerous individuals remained on which the frost had absolutely made nokind of impression. " Dr. Lindley, after alluding to this and other similarcases, remarks, "Among the lessons which the late formidable winter hastaught us, is that, even in their power of resisting cold, individuals ofthe same species of plants are remarkably different. " Near Salisbury, therewas a sharp frost on the night of May 24th, 1836, and all the French beans(_Phaseolus vulgaris_) in a bed were killed except about one in thirty, which completely escaped. [784] On the same day of the month, but in theyear 1864, there was a severe frost in Kent, and two rows ofscarlet-runners (_P. Multiflorus_) in my garden, containing 390 plants ofthe same age and equally exposed, were all blackened and killed exceptabout a dozen plants. In an adjoining row of "Fulmer's dwarf bean" (_P. Vulgaris_), one single plant escaped. A still more severe frost occurredfour days afterwards, and of the dozen plants which had previously escapedonly three survived; these were not taller or more vigorous than the otheryoung plants, but they escaped completely, with not even the tips of theirleaves browned. It was impossible to behold these three plants, with theirblackened, withered, and dead brethren all round them, and not see at aglance that they differed widely in constitutional power of resistingfrost. This work is not the proper place to show that wild plants {310} of thesame species, naturally growing at different altitudes or under differentlatitudes, become to a certain extent acclimatised, as is proved by thedifferent behaviour of their seedlings when raised in England. In my'Origin of Species' I have alluded to some cases, and I could add others. One instance must suffice: Mr. Grigor, of Forres, [785] states thatseedlings of the Scotch fir (_Pinus sylvestris_), raised from seed from theContinent and from the forests of Scotland, differ much. "The difference isperceptible in one-year-old, and more so in two-year-old seedlings; but theeffects of the winter on the second year's growth almost uniformly makesthose from the Continent quite brown, and so damaged, that by the month ofMarch they are quite unsaleable, while the plants from the native Scotchpine, under the same treatment, and standing alongside, althoughconsiderably shorter, are rather stouter and quite green, so that the bedsof the one can be known from the other when seen from the distance of amile. " Closely similar facts have been observed with seedling larches. Hardy varieties would alone be valued or noticed in Europe; whilst tender varieties, requiring more warmth, would generally be neglected; but such occasionally arise. Thus Loudon[786] describes a Cornish variety of the elm which is almost an evergreen, and of which the shoots are often killed by the autumnal frosts, so that its timber is of little value. Horticulturists know that some varieties are much more tender than others: thus all the varieties of the broccoli are more tender than cabbages; but there is much difference in this respect in the sub-varieties of the broccoli; the pink and purple kinds are a little hardier than the white Cape broccoli, "but they are not to be depended on after the thermometer falls below 24° Fahr. :" the Walcheren broccoli is less tender than the Cape, and there are several varieties which will stand much severer cold than the Walcheren. [787] Cauliflowers seed more freely in India than cabbages. [788] To give one instance with flowers: eleven plants raised from a hollyhock, called the _Queen of the Whites_, [789] were found to be much more tender than various other seedlings. It may be presumed that all tender varieties would succeed better under a climate warmer than ours. With fruit-trees, it is well known that certain varieties, for instance of the peach, stand forcing in a hot-house better than others; and this shows {311} either pliability of organisation or some constitutional difference. The same individual cherry-tree, when forced, has been observed during successive years gradually to change its period of vegetation. [790] Few pelargoniums can resist the heat of a stove, but _Alba multiflora_ will, as a most skilful gardener asserts, "stand pine-apple top and bottom heat the whole winter, without looking any more drawn than if it had stood in a common greenhouse; and _Blanche Fleur_ seems as if it had been made on purpose for growing in winter, like many bulbs, and to rest all summer. "[791] There can hardly be a doubt that the _Alba multiflora_ pelargonium must have a widely different constitution from that of most other varieties of this plant; it would probably withstand even an equatorial climate. We have seen that according to Labat the vine and wheat require acclimatisation in order to succeed in the West Indies. Similar facts have been observed at Madras: "two parcels of mignonette-seed, one direct from Europe, the other saved at Bangalore (of which the mean temperature is much below that of Madras) were sown at the same time: they both vegetated equally favourably, but the former all died off a few days after they appeared above ground; the latter still survive, and are vigorous healthy plants. " So again, "turnip and carrot seed saved at Hyderabad are found to answer better at Madras than seed from Europe or from the Cape of Good Hope. "[792] Mr. J. Scott, of the Calcutta Botanic Gardens, informs me that seeds of the sweet-pea (_Lathyrus odoratus_) imported from England produce plants, with thick, rigid stems and small leaves, which rarely blossom and never yield seed; plants raised from French seed blossom sparingly, but all the flowers are sterile; on the other hand, plants raised from sweet-peas grown near Darjeeling in Upper India, but originally derived from England, can be successfully cultivated on the plains of India; for they flower and seed profusely, and their stems are lax and scandent. In some of the foregoing cases, as Dr. Hooker has remarked to me, the greater success may perhaps be attributed to the seeds having been more fully ripened under a more favourable climate; but this view can hardly be extended to so many cases, including plants, which, from being cultivated under a climate hotter than their native one, become fitted for a still hotter climate. We may therefore safely conclude that plants can to a certain extent become accustomed to a climate either hotter or colder than their own; although these latter cases have been more frequently observed. We will now consider the means by which acclimatisation may be effected, namely, through the spontaneous appearance of varieties having a differentconstitution, and through the effects of use or habit. In regard to thefirst process, there is no evidence that a change in the constitution ofthe {312} offspring necessarily stands in any direct relation with thenature of the climate inhabited by the parents. On the contrary, it iscertain that hardy and tender varieties of the same species appear in thesame country. New varieties thus spontaneously arising become fitted toslightly different climates in two different ways; firstly, they may havethe power, either as seedlings or when full-grown, of resisting intensecold, as with the Moscow pear, or of resisting intense heat, as with somekinds of Pelargonium, or the flowers may withstand severe frost, as withthe Forelle pear. Secondly, plants may become adapted to climates widelydifferent from their own, from flowering and fruiting either earlier orlater in the season. In both these cases the power of acclimatisation byman consists simply in the selection and preservation of new varieties. Butwithout any direct intention on his part of securing a hardier variety, acclimatisation may be unconsciously effected by merely raising tenderplants from seed, and by occasionally attempting their cultivation furtherand further northwards, as in the case of maize, the orange, and the peach. How much influence ought to be attributed to inherited habit or custom inthe acclimatisation of animals and plants is a much more difficultquestion. In many cases natural selection can hardly have failed to havecome into play and complicated the result. It is notorious that mountainsheep resist severe weather and storms of snow which would destroy lowlandbreeds; but then mountain sheep have been thus exposed from timeimmemorial, and all delicate individuals will have been destroyed, and thehardiest preserved. So with the Arrindy silk-moths of China and India; whocan tell how far natural selection may have taken a share in the formationof the two races, which are now fitted for such widely different climates?It seems at first probable that the many fruit-trees, which are so wellfitted for the hot summers and cold winters of North America, in contrastwith their poor success under our climate, have become adapted throughhabit; but when we reflect on the multitude of seedlings annually raised inthat country, and that none would succeed unless born with a fittingconstitution, it is possible that mere habit may have done nothing towardstheir acclimatisation. On the other hand, when we {313} hear that Merinosheep, bred during no great number of generations at the Cape of GoodHope--that some European plants raised during only a few generations in thecooler parts of India, withstand the hotter parts of that country muchbetter than the sheep or seeds imported directly from England, we mustattribute some influence to habit. We are led to the same conclusion whenwe hear from Naudin[793] that the races of melons, squashes, and gourds, which have long been cultivated in Northern Europe, are comparatively moreprecocious, and need much less heat for maturing their fruit, than thevarieties of the same species recently brought from tropical regions. Inthe reciprocal conversion of summer and winter wheat, barley, and vetchesinto each other, habit produces a marked effect in the course of a very fewgenerations. The same thing apparently occurs with the varieties of maize, which, when carried from the Southern to the Northern States of America, orinto Germany, soon become accustomed to their new homes. With vine-plantstaken to the West Indies from Madeira, which are said to succeed betterthan plants brought directly from France, we have some degree ofacclimatisation in the individual, independently of the production of newvarieties by seed. The common experience of agriculturists is of some value, and they oftenadvise persons to be cautious in trying in one country the productions ofanother. The ancient agricultural writers of China recommend thepreservation and cultivation of the varieties peculiar to each country. During the classical period, Columella wrote, "Vernaculum pecus peregrinolonge præstantius est. "[794] I am aware that the attempt to acclimatise either animals or plants hasbeen called a vain chimæra. No doubt the attempt in most cases deserves tobe thus called, if made independently of the production of new varietiesendowed with a different constitution. Habit, however much prolonged, rarely produces any effect on a plant propagated by buds; it apparentlyacts only through successive seminal generations. {314} The laurel, bay, laurestinus, &c. , and the Jerusalem artichoke, which are propagated bycuttings or tubers, are probably now as tender in England as when firstintroduced; and this appears to be the case with the potato, which untilrecently was seldom multiplied by seed. With plants propagated by seed, andwith animals, there will be little or no acclimatisation unless the hardierindividuals are either intentionally or unconsciously preserved. Thekidney-bean has often been advanced as an instance of a plant which has notbecome hardier since its first introduction into Britain. We hear, however, on excellent authority, [795] that some very fine seed, imported fromabroad, produced plants "which blossomed most profusely, but were nearlyall but abortive, whilst plants grown alongside from English seed poddedabundantly;" and this apparently shows some degree of acclimatisation inour English plants. We have also seen that seedlings of the kidney-beanoccasionally appear with a marked power of resisting frost; but no one, asfar as I can hear, has ever separated such hardy seedlings, so as toprevent accidental crossing, and then gathered their seed, and repeated theprocess year after year. It may, however, be objected with truth thatnatural selection ought to have had a decided effect on the hardiness ofour kidney-beans; for the tenderest individuals must have been killedduring every severe spring, and the hardier preserved. But it should beborne in mind that the result of increased hardiness would simply be thatgardeners, who are always anxious for as early a crop as possible, wouldsow their seed a few days earlier than formerly. Now, as the period ofsowing depends much on the soil and elevation of each district, and varieswith the season; and as new varieties have often been imported from abroad, can we feel sure that our kidney-beans are not somewhat hardier? I have notbeen able, by searching old horticultural works, to answer this questionsatisfactorily. On the whole the facts now given show that, though habit does somethingtowards acclimatisation, yet that the spontaneous appearance ofconstitutionally different individuals is a far more effective agent. As nosingle instance has been recorded, either with animals or plants, ofhardier individuals {315} having been long and steadily selected, thoughsuch selection is admitted to be indispensable for the improvement of anyother character, it is not surprising that man has done little in theacclimatisation of domesticated animals and cultivated plants. We need not, however, doubt that under nature new races and new species would becomeadapted to widely different climates, by spontaneous variation, aided byhabit, and regulated by natural selection. _Arrests of Development: Rudimentary and Aborted Organs. _ These subjects are here introduced because there is reason to believe that rudimentary organs are in many cases the result of disuse. Modifications of structure from arrested development, so great or so serious as to deserve to be called monstrosities, are of common occurrence, but, as they differ much from any normal structure, they require here only a passing notice. When a part or organ is arrested during its embryonic growth, a rudiment is generally left. Thus the whole head may be represented by a soft nipple-like projection, and the limbs by mere papillæ. These rudiments of limbs are sometimes inherited, as has been observed in a dog. [796] Many lesser anomalies in our domesticated animals appear to be due to arrested development. What the cause of the arrest may be, we seldom know, except in the case of direct injury to the embryo within the egg or womb. That the cause does not generally act at a very early embryonic period we may infer from the affected organ seldom being wholly aborted, --a rudiment being generally preserved. The external ears are represented by mere vestiges in a Chinese breed of sheep; and in another breed, the tail is reduced "to a little button, suffocated, in a manner, by fat. "[797] In tailless dogs and cats a stump is left; but I do not know whether it includes at an early embryonic age rudiments of all the caudal vertebræ. In certain breeds of fowls the comb and wattles are reduced to rudiments; in the Cochin-China breed scarcely more than rudiments of spurs exist. With polled Suffolk cattle, "rudiments of horns can often be felt at an early age;"[798] and with species in a state of nature, the relatively greater development of rudimentary organs at an early period of life is highly characteristic of such organs. With hornless breeds of cattle and sheep; another and singular kind of rudiment has been observed, namely, minute dangling horns attached to the skin alone, and which are often shed and grow again. With hornless goats, according to Desmarest, [799] {316} the bony protuberances which properly support the horns exist as mere rudiments. With cultivated plants it is far from rare to find the petals, stamens, and pistils represented by rudiments, like those observed in natural species. So it is with the whole seed in many fruits; thus near Astrakhan there is a grape with mere traces of seeds, "so small and lying so near the stalk that they are not perceived in eating the grape. "[800] In certain varieties of the gourd, the tendrils, according to Naudin, are represented by rudiments or by various monstrous growths. In the broccoli and cauliflower the greater number of the flowers are incapable of expansion, and include rudimentary organs. In the Feather hyacinth (_Muscari comosum_) the upper and central flowers are brightly coloured but rudimentary; under cultivation the tendency to abortion travels downwards and outwards, and all the flowers become rudimentary; but the abortive stamens and pistils are not so small in the lower as in the upper flowers. In the _Viburnum opulus_, on the other hand, the outer flowers naturally have their organs of fructification in a rudimentary state, and the corolla is of large size; under cultivation, the change spreads to the centre, and all the flowers become affected; thus the well-known Snow-ball bush is produced. In the Compositæ, the so-called doubling of the flowers consists in the greater development of the corolla of the central florets, generally accompanied with some degree of sterility; and it has been observed[801] that the progressive doubling invariably spreads from the circumference to the centre, --that is, from the ray florets, which so often include rudimentary organs, to those of the disc. I may add, as bearing on this subject, that, with Asters, seeds taken from the florets of the circumference have been found to yield the greatest number of double flowers. [802] In these several cases we have a natural tendency in certain parts to become rudimentary, and this under culture spreads either to, or from, the axis of the plant. It deserves notice, as showing how the same laws govern the changes which natural species and artificial varieties undergo, that in a series of species in the genus Carthamus, one of the Compositæ, a tendency in the seeds to the abortion of the pappus may be traced extending from the circumference to the centre of the disc: thus, according to A. De Jussieu, [803] the abortion is only partial in _Carthamus creticus_, but more extended in _C. Lanatus_; for in this species two or three alone of the central seeds are furnished with a pappus, the surrounding seeds being either quite naked or furnished with a few hairs; and lastly, in _C. Tinctorius_, even the central seeds are destitute of pappus, and the abortion is complete. With animals and plants under domestication, when an organ disappears, leaving only a rudiment, the loss has generally been sudden, as with hornless and tailless breeds; and such cases may be ranked as inherited monstrosities. But in some few cases the loss has been gradual, and {317} has been partly effected by selection, as with the rudimentary combs and wattles of certain fowls. We have also seen that the wings of some domesticated birds have been slightly reduced by disuse, and the great reduction of the wings in certain silk-moths, with mere rudiments left, has probably been aided by disuse. With species in a state of nature, rudimentary organs are so extremely common that scarcely one can be named which is wholly free from a blemish of this nature. Such organs are generally variable, as several naturalists have observed; for, being useless, they are not regulated by natural selection, and they are more or less liable to reversion. The same rule certainly holds good with parts which have become rudimentary under domestication. We do not know through what steps under nature rudimentary organs have passed in being reduced to their present condition; but we so incessantly see in species of the same group the finest gradations between an organ in a rudimentary and perfect state, that we are led to believe that the passage must have been extremely gradual. It may be doubted whether a change of structure so abrupt as the sudden loss of an organ would ever be of service to a species in a state of nature; for the conditions to which all organisms are closely adapted usually change very slowly. Even if an organ did suddenly disappear in some one individual by an arrest of development, intercrossing with the other individuals of the same species would cause it to reappear in a more or less perfect manner, so that its final reduction could only be effected by the slow process of continued disuse or natural selection. It is much more probable that, from changed habits of life, organs first become of less and less use, and ultimately superfluous; or their place may be supplied by some other organ; and then disuse, acting on the offspring through inheritance at corresponding periods of life, would go on reducing the organ; but as most organs could be of no use at an early embryonic period, they would not be affected by disuse; consequently they would be preserved at this stage of growth, and would remain as rudiments. In addition to the effects of disuse, the principle of economy of growth, already alluded to in this chapter, would lead to the still further reduction of all superfluous parts. With respect to the final and total suppression or abortion of any organ, another and distinct principle, which will be discussed in the chapter on pangenesis, probably takes a share in the work. With animals and plants reared by man there is no severe or recurrent struggle for existence, and the principle of economy will not come into action. So far, indeed, is this from being the case, that in some instances organs, which are naturally rudimentary in the parent-species, become partially redeveloped in the domesticated descendants. Thus cows, like most other ruminants, properly have four active and two rudimentary mammæ; but in our domesticated animals, the latter occasionally become considerably developed and yield milk. The atrophied mammæ, which, in male domesticated animals, including man, have in some rare cases grown to full size and secreted milk, perhaps offer an analogous case. The hind feet of dogs include rudiments of a fifth toe, and in certain large breeds these toes, though still rudimentary, become considerably developed {318} and are furnished with claws. In the common Hen, the spurs and comb are rudimentary, but in certain breeds these become, independently of age or disease of the ovaria, well developed. The stallion has canine teeth, but the mare has only traces of the alveoli, which, as I am informed by the eminent veterinary Mr. G. T. Brown, frequently contain minute irregular nodules of bone. These nodules, however, sometimes become developed into imperfect teeth, protruding through the gums and coated with enamel; and occasionally they grow to a third or even a fourth of the length of the canines in the stallion. With plants I do not know whether the redevelopment of rudimentary organs occurs more frequently under culture than under nature. Perhaps the pear-tree may be a case in point, for when wild it bears thorns, which though useful as a protection are formed of branches in a rudimentary condition, but, when the tree is cultivated, the thorns are reconverted into branches. Finally, though organs which must be classed as rudimentary frequentlyoccur in our domesticated animals and cultivated plants, these havegenerally been formed suddenly, through an arrest of development. Theyusually differ in appearance from the rudiments which so frequentlycharacterise natural species. In the latter, rudimentary organs have beenslowly formed through continued disuse, acting by inheritance at acorresponding age, aided by the principle of the economy of growth, allunder the control of natural selection. With domesticated animals, on theother hand, the principle of economy is far from coming into action, andtheir organs, although often slightly reduced by disuse, are not thusalmost obliterated with mere rudiments left. * * * * * {319} CHAPTER XXV. LAWS OF VARIATION, _continued_--CORRELATED VARIABILITY. EXPLANATION OF TERM--CORRELATION AS CONNECTED WITH DEVELOPMENT--MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED SIZE OF PARTS--CORRELATED VARIATION OF HOMOLOGOUS PARTS--FEATHERED FEET IN BIRDS ASSUMING THE STRUCTURE OF THE WINGS--CORRELATION BETWEEN THE HEAD AND THE EXTREMITIES--BETWEEN THE SKIN AND DERMAL APPENDAGES--BETWEEN THE ORGANS OF SIGHT AND HEARING--CORRELATED MODIFICATIONS IN THE ORGANS OF PLANTS--CORRELATED MONSTROSITIES--CORRELATION BETWEEN THE SKULL AND EARS--SKULL AND CREST OF FEATHERS--SKULL AND HORNS--CORRELATION OF GROWTH COMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL SELECTION--COLOUR AS CORRELATED WITH CONSTITUTIONAL PECULIARITIES. All the parts of the organisation are to a certain extent connected orcorrelated together; but the connexion may be so slight that it hardlyexists, as with compound animals or the buds on the same tree. Even in thehigher animals various parts are not at all closely related; for one partmay be wholly suppressed or rendered monstrous without any other part ofthe body being affected. But in some cases, when one part varies, certainother parts always, or nearly always, simultaneously vary; they are thensubject to the law of correlated variation. Formerly I used the somewhatvague expression of correlation of growth, which may be applied to manylarge classes of facts. Thus, all the parts of the body are admirablycoordinated for the peculiar habits of life of each organic being, and theymay be said, as the Duke of Argyll insists in his 'Reign of Law, ' to becorrelated for this purpose. Again, in large groups of animals certainstructures always co-exist; for instance, a peculiar form of stomach withteeth of peculiar form, and such structures may in one sense be said to becorrelated. But these cases have no necessary connexion with the law to bediscussed in the present chapter; for we do not know that {320} the initialor primary variations of the several parts were in any way related; slightmodifications or individual differences may have been preserved, first inone and then in another part, until the final and perfectly co-adaptedstructure was acquired; but to this subject I shall presently recur. Again, in many groups of animals the males alone are furnished with weapons, orare ornamented with gay colours; and these characters manifestly stand insome sort of correlation with the male reproductive organs, for when thelatter are destroyed these characters disappear. But it was shown in thetwelfth chapter that the very same peculiarity may become attached at anyage to either sex, and afterwards be exclusively transmitted by the samesex at a corresponding age. In these cases we have inheritance limited by, or correlated with, both sex and age; but we have no reason for supposingthat the original cause of the variation was necessarily connected with thereproductive organs, or with the age of the affected being. In cases of true correlated variation, we are sometimes able to see thenature of the connexion; but in most cases the bond is hidden from us, andcertainly differs in different cases. We can seldom say which of twocorrelated parts first varies, and induces a change in the other; orwhether the two are simultaneously produced by some distinct cause. Correlated variation is an important subject for us; for when one part ismodified through continued selection, either by man or under nature, otherparts of the organisation will be unavoidably modified. From thiscorrelation it apparently follows that, with our domesticated animals andplants, varieties rarely or never differ from each other by some singlecharacter alone. One of the simplest cases of correlation is that a modification whicharises during an early stage of growth tends to influence the subsequentdevelopment of the same part, as well as of other and intimately connectedparts. Isidore Geoffroy St. Hilaire states[804] that this may constantly beobserved with monstrosities {321} in the animal kingdom; andMoquin-Tandon[805] remarks, that, as with plants the axis cannot becomemonstrous without in some way affecting the organs subsequently producedfrom it, so axial anomalies are almost always accompanied by deviations ofstructure in the appended parts. We shall presently see that withshort-muzzled races of the dog certain histological changes in the basalelements of the bones arrest their development and shorten them, and thisaffects the position of the subsequently developed molar teeth. It isprobable that certain modifications in the larvæ of insects would affectthe structure of the mature insects. But we must be very careful not toextend this view too far, for, during the normal course of development, certain members in the same group of animals are known to pass through anextraordinary course of change, whilst other and closely allied membersarrive at maturity with little change of structure. Another simple case of correlation is that with the increased or decreaseddimensions of the whole body, or of any particular part, certain organs areincreased or diminished in number, or are otherwise modified. Thuspigeon-fanciers have gone on selecting pouters for length of body, and wehave seen that their vertebræ are generally increased in number, and theirribs in breadth. Tumblers have been selected for their small bodies, andtheir ribs and primary wing-feathers are generally lessened in number. Fantails have been selected for their large, widely-expanded tails, withnumerous tail-feathers, and the caudal vertebræ are increased in size andnumber. Carriers have been selected for length of beak, and their tongueshave become longer, but not in strict accordance with the length of beak. In this latter breed and in others having large feet, the number of thescutellæ on the toes is greater than in the breeds with small feet. Manysimilar cases could be given. In Germany it has been observed that theperiod of gestation is longer in large-sized than in small-sized breeds ofcattle. With our highly-improved animals of all kinds the period ofmaturity has advanced, both with respect to the full growth of the body andthe period of reproduction; and, in correspondence with this, the teeth arenow developed earlier than formerly, so that, {322} to the surprise ofagriculturists, the ancient rules for judging the age of an animal by thestate of its teeth are no longer trustworthy. [806] _Correlated Variation of Homologous Parts. _--Parts which are homologoustend to vary in the same manner; and this is what might have been expected, for such parts are identical in form and structure during an early periodof embryonic development, and are exposed in the egg or womb to similarconditions. The symmetry, in most kinds of animals, of the corresponding orhomologous organs on the right and left sides of the body, is the simplestcase in point; but this symmetry sometimes fails, as with rabbits havingonly one ear, or stags with one horn, or with many-horned sheep whichsometimes carry an additional horn on one side of their heads. With flowerswhich have regular corollas, the petals generally vary in the same manner, as we see in the same complicated and elegant pattern, on the flowers ofthe Chinese pink; but with irregular flowers, though the petals are ofcourse homologous, this symmetry often fails, as with the varieties of the_Antirrhinum_ or snapdragon, or that variety of the kidney-bean (_Phaseolusmultiflorus_) which has a white standard-petal. In the vertebrata the front and hind limbs are homologous, and they tend tovary in the same manner, as we see in long and short-legged, or in thickand thin-legged races of the horse and dog. Isidore Geoffroy[807] hasremarked on the tendency of supernumerary digits in man to appear, not onlyon the right and left sides, but on the upper and lower extremities. Meckelhas insisted[808] that, when the muscles of the arm depart in number orarrangement from their proper type, they almost always imitate those of theleg; and so conversely the varying muscles of the leg imitate the normalmuscles of the arm. In several distinct breeds of the pigeon and fowl, the legs and the twoouter toes are heavily feathered, so that in the trumpeter pigeon theyappear like little wings. In the feather-legged bantam the "boots" orfeathers, which grow from the outside of the leg and generally from the twoouter toes, have, {323} according to the excellent authority of Mr. Hewitt, [809] been seen to exceed the wing-feathers in length, and in onecase were actually nine and a half inches in length! As Mr. Blyth hasremarked to me, these leg-feathers resemble the primary wing-feathers, andare totally unlike the fine down which naturally grows on the legs of somebirds, such as grouse and owls. Hence it may be suspected that excess offood has first given redundancy to the plumage, and then that the law ofhomologous variation has led to the development of feathers on the legs, ina position corresponding with those on the wing, namely, on the outside ofthe tarsi and toes. I am strengthened in this belief by the followingcurious case of correlation, which for a long time seemed to me utterlyinexplicable, namely, that in pigeons of any breed, if the legs arefeathered, the two outer toes are partially connected by skin. These twoouter toes correspond with our third and fourth toes. Now, in the wing ofthe pigeon or any other bird, the first and fifth digits are whollyaborted; the second is rudimentary and carries the so-called"bastard-wing;" whilst the third and fourth digits are completely unitedand enclosed by skin, together forming the extremity of the wing. So thatin feather-footed pigeons, not only does the exterior surface support a rowof long feathers, like wing-feathers, but the very same digits which in thewing are completely united by skin become partially united by skin in thefeet; and thus by the law of the correlated variation of homologous partswe can understand the curious connection of feathered legs and membranebetween the two outer toes. Andrew Knight[810] has remarked that the face or head and the limbs varytogether in general proportions. Compare, for instance, the head and limbsof a dray and race-horse, or of a greyhound and mastiff. What a monster agreyhound would appear with the head of a mastiff! The _modern_ bulldog, however, has fine limbs, but this is a recently-selected character. Fromthe measurements given in the sixth chapter, we clearly see that in all thebreeds of the pigeon the length of the beak and the size of the feet arecorrelated. The view which, as before explained, seems the most probableis, that disuse in all cases tends {324} to diminish the feet, the beakbecoming at the same time through correlation shorter; but that in thosefew breeds in which length of beak has been a selected point, the feet, notwithstanding disuse, have through correlation increased in size. With the increased length of the beak in pigeons, not only the tongueincreases in length, but likewise the orifice of the nostrils. But theincreased length of the orifice of the nostrils perhaps stands in closercorrelation with the development of the corrugated skin or wattle at thebase of the beak; for when there is much wattle round the eyes, the eyelidsare greatly increased or even doubled in length. There is apparently some correlation even in colour between the head andthe extremities. Thus with horses a large white star or blaze on theforehead is generally accompanied by white feet. [811] With white rabbitsand cattle, dark marks often co-exist on the tips of the ears and on thefeet. In black and tan dogs of different breeds, tan-coloured spots overthe eyes and tan-coloured feet almost invariably go together. These lattercases of connected colouring may be due either to reversion or to analogousvariation, --subjects to which we shall hereafter return, --but this does notnecessarily determine the question of their original correlation. If thosenaturalists are correct who maintain that the jaw-bones are homologous withthe limb-bones, then we can understand why the head and limbs tend to varytogether in shape and even in colour; but several highly competent judgesdispute the correctness of this view. The lopping forwards and downwards of the immense ears of fancy rabbits isin part due to the disuse of the muscles, and in part to the weight andlength of the ears, which have been increased by selection during manygenerations. Now, with the increased size and changed direction of theears, not only has the bony auditory meatus become changed in outline, direction, and greatly in size, but the whole skull has been slightlymodified. This could be clearly seen in "half-lops"--that is, in rabbitswith one ear alone lopping forward--for the opposite sides of their skullswere not strictly symmetrical. This seems to me a curious instance ofcorrelation, between hard {325} bones and organs so soft and flexible, aswell as so unimportant under a physiological point of view, as the externalears. The result no doubt is largely due to mere mechanical action, thatis, to the weight of the ears, on the same principle that the skull of ahuman infant is easily modified by pressure. The skin and the appendages of hair, feathers, hoofs, horns, and teeth, arehomologous over the whole body. Every one knows that the colour of the skinand that of the hair usually vary together; so that Virgil advises theshepherd to look whether the mouth and tongue of the ram are black, lestthe lambs should not be purely white. With poultry and certain ducks wehave seen that the colour of the plumage stands in some connexion with thecolour of the shell of the egg, --that is, with the mucous membrane whichsecretes the shell. The colour of the skin and hair, and the odour emittedby the glands of the skin, are said[812] to be connected, even in the samerace of men. Generally the hair varies in the same way all over the body inlength, fineness, and curliness. The same rule holds good with feathers, aswe see with the laced and frizzled breeds both of fowls and pigeons. In thecommon cock the feathers on the neck and loins are always of a particularshape, called hackles: now in the Polish breed, both sexes arecharacterised by a tuft of feathers on the head; but through correlationthese feathers in the male always assume the form of hackles. The wing andtail-feathers, though arising from parts not homologous, vary in lengthtogether; so that long or short winged pigeons generally have long or shorttails. The case of the Jacobin-pigeon is more curious, for the wing andtail feathers are remarkably long; and this apparently has arisen incorrelation with the elongated and reversed feathers on the back of theneck, which form the hood. The hoofs and hair are homologous appendages; and a careful observer, namely Azara, [813] states that in Paraguay horses of various colours areoften born with their hair curled and twisted like that on the head of anegro. This peculiarity is strongly inherited. But what is remarkable isthat the hoofs of these horses "are absolutely like those of a mule. " Thehair also of the mane and tail is invariably much shorter than usual, beingonly from four {326} to twelve inches in length; so that curliness andshortness of the hair are here, as with the negro, apparently correlated. With respect to the horns of sheep, Youatt[814] remarks that "multiplicityof horns is not found in any breed of much value: it is generallyaccompanied by great length and coarseness of the fleece. " Several tropicalbreeds of sheep, which are clothed with hair instead of wool, have hornsalmost like those of a goat. Sturm[815] expressly declares that indifferent races the more the wool is curled the more the horns are spirallytwisted. We have seen in the third chapter, where other analogous factshave been given, that the parent of the Mauchamp breed, so famous for itsfleece, had peculiarly shaped horns. The inhabitants of Angora assert[816]that "only the white goats which have horns wear the fleece in the longcurly locks that are so much admired; those which are not horned having acomparatively close coat. " From these cases we may conclude that the hairor wool and the horns vary in a correlated manner. Those who have triedhydropathy are aware that the frequent application of cold water stimulatesthe skin; and whatever stimulates the skin tends to increase the growth ofthe hair, as is well shown in the abnormal growth of hair near old inflamedsurfaces. Now, Professor Low[817] is convinced that with the differentraces of British cattle thick skin and long hair depend on the humidity ofthe climate which they inhabit. We can thus see how a humid climate mightact on the horns--in the first place directly on the skin and hair, andsecondly by correlation on the horns. The presence or absence of horns, moreover, both in the case of sheep and cattle, acts, as will presently beshown, by some sort of correlation on the skull. With respect to hair and teeth, Mr. Yarrell[818] found many of the teethdeficient in three hairless "_Ægyptian_" dogs, and in a hairless terrier. The incisors, canines, and premolars suffered most, but in one case all theteeth, except the large tubercular molar on each side, were deficient. Withman several striking cases have been recorded[819] of inherited baldnesswith {327} inherited deficiency, either complete or partial, of the teeth. We see the same connexion in those rare cases in which the hair has beenrenewed in old age, for this has "usually been accompanied by a renewal ofthe teeth. " I have remarked in a former part of this volume that the greatreduction in the size of the tusks in domestic boars probably stands inclose relation with their diminished bristles, due to a certain amount ofprotection; and that the reappearance of the tusks in boars, which havebecome feral and are fully exposed to the weather, probably depends on thereappearance of the bristles. I may add, though not strictly connected withour present point, that an agriculturist[820] asserts that "pigs withlittle hair on their bodies are most liable to lose their tails, showing aweakness of the tegumental structure. It may be prevented by crossing witha more hairy breed. " In the previous cases deficient hair, and teeth deficient in number orsize, are apparently connected. In the following cases abnormally redundanthair, and teeth either deficient or redundant, are likewise connected. Mr. Crawfurd[821] saw at the Burmese Court a man, thirty years old, with hiswhole body, except the hands and feet, covered with straight silky hair, which on the shoulders and spine was five inches in length. At birth theears alone were covered. He did not arrive at puberty, or shed his milkteeth, until twenty years old; and at this period he acquired five teeth inthe upper jaw, namely four incisors and one canine, and four incisor teethin the lower jaw; all the teeth were small. This man had a daughter, whowas born with hair within her ears; and the hair soon extended over herbody. When Captain Yule[822] visited the Court, he found this girl grownup; and she presented a strange appearance with even her nose denselycovered with soft hair. Like her father, she was furnished with incisorteeth alone. The King had with difficulty bribed a man to marry her, and ofher two children, one, a boy fourteen months old, had hair growing out ofhis ears, with a beard and moustache. This strange peculiarity had, therefore, been inherited for three generations, with the molar teethdeficient in the grandfather and mother; whether {328} these teeth wouldlikewise fail in the infant could not be told. Here is another casecommunicated to me by Mr. Wallace on the authority of Dr. Purland, adentist: Julia Pastrana, a Spanish dancer, was a remarkably fine woman, butshe had a thick masculine beard and a hairy forehead; she was photographed, and her stuffed skin was exhibited as a show; but what concerns us is, thatshe had in both the upper and lower jaw an irregular double set of teeth, one row being placed within the other, of which Dr. Purland took a cast. From the redundancy of the teeth her mouth projected, and her face had agorilla-like appearance. These cases and those of the hairless dogsforcibly call to mind the fact, that the two orders of mammals--namely, theEdentata and Cetacea--which are the most abnormal in their dermal covering, are likewise the most abnormal either by deficiency or redundancy of teeth. The organs of sight and hearing are generally admitted to be homologous, both with each other and with the various dermal appendages; hence theseparts are liable to be abnormally affected in conjunction. Mr. White Cowpersays "that in all cases of double microphthalmia brought under his noticehe has at the same time met with defective development of the dentalsystem. " Certain forms of blindness seem to be associated with the colourof the hair; a man with black hair and a woman with light-coloured hair, both of sound constitution, married and had nine children, all of whom wereborn blind; of these children, five "with dark hair and brown iris wereafflicted with amaurosis; the four others, with light-coloured hair andblue iris, had amaurosis and cataract conjoined. " Several cases could begiven, showing that some relation exists between various affections of theeyes and ears; thus Liebreich states that out of 241 deaf-mutes in Berlin, no less than fourteen suffered from the rare disease called pigmentaryretinitis. Mr. White Cowper and Dr. Earle have remarked that inability todistinguish different colours, or colour-blindness, "is often associatedwith a corresponding inability to distinguish musical sounds. "[823] {329} Here is a more curious case: white cats, if they have blue eyes, are almostalways deaf. I formerly thought that the rule was invariable, but I haveheard of a few authentic exceptions. The first two notices were publishedin 1829, and relate to English and Persian cats: of the latter, the Rev. W. T. Bree possessed a female, and he states "that of the offspringproduced at one and the same birth, such as, like the mother, were entirelywhite (with blue eyes) were, like her, invariably deaf; while those thathad the least speck of colour on their fur, as invariably possessed theusual faculty of hearing. "[824] The Rev. W. Darwin Fox informs me that hehas seen more than a dozen instances of this correlation in English, Persian, and Danish cats; but he adds "that, if one eye, as I have severaltimes observed, be not blue, the cat hears. On the other hand, I have neverseen a white cat with eyes of the common colour that was deaf. " In FranceDr. Sichel[825] has observed during twenty years similar facts; he adds theremarkable case of the iris beginning, at the end of four months, to growdark-coloured, and then the cat first began to hear. This case of correlation in cats has struck many persons as marvellous. There is nothing unusual in the relation between blue eyes and white fur;and we have already seen that the organs of sight and hearing are oftensimultaneously affected. In the present instance the cause probably lies ina slight arrest of development in the nervous system in connection with thesense-organs. Kittens during the first nine days, whilst their eyes areclosed, appear to be completely deaf; I have made a great clanging noisewith a poker and shovel close to their heads, both when they were asleepand awake, without producing any effect. The trial must not be made byshouting close to their ears, for they are, even when asleep, extremelysensitive to a breath of air. Now, as long as the eyes continue closed, theiris is no doubt blue, for in all the kittens which I have seen this colourremains for some time after the eyelids open. Hence, if we suppose thedevelopment of the organs of sight and hearing to be arrested at the stageof the closed eyelids, the eyes would {330} remain permanently blue and theears would be incapable of perceiving sound; and we should thus understandthis curious case. As, however, the colour of the fur is determined longbefore birth, and as the blueness of the eyes and the whiteness of the furare obviously connected, we must believe that some primary cause acts at anearly period. The instances of correlated variability hitherto given have been chieflydrawn from the animal kingdom, and we will now turn to plants. Leaves, sepals, petals, stamens, and pistils are all homologous. In double flowerswe see that the stamens and pistils vary in the same manner, and assume theform and colour of the petals. In the double columbine (_Aquilegiavulgaris_), the successive whorls of stamens are converted intocornucopias, which are enclosed within each other and resemble the petals. In hose-and-hose flowers the sepals mock the petals. In some cases theflowers and leaves vary together in tint: in all the varieties of thecommon pea, which have purple flowers, a purple mark may be seen on thestipules. In other cases the leaves and fruit and seeds vary together incolour, as in a curious pale-leaved variety of the sycamore, which hasrecently been described in France, [826] and as in the purple-leaved hazel, in which the leaves, the husk of the nut, and the pellicle round the kernelare all coloured purple. [827] Pomologists can predict to a certain extent, from the size and appearance of the leaves of their seedlings, the probablenature of the fruit; for, as Van Mons remarks, [828] variations in theleaves are generally accompanied by some modification in the flower, andconsequently in the fruit. In the Serpent melon, which has a narrowtortuous fruit above a yard in length, the stem of the plant, the peduncleof the female flower, and the middle lobe of the leaf, are all elongated ina remarkable manner. On the other hand, several varieties of Cucurbita, which have dwarfed stems, all produce, as Naudin remarks with surprise, leaves of the same peculiar shape. Mr. G. Maw informs me that all thevarieties of the scarlet Pelargoniums which have contracted or imperfectleaves have contracted flowers: the difference between {331} "Brilliant"and its parent "Tom Thumb" is a good instance of this. It may be suspectedthat the curious case described by Risso, [829] of a variety of the Orangewhich produces on the young shoots rounded leaves with winged petioles, andafterwards elongated leaves on long but wingless petioles, is connectedwith the remarkable change in form and nature which the fruit undergoesduring its development. In the following instance we have the colour and form of the petalsapparently correlated, and both dependent on the nature of the season. Anobserver, skilled in the subject, writes, [830] "I noticed, during the year1842, that every Dahlia, of which the colour had any tendency to scarlet, was deeply notched--indeed to so great an extent as to give the petals theappearance of a saw; the indentures were, in some instances, more than aquarter of an inch deep. " Again, Dahlias which have their petals tippedwith a different colour from the rest are very inconstant, and duringcertain years some, or even all the flowers, become uniformly coloured; andit has been observed with several varieties, [831] that when this happensthe petals grow much elongated and lose their proper shape. This, however, may be due to reversion, both in colour and form, to the aboriginalspecies. * * * * * In this discussion on correlation, we have hitherto treated of cases inwhich we can partly understand the bond of connexion; but I will now givecases in which we cannot even conjecture, or can only very obscurely see, what is the nature of the bond. Isidore Geoffroy St. Hilaire, in his workon Monstrosities, insists, [832] "que certaines anomalies coexistentrarement entr'elles, d'autres fréquemment, d'autres enfin presqueconstamment, malgré la différence très-grande de leur nature, etquoiqu'elles puissent paraître _complètement indépendantes_ les unes desautres. " We see something analogous in certain diseases: thus I hear fromMr. Paget that in a rare affection of the {332} renal capsules (of whichthe functions are unknown), the skin becomes bronzed; and in hereditarysyphilis, both the milk and the second teeth assume a peculiar andcharacteristic form. Professor Rolleston, also, informs me that the incisorteeth are sometimes furnished with a vascular rim in correlation withintra-pulmonary deposition of tubercles. In other cases of phthisis and ofcyanosis the nails and finger-ends become clubbed like acorns. I believethat no explanation has been offered of these and of many other cases ofcorrelated disease. What can be more curious and less intelligible than the fact previouslygiven, on the authority of Mr. Tegetmeier, that young pigeons of allbreeds, which when mature have white, yellow, silver-blue, or dun-colouredplumage, come out of the egg almost naked; whereas pigeons of other colourswhen first born are clothed with plenty of down? White Pea-fowls, as hasbeen observed both in England and France, [833] and as I have myself seen, are inferior in size to the common coloured kind; and this cannot beaccounted for by the belief that albinism is always accompanied byconstitutional weakness; for white or albino moles are generally largerthan the common kind. To turn to more important characters: the niata cattle of the Pampas areremarkable from their short foreheads, upturned muzzles, and curved lowerjaws. In the skull the nasal and premaxillary bones are much shortened, themaxillaries are excluded from any junction with the nasals, and all thebones are slightly modified, even to the plane of the occiput. From theanalogical case of the dog, hereafter to be given, it is probable that theshortening of the nasal and adjoining bones is the proximate cause of theother modifications in the skull, including the upward curvature of thelower jaw, though we cannot follow out the steps by which these changeshave been effected. Polish fowls have a large tuft of feathers on their heads; and their skullsare perforated by numerous holes, so that a pin can be driven into thebrain without touching any bone. That this deficiency of bone is in someway connected with the tuft of feathers is clear from tufted ducks andgeese likewise having {333} perforated skulls. The case would probably beconsidered by some authors as one of balancement or compensation. In thechapter on Fowls, I have shown that with Polish fowls the tuft of featherswas probably at first small; by continued selection it became larger, andthen rested on a fleshy or fibrous mass; and finally, as it became stilllarger, the skull itself became more and more protuberant until it acquiredits present extraordinary structure. Through correlation with theprotuberance of the skull, the shape and even the relative connexion of thepremaxillary and nasal bones, the shape of the orifice of the nostrils, thebreadth of the frontal bone, the shape of the post-lateral processes of thefrontal and squamosal bones, and the direction of the bony cavity of theear, have all been modified. The internal configuration of the skull andthe whole shape of the brain have likewise been altered in a trulymarvellous manner. After this case of the Polish fowl it would be superfluous to do more thanrefer to the details previously given on the manner in which the changedform of the comb, in various breeds of the fowl, has affected the skull, causing by correlation crests, protuberances, and depressions on itssurface. With our cattle and sheep the horns stand in close connexion with the sizeof the skull, and with the shape of the frontal bones; thus Cline[834]found that the skull of a horned ram weighed five times as much as that ofa hornless ram of the same age. When cattle become hornless, the frontalbones are "materially diminished in breadth towards the poll;" and thecavities between the bony plates "are not so deep, nor do they extendbeyond the frontals. "[835] * * * * * It may be well here to pause and observe how the effects of correlatedvariability, of the increased use of parts, and of the accumulation throughnatural selection of so-called spontaneous variations, are in many casesinextricably commingled. We may borrow an illustration from Mr. HerbertSpencer, who remarks that, when the Irish elk acquired its gigantic horns, weighing above one hundred pounds, numerous co-ordinated {334} changes ofstructure would have been indispensable, --namely, a thickened skull tocarry the horns; strengthened cervical vertebræ, with strengthenedligaments; enlarged dorsal vertebræ to support the neck, with powerfulfore-legs and feet; all these parts being supplied with proper muscles, blood-vessels, and nerves. How then could these admirably co-ordinatedmodifications of structure have been acquired? According to the doctrinewhich I maintain, the horns of the male elk were slowly gained throughsexual selection, --that is, by the best-armed males conquering theworse-armed, and leaving a greater number of descendants. But it is not atall necessary that the several parts of the body should have simultaneouslyvaried. Each stag presents individual differences, and in the same districtthose which had slightly heavier horns, or stronger necks, or strongerbodies, or were the most courageous, would secure the greater number ofdoes, and consequently leave a greater number of offspring. The offspringwould inherit, in a greater or less degree, these same qualities, wouldoccasionally intercross with each other, or with other individuals varyingin some favourable manner; and of their offspring, those which were thebest endowed in any respect would continue multiplying; and so onwards, always progressing, sometimes in one direction, and sometimes in another, towards the present excellently co-ordinated structure of the male elk. Tomake this clear, let us reflect on the probable steps, as shown in thetwentieth chapter, by which our race and dray-horses have arrived at theirpresent state of excellence; if we could view the whole series ofintermediate forms between one of these animals and an early unimprovedprogenitor, we should behold a vast number of animals, not equally improvedin each generation throughout their entire structure, but sometimes alittle more in one point, and sometimes in another, yet on the wholegradually approaching in character to our present race or dray-horses, which are so admirably fitted in the one case for fleetness and in theother for draught. Although natural selection would thus[836] tend to give to the {335} maleelk its present structure, yet it is probable that the inherited influenceof use has played an equal or more important part. As the horns graduallyincreased in weight, the muscles of the neck, with the bones to which theyare attached, would increase in size and strength; and these parts wouldreact on the body and legs. Nor must we overlook the fact that certainparts of the skull and the extremities would, judging by analogy, tend fromthe first to vary in a correlated manner. The increased weight of the hornswould also act directly on the skull, in the same manner as, when one boneis removed in the leg of a dog, the other bone, which has to carry thewhole weight of the body, increases in thickness. But from the facts givenwith respect to horned and hornless cattle, it is probable that the hornsand skull would immediately act on each other through the principle ofcorrelation. Lastly, the growth and subsequent wear and tear of theaugmented muscles and bones would require an increased supply of blood, andconsequently an increased supply of food; and this again would requireincreased powers of mastication, digestion, respiration, and excretion. _Colour as Correlated with Constitutional Peculiarities. _ It is an old belief that with man there is a connexion between complexionand constitution; and I find that some of the best authorities believe inthis to the present day. [837] Thus Dr. Beddoe by his tables shows[838] thata relation exists between liability to consumption and the colour of thehair, eyes, and skin. It has been affirmed[839] that, in the French armywhich invaded Russia, soldiers having a dark complexion, from the {336}southern parts of Europe, withstood the intense cold better than those withlighter complexions from the north; but no doubt such statements are liableto error. In the second chapter on Selection I have given several cases proving thatwith animals and plants differences in colour are correlated withconstitutional differences, as shown by greater or less immunity fromcertain diseases, from the attacks of parasitic plants and animals, fromburning by the sun, and from the action of certain poisons. When all theindividuals of any one variety possess an immunity of this nature, wecannot feel sure that it stands in any sort of correlation with theircolour; but when several varieties of the same species, which are similarlycoloured, are thus characterised, whilst other coloured varieties are notthus favoured, we must believe in the existence of a correlation of thiskind. Thus in the United States purple-fruited plums of many kinds are farmore affected by a certain disease than green or yellow-fruited varieties. On the other hand, yellow-fleshed peaches of various kinds suffer fromanother disease much more than the white-fleshed varieties. In theMauritius red sugar-canes are much less affected by a particular diseasethan the white canes. White onions and verbenas are the most liable tomildew; and in Spain the green-fruited grapes suffered from thevine-disease more than other coloured varieties. Dark-coloured pelargoniumsand verbenas are more scorched by the sun than varieties of other colours. Red wheats are believed to be hardier than white; whilst red-floweredhyacinths were more injured during one particular winter in Holland thanother coloured varieties. With animals, white terriers suffer most from thedistemper, white chickens from a parasitic worm in their tracheæ, whitepigs from scorching by the sun, and white cattle from flies; but thecaterpillars of the silk-moth which yield white cocoons suffered in Franceless from the deadly parasitic fungus than those producing yellow silk. The cases of immunity from the action of certain vegetable poisons, inconnexion with colour, are more interesting, and are at present whollyinexplicable. I have already given a remarkable instance, on the authorityof Professor Wyman, of all the hogs, excepting those of a black colour, suffering severely in Virginia from eating the root of the _Lachnanthestinctoria_. {337} According to Spinola and others, [840] buckwheat(_Polygonum fagopyrum_), when in flower, is highly injurious to white orwhite-spotted pigs, if they are exposed to the heat of the sun, but isquite innocuous to black pigs. By two accounts, the _Hypericum crispum_ inSicily is poisonous to white sheep alone; their heads swell, their woolfalls off, and they often die; but this plant, according to Lecce, ispoisonous only when it grows in swamps; nor is this improbable, as we knowhow readily the poisonous principle in plants is influenced by theconditions under which they grow. Three accounts have been published in Eastern Prussia, of white andwhite-spotted horses being greatly injured by eating mildewed andhoneydewed vetches; every spot of skin bearing white hairs becominginflamed and gangrenous. The Rev. J. Rodwell informs me that his fatherturned out about fifteen cart-horses into a field of tares which in partsswarmed with black aphides, and which no doubt were honeydewed, andprobably mildewed; the horses, with two exceptions, were chesnuts and bayswith white marks on their faces and pasterns, and the white parts aloneswelled and became angry scabs. The two bay horses with no white marksentirely escaped all injury. In Guernsey, when horses eat fools' parsley(_Æthusa cynapium_) they are sometimes violently purged; and this plant"has a peculiar effect on the nose and lips, causing deep cracks andulcers, particularly on horses with white muzzles. "[841] With cattle, independently of the action of any poison, cases have been published byYouatt and Erdt of cutaneous diseases with much constitutional disturbance(in one instance after exposure to a hot sun) affecting every single pointwhich bore a white hair, but completely passing over other parts of thebody. Similar cases have been observed with horses. [842] We thus see that not only do those parts of the skin which bear white hairdiffer in a remarkable manner from those bearing {338} hair of any othercolour, but that in addition some great, constitutional difference muststand in correlation with the colour of the hair; for in theabove-mentioned cases, vegetable poisons caused fever, swelling of thehead, as well as other symptoms, and even death, to all the white orwhite-spotted animals. * * * * * {339} CHAPTER XXVI. LAWS OF VARIATION, _continued_--SUMMARY. ON THE AFFINITY AND COHESION OF HOMOLOGOUS PARTS--ON THE VARIABILITY OF MULTIPLE AND HOMOLOGOUS PARTS--COMPENSATION OF GROWTH--MECHANICAL PRESSURE--RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS OF THE PLANT, AND OF SEEDS IN THE CAPSULE, AS INDUCING VARIATION--ANALOGOUS OR PARALLEL VARIETIES--SUMMARY OF THE THREE LAST CHAPTERS. _On the Affinity of Homologous Parts. _--This law was first generalised byGeoffroy Saint Hilaire, under the expression of _La loi de l'affinité desoi pour soi_. It has been fully discussed and illustrated by his son, Isidore Geoffroy, with respect to monsters in the animal kingdom, [843] andby Moquin-Tandon, with respect to monstrous plants. When similar orhomologous parts, whether belonging to the same embryo or to two distinctembryos, are brought during an early stage of development into contact, they often blend into a single part or organ; and this complete fusionindicates some mutual affinity between the parts, otherwise they wouldsimply cohere. Whether any power exists which tends to bring homologousparts into contact seems more doubtful. The tendency to complete fusion isnot a rare or exceptional fact. It is exhibited in the most striking mannerby double monsters. Nothing can be more extraordinary than the manner, asshown in various published plates, in which the corresponding parts of twoembryos become intimately fused together. This is perhaps best seen inmonsters with two heads, which are united, summit to summit, or face toface, or, Janus-like, back to back, or obliquely side to side. In oneinstance of two heads united almost face to face, but a little obliquely, four ears were developed, and on one side a perfect face, which wasmanifestly formed by the union of two {340} half-faces. Whenever two bodiesor two heads are united, each bone, muscle, vessel, and nerve on the lineof junction seems to seek out its fellow, and becomes completely fused withit. Lereboullet, [844] who carefully studied the development of doublemonsters in fishes, observed in fifteen instances the steps by which twoheads gradually became fused into one. In this and other such cases, noone, I presume, supposes that the two already formed heads actually blendtogether, but that the corresponding parts of each head grow into oneduring the further progress of development, accompanied as it always iswith incessant absorption and renovation. Double monsters were formerlythought to be formed by the union of two originally distinct embryosdeveloped upon distinct vitelli; but now it is admitted that "theirproduction is due to the spontaneous divarication of the embryonic massinto two halves;"[845] this, however, is effected by different methods. Butthe belief that double monsters originate from the division of one germ, does not necessarily affect the question of subsequent fusion, or renderless true the law of the affinity of homologous parts. The cautious and sagacious J. Müller, [846] when speaking of Janus-likemonsters, says, that "without the supposition that some kind of affinity orattraction is exerted between corresponding parts, unions of this kind areinexplicable. " On the other hand, Vrolik, and he is followed by others, disputes this conclusion, and argues from the existence of a whole seriesof monstrosities, graduating from a perfectly double monster to a mererudiment of an additional digit, that "an excess of formative power" is thecause and origin of every monstrous duplicity. That there are two distinctclasses of cases, and that parts may be doubled independently of theexistence of two embryos, is certain; for a single embryo, or even a singleadult animal, may produce doubled organs. Thus Valentin, as quoted byVrolik, injured the caudal extremity of an embryo, and three daysafterwards it produced rudiments of a double pelvis and of double hindlimbs. {341} Hunter and others have observed lizards with their tailsreproduced and doubled. When Bonnet divided longitudinally the foot of thesalamander, several additional digits were occasionally formed. But neitherthese cases, nor the perfect series from a double monster to an additionaldigit, seem to me opposed to the belief that corresponding parts have amutual affinity, and consequently tend to fuse together. A part may bedoubled and remain in this state, or the two parts thus formed mayafterwards through the law of affinity become blended; or two homologousparts in two separate embryos may, through the same principle, unite andform a single part. The law of the affinity and fusion of similar parts applies to thehomologous organs of the same individual animal, as well as to doublemonsters. Isidore Geoffroy gives a number of instances of two or moredigits, of two whole legs, of two kidneys, and of several teeth becomingsymmetrically fused together in a more or less perfect manner. Even the twoeyes have been known to unite into a single eye, forming a cyclopeanmonster, as have the two ears, though naturally standing so far apart. AsGeoffroy remarks, these facts illustrate in an admirable manner the normalfusion of various organs which during an early embryonic period are double, but which afterwards always unite into a single median organ. Organs ofthis nature are generally found in a permanently double condition in othermembers of the same class. These cases of normal fusion appear to me toafford the strongest support in favour of the present law. Adjoining partswhich are not homologous sometimes cohere; but this cohesion appears toresult from mere juxtaposition, and not from mutual affinity. In the vegetable kingdom Moquin-Tandon[847] gives a long list of cases, showing how frequently homologous parts, such as leaves, petals, stamens, and pistils, as well as aggregates of homologous parts, such as buds, flowers, and fruit, become blended into each other with perfect symmetry. It is interesting to examine a compound flower of this nature, formed ofexactly double the proper number of sepals, petals, stamens, and pistils, with each whorl of organs circular, and with no trace left of the {342}process of fusion. The tendency in homologous parts to unite during theirearly development, Moquin-Tandon considers as one of the most striking lawsgoverning the production of monsters. It apparently explains a multitude ofcases, both in the animal and vegetable kingdoms; it throws a clear lighton many normal structures which have evidently been formed by the union oforiginally distinct parts, and it possesses, as we shall see in a futurechapter, much theoretical interest. * * * * * _On the Variability of Multiple and Homologous Parts. _--IsidoreGeoffroy[848] insists that, when any part or organ is repeated many timesin the same animal, it is particularly liable to vary both in number andstructure. With respect to number, the proposition may, I think, beconsidered as fully established; but the evidence is chiefly derived fromorganic beings living under their natural conditions, with which we are nothere concerned. When the vertebræ, or teeth, or rays in the fins of fishes, or feathers in the tails of birds, or petals, stamens, pistils, and seedsin plants, are very numerous, the number is generally variable. Theexplanation of this simple fact is by no means obvious. With respect to thevariability in structure of multiple parts, the evidence is not sodecisive; but the fact, as far as it may be trusted, probably depends onmultiple parts being of less physiological importance than single parts;consequently their perfect standard of structure has been less rigorouslyenforced by natural selection. * * * * * _Compensation of Growth, or Balancement. _--This law, as applied to naturalspecies, was propounded by Goethe and Geoffroy St. Hilaire at nearly thesame time. It implies that, when much organised matter is used in buildingup some one part, other parts are starved and become reduced. Severalauthors, especially botanists, believe in this law; others reject it. Asfar as I can judge, it occasionally holds good; but its importance hasprobably been exaggerated. It is scarcely possible to distinguish betweenthe supposed effects of such compensation of growth, and the effects oflong-continued selection, which {343} may at the same time lead to theaugmentation of one part and the diminution of another. There can be nodoubt that an organ may be greatly increased without any correspondingdiminution in the adjoining parts. To recur to our former illustration ofthe Irish elk, it may be asked what part has suffered in consequence of theimmense development of the horns? It has already been observed that the struggle for existence does not bearhard on our domesticated productions; consequently the principle of economyof growth will seldom affect them, and we ought not to expect to findfrequent evidence of compensation. We have, however, some such cases. Moquin-Tandon describes a monstrous bean, [849] in which the stipules wereenormously developed, and the leaflets apparently in consequence completelyaborted; this case is interesting, as it represents the natural conditionof _Lathyrus aphaca_, with its stipules of great size, and its leavesreduced to mere threads, which act as tendrils. De Candolle[850] hasremarked that the varieties of _Raphanus sativus_ which have small rootsyield numerous seed, valuable from containing oil, whilst those with largeroots are not productive in this latter respect; and so it is with_Brassica asperifolia_. The varieties of the potato which produce tubersvery early in the season rarely bear flowers; but Andrew Knight, [851] bychecking the growth of the tubers, forced the plants to flower. Thevarieties of _Cucurbita pepo_ which produce large fruit yield, according toNaudin, few in number; whilst those producing small fruit yield a vastnumber. Lastly, I have endeavoured to show in the eighteenth chapter thatwith many cultivated plants unnatural treatment checks the full and properaction of the reproductive organs, and they are thus rendered more or lesssterile; consequently, in the way of compensation, the fruit becomesgreatly enlarged, and, in double flowers, the petals are greatly increasedin number. With animals, it has been found difficult to produce cows which shouldfirst yield much milk, and afterwards be capable of {344} fattening well. With fowls which have large topknots and beards the comb and wattles aregenerally much reduced in size. Perhaps the entire absence of the oil-glandin fantail pigeons may be connected with the great development of theirtails. * * * * * _Mechanical Pressure as a Cause of Modifications. _--In some few cases thereis reason to believe that mere mechanical pressure has affected certainstructures. Every one knows that savages alter the shape of their infants'skulls by pressure at an early age; but there is no reason to believe thatthe result is ever inherited. Nevertheless Vrolik and Weber[852] maintainthat the shape of the human head is influenced by the shape of the mother'spelvis. The kidneys in different birds differ much in form, and St. Ange[853] believes that this is determined by the form of the pelvis, whichagain, no doubt, stands in close relation with their various habits oflocomotion. In snakes, the viscera are curiously displaced, in comparisonwith their position in other vertebrates; and this has been attributed bysome authors to the elongation of their bodies; but here, as in so manyprevious cases, it is impossible to disentangle any direct result of thiskind from that consequent on natural selection. Godron has argued[854] thatthe normal abortion of the spur on the inner side of the flower inCorydalis, is caused by the buds being closely pressed at a very earlyperiod of growth, whilst under ground, against each other and against thestem. Some botanists believe that the singular difference in the shape bothof the seed and corolla, in the interior and exterior florets in certaincompositous and umbelliferous plants, is due to the pressure to which theinner florets are subjected; but this conclusion is doubtful. The facts just given do not relate to domesticated productions, andtherefore do not strictly concern us. But here is a more appropriate case:H. Müller[855] has shown that in {345} short-faced races of the dog some ofthe molar teeth are placed in a slightly different position from that whichthey occupy in other dogs, especially in those having elongated muzzles;and as he remarks, any inherited change in the arrangement of the teethdeserves notice, considering their classificatory importance. Thisdifference in position is due to the shortening of certain facial bones, and the consequent want of space; and the shortening results from apeculiar and abnormal state of the basal cartilages of the bones. _Relative Position of Flowers with respect to the Axis, and of Seeds in theCapsule, as inducing Variation. _ In the thirteenth chapter various peloric flowers were described, and their production was shown to be due either to arrested development, or to reversion to a primordial condition. Moquin-Tandon has remarked that the flowers which stand on the summit of the main stem or of a lateral branch are more liable to become peloric than those on the sides;[856] and he adduces, amongst other instances, that of _Teucrium campanulatum_. In another Labiate plant grown by me, viz. The _Galeobdolon luteum_, the peloric flowers were always produced on the summit of the stem, where flowers are not usually borne. In Pelargonium, a _single_ flower in the truss is frequently peloric, and when this occurs I have during several years invariably observed it to be the central flower. This is of such frequent occurrence that one observer[857] gives the names of ten varieties flowering at the same time, in every one of which the central flower was peloric. Occasionally more than one flower in the truss is peloric, and then of course the additional ones must be lateral. These flowers are interesting as showing how the whole structure is correlated. In the common Pelargonium the upper sepal is produced into a nectary which coheres with the flower-peduncle; the two upper petals differ a little in shape from the three lower ones, and are marked with dark shades of colour; the stamens are graduated in length and upturned. In the peloric flowers, the nectary aborts; all the petals become alike both in shape and colour; the stamens are generally reduced in number and become straight, so that the whole flower resembles that of the allied genus Erodium. The correlation between these changes is well shown when one of the two upper petals alone loses its dark mark, for in this case the nectary does not entirely abort, but is usually much reduced in length. [858] {346} Morren has described[859] a marvellous flask-shaped flower of the Calceolaria, nearly four inches in length, which was almost completely peloric; it grew on the summit of the plant, with a normal flower on each side; Prof. Westwood also has described[860] three similar peloric flowers, which all occupied a central position on the flower-branches. In the Orchideous genus, Phalænopsis, the terminal flower has been seen to become peloric. In a Laburnum-tree I observed that about a fourth part of the racemes produced terminal flowers which had lost their papilionaceous structure. These were produced after almost all the other flowers on the same racemes had withered. The most perfectly pelorised examples had six petals, each marked with black striæ like those on the standard-petal. The keel seemed to resist the change more than the other petals. Dutrochet has described[861] an exactly similar case in France, and I believe these are the only two instances of pelorism in the laburnum which have been recorded. Dutrochet remarks that the racemes on this tree do not properly produce a terminal flower, so that, as in the case of the Galeobdolon, their position as well as their structure are both anomalies, which no doubt are in some manner related. Dr. Masters has briefly described another leguminous plant, [862] namely, a species of clover, in which the uppermost and central flowers were regular or had lost their papilionaceous structure. In some of these plants the flower-heads were also proliferous. Lastly, Linaria produces two kinds of peloric flowers, one having simple petals, and the other having them all spurred. The two forms, as Naudin remarks, [863] not rarely occur on the same plant, but in this case the spurred form almost invariably stands on the summit of the spike. The tendency in the terminal or central flower to become peloric more frequently than other flowers, probably results from "the bud which stands on the end of a shoot receiving the most sap; it grows out into a stronger shoot than those situated lower down. "[864] I have discussed the connection between pelorism and a central position, partly because some few plants are known normally to produce a terminal flower different in structure from the lateral ones; but chiefly on account of the following case, in which we see a tendency to variability or to reversion connected with the same position. A great judge of Auriculas[865] states that when an Auricula throws up a side bloom it is pretty sure to keep its character; but that if it grows from the centre or heart of the plant, whatever the colour of the edging ought to be, "it is just as likely to come in any other class as in the one to which it properly belongs. " This is so notorious a {347} fact, that some florists regularly pinch off the central trusses of flowers. Whether in the highly improved varieties the departure of the central trusses from their proper type is due to reversion, I do not know. Mr. Dombrain insists that, whatever may be the commonest kind of imperfection in each variety, this is generally exaggerated in the central truss. Thus one variety "sometimes has the fault of producing a little green floret in the centre of the flower, " and in central blooms these become excessive in size. In some central blooms, sent to me by Mr. Dombrain, all the organs of the flower were rudimentary in structure, of minute size, and of a green colour, so that by a little further change all would have been converted into small leaves. In this case we clearly see a tendency to prolification--a term which, I may explain to those who have never attended to botany, means the production of a branch or flower, or head of flowers, out of another flower. Now Dr. Masters[866] states that the central or uppermost flower on a plant is generally the most liable to prolification. Thus, in the varieties of the Auricula, the loss of their proper character and a tendency to prolification, and in other plants a tendency to prolification and pelorism, are all connected together, and are due either to arrested development, or to reversion to a former condition. The following is a more interesting case; Metzger[867] cultivated in Germany several kinds of maize brought from the hotter parts of America, and he found, as has been previously described, that in two or three generations the grains became greatly changed in form, size, and colour; and with respect to two races he expressly states that in the first generation, whilst the lower grains on each head retained their proper character, the uppermost grains already began to assume that character which in the third generation all the grains acquired. As we do not know the aboriginal parent of the maize, we cannot tell whether these changes are in any way connected with reversion. In the two following cases, reversion, as influenced by the position of the seed in the capsule, evidently acts. The Blue Imperial pea is the offspring of the Blue Prussian, and has larger seed and broader pods than its parent. Now Mr. Masters, of Canterbury, a careful observer and a raiser of new varieties of the pea, states[868] that the Blue Imperial always has a strong tendency to revert to its parent-stock, and the reversion "occurs in this manner: the last (or uppermost) pea in the pod is frequently much smaller than the rest; and if these small peas are carefully collected and sown separately, very many more, in proportion, will revert to their origin, than those taken from the other parts of the pod. " Again M. Chaté[869] says that in raising seedling stocks he succeeds in getting eighty per cent. To bear double flowers, by leaving only a few of the secondary branches to seed; but in addition to this, "at the time of extracting the seeds, the upper portion of the pod is separated and {348} placed aside, because it has been ascertained that the plants coming from the seeds situated in this portion of the pod, give eighty per cent. Of single flowers. " Now the production of single-flowering plants from the seed of double-flowering plants is clearly a case of reversion. These latter facts, as well as the connection between a central position and pelorism and prolification, show in an interesting manner how small a difference--namely a little greater freedom in the flow of sap towards one part of the same plant--determines important changes of structure. * * * * * _Analogous or Parallel Variation. _--By this term I wish to express thatsimilar characters occasionally make their appearance in the severalvarieties or races descended from the same species, and more rarely in theoffspring of widely distinct species. We are here concerned, not ashitherto with the causes of variation, but with the results; but thisdiscussion could not have been more conveniently introduced elsewhere. Thecases of analogous variation, as far as their origin is concerned, may begrouped, disregarding minor subdivisions, under two main heads; firstly, those due to unknown causes having acted on organic beings with nearly thesame constitution, and which consequently vary in an analogous manner; andsecondly, those due to the reappearance of characters which were possessedby a more or less remote progenitor. But these two main divisions can oftenbe only conjecturally separated, and graduate, as we shall presently see, into each other. Under the first head of analogous variations, not due to reversion, we have the many cases of trees belonging to quite different orders which have produced pendulous and fastigate varieties. The beech, hazel, and barberry have given rise to purple-leaved varieties; and as Bernhardi has remarked, [870] a multitude of plants, as distinct as possible, have yielded varieties with deeply-cut or laciniated leaves. Varieties descended from three distinct species of Brassica have their stems, or so-called roots, enlarged into globular masses. The nectarine is the offspring of the peach; and the varieties of both these trees offer a remarkable parallelism in the fruit being white, red, or yellow fleshed--in being clingstones or freestones--in the flowers being large or small--in the leaves being serrated or crenated, furnished with globose or reniform glands, or quite destitute of glands. It should be remarked that each variety of the nectarine has not derived its character from a corresponding variety of the peach. The several varieties also of a closely allied genus, namely the apricot, differ from each other in nearly the same parallel manner. There is no reason {349} to believe that in any of these cases long-lost characters have reappeared, and in most of them this certainly has not occurred. Three species of Cucurbita have yielded a multitude of races, which correspond so closely in character that, as Naudin insists, they may be arranged in an almost strictly parallel series. Several varieties of the melon are interesting from resembling in important characters other species, either of the same genus or of allied genera; thus, one variety has fruit so like, both externally and internally, the fruit of a perfectly distinct species, namely, the cucumber, as hardly to be distinguished from it; another has long cylindrical fruit twisting about like a serpent; in another the seeds adhere to portions of the pulp; in another the fruit, when ripe, suddenly cracks and falls into pieces; and all these highly remarkable peculiarities are characteristic of species belonging to allied genera. We can hardly account for the appearance of so many unusual characters by reversion to a single ancient form; but we must believe that all the members of the family have inherited a nearly similar constitution from an early progenitor. Our cereal and many other plants offer similar cases. With animals we have fewer cases of analogous variation, independently of direct reversion. We see something of the kind in the resemblance between the short-muzzled races of the dog, such as the pug and bulldog; in feather-footed races of the fowl, pigeon, and canary-bird; in horses of the most different races presenting the same range of colour; in all black-and-tan dogs having tan-coloured eye-spots and feet, but in this latter case reversion may possibly have played a part. Low has remarked[871] that several breeds of cattle are "sheeted, "--that is, have a broad band of white passing round their bodies like a sheet; this character is strongly inherited and sometimes originates from a cross; it may be the first step in reversion to an original or early type, for, as was shown in the third chapter, white cattle with dark ears, feet, and tip of tail formerly existed, and now exist in a feral or semi-feral condition in several quarters of the world. Under our second main division, namely, of analogous variations due to reversion, the best cases are afforded by animals, and by none better than by pigeons. In all the most distinct breeds sub-varieties occasionally appear coloured exactly like the parent rock-pigeon, with black wing-bars, white loins, banded tail, &c. ; and no one can doubt that these characters are simply due to reversion. So with minor details; turbits properly have white tails, but occasionally a bird is born with a dark-coloured and banded tail; pouters properly have white primary wing-feathers, but not rarely a "sword-flighted" bird, that is, one with the few first primaries dark-coloured, appears; and in these cases we have characters proper to the rock-pigeon, but new to the breed, evidently appearing from reversion. In some domestic varieties the wing-bars, instead of being simply black, as in the rock-pigeon, are beautifully edged with different zones of colour, and they then present a striking analogy with the wing-bars in certain natural species of the same family, such as _Phaps chalcoptera_; and this may probably be accounted for by {350} all the forms descended from the same remote progenitor having a tendency to vary in the same manner. Thus also we can perhaps understand the fact of some Laugher-pigeons cooing almost like turtle-doves, and of several races having peculiarities in their flight, for certain natural species (viz. _C. Torquatrix_ and _palumbus_) display singular vagaries in this respect. In other cases a race, instead of imitating in character a distinct species, resembles some other race; thus certain runts tremble and slightly elevate their tails, like fantails; and turbits inflate the upper part of their oesophagus, like pouter-pigeons. It is a common circumstance to find certain coloured marks persistently characterising all the species of a genus, but differing much in tint; and the same thing occurs with the varieties of the pigeon: thus, instead of the general plumage being blue with the wing-bars black, there are snow-white varieties with red bars, and black varieties with white bars; in other varieties the wing-bars, as we have seen, are elegantly zoned with different tints. The Spot pigeon is characterised by the whole plumage being white, excepting the tail and a spot on the forehead; but these parts may be red, yellow, or black. In the rock-pigeon and in many varieties the tail is blue, with the outer edges of the outer feathers white; but in one sub-variety of the monk-pigeon we have a reversed variation, for the tail is white, except the outer edges of the outer feathers, which are black. [872] With some species of birds, for instance with gulls, certain coloured parts appear as if almost washed out, and I have observed exactly the same appearance in the terminal dark tail-bar in certain pigeons, and in the whole plumage of certain varieties of the duck. Analogous facts in the vegetable kingdom could be given. Many sub-varieties of the pigeon have reversed and somewhat lengthened feathers on the back part of their heads, and this is certainly not due to reversion to the parent-species, which shows no trace of such structure; but when we remember that sub-varieties of the fowl, turkey, canary-bird, duck, and goose, all have topknots or reversed feathers on their heads; and when we remember that scarcely a single large natural group of birds can be named, in which some members have not a tuft of feathers on their heads, we may suspect that reversion to some extremely remote form has come into action. Several breeds of the fowl have either spangled or pencilled feathers; and these cannot be derived from the parent-species, the _Gallus bankiva_; though of course it is possible that an early progenitor of this species may have been spangled, and a still earlier or a later progenitor may have been pencilled. But as many gallinaceous birds are spangled or pencilled, it is a more probable view that the several domestic breeds of the fowl have acquired this kind of plumage from all the members of the family inheriting a tendency to vary in a like manner. The same principle may account for the ewes in certain breeds of sheep being hornless, like the females of some other hollow-horned ruminants; it may account for certain domestic cats having slightly-tufted ears, like those of the lynx; and for the skulls of domestic rabbits often differing from each {351} other in the same characters by which the skulls of the various species of the genus Lepus differ. I will only allude to one other case, already discussed. Now that we know that the wild parent of the ass has striped legs, we may feel confident that the occasional appearance of stripes on the legs of the domestic ass is due to direct reversion; but this will not account for the lower end of the shoulder-stripe being sometimes angularly bent or slightly forked. So, again, when we see dun and other coloured horses with stripes on the spine, shoulders, and legs, we are led, from reasons formerly given, to believe that they reappear from direct reversion to the wild parent-horse. But when horses have two or three shoulder-stripes with one of them occasionally forked at the lower end, or when they have stripes on their faces, or as foals are faintly striped over nearly their whole bodies, with the stripes angularly bent one under the other on the forehead, or irregularly branched in other parts, it would be rash to attribute such diversified characters to the reappearance of those proper to the aboriginal wild horse. As three African species of the genus are much striped, and as we have seen that the crossing of the unstriped species often leads to the hybrid offspring being conspicuously striped--bearing also in mind that the act of crossing certainly causes the reappearance of long-lost characters--it is a more probable view that the above-specified stripes are due to reversion, not to the immediate wild parent-horse, but to the striped progenitor of the whole genus. I have discussed this subject of analogous variation at considerablelength, because, in a future work on natural species, it will be shown thatthe varieties of one species frequently mock distinct species--a fact inperfect harmony with the foregoing cases, and explicable only on the theoryof descent. Secondly, because these facts are important from showing, asremarked in a former chapter, that each trifling variation is governed bylaw, and is determined in a much higher degree by the nature of theorganisation, than by the nature of the conditions to which the varyingbeing has been exposed. Thirdly, because these facts are to a certainextent related to a more general law, namely, that which Mr. B. D. Walsh[873] has called the "Law of _Equable Variability_, " or, as heexplains it, "if any given character is very variable in one species of agroup, it will tend to be variable in allied species; and if any givencharacter is perfectly constant in one species of a group, it will tend tobe constant in allied species. " This leads me to recall a discussion in the chapter on Selection, in whichit was shown that with domestic races, which are {352} now undergoing rapidimprovement, those parts or characters which are the most valued vary themost. This naturally follows from recently selected characters continuallytending to revert to their former less improved standard, and from theirbeing still acted on by the same agencies, whatever these may be, whichfirst caused the characters in question to vary. The same principle isapplicable to natural species, for, as stated in my 'Origin of Species, 'generic characters are less variable than specific characters; and thelatter are those which have been modified by variation and naturalselection, since the period when all the species belonging to the samegenus branched off from a common progenitor, whilst generic characters arethose which have remained unaltered from a much more remote epoch, andaccordingly are now less variable. This statement makes a near approach toMr. Walsh's law of Equable Variability. Secondary sexual characters, it maybe added, rarely serve to characterise distinct genera, for they usuallydiffer much in the species of the same genus, and are highly variable inthe individuals of the same species; we have also seen in the earlierchapters of this work how variable secondary sexual characters become underdomestication. _Summary of the three previous Chapters, on the Laws of Variation. _ In the twenty-third chapter we have seen that changed conditionsoccasionally act in a definite manner on the organisation, so that all, ornearly all, the individuals thus exposed become modified in the samemanner. But a far more frequent result of changed conditions, whetheracting directly on the organisation or indirectly through the reproductivesystem being affected is indefinite and fluctuating variability. In thethree latter chapters we have endeavoured to trace some of the laws bywhich such variability is regulated. Increased use adds the size of a muscle, together with the blood-vessels, nerves, ligaments, the crests of bone to which these are attached, thewhole bone and other connected bones. So it is with various glands. Increased functional activity strengthens the sense-organs. Increased andintermittent pressure thickens the epidermis; and a change in the nature ofthe food sometimes modifies the coats of the stomach, and increases or{353} decreases the length of the intestines. Continued disuse, on theother hand, weakens and diminishes all parts of the organisation. Animalswhich during many generations have taken but little exercise, have theirlungs reduced in size, and as a consequence the bony fabric of the chest, and the whole form of the body, become modified. With our ancientlydomesticated birds, the wings have been little used, and they are slightlyreduced; with their decrease, the crest of the sternum, the scapulæ, coracoids, and furcula, have all been reduced. With domesticated animals, the reduction of a part from disuse is nevercarried so far that a mere rudiment is left, but we have good reason tobelieve that this has often occurred under nature. The cause of thisdifference probably is that with domestic animals not only sufficient timehas not been granted for so profound a change, but that, from not beingexposed to a severe struggle for life, the principle of the economy oforganisation does not come into action. On the contrary, we sometimes seethat structures which are rudimentary in the parent-species becomepartially redeveloped in their domesticated progeny. When rudiments areformed or left under domestication, they are the result of a sudden arrestof development, and not of long-continued disuse with the absorption of allsuperfluous parts; nevertheless they are of interest, as showing thatrudiments are the relics of organs once perfectly developed. Corporeal, periodical, and mental habits, though the latter have beenalmost passed over in this work, become changed under domestication, andthe changes are often inherited. Such changed habits in any organic being, especially when living a free life, would often lead to the augmented ordiminished use of various organs, and consequently to their modification. From long-continued habit, and more especially from the occasional birth ofindividuals with a slightly different constitution, domestic animals andcultivated plants become to a certain extent acclimatised, or adapted to aclimate different from that proper to the parent-species. Through the principle of correlated variability, when one part varies otherparts vary, --either simultaneously, or one after the other. Thus an organmodified during an early embryonic period affects other parts subsequentlydeveloped. When an {354} organ, such as the beak, increases or decreases inlength, adjoining or correlated parts, as the tongue and the orifice of thenostrils, tend to vary in the same manner. When the whole body increases ordecreases in size, various parts become modified; thus with pigeons theribs increase or decrease in number and breadth. Homologous parts, whichare identical during their early development and are exposed to similarconditions, tend to vary in the same or in some connected manner, --as inthe case of the right and left sides of the body, of the front and hindlimbs, and even of the head and limbs. So it is with the organs of sightand hearing; for instance, white cats with blue eyes are almost alwaysdeaf. There is a manifest relation throughout the body between the skin andits various appendages of hair, feathers, hoofs, horns, and teeth. InParaguay, horses with curly hair have hoofs like those of a mule; the wooland the horns of sheep vary together; hairless dogs are deficient in theirteeth; men with redundant hair have abnormal teeth, either deficient or inexcess. Birds with long wing-feathers usually have long tail-feathers. Whenlong feathers grow from the outside of the legs and toes of pigeons, thetwo outer toes are connected by membrane; for the whole leg tends to assumethe structure of the wing. There is a manifest relation between a crest offeathers on the head and a marvellous amount of change in the skull ofvarious fowls; and in a lesser degree, between the greatly elongated, lopping ears of rabbits and the structure of their skulls. With plants, theleaves, various parts of the flower, and the fruit, often vary together ina correlated manner. In some cases we find correlation without being able even to conjecturewhat is the nature of the connexion, as with various correlatedmonstrosities and diseases. This is likewise the case with the colour ofthe adult pigeon, in connexion with the presence of down on the young bird. Numerous curious instances have been given of peculiarities ofconstitution, in correlation with colour, as shown by the immunity ofindividuals of some one colour from certain diseases, from the attacks ofparasites, and from the action of certain vegetable poisons. Correlation is an important subject; for with species, and in a lesserdegree with domestic races, we continually find that {355} certain partshave been greatly modified to serve some useful purpose; but we almostinvariably find that other parts have likewise been more or less modified, without our being able to discover any advantage in the change. No doubtgreat caution is necessary in coming to this conclusion, for it isdifficult to overrate our ignorance on the use of various parts of theorganisation; but from what we have now seen, we may believe that manymodifications are of no direct service, having arisen in correlation withother and useful changes. Homologous parts during their early development evince an affinity for eachother, --that is, they tend to cohere and fuse together much more readilythan other parts. This tendency to fusion explains a multitude of normalstructures. Multiple and homologous organs are especially liable to vary innumber and probably in form. As the supply of organised matter is notunlimited, the principle of compensation sometimes comes into action; sothat, when one part is greatly developed, adjoining parts or functions areapt to be reduced; but this principle is probably of much less importancethan the more general one of the economy of growth. Through mere mechanicalpressure hard parts occasionally affect soft adjoining parts. With plantsthe position of the flowers on the axis, and of the seeds in the capsule, sometimes leads, through a freer flow of sap, to changes of structure; butthese changes are often due to reversion. Modifications, in whatever mannercaused, will be to a certain extent regulated by that co-ordinating poweror _nisus formativus_, which is in fact a remnant of one of the forms ofreproduction, displayed by many lowly organised beings in their power offissiparous generation and budding. Finally, the effects of the laws, whichdirectly or indirectly govern variability, may be largely influenced byman's selection, and will so far be determined by natural selection thatchanges advantageous to any race will be favoured and disadvantageouschanges checked. Domestic races descended from the same species, or from two or more alliedspecies, are liable to revert to characters derived from their commonprogenitor, and, as they have much in common in their constitutions, theyare also liable under changed conditions to vary in the same manner; fromthese {356} two causes analogous varieties often arise. When we reflect onthe several foregoing laws, imperfectly as we understand them, and when webear in mind how much remains to be discovered, we need not be surprised atthe extremely intricate manner in which our domestic productions havevaried, and still go on varying. * * * * * {357} CHAPTER XXVII. PROVISIONAL HYPOTHESIS OF PANGENESIS. PRELIMINARY REMARKS. --FIRST PART:--THE FACTS TO BE CONNECTED UNDER A SINGLE POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION--THE DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE FUNCTIONAL INDEPENDENCE OF THE ELEMENTS OR UNITS OF THE BODY--VARIABILITY--INHERITANCE--REVERSION. SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY ASSUMPTIONS ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE SEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART--CONCLUSION. In the previous chapters large classes of facts, such as those bearing onbud-variation, the various forms of inheritance, the causes and laws ofvariation, have been discussed; and it is obvious that these subjects, aswell as the several modes of reproduction, stand in some sort of relationto each other. I have been led, or rather forced, to form a view which to acertain extent connects these facts by a tangible method. Every one wouldwish to explain to himself, even in an imperfect manner, how it is possiblefor a character possessed by some remote ancestor suddenly to reappear inthe offspring; how the effects of increased or decreased use of a limb canbe transmitted to the child; how the male sexual element can act not solelyon the ovule, but occasionally on the mother-form; how a limb can bereproduced on the exact line of amputation, with neither too much nor toolittle added; how the various modes of reproduction are connected, and soforth. I am aware that my view is merely a provisional hypothesis orspeculation; but until a better one be advanced, it may be serviceable bybringing together a multitude of facts which are at present leftdisconnected by any efficient cause. As Whewell, the historian of theinductive sciences, remarks:--"Hypotheses may often be of service toscience, when they involve a certain portion of incompleteness, and even oferror. " Under this point of view I venture to advance the hypothesis ofPangenesis, which {358} implies that the whole organisation, in the senseof every separate atom or unit, reproduces itself. Hence ovules andpollen-grains, --the fertilised seed or egg, as well as buds, --include andconsist of a multitude of germs thrown off from each separate atom of theorganism. In the First Part I will enumerate as briefly as I can the groups of factswhich seem to demand connection; but certain subjects, not hithertodiscussed, must be treated at disproportionate length. In the Second Partthe hypothesis will be given; and we shall see, after considering how farthe necessary assumptions are in themselves improbable, whether it servesto bring under a single point of view the various facts. PART I. Reproduction may be divided into two main classes, namely, sexual andasexual. The latter is effected in many ways--by gemmation, that is by theformation of buds of various kinds, and by fissiparous generation, that isby spontaneous or artificial division. It is notorious that some of thelower animals, when cut into many pieces, reproduce so many perfectindividuals: Lyonnet cut a Nais or freshwater worm into nearly fortypieces, and these all reproduced perfect animals. [874] It is probable thatsegmentation could be carried much further in some of the protozoa, andwith some of the lowest plants each cell will reproduce the parent-form. Johannes Müller thought that there was an important distinction betweengemmation and fission; for in the latter case the divided portion, howeversmall, is more perfectly organised; but most physiologists are nowconvinced that the two processes are essentially alike. [875] Prof. Huxleyremarks, "fission is little more than a peculiar {359} mode of budding, "and Prof. H. J. Clark, who has especially attended to this subject, showsin detail that there is sometimes "a compromise between self-division andbudding. " When a limb is amputated, or when the whole body is bisected, thecut extremities are said to bud forth; and as the papilla, which is firstformed, consists of undeveloped cellular tissue like that forming anordinary bud, the expression is apparently correct. We see the connectionof the two processes in another way; for Trembley observed that with thehydra the reproduction of the head after amputation was checked as soon asthe animal began to bud. [876] Between the production, by fissiparous generation, of two or more completeindividuals, and the repair of even a very slight injury, we have, asremarked in a former chapter, so perfect and insensible a gradation, thatit is impossible to doubt that they are connected processes. Between thepower which repairs a trifling injury in any part, and the power whichpreviously "was occupied in its maintenance by the continued mutation ofits particles, " there cannot be any great difference; and we may follow Mr. Paget in believing them to be the selfsame power. As at each stage ofgrowth an amputated part is replaced by one in the same state ofdevelopment, we must likewise follow Mr. Paget in admitting "that thepowers of development from the embryo are identical with those exercisedfor the restoration from injuries: in other words, that the powers are thesame by which perfection is first achieved, and by which, when lost, it isrecovered. "[877] Finally, we may conclude that the several forms ofgemmation, and of fissiparous generation, the repair of injuries, themaintenance of each part in its proper state, and the growth or progressivedevelopment of the whole structure of the embryo, are all essentially theresults of one and the same great power. _Sexual Generation. _--The union of the two sexual elements seems to make abroad distinction between sexual and asexual reproduction. But thewell-ascertained cases of Parthenogenesis prove that the distinction is notreally so great as it at first appears; for ovules occasionally, and evenin some cases {360} frequently, become developed into perfect beings, without the concourse of the male element. J. Müller and others admit thatovules and buds have the same essential nature. Certain bodies, whichduring their early development cannot be distinguished by any externalcharacter from true ovules, nevertheless must be classed as buds, forthough formed within the ovarium they are incapable of fertilisation. Thisis the case with the germ-balls of the Cecidomyide larvæ, as described byLeuckart. [878] Ovules and the male element, before they become united, have, like buds, an independent existence. [879] Both have the power oftransmitting every single character possessed by the parent-form. We seethis clearly when hybrids are paired _inter se_, for the characters ofeither grandparent often reappear, either perfectly or by segments, in theprogeny. It is an error to suppose that the male transmits certaincharacters and the female other characters; though no doubt, from unknowncauses, one sex sometimes has a stronger power of transmission than theother. It has been maintained by some authors that a bud differs essentially froma fertilised germ, by always reproducing the perfect character of theparent-stock; whilst fertilised germs become developed into beings whichdiffer, in a greater or less degree, from each other and from theirparents. But there is no such broad distinction as this. In the eleventhchapter, numerous cases were given showing that buds occasionally grow intoplants having new and strongly marked characters; and varieties thusproduced can be propagated for a length of time by buds, and occasionallyby seed. Nevertheless, it must be admitted that beings produced sexuallyare much more liable to vary than those produced asexually; and of thisfact a partial explanation will hereafter be attempted. The variability inboth cases is determined by the same general causes, and is governed by thesame laws. Hence new varieties arising from buds cannot be distinguishedfrom those arising from seed. Although bud-varieties usually retain theircharacter during {361} successive bud-generations, yet they occasionallyrevert, even after a long series of bud-generations, to their formercharacter. This tendency to reversion in buds is one of the most remarkableof the several points of agreement between the offspring from bud andseminal reproduction. There is, however, one difference between beings produced sexually andasexually, which is very general. The former usually pass in the course oftheir development from a lower to a higher grade, as we see in themetamorphoses of insects and in the concealed metamorphoses of thevertebrata; but this passage from a lower to a higher grade cannot beconsidered as a necessary accompaniment of sexual reproduction, for hardlyanything of the kind occurs in the development of Aphis amongst insects, orwith certain crustaceans, cephalopods, or with any of the higher vascularplants. Animals propagated asexually by buds or fission are on the otherhand never known to undergo a retrogressive metamorphosis; that is, they donot first sink to a lower, before passing on to their higher and finalstage of development. But during the act of asexual production orsubsequently to it, they often advance in organisation, as we see in themany cases of "alternate generation. " In thus speaking of alternategeneration, I follow those naturalists who look at the process asessentially one of internal budding or of fissiparous generation. Some ofthe lower plants, however, such as mosses and certain algæ, according toDr. L. Radlkofer, [880] when propagated asexually, do undergo aretrogressive metamorphosis. We can to a certain extent understand, as faras the final cause is concerned, why beings propagated by buds should sorarely retrogress during development; for with each organism the structureacquired at each stage of development must be adapted to its peculiarhabits. Now, with beings produced by gemmation, --and this, differently fromsexual reproduction, may occur at any period of growth, --if there wereplaces for the support of many individuals at some one stage ofdevelopment, the simplest plan would be that they should be multiplied bygemmation at that stage, and not that they should first retrograde in theirdevelopment to an earlier or simpler structure, which might not be fittedfor the surrounding conditions. {362} From the several foregoing considerations we may conclude that thedifference between sexual and asexual generation is not nearly so great asit at first appears; and we have already seen that there is the closestagreement between gemmation, fissiparous generation, the repair ofinjuries, and ordinary growth or development. The capacity of fertilisationby the male element seems to be the chief distinction between an ovule anda bud; and this capacity is not invariably brought into action, as in thecases of parthenogenetic reproduction. We are here naturally led to inquirewhat the final cause can be of the necessity in ordinary generation for theconcourse of the two sexual elements. Seeds and ova are often highly serviceable as the means of disseminatingplants and animals, and of preserving them during one or more seasons in adormant state; but unimpregnated seeds or ova, and detached buds, would beequally serviceable for both purposes. We can, however, indicate twoimportant advantages gained by the concourse of the two sexes, or rather oftwo individuals belonging to opposite sexes; for, as I have shown in aformer chapter, the structure of every organism appears to be especiallyadapted for the concurrence, at least occasionally, of two individuals. Innearly the same manner as it is admitted by naturalists that hybridism, from inducing sterility, is of service in keeping the forms of lifedistinct and fitted for their proper places; so, when species are renderedhighly variable by changed conditions of life, the free intercrossing ofthe varying individuals will tend to keep each form fitted for its properplace in nature; and crossing can be effected only by sexual generation, but whether the end thus gained is of sufficient importance to account forthe first origin of sexual intercourse is very doubtful. Secondly, I haveshown, from the consideration of a large body of facts, that, as a slightchange in the conditions of life is beneficial to each creature, so, in ananalogous manner, is the change effected in the germ by sexual union with adistinct individual; and I have been led, from observing the manywidely-extended provisions throughout nature for this purpose, and from thegreater vigour of crossed organisms of all kinds, as proved by directexperiments, as well as from the evil effects of close interbreeding whenlong {363} continued, to believe that the advantage thus gained is verygreat. Besides these two important ends, there may, of course, be others, as yet unknown to us, gained by the concourse of the two sexes. Why the germ, which before impregnation undergoes a certain amount ofdevelopment, ceases to progress and perishes, unless it be acted on by themale element; and why conversely the male element, which is enabled to keepalive for even four or five years within the spermatheca of a femaleinsect, likewise perishes, unless it acts on or unites with the germ, arequestions which cannot be answered with any certainty. It is, however, possible that both sexual elements perish, unless brought into union, simply from including too little formative matter for independent existenceand development; for certainly they do not in ordinary cases differ intheir power of giving character to the embryo. This view of the importanceof the quantity of formative matter seems probable from the followingconsiderations. There is no reason to suspect that the spermatozoa orpollen-grains of the same individual animal or plant differ from eachother; yet Quatrefages has shown in the case of the Teredo, [881] as didformerly Prevost and Dumas with other animals, that more than onespermatozoon is requisite to fertilise an ovule. This has likewise beenclearly proved by Newport, [882] who adds the important fact, established bynumerous experiments, that, when a very small number of spermatozoa areapplied to the ova of Batrachians, they are only partially impregnated andthe embryo is never fully developed: the first step, however, towardsdevelopment, namely, the partial segmentation of the yelk, does occur to agreater or less extent, but is never completed up to granulation. The rateof the segmentation is likewise determined by the number of thespermatozoa. With respect to plants, nearly the same results were obtainedby Kölreuter and Gärtner. This last careful observer found, [883] aftermaking successive trials on a Malva with more and more pollen-grains, thateven thirty grains did not fertilise a single seed; but when forty grainswere applied to the {364} stigma, a few seeds of small size were formed. The pollen-grains of Mirabilis are extraordinarily large, and the ovariumcontains only a single ovule; and these circumstances led Naudin[884] tomake the following interesting experiments: a flower was fertilised bythree grains and succeeded perfectly; twelve flowers were fertilised by twograins, and seventeen flowers by a single grain, and of these one floweralone in each lot perfected its seed; and it deserves especial notice thatthe plants produced by these two seeds never attained their properdimensions, and bore flowers of remarkably small size. From these facts weclearly see that the quantity of the peculiar formative matter which iscontained within the spermatozoa and pollen-grains is an all-importantelement in the act of fertilisation, not only in the full development ofthe seed, but in the vigour of the plant produced from such seed. We seesomething of the same kind in certain cases of parthenogenesis, that is, when the male element is wholly excluded; for M. Jourdan[885] found that, out of about 58, 000 eggs laid by unimpregnated silk-moths, many passedthrough their early embryonic stages, showing that they were capable ofself-development, but only twenty-nine out of the whole number producedcaterpillars. Therefore it is not an improbable view that deficient bulk orquantity in the formative matter, contained within the sexual elements, isthe main cause of their not having the capacity of prolonged separateexistence and development. The belief that it is the function of thespermatozoa to communicate life to the ovule seems a strange one, seeingthat the unimpregnated ovule is already alive and continues for aconsiderable time alive. We shall hereafter see that it is probable thatthe sexual elements, or possibly only the female element, include certainprimordial cells, that is, such as have undergone no differentiation, andwhich are not present in an active state in buds. _Graft-hybrids. _--When discussing in the eleventh chapter the curious caseof the _Cytisus adami_, facts were given which render it to a certaindegree probable, in accordance with the belief of some distinguishedbotanists, that, when the tissues of two plants {365} belonging to distinctspecies or varieties are intimately united, buds are afterwardsoccasionally produced which, like hybrids, combine the characters of thetwo united forms. It is certain that when trees with variegated leaves aregrafted or budded on a common stock, the latter sometimes produces budsbearing variegated leaves; but this may perhaps be looked at as a case ofinoculated disease. Should it ever be proved that hybridised buds can beformed by the union of two distinct vegetative tissues, the essentialidentity of sexual and asexual reproduction would be shown in the mostinteresting manner; for the power of combining in the offspring thecharacters of both parents, is the most striking of all the functions ofsexual generation. _Direct Action of the Male Element on the Female. _--In the chapter justreferred to, I have given abundant proofs that foreign pollen occasionallyaffects the mother-plant in a direct manner. Thus, when Gallesio fertilisedan orange-flower with pollen from the lemon, the fruit bore stripes ofperfectly characterised lemon-peel: with peas, several observers have seenthe colour of the seed-coats and even of the pod directly affected by thepollen of a distinct variety; so it has been with the fruit of the apple, which consists of the modified calyx and upper part of the flower-stalk. These parts in ordinary cases are wholly formed by the mother-plant. Wehere see the male element affecting and hybridising not that part which itis properly adapted to affect, namely the ovule, but the partiallydeveloped tissues of a distinct individual. We are thus brought half-waytowards a graft-hybrid, in which the cellular tissue of one form, insteadof its pollen, is believed to hybridise the tissues of a distinct form. Iformerly assigned reasons for rejecting the belief that the mother-plant isaffected through the intervention of the hybridised embryo; but even ifthis view were admitted, the case would become one of graft-hybridism, forthe fertilised embryo and the mother-plant must be looked at as distinctindividuals. With animals which do not breed until nearly mature, and of which all theparts are then fully developed, it is hardly possible that the male elementshould directly affect the female. But we have the analogous and perfectlywell-ascertained case of the male element of a distinct form, as with the{366} quagga and Lord Morton's mare, affecting the ovarium of the female, so that the ovules and offspring subsequently produced by her whenimpregnated by other males are plainly affected and hybridised by the firstmale. _Development. _--The fertilised germ reaches maturity by a vast number ofchanges: these are either slight and slowly effected, as when the childgrows into the man, or are great and sudden, as with the metamorphoses ofmost insects. Between these extremes we have, even within the same class, every gradation: thus, as Sir J. Lubbock has shown, [886] there is anEphemerous insect which moults above twenty times, undergoing each time aslight but decided change of structure; and these changes, as he furtherremarks, probably reveal to us the normal stages of development which areconcealed and hurried through, or suppressed, in most other insects. Inordinary metamorphoses, the parts and organs appear to become changed intothe corresponding parts in the next stage of development; but there isanother form of development, which has been called by Professor Owenmetagenesis. In this case "the new parts are not moulded upon the innersurface of the old ones. The plastic force has changed its course ofoperation. The outer case, and all that gave form and character to theprecedent individual, perish and are cast off; they are not changed intothe corresponding parts of the new individual. These are due to a new anddistinct developmental process, " &c. [887] Metamorphosis, however, graduatesso insensibly into metagenesis, that the two processes cannot be distinctlyseparated. For instance, in the last change which Cirripedes undergo, thealimentary canal and some other organs are moulded on pre-existing parts;but the eyes of the old and the young animal are developed in entirelydifferent parts of the body; the tips of the mature limbs are formed withinthe larval limbs, and may be said to be metamorphosed from them; but theirbasal portions and the whole thorax are developed in a plane actually atright angles to the limbs and thorax of the larva; and this {367} may becalled metagenesis. The metagenetic process is carried to an extreme degreein the development of some Echinoderms, for the animal in the second stageof development is formed almost like a bud within the animal of the firststage, the latter being then cast off like an old vestment, yet sometimesstill maintaining for a short period an independent vitality. [888] If, instead of a single individual, several were to be thus developedmetagenetically within a pre-existing form, the process would be called oneof alternate generation. The young thus developed may either closelyresemble the encasing parent-form, as with the larvæ of Cecidomyia, or maydiffer to an astonishing degree, as with many parasitic worms and withjelly-fishes; but this does not make any essential difference in theprocess, any more than the greatness or abruptness of the change in themetamorphoses of insects. The whole question of development is of great importance for our presentsubject. When an organ, the eye for instance, is metagenetically formed ina part of the body where during the previous stage of development no eyeexisted, we must look at it as a new and independent growth. The absoluteindependence of new and old structures, which correspond in structure andfunction, is still more obvious when several individuals are formed withina previous encasing form, as in the cases of alternate generation. The sameimportant principle probably comes largely into play even in the case ofcontinuous growth, as we shall see when we consider the inheritance ofmodifications at corresponding ages. We are led to the same conclusion, namely, the independence of partssuccessively developed, by another and quite distinct group of facts. It iswell known that many animals belonging to the same class, and therefore notdiffering widely from each other, pass through an extremely differentcourse of development. Thus certain beetles, not in any way remarkablydifferent from others of the same order, undergo what has been called ahyper-metamorphosis--that is, they pass through an early stage whollydifferent from the ordinary grub-like larva. In the same sub-order ofcrabs, namely, the Macroura, as Fritz {368} Müller remarks, the rivercray-fish is hatched under the same form which it ever afterwards retains;the young lobster has divided legs, like a Mysis; the Palæmon appears underthe form of a Zoea, and Peneus under the Nauplius-form; and how wonderfullythese larval forms differ from each other, is known to everynaturalist. [889] Some other crustaceans, as the same author observes, startfrom the same point and arrive at nearly the same end, but in the middle oftheir development are widely different from each other. Still more strikingcases could be given with respect to the Echinodermata. With the Medusæ orjelly-fishes Professor Allman observes, "the classification of the Hydroidawould be a comparatively simple task if, as has been erroneously asserted, generically-identical medusoids always arose from generically-identicalpolypoids; and on the other hand, that generically-identical polypoidsalways gave origin to generically-identical medusoids. " So, again, Dr. Strethill Wright remarks, "in the life-history of the Hydroidæ any phase, planuloid, polypoid, or medusoid, may be absent. "[890] According to the belief now generally accepted by our best naturalists, allthe members of the same order or class, the Macrourous crustaceans forinstance, are descended from a common progenitor. During their descent theyhave diverged much in structure, but have retained much in common; and thisdivergence and retention of character has been effected, though they havepassed and still pass through marvellously different metamorphoses. Thisfact well illustrates how independent each structure must be from thatwhich precedes and follows it in the course of development. _The Functional Independence of the Elements or Units of theBody. _--Physiologists agree that the whole organism consists of a multitudeof elemental parts, which are to a great extent independent of each other. Each organ, says Claude Bernard, [891] {369} has its proper life, itsautonomy; it can develop and reproduce itself independently of theadjoining tissues. The great German authority, Virchow, [892] asserts stillmore emphatically that each system, as the nervous or osseous system, orthe blood, consists of an "enormous mass of minute centres of action.... Every element has its own special action, and even though it derive itsstimulus to activity from other parts, yet alone effects the actualperformance of its duties.... Every single epithelial and muscularfibre-cell leads a sort of parasitical existence in relation to the rest ofthe body.... Every single bone-corpuscle really possesses conditions ofnutrition peculiar to itself. " Each element, as Mr. Paget remarks, livesits appointed time, and then dies, and, after being cast off or absorbed, is replaced. [893] I presume that no physiologist doubts that, for instance, each bone-corpuscle of the finger differs from the corresponding corpusclein the corresponding joint of the toe; and there can hardly be a doubt thateven those on the corresponding sides of the body differ, though almostidentical in nature. This near approach to identity is curiously shown inmany diseases in which the same exact points on the right and left sides ofthe body are similarly affected; thus Mr. Paget[894] gives a drawing of adiseased pelvis, in which the bone has grown into a most complicatedpattern, but "there is not one spot or line on one side which is notrepresented, as exactly as it would be in a mirror, on the other. " Many facts support this view of the independent life of each minute elementof the body. Virchow insists that a single bone-corpuscle or a single cellin the skin may become diseased. The spur of a cock, after being insertedinto the eye of an ox, lived for eight years, and acquired a weight of 306grammes, or nearly fourteen ounces. [895] The tail of a pig has been graftedinto the middle of its back, and reacquired sensibility. Dr. Ollier[896]inserted a piece of periosteum from the bone of a young dog under the skinof a rabbit, and true bone was developed. A multitude of similar factscould be given. The {370} frequent presence of hairs and of perfectlydeveloped teeth, even teeth of the second dentition, in ovariantumours, [897] are facts leading to the same conclusion. Whether each of the innumerable autonomous elements of the body is a cellor the modified product of a cell, is a more doubtful question, even if sowide a definition be given to the term, as to include cell-like bodieswithout walls and without nuclei. [898] Professor Lionel Beale uses the term"germinal matter" for the contents of cells, taken in this wideacceptation, and he draws a broad distinction between germinal matter and"formed material" or the various products of cells. [899] But the doctrineof _omnis cellula e cellulâ_ is admitted for plants, and is a widelyprevalent belief with respect to animals. [900] Thus Virchow, the greatsupporter of the cellular theory, whilst allowing that difficulties exist, maintains that every atom of tissue is derived from cells, and these frompre-existing cells, and these primarily from the egg, which he regards as agreat cell. That cells, still retaining the same nature, increase byself-division or proliferation, is admitted by almost every one. But whenan organism undergoes a great change of structure during development, thecells, which at each stage are supposed to be directly derived frompreviously-existing cells, must likewise be greatly changed in nature; thischange is apparently attributed by the supporters of the cellular doctrineto some inherent power which the cells possess, and not to any externalagency. Another school maintains that cells and tissues of all kinds may be formed, independently of pre-existing cells, from plastic lymph or blastema; andthis it is thought is well exhibited in the repair of wounds. As I have notespecially attended to histology, it would be presumptuous in me to expressan opinion on the two opposed doctrines. But every one appears to admitthat the body consists of a multitude of "organic units, "[901] {371} eachof which possesses its own proper attributes, and is to a certain extentindependent of all others. Hence it will be convenient to use indifferentlythe terms cells or organic units or simply units. _Variability and Inheritance. _--We have seen in the twenty-second chapterthat variability is not a principle co-ordinate with life or reproduction, but results from special causes, generally from changed conditions actingduring successive generations. Part of the fluctuating variability thusinduced is apparently due to the sexual system being easily affected bychanged conditions, so that it is often rendered impotent; and when not soseriously affected, it often fails in its proper function of transmittingtruly the characters of the parents to the offspring. But variability isnot necessarily connected with the sexual system, as we see from the casesof bud-variation; and although we may not be able to trace the nature ofthe connexion, it is probable that many deviations of structure whichappear in sexual offspring result from changed conditions acting directlyon the organisation, independently of the reproductive organs. In someinstances we may feel sure of this, when all, or nearly all the individualswhich have been similarly exposed are similarly and definitely affected--asin the dwarfed and otherwise changed maize brought from hot countries whencultivated in Germany; in the change of the fleece in sheep within thetropics; to a certain extent in the increased size and early maturity ofour highly-improved domesticated animals; in inherited gout fromintemperance; and in many other such cases. Now, as such changed conditionsdo not especially affect the reproductive organs, it seems mysterious onany ordinary view why their product, the new organic being, should besimilarly affected. How, again, can we explain to ourselves the inherited effects of the use ordisuse of particular organs? The domesticated duck flies less and walksmore than the wild duck, and its limb-bones have become in a correspondingmanner diminished and increased in comparison with those of the wild duck. A horse is trained to certain paces, and the colt inherits similarconsensual movements. The domesticated rabbit becomes tame from closeconfinement; the dog intelligent from associating with man; the retrieveris taught to fetch and carry: and these {372} mental endowments and bodilypowers are all inherited. Nothing in the whole circuit of physiology ismore wonderful. How can the use or disuse of a particular limb or of thebrain affect a small aggregate of reproductive cells, seated in a distantpart of the body, in such a manner that the being developed from thesecells inherits the characters of either one or both parents? Even animperfect answer to this question would be satisfactory. Sexual reproduction does not essentially differ, as we have seen, frombudding or self-division, and these processes graduate through the repairof injuries into ordinary development and growth; it might therefore beexpected that every character would be as regularly transmitted by all themethods of reproduction as by continued growth. In the chapters devoted toinheritance it was shown that a multitude of newly-acquired characters, whether injurious or beneficial, whether of the lowest or highest vitalimportance, are often faithfully transmitted--frequently even when oneparent alone possesses some new peculiarity. It deserves especial attentionthat characters appearing at any age tend to reappear at a correspondingage. We may on the whole conclude that in all cases inheritance is therule, and non-inheritance the anomaly. In some instances a character is notinherited, from the conditions of life being directly opposed to itsdevelopment; in many instances, from the conditions incessantly inducingfresh variability, as with grafted fruit-trees and highly cultivatedflowers. In the remaining cases the failure may be attributed to reversion, by which the child resembles its grandparents or more remote progenitors, instead of its parents. This principle of Reversion is the most wonderful of all the attributes ofInheritance. It proves to us that the transmission of a character and itsdevelopment, which ordinarily go together and thus escape discrimination, are distinct powers; and these powers in some cases are even antagonistic, for each acts alternately in successive generations. Reversion is not arare event, depending on some unusual or favourable combination ofcircumstances, but occurs so regularly with crossed animals and plants, andso frequently with uncrossed breeds, that it is evidently an essential partof the principle of inheritance. We know that {373} changed conditions havethe power of evoking long-lost characters, as in the case of some feralanimals. The act of crossing in itself possesses this power in a highdegree. What can be more wonderful than that characters, which havedisappeared during scores, or hundreds, or even thousands of generations, should suddenly reappear perfectly developed, as in the case of pigeons andfowls when purely bred, and especially when crossed; or as with the zebrinestripes on dun-coloured horses, and other such cases? Many monstrositiescome under this same head, as when rudimentary organs are redeveloped, orwhen an organ which we must believe was possessed by an early progenitor, but of which not even a rudiment is left, suddenly reappears, as with thefifth stamen in some Scrophulariaceæ. We have already seen that reversionacts in bud-reproduction; and we know that it occasionally acts during thegrowth of the same individual animal, especially, but not exclusively, whenof crossed parentage, --as in the rare cases described of individual fowls, pigeons, cattle, and rabbits, which have reverted as they advanced in yearsto the colours of one of their parents or ancestors. We are led to believe, as formerly explained, that every character whichoccasionally reappears is present in a latent form in each generation, innearly the same manner as in male and female animals secondary charactersof the opposite sex lie latent, ready to be evolved when the reproductiveorgans are injured. This comparison of the secondary sexual characterswhich are latent in both sexes, with other latent characters, is the moreappropriate from the case recorded of the Hen, which assumed some of themasculine characters, not of her own race, but of an early progenitor; shethus exhibited at the same time the redevelopment of latent characters ofboth kinds and connected both classes. In every living creature we may feelassured that a host of lost characters lie ready to be evolved under properconditions. How can we make intelligible, and connect with other facts, this wonderful and common capacity of reversion, --this power of callingback to life long-lost characters? {374} PART II. I have now enumerated the chief facts which every one would desire toconnect by some intelligible bond. This can be done, as it seems to me, ifwe make the following assumptions; if the first and chief one be notrejected, the others, from being supported by various physiologicalconsiderations, will not appear very improbable. It is almost universallyadmitted that cells, or the units of the body, propagate themselves byself-division or proliferation, retaining the same nature, and ultimatelybecoming converted into the various tissues and substances of the body. Butbesides this means of increase I assume that cells, before their conversioninto completely passive or "formed material, " throw off minute granules oratoms, which circulate freely throughout the system, and when supplied withproper nutriment multiply by self-division, subsequently becoming developedinto cells like those from which they were derived. These granules for thesake of distinctness may be called cell-gemmules, or, as the cellulartheory is not fully established, simply gemmules. They are supposed to betransmitted from the parents to the offspring, and are generally developedin the generation which immediately succeeds, but are often transmitted ina dormant state during many generations and are then developed. Theirdevelopment is supposed to depend on their union with other partiallydeveloped cells or gemmules which precede them in the regular course ofgrowth. Why I use the term union, will be seen when we discuss the directaction of pollen on the tissues of the mother-plant. Gemmules are supposedto be thrown off by every cell or unit, not only during the adult state, but during all the stages of development. Lastly, I assume that thegemmules in their dormant state have a mutual affinity for each other, leading to their aggregation either into buds or into the sexual elements. Hence, speaking strictly, it is not the reproductive elements, nor thebuds, which generate new organisms, but the cells themselves throughout thebody. These assumptions constitute the provisional hypothesis which I havecalled Pangenesis. Nearly {375} similar views have been propounded, as Ifind, by other authors, more especially by Mr. Herbert Spencer;[902] butthey are here modified and amplified. {376} Before proceeding to show, firstly, how far these assumptions are inthemselves probable, and secondly, how far they connect and explain thevarious groups of facts with which we are concerned, it may be useful togive an illustration of the hypothesis. If one of the simplest Protozoa beformed, as appears under the microscope, of a small mass of homogeneousgelatinous matter, a minute atom thrown off from any part and nourishedunder favourable circumstances would naturally reproduce the whole; but ifthe upper and lower surfaces were to differ in texture from the centralportion, then all three parts would have to throw off atoms or gemmules, which when aggregated by mutual affinity would form either buds or thesexual elements. Precisely the same view may be extended to one of thehigher animals; although in this case many thousand gemmules must be thrownoff from the various parts of the body. Now, when the leg, for instance, ofa salamander is cut off, a slight crust forms over the wound, and beneaththis crust the uninjured cells or units of bone, muscle, nerves, &c. , aresupposed to unite with the diffused gemmules of those cells which in theperfect leg come next in order; and these as they become slightly developedunite with others, and so on until a papilla of soft cellular tissue, the"budding leg, " is formed, and in time a perfect leg. [903] Thus, thatportion of the leg which had {377} been cut off, neither more nor less, would be reproduced. If the tail or leg of a young animal had been cut off, a young tail or leg would have been reproduced, as actually occurs with theamputated tail of the tadpole; for gemmules of all the units which composethe tail are diffused throughout the body at all ages. But during the adultstate the gemmules of the larval tail would remain dormant, for they wouldnot meet with pre-existing cells in a proper state of development withwhich to unite. If from changed conditions or any other cause any part ofthe body should become permanently modified, the gemmules, which are merelyminute portions of the contents of the cells forming the part, wouldnaturally reproduce the same modification. But gemmules previously derivedfrom the same part before it had undergone any change, would still bediffused throughout the organisation, and would be transmitted fromgeneration to generation, so that under favourable circumstances they mightbe redeveloped, and then the new modification would be for a time or forever lost. The aggregation of gemmules derived from every part of the body, through their mutual affinity, would form buds, and their aggregation insome special manner, apparently in small quantity, together probably withthe presence of gemmules of certain primordial cells, would constitute thesexual elements. By means of these illustrations the hypothesis ofpangenesis has, I hope, been rendered intelligible. * * * * * Physiologists maintain, as we have seen, that each cell, though to a largeextent dependent on others, is likewise, to a certain extent, independentor autonomous. I go one small step further, and assume that each cell castsoff a free gemmule, which is capable of reproducing a similar cell. Thereis some analogy between this view and what we see in compound animals andin the flower-buds on the same tree; for these are distinct individualscapable of true or seminal reproduction, yet have parts in common and aredependent on each other; thus {378} the tree has its bark and trunk, andcertain corals, as the Virgularia, have not only parts, but movements incommon. The existence of free gemmules is a gratuitous assumption, yet can hardlybe considered as very improbable, seeing that cells have the power ofmultiplication through the self-division of their contents. Gemmules differfrom true ovules or buds inasmuch as they are supposed to be capable ofmultiplication in their undeveloped state. No one probably will object tothis capacity as improbable. The blastema within the egg has been known todivide and give birth to two embryos; and Thuret[904] has seen the zoosporeof an alga divide itself, and both halves germinate. An atom of small-poxmatter, so minute as to be borne by the wind, must multiply itself manythousand-fold in a person thus inoculated. [905] It has recently beenascertained[906] that a minute portion of the mucous discharge from ananimal affected with rinderpest, if placed in the blood of a healthy ox, increases so fast that in a short space of time "the whole mass of blood, weighing many pounds, is infected, and every small particle of that bloodcontains enough poison to give, within less than forty-eight hours, thedisease to another animal. " The retention of free and undeveloped gemmules in the same body from earlyyouth to old age may appear improbable, but we should remember how longseeds lie dormant in the earth and buds in the bark of a tree. Theirtransmission from generation to generation may appear still moreimprobable; but here again we should remember that many rudimentary anduseless organs are transmitted and have been transmitted during anindefinite number of generations. We shall presently see how well thelong-continued transmission of undeveloped gemmules explains many facts. As each unit, or group of similar units throughout the body, casts off itsgemmules, and as all are contained within the smallest egg or seed, andwithin each spermatozoon or pollen-grain, their number and minuteness mustbe something {379} inconceivable. I shall hereafter recur to thisobjection, which at first appears so formidable; but it may here beremarked that a cod-fish has been found to produce 4, 872, 000 eggs, a singleAscaris about 64, 000, 000 eggs, and a single Orchidaceous plant probably asmany million seeds. [907] In these several cases, the spermatozoa andpollen-grains must exist in considerably larger numbers. Now, when we haveto deal with numbers such as these, which the human intellect cannot grasp, there is no good reason for rejecting our present hypothesis on account ofthe assumed existence of cell-gemmules a few thousand times more numerous. The gemmules in each organism must be thoroughly diffused; nor does thisseem improbable considering their minuteness, and the steady circulation offluids throughout the body. So it must be with the gemmules of plants, forwith certain kinds even a minute fragment of a leaf will reproduce thewhole. But a difficulty here occurs; it would appear that with plants, andprobably with compound animals, such as corals, the gemmules do not spreadfrom bud to bud, but only through the tissues developed from each separatebud. We are led to this conclusion from the stock being rarely affected bythe insertion of a bud or graft from a distinct variety. This non-diffusionof the gemmules is still more plainly shown in the case of ferns; for Mr. Bridgman[908] has proved that, when spores (which it should be rememberedare of the nature of buds) are taken from a monstrous part of a frond, andothers from an ordinary part, {380} each reproduces the form of the partwhence derived. But this non-diffusion of the gemmules from bud to bud maybe only apparent, depending, as we shall hereafter see, on the nature ofthe first-formed cells in the buds. The assumed elective affinity of each gemmule for that particular cellwhich precedes it in the order of development is supported by manyanalogies. In all ordinary cases of sexual reproduction the male and femaleelements have a mutual affinity for each other: thus, it is believed thatabout ten thousand species of Compositæ exist, and there can be no doubtthat if the pollen of all these species could be, simultaneously orsuccessively, placed on the stigma of any one species, this one would electwith unerring certainty its own pollen. This elective capacity is all themore wonderful, as it must have been acquired since the many species ofthis great group of plants branched off from a common progenitor. On anyview of the nature of sexual reproduction, the protoplasm contained withinthe ovules and within the sperm-cells (or the "spermatic force" of thelatter, if so vague a term be preferred) must act on each other by some lawof special affinity, either during or subsequently to impregnation, so thatcorresponding parts alone affect each other; thus, a calf produced from ashort-horned cow by a long-horned bull has its horns and not its hornyhoofs affected by the union of the two forms, and the offspring from twobirds with differently coloured tails have their tails and not their wholeplumage affected. The various tissues of the body plainly show, as many physiologists haveinsisted, [909] an affinity for special organic substances, whether naturalor foreign to the body. We see this in the cells of the kidneys attractingurea from the blood; in the worrara poison affecting the nerves; upas anddigitalis the muscles; the Lytta vesicatoria the kidneys; and in thepoisonous matter of many diseases, as small-pox, scarlet-fever, hooping-cough, glanders, cancer, and hydrophobia, affecting certaindefinite parts of the body or certain tissues or glands. The affinity of various parts of the body for each other during {381} theirearly development was shown in the last chapter, when discussing thetendency to fusion in homologous parts. This affinity displays itself inthe normal fusion of organs which are separate at an early embryonic age, and still more plainly in those marvellous cases of double monsters inwhich each bone, muscle, vessel, and nerve in the one embryo, blends withthe corresponding part in the other. The affinity between homologous organsmay come into action with single parts, or with the entire individual, asin the case of flowers or fruits which are symmetrically blended togetherwith all their parts doubled, but without any other trace of fusion. It has also been assumed that the development of each gemmule depends onits union with another cell or unit which has just commenced itsdevelopment, and which, from preceding it in order of growth, is of asomewhat different nature. Nor is it a very improbable assumption that thedevelopment of a gemmule is determined by its union with a cell slightlydifferent in nature, for abundant evidence was given in the seventeenthchapter, showing that a slight degree of differentiation in the male andfemale sexual elements favours in a marked manner their union andsubsequent development. But what determines the development of the gemmulesof the first-formed or primordial cell in the unimpregnated ovule, isbeyond conjecture. It must also be admitted that analogy fails to guide us towards anydetermination on several other points: for instance, whether cells, derivedfrom the same parent-cell, may, in the regular course of growth, becomedeveloped into different structures, from absorbing peculiar kinds ofnutriment, independently of their union with distinct gemmules. We shallappreciate this difficulty if we call to mind, what complex yet symmetricalgrowths the cells of plants yield when they are inoculated by the poison ofa gall-insect. With animals various polypoid excrescences and tumours arenow generally admitted[910] to be the direct product, throughproliferation, of normal cells which have become abnormal. In the regulargrowth and repair of bones, the tissues undergo, as Virchow remarks, [911] awhole series of permutations and substitutions. "The cartilage-cells may be{382} converted by a direct transformation into marrow-cells, and continueas such; or they may first be converted into osseous and then intomedullary tissue; or lastly, they may first be converted into marrow andthen into bone. So variable are the permutations of these tissues, inthemselves so nearly allied, and yet in their external appearance socompletely distinct. " But as these tissues thus change their nature at anyage, without any obvious change in their nutrition, we must suppose inaccordance with our hypothesis that gemmules derived from one kind oftissue combine with the cells of another kind, and cause the successivemodifications. It is useless to speculate at what period of development each organic unitcasts off its gemmules; for the whole subject of the development of thevarious elemental tissues is as yet involved in much doubt. Somephysiologists, for instance, maintain that muscle or nerve-fibres aredeveloped from cells, which are afterwards nourished by their own properpowers of absorption; whilst other physiologists deny their cellularorigin; and Beale maintains that such fibres are renovated exclusively bythe conversion of fresh germinal matter (that is the so-called nuclei) into"formed material. " However this may be, it appears probable that allexternal agencies, such as changed nutrition, increased use or disuse, &c. , which induced any permanent modification in a structure, would at the sametime or previously act on the cells, nuclei, germinal or formative matter, from which the structures in question were developed, and consequentlywould act on the gemmules or cast-off atoms. There is another point on which it is useless to speculate, namely, whetherall gemmules are free and separate, or whether some are from the firstunited into small aggregates. A feather, for instance, is a complexstructure, and, as each separate part is liable to inherited variations, Iconclude that each feather certainly generates a large number of gemmules;but it is possible that these may be aggregated into a compound gemmule. The same remark applies to the petals of a flower, which in some cases arehighly complex, with each ridge and hollow contrived for special purposes, so that each part must have been separately modified, and the modificationstransmitted; consequently, separate gemmules, according to our hypothesis, {383} must have been thrown off from each cell or part. But, as wesometimes see half an anther or a small portion of a filament becomingpetaliform, or parts or mere stripes of the calyx assuming the colour andtexture of the corolla, it is probable that with petals the gemmules ofeach cell are not aggregated together into a compound gemmule, but arefreely and separately diffused. * * * * * Having now endeavoured to show that the several foregoing assumptions areto a certain extent supported by analogous facts, and having discussed someof the most doubtful points, we will consider how far the hypothesis bringsunder a single point of view the various cases enumerated in the FirstPart. All the forms of reproduction graduate into each other and agree intheir product; for it is impossible to distinguish between organismsproduced from buds, from self-division, or from fertilised germs; suchorganisms are liable to variations of the same nature and to reversion ofcharacter; and as we now see that all the forms of reproduction depend onthe aggregation of gemmules derived from the whole body, we can understandthis general agreement. It is satisfactory to find that sexual and asexualgeneration, by both of which widely different processes the same livingcreature is habitually produced, are fundamentally the same. Parthenogenesis is no longer wonderful; in fact, the wonder is that itshould not oftener occur. We see that the reproductive organs do notactually create the sexual elements; they merely determine or permit theaggregation of the gemmules in a special manner. These organs, togetherwith their accessory parts, have, however, high functions to perform; theygive to both elements a special affinity for each other, independently ofthe contents of the male and female cells, as is shown in the case ofplants by the mutual reaction of the stigma and pollen-grains; they adaptone or both elements for independent temporary existence, and for mutualunion. The contrivances for these purposes are sometimes wonderfullycomplex, as with the spermatophores of the Cephalopoda. The male elementsometimes possesses attributes which, if observed in an independent animal, would be put down to instinct guided by sense-organs, as when the {384}spermatozoon of an insect finds its way into the minute micropyle of theegg, or as when the antherozoids of certain algæ swim by the aid of theirciliæ to the female plant, and force themselves into a minute orifice. Inthese latter cases, however, we must believe that the male element hasacquired its powers, on the same principle with the larvæ of animals, namely by successive modifications developed at corresponding periods oflife: we can hardly avoid in these cases looking at the male element as asort of premature larva, which unites, or, like one of the lower algæ, conjugates, with the female element. What determines the aggregation of thegemmules within the sexual organs we do not in the least know; nor do weknow why buds are formed in certain definite places, leading to thesymmetrical growth of trees and corals, nor why adventitious buds may beformed almost anywhere, even on a petal, and frequently upon healedwounds. [912] As soon as the gemmules have aggregated themselves, development apparently commences, but in the case of buds is oftenafterwards suspended, and in the case of the sexual elements soon ceases, unless the elements of the opposite sexes combine; even after this hasoccurred, the fertilised germ, as with seeds buried in the ground, mayremain during a lengthened period in a dormant state. The antagonism which has long been observed, [913] though exceptionsoccur, [914] between active growth and the power of sexualreproduction--between the repair of injuries and gemmation--and withplants, between rapid increase by buds, rhizomes, &c. , and the productionof seed, is partly explained by the gemmules not existing in sufficientnumbers for both processes. {385} But this explanation hardly applies tothose plants which naturally produce a multitude of seeds, but which, through a comparatively small increase in the number of the buds on theirrhizomes or offsets, yield few or no seed. As, however, we shall presentlysee that buds probably include tissue which has already been to a certainextent developed or differentiated, some additional organised matter willthus have been expended. From one of the forms of Reproduction, namely, spontaneous self-division, we are led by insensible steps to the repair of the slightest injury; andthe existence of gemmules, derived from every cell or unit throughout thebody and everywhere diffused, explains all such cases, --even the wonderfulfact that, when the limbs of the salamander were cut off many timessuccessively by Spallanzani and Bonnet, they were exactly and completelyreproduced. I have heard this process compared with the recrystallisationwhich occurs when the angles of a broken crystal are repaired; and the twoprocesses have this much in common, that in the one case the polarity ofthe molecules is the efficient cause, and in the other the affinity of thegemmules for particular nascent cells. Pangenesis does not throw much light on Hybridism, but agrees well withmost of the ascertained facts. We may conclude from the fact of a singlespermatozoon or pollen-grain being insufficient for impregnation, that acertain number of gemmules derived from each cell or unit are required forthe development of each part. From the occurrence of parthenogenesis, moreespecially in the case of the silk-moth, in which the embryo is oftenpartially formed, we may also infer that the female element includes nearlysufficient gemmules of all kinds for independent development, so that whenunited with the male element the gemmules must be superabundant. Now, as ageneral rule, when two species or races are crossed reciprocally, theoffspring do not differ, and this shows that both sexual elements agree inpower, in accordance with the view that they include the same gemmules. Hybrids and mongrels are generally intermediate in character between thetwo parent-forms, yet occasionally they closely resemble one parent in onepart and the other parent in another part, or even in their wholestructure: nor is this difficult to understand on {386} the admission thatthe gemmules in the fertilised germ are superabundant in number, and thatthose derived from one parent have some advantage in number, affinity, orvigour over those derived from the other parent. Crossed forms sometimesexhibit the colour or other characters of either parent in stripes orblotches; and this may occur in the first generation, or through reversionin succeeding bud and seminal generations, as in the several instancesgiven in the eleventh chapter. In these cases we must follow Naudin, [915]and admit that the "essence" or "element" of the two species, which terms Ishould translate into the gemmules, have an affinity for their own kind, and thus separate themselves into distinct stripes or blotches; and reasonswere given, when discussing in the fifteenth chapter the incompatibility ofcertain characters to unite, for believing in such mutual affinity. Whentwo forms are crossed, one is not rarely found to be prepotent in thetransmission of character over the other; and this we can explain only byagain assuming that the one form has some advantage in the number, vigour, or affinity of its gemmules, except in those cases, where certaincharacters are present in the one form and latent in the other. Forinstance, there is a latent tendency in all pigeons to become blue, and, when a blue pigeon is crossed with one of any other colour, the blue tintis generally prepotent. When we consider latent characters, the explanationof this form of prepotency will be obvious. When one species is crossed with another it is notorious that they do notyield the full or proper number of offspring; and we can only say on thishead that, as the development of each organism depends on suchnicely-balanced affinities between a host of gemmules and developing cellsor units, we need not feel at all surprised that the commixture of gemmulesderived from two distinct species should lead to a partial or completefailure of development. With respect to the sterility of hybrids producedfrom the union of two distinct species, it was shown in the nineteenthchapter that this depends exclusively on the reproductive organs beingspecially affected; but why these organs should be thus affected we do notknow, any more than {387} why unnatural conditions of life, thoughcompatible with health, should cause sterility; or why continued closeinterbreeding, or the illegitimate unions of dimorphic and trimorphicplants, induce the same result. The conclusion that the reproductive organsalone are affected, and not the whole organisation, agrees perfectly withthe unimpaired or even increased capacity in hybrid plants for propagationby buds; for this implies, according to our hypothesis, that the cells ofthe hybrids throw off hybridised cell-gemmules, which become aggregatedinto buds, but fail to become aggregated within the reproductive organs, soas to form the sexual elements. In a similar manner many plants, whenplaced under unnatural conditions, fail to produce seed, but can readily bepropagated by buds. We shall presently see that pangenesis agrees well withthe strong tendency to reversion exhibited by all crossed animals andplants. It was shown in the discussion on graft-hybrids that there is some reasonto believe that portions of cellular tissue taken from distinct plantsbecome so intimately united, as afterwards occasionally to produce crossedor hybridised buds. If this fact were fully established, it would, by theaid of our hypothesis, connect gemmation and sexual reproduction in theclosest manner. Abundant evidence has been advanced proving that pollen taken from onespecies or variety and applied to the stigma of another sometimes directlyaffects the tissues of the mother-plant. It is probable that this occurswith many plants during fertilisation, but can only be detected whendistinct forms are crossed. On any ordinary theory of reproduction this isa most anomalous circumstance, for the pollen-grains are manifestly adaptedto act on the ovule, but in these cases they act on the colour, texture, and form of the coats of the seeds, on the ovarium itself, which is amodified leaf, and even on the calyx and upper part of the flower-peduncle. In accordance with the hypothesis of pangenesis pollen includes gemmules, derived from every part of the organisation, which diffuse themselves andmultiply by self-division; hence it is not surprising that gemmules withinthe pollen, which are derived from the parts near the reproductive organs, should sometimes be able to affect the same parts, whilst still undergoingdevelopment, in the mother-plant. {388} As, during all the stages of development, the tissues of plants consist ofcells, and as new cells are not known to be formed between, orindependently of, pre-existing cells, we must conclude that the gemmulesderived from the foreign pollen do not become developed merely in contactwith pre-existing cells, but actually penetrate the nascent cells of themother-plant. This process may be compared with the ordinary act offertilisation, during which the contents of the pollen-tubes penetrate theclosed embryonic sack within the ovule, and determine the development ofthe embryo. According to this view, the cells of the mother-plant mayalmost literally be said to be fertilised by the gemmules derived from theforeign pollen. With all organisms, as we shall presently see, the cells ororganic units of the embryo during the successive stages of development mayin like manner be said to be fertilised by the gemmules of the cells, whichcome next in the order of formation. Animals, when capable of sexual reproduction, are fully developed, and itis scarcely possible that the male element should affect the tissues of themother in the same direct manner as with plants; nevertheless it is certainthat her ovaria are sometimes affected by a previous impregnation, so thatthe ovules subsequently fertilised by a distinct male are plainlyinfluenced in character; and this, as in the case of foreign pollen, isintelligible through the diffusion, retention, and action of the gemmulesincluded within the spermatozoa of the previous male. Each organism reaches maturity through a longer or shorter course ofdevelopment. The changes may be small and insensibly slow, as when a childgrows into a man, or many, abrupt, and slight, as in the metamorphoses ofcertain ephemerous insects, or again few and strongly marked, as with mostother insects. Each part may be moulded within a previously existing andcorresponding part, and in this case it will appear, falsely as I believe, to be formed from the old part; or it may be developed within a whollydistinct part of the body, as in the extreme cases of metagenesis. An eye, for instance, may be developed at a spot where no eye previously existed. We have also seen that allied organic beings in the course of theirmetamorphoses sometimes attain nearly the same structure after passing{389} through widely different forms; or conversely, after passing throughnearly the same early forms, arrive at a widely different termination. Inthese cases it is very difficult to believe that the early cells or unitspossess the inherent power, independently of any external agent, ofproducing new structures wholly different in form, position, and function. But these cases become plain on the hypothesis of pangenesis. The organicunits, during each stage of development, throw off gemmules, which, multiplying, are transmitted to the offspring. In the offspring, as soon asany particular cell or unit in the proper order of development becomespartially developed, it unites with (or to speak metaphorically isfertilised by) the gemmule of the next succeeding cell, and so onwards. Now, supposing that at any stage of development, certain cells oraggregates of cells had been slightly modified by the action of somedisturbing cause, the cast-off gemmules or atoms of the cell-contents couldhardly fail to be similarly affected, and consequently would reproduce thesame modification. This process might be repeated until the structure ofthe part at this particular stage of development became greatly changed, but this would not necessarily affect other parts whether previously orsubsequently developed. In this manner we can understand the remarkableindependence of structure in the successive metamorphoses, and especiallyin the successive metageneses of many animals. The term growth ought strictly to be confined to mere increase of size, anddevelopment to change of structure. [916] Now, a child is said to grow intoa man, and a foal into a horse, but, as in these cases there is much changeof structure, the process properly belongs to the order of development. Wehave indirect evidence of this in many variations and diseases superveningduring so-called growth at a particular period, and being inherited at acorresponding period. In the case, however, of diseases which superveneduring old age, subsequently to the ordinary period of procreation, andwhich nevertheless are sometimes inherited, as occurs with brain and heartcomplaints, we {390} must suppose that the organs were in fact affected atan earlier age and threw off at this period affected gemmules; but that theaffection became visible or injurious only after the prolonged growth ofthe part in the strict sense of the word. In all the changes of structurewhich regularly supervene during old age, we see the effects ofdeteriorated growth, and not of true development. In the so-called process of _alternate generation_ many individuals aregenerated asexually during very early or later stages of development. Theseindividuals may closely resemble the preceding larval form, but generallyare wonderfully dissimilar. To understand this process we must suppose thatat a certain stage of development the gemmules are multiplied at an unusualrate, and become aggregated by mutual affinity at many centres ofattraction, or buds. These buds, it may be remarked, must include gemmulesnot only of all the succeeding but likewise of all the preceding stages ofdevelopment; for when mature they have the power of transmitting by sexualgeneration gemmules of all the stages, however numerous these may be. Itwas shown in the First Part, at least in regard to animals, that the newbeings which are thus at any period asexually generated do not retrogradein development--that is, they do not pass through those earlier stages, through which the fertilised germ of the same animal has to pass; and anexplanation of this fact was attempted as far as the final or teleologicalcause is concerned. We can likewise understand the proximate cause, if weassume, and the assumption is far from improbable, that buds, likechopped-up fragments of a hydra, are formed of tissue which has alreadypassed through several of the earlier stages of development; for in thiscase their component cells or units would not unite with the gemmulesderived from the earlier-formed cells, but only with those which came nextin the order of development. On the other hand, we must believe that, inthe sexual elements, or probably in the female alone, gemmules of certainprimordial cells are present; and these, as soon as their developmentcommences, unite in due succession with the gemmules of every part of thebody, from the first to the last period of life. The principle of the independent formation of each part, in {391} so far asits development depends on the union of the proper gemmules with certainnascent cells, together with the superabundance of the gemmules derivedfrom both parents and self-multiplied, throws light on a widely differentgroup of facts, which on any ordinary view of development appears verystrange. I allude to organs which are abnormally multiplied or transposed. Thus gold-fish often have supernumerary fins placed on various parts oftheir bodies. We have seen that, when the tail of a lizard is broken off, adouble tail is sometimes reproduced, and when the foot of the salamander isdivided longitudinally, additional digits are occasionally formed. Whenfrogs, toads, &c. , are born with their limbs doubled, as sometimes occurs, the doubling, as Gervais remarks, [917] cannot be due to the complete fusionof two embryos, with the exception of the limbs, for the larvæ arelimbless. The same argument is applicable[918] to certain insects producedwith multiple legs or antennæ, for these are metamorphosed from apodal orantennæless larvæ. Alphonse Milne-Edwards[919] has described the curiouscase of a crustacean in which one eye-peduncle supported, instead of acomplete eye, only an imperfect cornea, out of the centre of which aportion of an antenna was developed. A case has been recorded[920] of a manwho had during both dentitions a double tooth in place of the left secondincisor, and he inherited this peculiarity from his paternal grandfather. Several cases are known[921] of additional teeth having been developed inthe palate, more especially with horses, and in the orbit of the eye. Certain breeds of sheep bear a whole crowd of horns on their foreheads. Hairs occasionally appear in strange situations, as within the ears of theSiamese hairy family; and hairs "quite natural in structure" have beenobserved "within the substance of the brain. "[922] As many as five spurshave been seen on both legs in certain Game-fowls. In the Polish fowl themale is ornamented with a topknot of hackles {392} like those on his neck, whilst the female has one of common feathers. In feather-footed pigeons andfowls, feathers like those on the wing arise from the outer side of thelegs and toes. Even the elemental parts of the same feather may betransposed; for in the Sebastopol goose, barbules are developed on thedivided filaments of the shaft. Analogous cases are of such frequent occurrence with plants that they donot strike us with sufficient surprise. Supernumerary petals, stamens, andpistils, are often produced. I have seen a leaflet low down in the compoundleaf of _Vicia sativa_ converted into a tendril, and a tendril possessesmany peculiar properties, such as spontaneous movement and irritability. The calyx sometimes assumes, either wholly or by stripes, the colour andtexture of the corolla. Stamens are so frequently converted, more or lesscompletely, into petals, that such cases are passed over as not deservingnotice; but as petals have special functions to perform, namely, to protectthe included organs, to attract insects, and in not a few cases to guidetheir entrance by well-adapted contrivances, we can hardly account for theconversion of stamens into petals merely by unnatural or superfluousnourishment. Again, the edge of a petal may occasionally be found includingone of the highest products of the plant, namely the pollen; for instance, I have seen in an Ophrys a pollen-mass with its curious structure of littlepackets, united together and to the caudicle by elastic threads, formedbetween the edges of an upper petal. The segments of the calyx of thecommon pea have been observed partially converted into carpels, includingovules, and with their tips converted into stigmas. Numerous analogousfacts could be given. [923] I do not know how physiologists look at such facts as the foregoing. According to the doctrine of pangenesis, the free and superabundantgemmules of the transposed organs are developed in the wrong place, fromuniting with wrong cells or aggregates of cells during their nascent state;and this would follow from a slight modification in the elective affinityof such cells, or possibly of certain gemmules. Nor ought we to feel muchsurprise at the affinities of cells and gemmules varying {393} underdomestication, when we remember the many curious cases given, in theseventeenth chapter, of cultivated plants which absolutely refuse to befertilised by their own pollen or by that of the same species, but areabundantly fertile with pollen of a distinct species; for this implies thattheir sexual elective affinities--and this is the term used byGärtner--have been modified. As the cells of adjoining or homologous partswill have nearly the same nature, they will be liable to acquire byvariation each other's elective affinities; and we can thus to a certainextent understand such cases as a crowd of horns on the heads in certainsheep, of several spurs on the leg, and of hackles on the head of the fowl, and with the pigeon the occurrence of wing-feathers on their legs and ofmembrane between their toes; for the leg is the homologue of the wing. Asall the organs of plants are homologous and spring from a common axis, itis natural that they should be eminently liable to transposition. It oughtto be observed that when any compound part, such as an additional limb oran antenna, springs from a false position, it is only necessary that thefew first gemmules should be wrongly attached; for these whilst developingwould attract others in due succession, as in the regrowth of an amputatedlimb. When parts which are homologous and similar in structure, as thevertebræ in snakes or the stamens in polyandrous flowers, &c. , are repeatedmany times in the same organism, closely allied gemmules must be extremelynumerous, as well as the points to which they ought to become united; and, in accordance with the foregoing views, we can to a certain extentunderstand Isid. Geoffroy St. Hilaire's law, namely, that parts, which arealready multiple, are extremely liable to vary in number. The same general principles apply to the fusion of homologous parts; andwith respect to mere cohesion there is probably always some degree offusion, at least near the surface. When two embryos during their earlydevelopment come into close contact, as both include correspondinggemmules, which must be in all respects almost identical in nature, it isnot surprising that some derived from one embryo and some from the othershould unite at the point of contact with a single nascent cell oraggregate of cells, and thus give rise to a single part or organ. Forinstance, two embryos might thus come to have on their {394} adjoiningsides a single symmetrical arm, which in one sense will have been formed bythe fusion of the bones, muscles, &c. , belonging to the arms of bothembryos. In the case of the fish described by Lereboullet, in which adouble head was seen gradually to fuse into a single one, the same processmust have taken place, together with the absorption of all the parts whichhad been already formed. These cases are exactly the reverse of those inwhich a part is doubled either spontaneously or after an injury; for in thecase of doubling, the superabundant gemmules of the same part areseparately developed in union with adjoining points; whilst in the case offusion the gemmules derived from two homologous parts become mingled andform a single part; or it may be that the gemmules from one of twoadjoining embryos alone become developed. * * * * * Variability often depends, as I have attempted to show, on the reproductiveorgans being injuriously affected by changed conditions; and in this casethe gemmules derived from the various parts of the body are probablyaggregated in an irregular manner, some superfluous and others deficient. Whether a superabundance of gemmules, together with fusion duringdevelopment, would lead to the increased size of any part cannot be told;but we can see that their partial deficiency, without necessarily leadingto the entire abortion of the part, might cause considerable modifications;for in the same manner as a plant, if its own pollen be excluded, is easilyhybridised, so, in the case of a cell, if the properly succeeding gemmuleswere absent, it would probably combine easily with other and alliedgemmules. We see this in the case of imperfect nails growing on the stumpsof amputated fingers, [924] for the gemmules of the nails have manifestlybeen developed at the nearest point. In variations caused by the direct action of changed conditions, whether ofa definite or indefinite nature, as with the fleeces of sheep in hotcountries, with maize grown in cold countries, with inherited gout, &c. , the tissues of the body, according to the doctrine of pangenesis, aredirectly affected by the new conditions, and consequently throw offmodified gemmules, which are transmitted with their newly acquiredpeculiarities to the offspring. On any ordinary view it is unintelligiblehow changed {395} conditions, whether acting on the embryo, the young oradult animal, can cause inherited modifications. It is equally or even moreunintelligible on any ordinary view, how the effects of the long-continueduse or disuse of any part, or of changed habits of body or mind, can beinherited. A more perplexing problem can hardly be proposed; but on ourview we have only to suppose that certain cells become at last not onlyfunctionally but structurally modified; and that these throw off similarlymodified gemmules. This may occur at any period of development, and themodification will be inherited at a corresponding period; for the modifiedgemmules will unite in all ordinary cases with the proper preceding cells, and they will consequently be developed at the same period at which themodification first arose. With respect to mental habits or instincts, weare so profoundly ignorant on the relation between the brain and the powerof thought that we do not know whether an inveterate habit or trick inducesany change in the nervous system; but when any habit or other mentalattribute, or insanity, is inherited, we must believe that some actualmodification is transmitted;[925] and this implies, according to ourhypothesis, that gemmules derived from modified nerve-cells are transmittedto the offspring. It is generally, perhaps always, necessary that an organism should beexposed during several generations to changed conditions or habits, inorder that any modification in the structure of the offspring should ensue. This may be partly due to the changes not being at first marked enough tocatch the attention, but this explanation is insufficient; and I canaccount for the fact, only by the assumption, which we shall see under thehead of reversion is strongly supported, that gemmules derived from eachcell before it had undergone the least modification are transmitted inlarge numbers to successive generations, but that the gemmules derived fromthe same cells after modification, naturally go on increasing under thesame favouring conditions, until at last they become sufficiently numerousto overpower and supplant the old gemmules. Another difficulty may be here noticed; we have seen that {396} there is animportant difference in the frequency, though not in the nature, of thevariations in plants propagated by sexual and asexual generation. As far asvariability depends on the imperfect action of the reproductive organsunder changed conditions, we can at once see why seedlings should be farmore variable than plants propagated by buds. We know that extremely slightcauses, --for instance, whether a tree has been grafted or grows on its ownstock, the position of the seeds within the capsule, and of the flowers onthe spike, --sometimes suffice to determine the variation of a plant, whenraised from seed. Now, it is probable, as explained when discussingalternate generation, that a bud is formed of a portion of alreadydifferentiated tissue; consequently an organism thus formed does not passthrough the earlier phases of development, and cannot be so freely exposed, at the age when its structure would be most readily modified, to thevarious causes inducing variability; but it is very doubtful whether thisis a sufficient explanation of the difficulty. With respect to the tendency to reversion, there is a similar differencebetween plants propagated from buds and seed. Many varieties, whetheroriginally produced from seed or buds, can be securely propagated by buds, but generally or invariably revert by seed. So, also, hybridised plants canbe multiplied to any extent by buds, but are continually liable toreversion by seed, --that is, to the loss of their hybrid or intermediatecharacter. I can offer no satisfactory explanation of this fact. Here is astill more perplexing case: certain plants with variegated leaves, phloxeswith striped flowers, barberries with seedless fruit, can all be securelypropagated by the buds on cuttings; but the buds developed from the rootsof these cuttings almost invariably lose their character and revert totheir former condition. Finally, we can see on the hypothesis of pangenesis that variabilitydepends on at least two distinct groups of causes. Firstly, on thedeficiency, superabundance, fusion, and transposition of gemmules, and onthe redevelopment of those which have long been dormant. In these cases thegemmules themselves have undergone no modification; but the mutations inthe above respects will amply account for much fluctuating {397}variability. Secondly, in the cases in which the organisation has beenmodified by changed conditions, the increased use or disuse of parts, orany other cause, the gemmules cast off from the modified units of the bodywill be themselves modified, and, when sufficiently multiplied, will bedeveloped into new and changed structures. * * * * * Turning now to Inheritance: if we suppose a homogeneous gelatinousprotozoon to vary and assume a reddish colour, a minute separated atom weaid naturally, as it grew to full size, retain the same colour; and weshould have the simplest form of inheritance. [926] Precisely the same viewmay be extended to the infinitely numerous and diversified units of whichthe whole body in one of the higher animals is composed; and the separatedatoms are our gemmules. We have already sufficiently discussed theinheritance of the direct effects of changed conditions, and of increaseduse or disuse of parts, and, by implication, the important principle ofinheritance at corresponding ages. These groups of facts are to a largeextent intelligible on the hypothesis of pangenesis, and on no otherhypothesis as yet advanced. A few words must be added on the complete abortion or suppression oforgans. When a part becomes diminished by disuse prolonged during manygenerations, the principle of economy of growth, as previously explained, will tend to reduce it still further; but this will not account for thecomplete or almost complete obliteration of, for instance, a minute papillaof cellular tissue representing a pistil, or of a microscopically minutenodule of bone representing a tooth. In certain cases of suppression notyet completed, in which a rudiment occasionally reappears throughreversion, diffused gemmules derived from this part must, according to ourview, still exist; hence we must suppose that the cells, in union withwhich the rudiment was formerly developed, in these cases fail in theiraffinity for such gemmules. But in the cases of complete and final abortionthe gemmules themselves no doubt have perished; nor is this {398} in anyway improbable, for, though a vast number of active and long-dormantgemmules are diffused and nourished in each living creature, yet there mustbe some limit to their number; and it appears natural that gemmules derivedfrom an enfeebled and useless rudiment would be more liable to perish thanthose derived from other parts which are still in full functional activity. With respect to mutilations, it is certain that a part may be removed orinjured during many generations, and no inherited result follow; and thisis an apparent objection to the hypothesis which will occur to every one. But, in the first place, a being can hardly be intentionally mutilatedduring its early stages of growth whilst in the womb or egg; and suchmutilations, when naturally caused, would appear like congenitaldeficiencies, which are occasionally inherited. In the second place, according to our hypothesis, gemmules multiply by self-division and aretransmitted from generation to generation; so that during a long periodthey would be present and ready to reproduce a part which was repeatedlyamputated. Nevertheless it appears, from the facts given in the twelfthchapter, that in some rare cases mutilations have been inherited, but inmost of these the mutilated surface became diseased. In this case it may beconjectured that the gemmules of the lost part were gradually all attractedby the partially diseased surface, and thus perished. Although this wouldoccur in the injured individual alone, and therefore in only one parent, yet this might suffice for the inheritance of a mutilation, on the sameprinciple that a hornless animal of either sex, when crossed with a perfectanimal of the opposite sex, often transmits its deficiency. The last subject that need here be discussed, namely Reversion, rests onthe principle that transmission and development, though generally acting inconjunction, are distinct powers; and the transmission of gemmules andtheir subsequent development show us how the existence of these twodistinct powers is possible. We plainly see this distinction in the manycases in which a grandfather transmits to his grandson, through hisdaughter, characters which she does not, or cannot, possess. Why thedevelopment of certain characters, not necessarily in any way connectedwith the reproductive organs, should be confined to one sex alone--that is, why certain cells in one sex {399} should unite with and cause thedevelopment of certain gemmules--we do not in the least know; but it is thecommon attribute of most organic beings in which the sexes are separate. The distinction between transmission and development is likewise seen inall ordinary cases of Reversion; but before discussing this subject it maybe advisable to say a few words on those characters which I have calledlatent, and which would not be classed under Reversion in its usual sense. Most, or perhaps all, the secondary characters, which appertain to one sex, lie dormant in the other sex; that is, gemmules capable of development intothe secondary male sexual characters are included within the female; andconversely female characters in the male. Why in the female, when herovaria become diseased or fail to act, certain masculine gemmules becomedeveloped, we do not clearly know, any more than why when a young bull iscastrated his horns continue growing until they almost resemble those of acow; or why, when a stag is castrated, the gemmules derived from theantlers of his progenitors quite fail to be developed. But in many cases, with variable organic beings, the mutual affinities of the cells andgemmules become modified, so that parts are transposed or multiplied; andit would appear that a slight change in the constitution of an animal, inconnection with the state of the reproductive organs, leads to changedaffinities in the tissues of various parts of the body. Thus, when maleanimals first arrive at puberty, and subsequently during each recurrentseason, certain cells or parts acquire an affinity for certain gemmules, which become developed into the secondary masculine characters; but if thereproductive organs be destroyed, or even temporarily disturbed by changedconditions, these affinities are not excited. Nevertheless, the male, before he arrives at puberty, and during the season when the species doesnot breed, must include the proper gemmules in a latent state. The curiouscase formerly given of a Hen which assumed the masculine characters, not ofher own breed but of a remote progenitor, illustrates the connexion betweenlatent sexual characters and ordinary reversion. With those animals andplants which habitually produce several forms, as with certain butterfliesdescribed by Mr. Wallace, in which three female forms and {400} the maleexist, or as with the trimorphic species of Lythrum and Oxalis, gemmulescapable of reproducing several widely-different forms must be latent ineach individual. The same principle of the latency of certain characters, combined with thetransposition of organs, may be applied to those singular cases ofbutterflies and other insects, in which exactly one half or one quarter ofthe body resembles the male, and the other half or three quarters thefemale; and when this occurs the opposite sides of the body, separated fromeach other by a distinct line, sometimes differ in the most conspicuousmanner. Again, these same principles apply to the cases given in thethirteenth chapter, in which the right and left sides of the body differ toan extraordinary degree, as in the spiral winding of certain shells, and asin the genus Verruca among cirripedes; for in these cases it is known thateither side indifferently may undergo the same remarkable change ofdevelopment. Reversion, in the ordinary sense of the word, comes into action soincessantly, that it evidently forms an essential part of the general lawof inheritance. It occurs with beings, however propagated, whether by budsor seminal generation, and sometimes may even be observed in the sameindividual as it advances in age. The tendency to reversion is ofteninduced by a change of conditions, and in the plainest manner by the act ofcrossing. Crossed forms are generally at first nearly intermediate incharacter between their two parents; but in the next generation theoffspring generally revert to one or both of their grandparents, andoccasionally to more remote ancestors. How can we account for these facts?Each organic unit in a hybrid must throw off, according to the doctrine ofpangenesis, an abundance of hybridised gemmules, for crossed plants can bereadily and largely propagated by buds; but by the same hypothesis therewill likewise be present dormant gemmules derived from both pureparent-forms; and as these latter retain their normal condition, theywould, it is probable, be enabled to multiply largely during the lifetimeof each hybrid. Consequently the sexual elements of a hybrid will includeboth pure and hybridised gemmules; and when two hybrids pair, thecombination of pure gemmules derived from the one hybrid with the puregemmules of the same parts derived from the other would {401} necessarilylead to complete reversion of character; and it is, perhaps, not too bold asupposition that unmodified and undeteriorated gemmules of the same naturewould be especially apt to combine. Pure gemmules in combination withhybridised gemmules would lead to partial reversion. And lastly, hybridisedgemmules derived from both parent-hybrids would simply reproduce theoriginal hybrid form. [927] All these cases and degrees of reversionincessantly occur. It was shown in the fifteenth chapter that certain characters areantagonistic to each other or do not readily blend together; hence, whentwo animals with antagonistic characters are crossed, it might well happenthat a sufficiency of gemmules in the male alone for the reproduction ofhis peculiar characters, and in the female alone for the reproduction ofher peculiar characters, would not be present; and in this case dormantgemmules derived from some remote progenitor might easily gain theascendency, and cause the reappearance of long-lost characters. Forinstance, when black and white pigeons, or black and white fowls, arecrossed, --colours which do not readily blend, --blue plumage in the onecase, evidently derived from the rock-pigeon, and red plumage in the othercase, derived from the wild jungle-cock, occasionally reappear. Withuncrossed breeds the same result would follow, under conditions whichfavoured the multiplication and development of certain dormant gemmules, aswhen animals become feral and revert to their pristine character. A certainnumber of gemmules being requisite for the development of each character, as is known to be the case from several spermatozoa or pollen-grains beingnecessary for fertilisation, and time favouring their multiplication, willtogether account for the curious cases, insisted on by Mr. Sedgwick, ofcertain diseases regularly appearing in alternate generations. Thislikewise holds good, more or less strictly, with other weakly inheritedmodifications. Hence, as I have heard it remarked, certain diseases appearactually to gain strength by the intermission of a generation. Thetransmission of dormant gemmules during many successive generations ishardly in itself more improbable, as {402} previously remarked, than theretention during many ages of rudimentary organs, or even only of atendency to the production of a rudiment; but there is no reason to supposethat all dormant gemmules would be transmitted and propagated for ever. Excessively minute and numerous as they are believed to be, an infinitenumber derived, during a long course of modification and descent, from eachcell of each progenitor, could not be supported or nourished by theorganism. On the other hand, it does not seem improbable that certaingemmules, under favourable conditions, should be retained and go onmultiplying for a longer period than others. Finally, on the views heregiven, we certainly gain some clear insight into the wonderful fact thatthe child may depart from the type of both its parents, and resemble itsgrandparents, or ancestors removed by many generations. _Conclusion. _ The hypothesis of Pangenesis, as applied to the several great classes offacts just discussed, no doubt is extremely complex; but so assuredly arethe facts. The assumptions, however, on which the hypothesis rests cannotbe considered as complex in any extreme degree--namely, that all organicunits, besides having the power, as is generally admitted, of growing byself-division, throw off free and minute atoms of their contents, that isgemmules. These multiply and aggregate themselves into buds and the sexualelements; their development depends on their union with other nascent cellsor units; and they are capable of transmission in a dormant state tosuccessive generations. In a highly organised and complex animal, the gemmules thrown off from eachdifferent cell or unit throughout the body must be inconceivably numerousand minute. Each unit of each part, as it changes during development, andwe know that some insects undergo at least twenty metamorphoses, must throwoff its gemmules. All organic beings, moreover, include many dormantgemmules derived from their grandparents and more remote progenitors, butnot from all their progenitors. These almost infinitely numerous and minutegemmules must be included in each bud, ovule, spermatozoon, andpollen-grain. Such an admission will be declared impossible; but, aspreviously {403} remarked, number and size are only relative difficulties, and the eggs or seeds produced by certain animals or plants are so numerousthat they cannot be grasped by the intellect. The organic particles with which the wind is tainted over miles of space bycertain offensive animals must be infinitely minute and numerous; yet theystrongly affect the olfactory nerves. An analogy more appropriate isafforded by the contagious particles of certain diseases, which are sominute that they float in the atmosphere and adhere to smooth paper; yet weknow how largely they increase within the human body, and how powerfullythey act. Independent organisms exist which are barely visible under thehighest powers of our recently-improved microscopes, and which probably arefully as large as the cells or units in one of the higher animals; yetthese organisms no doubt reproduce themselves by germs of extrememinuteness, relatively to their own minute size. Hence the difficulty, which at first appears insurmountable, of believing in the existence ofgemmules so numerous and so small as they must be according to ourhypothesis, has really little weight. The cells or units of the body are generally admitted by physiologists tobe autonomous, like the buds on a tree, but in a less degree. I go one stepfurther and assume that they throw off reproductive gemmules. Thus ananimal does not, as a whole, generate its kind through the sole agency ofthe reproductive system, but each separate cell generates its kind. It hasoften been said by naturalists that each cell of a plant has the actual orpotential capacity of reproducing the whole plant; but it has this poweronly in virtue of containing gemmules derived from every part. If ourhypothesis be provisionally accepted, we must look at all the forms ofasexual reproduction, whether occurring at maturity or as in the case ofalternate generation during youth, as fundamentally the same, and dependenton the mutual aggregation and multiplication of the gemmules. The regrowthof an amputated limb or the healing of a wound is the same processpartially carried out. Sexual generation differs in some importantrespects, chiefly, as it would appear, in an insufficient number ofgemmules being aggregated within the separate sexual elements, and probablyin the presence of certain primordial cells. The development of each being, including all the {404} forms of metamorphosis and metagenesis, as well asthe so-called growth of the higher animals, in which structure changesthough not in a striking manner, depends on the presence of gemmules thrownoff at each period of life, and on their development, at a correspondingperiod, in union with preceding cells. Such cells may be said to befertilised by the gemmules which come next in the order of development. Thus the ordinary act of impregnation and the development of each being areclosely analogous processes. The child, strictly speaking, does not growinto the man, but includes germs which slowly and successively becomedeveloped and form the man. In the child, as well as in the adult, eachpart generates the same part for the next generation. Inheritance must belooked at as merely a form of growth, like the self-division of alowly-organised unicellular plant. Reversion depends on the transmissionfrom the forefather to his descendants of dormant gemmules, whichoccasionally become developed under certain known or unknown conditions. Each animal and plant may be compared to a bed of mould full of seeds, mostof which soon germinate, some lie for a period dormant, whilst othersperish. When we hear it said that a man carries in his constitution theseeds of an inherited disease, there is much literal truth in theexpression. Finally, the power of propagation possessed by each separatecell, using the term in its largest sense, determines the reproduction, thevariability, the development and renovation of each living organism. Noother attempt, as far as I am aware, has been made, imperfect as thisconfessedly is, to connect under one point of view these several grandclasses of facts. We cannot fathom the marvellous complexity of an organicbeing; but on the hypothesis here advanced this complexity is muchincreased. Each living creature must be looked at as a microcosm--a littleuniverse, formed of a host of self-propagating organisms, inconceivablyminute and as numerous as the stars in heaven. * * * * * {405} CHAPTER XXVIII. CONCLUDING REMARKS. DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE AND DISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE QUESTION WHETHER EACH PARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED. As summaries have been added to nearly all the chapters, and as, in thechapter on pangenesis, various subjects, such as the forms of reproduction, inheritance, reversion, the causes and laws of variability, &c. , have beenrecently discussed, I will here only make a few general remarks on the moreimportant conclusions which may be deduced from the multifarious detailsgiven throughout this work. Savages in all parts of the world easily succeed in taming wild animals;and those inhabiting any country or island, when first invaded by man, would probably have been still more easily tamed. Complete subjugationgenerally depends on an animal being social in its habits, and on receivingman as the chief of the herd or family. Domestication implies almostcomplete fertility under new and changed conditions of life, and this isfar from being invariably the case. An animal would not have been worth thelabour of domestication, at least during early times, unless of service toman. From these circumstances the number of domesticated animals has neverbeen large. With respect to plants, I have shown in the ninth chapter howtheir varied uses were probably first discovered, and the early steps intheir cultivation. Man could not have known, when he first domesticated ananimal or plant, whether it would flourish and multiply when transported toother countries, therefore he could not have been thus influenced in hischoice. We see that the close adaptation of the reindeer and camel toextremely cold and hot countries has not prevented their domestication. Still less {406} could man have foreseen whether his animals and plantswould vary in succeeding generations and thus give birth to new races; andthe small capacity of variability in the goose and ass has not preventedtheir domestication from the remotest epoch. With extremely few exceptions, all animals and plants which have been longdomesticated, have varied greatly. It matters not under what climate, orfor what purpose, they are kept, whether as food for man or beast, fordraught or hunting, for clothing or mere pleasure, --under all thesecircumstances domesticated animals and plants have varied to a much greaterextent than the forms which in a state of nature are ranked as one species. Why certain animals and plants have varied more under domestication thanothers we do not know, any more than why some are rendered more sterilethan others under changed conditions of life. But we frequently judge ofthe amount of variation by the production of numerous and diversifiedraces, and we can clearly see why in many cases this has not occurred, namely, because slight successive variations have not been steadilyaccumulated; and such variations will never be accumulated when an animalor plant is not closely observed, or much valued, or kept in large numbers. The fluctuating, and, as far as we can judge, never-ending variability ofour domesticated productions, --the plasticity of their wholeorganisation, --is one of the most important facts which we learn from thenumerous details given in the earlier chapters of this work. Yetdomesticated animals and plants can hardly have been exposed to greaterchanges in their conditions than have many natural species during theincessant geological, geographical, and climatal changes of the wholeworld. The former will, however, commonly have been exposed to more suddenchanges and to less continuously uniform conditions. As man hasdomesticated so many animals and plants belonging to widely differentclasses, and as he certainly did not with prophetic instinct choose thosespecies which would vary most, we may infer that all natural species, ifsubjected to analogous conditions, would, on an average, vary to the samedegree. Few men at the present day will maintain that animals and plantswere created with a tendency to vary, which long remained dormant, in orderthat fanciers in after ages might {407} rear, for instance, curious breedsof the fowl, pigeon, or canary-bird. From several causes it is difficult to judge of the amount of modificationwhich our domestic productions have undergone. In some cases the primitiveparent-stock has become extinct, or cannot be recognised with certaintyowing to its supposed descendants having been so much modified. In othercases two or more closely allied forms, after being domesticated, havecrossed; and then it is difficult to estimate how much of the change oughtto be attributed to variation. But the degree to which our domestic breedshave been modified by the crossing of distinct natural forms has probablybeen exaggerated by some authors. A few individuals of one form wouldseldom permanently affect another form existing in much greater numbers;for, without careful selection, the stain of the foreign blood would soonbe obliterated, and during early and barbarous times, when our animals werefirst domesticated, such care would seldom have been taken. There is good reason to believe that several of the breeds of the dog, ox, pig, and of some other animals, are respectively descended from distinctwild prototypes; nevertheless the belief in the multiple origin of ourdomesticated animals has been extended by some few naturalists and by manybreeders to an unauthorised extent. Breeders refuse to look at the wholesubject under a single point of view; I have heard one, who maintained thatour fowls were the descendants of at least half-a-dozen aboriginal species, protest that he was in no way concerned with the origin of pigeons, ducks, rabbits, horses, or any other animal. They overlook the improbability ofmany species having been domesticated at an early and barbarous period. They do not consider the improbability of species having existed in a stateof nature which, if like our present domestic breeds, would have beenhighly abnormal in comparison with all their congeners. They maintain thatcertain species, which formerly existed, have become extinct or unknown, although the world is now so much better known. The assumption of so muchrecent extinction is no difficulty in their eyes; for they do not judge ofits probability by the facility or difficulty of the extinction of otherclosely allied wild forms. Lastly, {408} they often ignore the wholesubject of geographical distribution as completely as if its laws were theresult of chance. Although from the reasons just assigned it is often difficult to judgeaccurately of the amount of change which our domesticated productions haveundergone, yet this can be ascertained in the cases in which we know thatall the breeds are descended from a single species, as with the pigeon, duck, rabbit, and almost certainly with the fowl; and by the aid of analogythis is to a certain extent possible in the case of animals descended fromseveral wild stocks. It is impossible to read the details given in theearlier chapters, and in many published works, or to visit our variousexhibitions, without being deeply impressed with the extreme variability ofour domesticated animals and cultivated plants. I have in many instancespurposely given details on new and strange peculiarities which have arisen. No part of the organisation escapes the tendency to vary. The variationsgenerally affect parts of small vital or physiological importance, but soit is with the differences which exist between closely allied species. Inthese unimportant characters there is often a greater difference betweenthe breeds of the same species than between the natural species of the samegenus, as Isidore Geoffroy has shown to be the case with size, and as isoften the case with the colour, texture, form, &c. , of the hair, feathers, horns, and other dermal appendages. It has often been asserted that important parts never vary underdomestication, but this is a complete error. Look at the skull of the pigin any one of the highly improved breeds, with the occipital condyles andother parts greatly modified; or look at that of the niata ox. Or again, inthe several breeds of the rabbit, observe the elongated skull, with thedifferently shaped occipital foramen, atlas, and other cervical vertebræ. The whole shape of the brain, together with the skull, has been modified inPolish fowls; in other breeds of the fowl the number of the vertebræ andthe forms of the cervical vertebræ have been changed. In certain pigeonsthe shape of the lower jaw, the relative length of the tongue, the size ofthe nostrils and eyelids, the number and shape of the ribs, the form andsize of the oesophagus, have all varied. In certain quadrupeds the lengthof the intestines has been much increased or {409} diminished. With plantswe see wonderful differences in the stones of various fruits. In theCucurbitaceæ several highly important characters have varied, such as thesessile position of the stigmas on the ovarium, the position of the carpelswithin the ovarium, and its projection out of the receptacle. But it wouldbe useless to run through the many facts given in the earlier chapters. It is notorious how greatly the mental disposition, tastes, habits, consensual movements, loquacity or silence, and the tone of voice havevaried and been inherited with our domesticated animals. The dog offers themost striking instance of changed mental attributes, and these differencescannot be accounted for by descent from distinct wild types. New mentalcharacters have certainly often been acquired, and natural ones lost, underdomestication. New characters may appear and disappear at any stage of growth, and beinherited at a corresponding period. We see this in the difference betweenthe eggs of various breeds of the fowl, and in the down on chickens; andstill more plainly in the differences between the caterpillars and cocoonsof various breeds of the silk-moth. These facts, simple as they appear, throw light on the characters which distinguish the larval and adult statesof natural species, and on the whole great subject of embryology. Newcharacters are liable to become attached exclusively to that sex in whichthey first appeared, or they may be developed in a much higher degree inthe one than the other sex; or again, after having become attached to onesex, they may be partially transferred to the opposite sex. These facts, and more especially the circumstance that new characters seem to beparticularly liable, from some unknown cause, to become attached to themale sex, have an important bearing on the acquirement by animals in astate of nature of secondary sexual characters. It has sometimes been said that our domestic productions do not differ inconstitutional peculiarities, but this cannot be maintained. In ourimproved cattle, pigs, &c. , the period of maturity, including that of thesecond dentition, has been much hastened. The period of gestation variesmuch, but has been modified in a fixed manner in only one or two cases. In{410} our poultry and pigeons the acquirement of down and of the firstplumage by the young, and of the secondary sexual characters by the males, differ. The number of moults through which the larvæ of silk-moths pass, varies. The tendency to fatten, to yield much milk, to produce many youngor eggs at a birth or during life, differs in different breeds. We finddifferent degrees of adaptation to climate, and different tendencies tocertain diseases, to the attacks of parasites, and to the action of certainvegetable poisons. With plants, adaptation to certain soils, as with somekinds of plums, the power of resisting frost, the period of flowering andfruiting, the duration of life, the period of shedding the leaves and ofretaining them throughout the winter, the proportion and nature of certainchemical compounds in the tissues or seeds, all vary. There is, however, one important constitutional difference between domesticraces and species; I refer to the sterility which almost invariablyfollows, in a greater or less degree, when species are crossed, and to theperfect fertility of the most distinct domestic races, with the exceptionof a very few plants, when similarly crossed. It certainly appears aremarkable fact that many closely allied species which in appearance differextremely little should yield when united only a few, more or less sterileoffspring, or none at all; whilst domestic races which differ conspicuouslyfrom each other, are when united remarkably fertile, and yield perfectlyfertile offspring. But this fact is not in reality so inexplicable as it atfirst appears. In the first place, it was clearly shown in the nineteenthchapter that the sterility of crossed species does not closely depend ondifferences in their external structure or general constitution, butresults exclusively from differences in the reproductive system, analogouswith those which cause the lessened fertility of the illegitimate unionsand illegitimate offspring of dimorphic and trimorphic plants. In thesecond place, the Pallasian doctrine, that species after having been longdomesticated lose their natural tendency to sterility when crossed, hasbeen shown to be highly probable; we can scarcely avoid this conclusionwhen we reflect on the parentage and present fertility of the severalbreeds of the dog, of Indian and European cattle, sheep, and pigs. Hence itwould be unreasonable to expect that races formed under domestication {411}should acquire sterility when crossed, whilst at the same time we admitthat domestication eliminates the normal sterility of crossed species. Whywith closely allied species their reproductive systems should almostinvariably have been modified in so peculiar a manner as to be mutuallyincapable of acting on each other--though in unequal degrees in the twosexes, as shown by the difference in fertility between reciprocal crossesin the same species--we do not know, but may with much probability inferthe cause to be as follows. Most natural species have been habituated tonearly uniform conditions of life for an incomparably longer period of timethan have domestic races; and we positively know that changed conditionsexert an especial and powerful influence on the reproductive system. Hencethis difference in habituation may well account for the different action ofthe reproductive organs when domestic races and when species are crossed. It is a nearly analogous fact, that most domestic races may be suddenlytransported from one climate to another, or be placed under widelydifferent conditions, and yet retain their fertility unimpaired; whilst amultitude of species subjected to lesser changes are rendered incapable ofbreeding. With the exception of fertility, domestic varieties resemble species whencrossed in transmitting their characters in the same unequal manner totheir offspring, in being subject to the prepotency of one form over theother, and in their liability to reversion. By repeated crosses a varietyor a species may be made completely to absorb another. Varieties, as weshall see when we treat of their antiquity, sometimes inherit their newcharacters almost, or even quite, as firmly as species. With both, theconditions leading to variability and the laws governing its nature appearto be the same. Domestic varieties can be classed in groups under groups, like species under genera, and these under families and orders; and theclassification may be either artificial, --that is, founded on any arbitrarycharacter, --or natural. With varieties a natural classification iscertainly founded, and with species is apparently founded, on community ofdescent, together with the amount of modification which the forms haveundergone. The characters by which domestic varieties differ from eachother are more {412} variable than those distinguishing species, thoughhardly more so than with certain protean species; but this greater degreeof variability is not surprising, as varieties have generally been exposedwithin recent times to fluctuating conditions of life, are much more liableto have been crossed, and are still in many cases undergoing, or haverecently undergone, modification by man's methodical or unconsciousselection. Domestic varieties as a general rule certainly differ from each other inless important parts of their organisation than do species; and whenimportant differences occur, they are seldom firmly fixed; but this fact isintelligible if we consider man's method of selection. In the living animalor plant he cannot observe internal modifications in the more importantorgans; nor does he regard them as long as they are compatible with healthand life. What does the breeder care about any slight change in the molarteeth of his pigs, or for an additional molar tooth in the dog; or for anychange in the intestinal canal or other internal organ? The breeder caresfor the flesh of his cattle being well marbled with fat, and for anaccumulation of fat within the abdomen of his sheep, and this he haseffected. What would the floriculturist care for any change in thestructure of the ovarium or of the ovules? As important internal organs arecertainly liable to numerous slight variations, and as these would probablybe inherited, for many strange monstrosities are transmitted, man couldundoubtedly effect a certain amount of change in these organs. When he hasproduced any modification in an important part, it has generally beenunintentionally in correlation with some other conspicuous part, as when hehas given ridges and protuberances to the skulls of fowls, by attending tothe form of the comb, and in the case of the Polish fowl to the plume offeathers on the head. By attending to the external form of thepouter-pigeon, he has enormously increased the size of the oesophagus, andhas added to the number of the ribs, and given them greater breadth. Withthe carrier-pigeon, by increasing, through steady selection, the wattles onthe upper mandible, he has greatly modified the form of the lower mandible;and so in many other cases. Natural species, on the other hand, have beenmodified exclusively for their own good, to fit them for infinitely {413}diversified conditions of life, to avoid enemies of all kinds, and tostruggle against a host of competitors. Hence, under such complexconditions, it would often happen that modifications of the most variedkinds, in important as well as in unimportant parts, would be advantageousor even necessary; and they would slowly but surely be acquired through thesurvival of the fittest. Various indirect modifications would likewisearise through the law of correlated variation. Domestic breeds often have an abnormal or semi-monstrous character, as theItalian greyhound, bulldog, Blenheim spaniel, and bloodhound amongstdogs, --some breeds of cattle and pigs, several breeds of the fowl, and thechief breeds of the pigeon. The differences between such abnormal breedsoccur in parts which in closely-allied natural species differ but slightlyor not at all. This may be accounted for by man's often selecting, especially at first, conspicuous and semi-monstrous deviations ofstructure. We should, however, be cautious in deciding what deviationsought to be called monstrous: there can hardly be a doubt that, if thebrush of horse-like hair on the breast of the turkey-cock had firstappeared on the domesticated bird, it would have been considered amonstrosity; the great plume of feathers on the head of the Polish cock hasbeen thus designated, though plumes are common with many kinds of birds; wemight call the wattle or corrugated skin round the base of the beak of theEnglish carrier-pigeon a monstrosity, but we do not thus speak of theglobular fleshy excrescence at the base of the beak of the male _Carpophagaoceanica_. Some authors have drawn a wide distinction between artificial and naturalbreeds; although in extreme cases the distinction is plain, in many othercases an arbitrary line has to be drawn. The difference depends chiefly onthe kind of selection which has been applied. Artificial breeds are thosewhich have been intentionally improved by man; they frequently have anunnatural appearance, and are especially liable to loss of excellencethrough reversion and continued variability. The so-called natural breeds, on the other hand, are those which are now found in semi-civilisedcountries, and which formerly inhabited separate districts in nearly allthe European kingdoms. They have been rarely acted on by man's {414}intentional selection; more frequently, it is probable, by unconsciousselection, and partly by natural selection, for animals kept insemi-civilised countries have to provide largely for their own wants. Suchnatural breeds will also, it may be presumed, have been directly acted onto some extent by the differences, though slight, in the surroundingphysical conditions. It is a much more important distinction that some breeds have been fromtheir first origin modified in so slow and insensible a manner, that if wecould see their early progenitors we should hardly be able to say when orhow the breed first arose; whilst other breeds have originated from astrongly-marked or semi-monstrous deviation of structure, which, however, may subsequently have been augmented by selection. From what we know of thehistory of the racehorse, greyhound, gamecock, &c. , and from their generalappearance, we may feel nearly confident that they were formed by a slowprocess of improvement: and with the carrier-pigeon, as well as with someother pigeons, we know that this has been the case. On the other hand, itis certain that the ancon and mauchamp breeds of sheep, and almost certainthat the niata cattle, turnspit and pug-dogs, jumper and frizzled fowls, short-faced tumbler pigeons, hook-billed ducks, &c. , and with plants amultitude of varieties, suddenly appeared in nearly the same state as wenow see them. The frequency of these cases is likely to lead to the falsebelief that natural species have often originated in the same abruptmanner. But we have no evidence of the appearance, or at least of thecontinued procreation, under nature, of abrupt modifications of structure;and various general reasons could be assigned against such a belief: forinstance, without separation a single monstrous variation would almostcertainly be soon obliterated by crossing. On the other hand, we have abundant evidence of the constant occurrenceunder nature of slight individual differences of the most diversifiedkinds; and thus we are led to conclude that species have generallyoriginated by the natural selection, not of abrupt modifications, but ofextremely slight differences. This process may be strictly compared withthe slow and gradual improvement of the racehorse, greyhound, and gamecock. As every detail of structure in each species is closely adapted to itsgeneral {415} habits of life, it will rarely happen that one part alonewill be modified; but the co-adapted modifications, as formerly shown, neednot be absolutely simultaneous. Many variations, however, are from thefirst connected by the law of correlation. Hence it follows that evenclosely-allied species rarely or never differ from each other by some onecharacter alone; and this same remark applies to a certain extent todomestic races; for these, if they differ much, generally differ in manyrespects. Some naturalists boldly insist[928] that species are absolutely distinctproductions, never passing by intermediate links into each other; whilstthey maintain that domestic varieties can always be connected either witheach other or with their parent-forms. But if we could always find thelinks between the several breeds of the dog, horse, cattle, sheep, pigs, &c. , the incessant doubts whether they are descended from one or severalspecies would not have arisen. The greyhound genus, if such a term may beused, cannot be closely connected with any other breed, unless, perhaps, wego back to the ancient Egyptian monuments. Our English bulldog also forms avery distinct breed. In all these cases crossed breeds must of course beexcluded, for the most distinct natural species can thus be connected. Bywhat links can the Cochin fowl be closely united with others? By searchingfor breeds still preserved in distant lands, and by going back tohistorical records, tumbler-pigeons, carriers, and barbs can be closelyconnected with the parent rock-pigeon; but we cannot thus connect theturbit or the pouter. The degree of distinctness between the variousdomestic breeds depends on the amount of modification which they haveundergone, and especially on the neglect and final extinction of thelinking, intermediate, and less valued forms. It has often been argued that no light is thrown, from the admitted changesof domestic races, on the changes which natural species are believed toundergo, as the former are said to be mere temporary productions, alwaysreverting, as soon as they become feral, to their pristine form. Thisargument has been well combated by Mr. Wallace;[929] and full details weregiven in the thirteenth chapter, showing that the tendency to reversion inferal {416} animals and plants has been greatly exaggerated, though nodoubt to a certain extent it exists. It would be opposed to all theprinciples inculcated in this work, if domestic animals, when exposed tonew conditions and compelled to struggle for their own wants against a hostof foreign competitors, were not in the course of time in some mannermodified. It should also be remembered that many characters lie latent inall organic beings ready to be evolved under fitting conditions; and inbreeds modified within recent times the tendency to reversion isparticularly strong. But the antiquity of various breeds clearly provesthat they remain nearly constant as long as their conditions of life remainthe same. It has been boldly maintained by some authors that the amount of variationto which our domestic productions are liable is strictly limited; but thisis an assertion resting on little evidence. Whether or not the amount inany particular direction is fixed, the tendency to general variabilityseems unlimited. Cattle, sheep, and pigs have been domesticated and havevaried from the remotest period, as shown by the researches of Rütimeyerand others, yet these animals have, within quite recent times, beenimproved in an unparalleled degree; and this implies continued variabilityof structure. Wheat, as we know from the remains found in the Swisslake-habitations, is one of the most anciently cultivated plants, yet atthe present day new and better varieties occasionally arise. It may be thatan ox will never be produced of larger size or finer proportions than ourpresent animals, or a race-horse fleeter than Eclipse, or a gooseberrylarger than the London variety; but he would be a bold man who would assertthat the extreme limit in these respects has been finally attained. Withflowers and fruit it has repeatedly been asserted that perfection has beenreached, but the standard has soon been excelled. A breed of pigeons maynever be produced with a beak shorter than that of the present short-facedtumbler, or with one longer than that of the English carrier, for thesebirds have weak constitutions and are bad breeders; but the shortness andlength of the beak are the points which have been steadily improved duringat least the last 150 years; and some of the best judges deny that the goalhas yet been reached. We may, also, reasonably suspect, from what {417} wesee in natural species of the variability of extremely modified parts, thatany structure, after remaining constant during a long series ofgenerations, would, under new and changed conditions of life, recommenceits course of variability, and might again be acted on by selection. Nevertheless, as Mr. Wallace[930] has recently remarked with much force andtruth, there must be both with natural and domestic productions a limit tochange in certain directions; for instance, there must be a limit to thefleetness of any terrestrial animal, as this will be determined by thefriction to be overcome, the weight to be carried, and the power ofcontraction in the muscular fibres. The English racehorse may have reachedthis limit; but it already surpasses in fleetness its own wild progenitor, and all other equine species. It is not surprising, seeing the great difference between many domesticbreeds, that some few naturalists have concluded that all are descendedfrom distinct aboriginal stocks, more especially as the principle ofselection has been ignored, and the high antiquity of man, as a breeder ofanimals, has only recently become known. Most naturalists, however, freelyadmit that various extremely dissimilar breeds are descended from a singlestock, although they do not know much about the art of breeding, cannotshow the connecting links, nor say where and when the breeds arose. Yetthese same naturalists will declare, with an air of philosophical caution, that they can never admit that one natural species has given birth toanother until they behold all the transitional steps. But fanciers haveused exactly the same language with respect to domestic breeds; thus anauthor of an excellent treatise says he will never allow that carrier andfantail pigeons are the descendants of the wild rock-pigeon, until thetransitions have "actually been observed, and can be repeated whenever manchooses to set about the task. " No doubt it is difficult to realise thatslight changes added up during long centuries can produce such results; buthe who wishes to understand the origin of domestic breeds or naturalspecies must overcome this difficulty. The causes inducing and the laws governing variability have been so latelydiscussed, that I need here only enumerate the leading points. Asdomesticated organisms are much more {418} liable to slight deviations ofstructure and to monstrosities, than species living under their naturalconditions, and as widely-ranging species vary more than those whichinhabit restricted areas, we may infer that variability mainly depends onchanged conditions of life. We must not overlook the effects of the unequalcombination of the characters derived from both parents, nor reversion toformer progenitors. Changed conditions have an especial tendency to renderthe reproductive organs more or less impotent, as shown in the chapterdevoted to this subject; and these organs consequently often fail totransmit faithfully the parental characters. Changed conditions also actdirectly and definitely on the organisation, so that all or nearly all theindividuals of the same species thus exposed become modified in the samemanner; but why this or that part is especially affected we can seldom ornever say. In most cases, however, of the direct action of changedconditions, independently of the indirect variability caused by thereproductive organs being affected, indefinite modifications are theresult; in nearly the same manner as exposure to cold or the absorption ofthe same poison affects different individuals in various ways. We havereason to suspect that an habitual excess of highly nutritious food, or anexcess relatively to the wear and tear of the organisation from exercise, is a powerful exciting cause of variability. When we see the symmetricaland complex outgrowths, caused by a minute atom of the poison of agall-insect, we may believe that slight changes in the chemical nature ofthe sap or blood would lead to extraordinary modifications of structure. The increased use of a muscle with its various attached parts, and theincreased activity of a gland or other organ, lead to their increaseddevelopment. Disuse has a contrary effect. With domesticated productionsorgans sometimes become rudimentary through abortion; but we have no reasonto suppose that this has ever followed from mere disuse. With naturalspecies, on the contrary, many organs appear to have been renderedrudimentary through disuse, aided by the principle of the economy ofgrowth, and by the hypothetical principle discussed in the last chapter, namely, the final destruction of the germs or gemmules of such uselessparts. This difference may be partly {419} accounted for by disuse havingacted on domestic forms for an insufficient length of time, and partly fromtheir exemption from any severe struggle for existence, entailing rigideconomy in the development of each part, to which all species under natureare subjected. Nevertheless the law of compensation or balancementapparently affects, to a certain extent, our domesticated productions. We must not exaggerate the importance of the definite action of changedconditions in modifying all the individuals of the same species in the samemanner, or of use and disuse. As every part of the organisation is highlyvariable, and as variations are so easily selected, both consciously andunconsciously, it is very difficult to distinguish between the effects ofthe selection of indefinite variations, and the direct action of theconditions of life. For instance, it is possible that the feet of ourwater-dogs, and of the American dogs which have to travel much over thesnow, may have become partially webbed from the stimulus of widelyextending their toes; but it is far more probable that the webbing, likethe membrane between the toes of certain pigeons, spontaneously appearedand was afterwards increased by the best swimmers and the bestsnow-travellers being preserved during many generations. A fancier whowished to decrease the size of his bantams or tumbler-pigeons would neverthink of starving them, but would select the smallest individuals whichspontaneously appeared. Quadrupeds are sometimes born destitute of hair, and hairless breeds have been formed, but there is no reason to believethat this is caused by a hot climate. Within the tropics heat often causessheep to lose their fleeces, and on the other hand wet and cold act as adirect stimulus to the growth of hair; it is, however, possible that thesechanges may merely be an exaggeration of the regular yearly change of coat;and who will pretend to decide how far this yearly change, or the thick furof arctic animals, or as I may add their white colour, is due to the directaction of a severe climate, and how far to the preservation of the bestprotected individuals during a long succession of generations? Of all the laws governing variability, that of correlation is the mostimportant. In many cases of slight deviations of structure as well as ofgrave monstrosities, we cannot even {420} conjecture what is the nature ofthe bond of connexion. But between homologous parts--between the fore andhind limbs--between the hair, hoofs, horns, and teeth--we can see thatparts which are closely similar during their early development, and whichare exposed to similar conditions, would be liable to be modified in thesame manner. Homologous parts, from having the same nature, are apt toblend together and, when many exist, to vary in number. Although every variation is either directly or indirectly caused by somechange in the surrounding conditions, we must never forget that the natureof the organisation which is acted on essentially governs the result. Distinct organisms, when placed under similar conditions, vary in differentmanners, whilst closely-allied organisms under dissimilar conditions oftenvary in nearly the same manner. We see this in the same modificationfrequently reappearing at long intervals of time in the same variety, andlikewise in the several striking cases given of analogous or parallelvarieties. Although some of these latter cases are simply due to reversion, others cannot thus be accounted for. From the indirect action of changed conditions on the organisation, throughthe impaired state of the reproductive organs--from the direct action ofsuch conditions (and this will cause the individuals of the same specieseither to vary in the same manner, or differently in accordance with slightdifferences in their constitution)--from the effects of the increased ordecreased use of parts, --and from correlation, --the variability of ourdomesticated productions is complicated in an extreme degree. The wholeorganisation becomes slightly plastic. Although each modification must haveits proper exciting cause, and though each is subjected to law, yet we canso rarely trace the precise relation between cause and effect, that we aretempted to speak of variations as if they spontaneously arose. We may evencall them accidental, but this must be only in the sense in which we saythat a fragment of rock dropped from a height owes its shape to accident. * * * * * It may be worth while briefly to consider the results of the exposure tounnatural conditions of a large number of animals of the same species, allowed to cross freely, with no selection of any {421} kind; andafterwards to consider the results when selection is brought into play. Letus suppose that 500 wild rock-pigeons were confined in their native land inan aviary, and fed in the same manner as pigeons usually are; and that theywere not allowed to increase in number. As pigeons propagate so rapidly, Isuppose that a thousand or fifteen hundred birds would have to be annuallykilled by mere chance. After several generations had been thus reared, wemay feel sure that some of the young birds would vary, and the variationswould tend to be inherited; for at the present day slight deviations ofstructure often occur, but, as most breeds are already well established, these modifications are rejected as blemishes. It would be tedious even toenumerate the multitude of points which still go on varying or haverecently varied. Many variations would occur in correlation, as the lengthof the wing and tail feathers--the number of the primary wing-feathers, aswell as the number and breadth of the ribs, in correlation with the sizeand form of the body--the number of the scutellæ, with the size of thefeet--the length of the tongue, with the length of the beak--the size ofthe nostrils and eyelids and the form of lower jaw in correlation with thedevelopment of wattle--the nakedness of the young with the future colour ofthe plumage--the size of the feet and beak, and other such points. Lastly, as our birds are supposed to be confined in an aviary, they would use theirwings and legs but little, and certain parts of the skeleton, such as thesternum and scapulæ and the feet, would in consequence become slightlyreduced in size. As in our assumed case many birds have to be indiscriminately killed everyyear, the chances are against any new variety surviving long enough tobreed. And as the variations which arise are of an extremely diversifiednature, the chances are very great against two birds pairing which havevaried in the same manner; nevertheless, a varying bird even when not thuspaired would occasionally transmit its character to its young; and thesewould not only be exposed to the same conditions which first caused thevariation in question to appear, but would in addition inherit from theirone modified parent a tendency again to vary in the same manner. So that, if the conditions decidedly tended to induce some particular variation, allthe birds might {422} in the course of time become similarly modified. Buta far commoner result would be, that one bird would vary in one way andanother bird in another way; one would be born with a little longer beak, and another with a shorter beak; one would gain some black feathers, another some white or red feathers. And as these birds would be continuallyintercrossing, the final result would be a body of individuals differingfrom each other slightly in many ways, yet far more than did the originalrock-pigeons. But there would not be the least tendency to the formation ofdistinct breeds. If two separate lots of pigeons were to be treated in the manner justdescribed, one in England and the other in a tropical country, the two lotsbeing supplied with different food, would they, after many generations hadpassed, differ? When we reflect on the cases given in the twenty-thirdchapter, and on such facts as the difference in former times between thebreeds of cattle, sheep, &c. , in almost every district of Europe, we arestrongly inclined to admit that the two lots would be differently modifiedthrough the influence of climate and food. But the evidence on the definiteaction of changed conditions is in most cases insufficient; and, withrespect to pigeons, I have had the opportunity of examining a largecollection of domesticated birds, sent to me by Sir W. Elliot from India, and they varied in a remarkably similar manner with our European birds. If two distinct breeds were to be confined together in equal numbers, thereis reason to suspect that they would to a certain extent prefer pairingwith their own kind; but they would likewise intercross. From the greatervigour and fertility of the crossed offspring, the whole body would by thismeans become interblended sooner than would otherwise have occurred. Fromcertain breeds being prepotent over others, it does not follow that theinterblended progeny would be strictly intermediate in character. I have, also, proved that the act of crossing in itself gives a strong tendency toreversion, so that the crossed offspring would tend to revert to the stateof the aboriginal rock-pigeon. In the course of time they would probably benot much more heterogeneous in character than in our first case, when birdsof the same breed were confined together. {423} I have just said that the crossed offspring would gain in vigour andfertility. From the facts given in the seventeenth chapter there can be nodoubt of this; and there can be little doubt, though the evidence on thishead is not so easily acquired, that long-continued close interbreedingleads to evil results. With hermaphrodites of all kinds, if the sexualelements of the same individual habitually acted on each other, the closestpossible interbreeding would be perpetual. Therefore we should bear in mindthat with all hermaphrodite animals, as far as I can learn, their structurepermits and frequently necessitates a cross with a distinct individual. With hermaphrodite plants we incessantly meet with elaborate and perfectcontrivances for this same end. It is no exaggeration to assert that, ifthe use of the talons and tusks of a carnivorous animal, or the use of theviscid threads of a spider's web, or of the plumes and hooks on a seed maybe safely inferred from their structure, we may with equal safety inferthat many flowers are constructed for the express purpose of ensuring across with a distinct plant. From these various considerations, theconclusion arrived at in the chapter just referred to--namely, that greatgood of some kind is derived from the sexual concourse of distinctindividuals--must be admitted. To return to our illustration: we have hitherto assumed that the birds werekept down to the same number by indiscriminate slaughter; but if the leastchoice be permitted in their preservation and slaughter, the whole resultwill be changed. Should the owner observe any slight variation in one ofhis birds, and wish to obtain a breed thus characterised, he would succeedin a surprisingly short time by carefully selecting and pairing the young. As any part which has once varied generally goes on varying in the samedirection, it is easy, by continually preserving the most strongly markedindividuals, to increase the amount of difference up to a high, predetermined standard of excellence. This is methodical selection. If the owner of the aviary, without any thought of making a new breed, simply admired, for instance, short-beaked more than long-beaked birds, hewould, when he had to reduce the number, generally kill the latter; andthere can be no doubt that he would thus in the course of time sensiblymodify his {424} stock. It is improbable, if two men were to keep pigeonsand act in this manner, that they would prefer exactly the same characters;they would, as we know, often prefer directly opposite characters, and thetwo lots would ultimately come to differ. This has actually occurred withstrains or families of cattle, sheep, and pigeons, which have been longkept and carefully attended to by different breeders without any wish ontheir part to form new and distinct sub-breeds. This unconscious kind ofselection will more especially come into action with animals which arehighly serviceable to man; for every one tries to get the best dog, horse, cow, or sheep, and these animals will transmit more or less surely theirgood qualities to their offspring. Hardly any one is so careless as tobreed from his worst animals. Even savages, when compelled from extremewant to kill some of their animals, would destroy the worst and preservethe best. With animals kept for use and not for mere amusement, differentfashions prevail in different districts, leading to the preservation, andconsequently to the transmission, of all sorts of trifling peculiarities ofcharacter. The same process will have been pursued with our fruit-trees andvegetables, for the best will always have been the most largely cultivated, and will occasionally have yielded seedlings better than their parents. The different strains, just alluded to, which have been raised by differentbreeders without any wish for such a result, and the unintentionalmodification of foreign breeds in their new homes, both afford excellentevidence of the power of unconscious selection. This form of selection hasprobably led to far more important results than methodical selection, andis likewise more important under a theoretical point of view from closelyresembling natural selection. For during this process the best or mostvalued individuals are not separated and prevented crossing with others ofthe same breed, but are simply preferred and preserved; but this inevitablyleads during a long succession of generations to their increase in numberand to their gradual improvement; so that finally they prevail to theexclusion of the old parent-form. With our domesticated animals natural selection checks the production ofraces with any injurious deviation of {425} structure. In the case ofanimals kept by savages and semi-civilised people, which have to providelargely for their own wants under different circumstances, naturalselection will probably play a more important part. Hence such animalsoften closely resemble natural species. As there is no limit to man's desire to possess animals and plants more andmore useful in any respect, and as the fancier always wishes, from fashionrunning into extremes, to produce each character more and more stronglypronounced, there is a constant tendency in every breed, through theprolonged action of methodical and unconscious selection, to become moreand more different from its parent-stock; and when several breeds have beenproduced and are valued for different qualities, to differ more and morefrom each other. This leads to Divergence of Character. As improvedsub-varieties and races are slowly formed, the older and less improvedbreeds are neglected and decrease in number. When few individuals of anybreed exist within the same locality, close interbreeding, by lesseningtheir vigour and fertility, aids in their final extinction. Thus theintermediate links are lost, and breeds which have already diverged gainDistinctness of Character. In the chapters on the Pigeon, it was proved by historical details and bythe existence of connecting sub-varieties in distant lands that severalbreeds have steadily diverged in character, and that many old andintermediate sub-breeds have become extinct. Other cases could be adducedof the extinction of domestic breeds, as of the Irish wolf-dog, the oldEnglish hound, and of two breeds in France, one of which was formerlyhighly valued. [931] Mr. Pickering remarks[932] that "the sheep figured onthe most ancient Egyptian monuments is unknown at the present day; and atleast one variety of the bullock, formerly known in Egypt, has in likemanner become extinct. " So it has been with some animals, and with severalplants cultivated by the ancient inhabitants of Europe during the neolithicperiod. In Peru, Von Tschudi[933] found in certain tombs, apparently priorto the dynasty of the Incas, two kinds of maize not now known in thecountry. With our flowers and culinary vegetables, {426} the production ofnew varieties and their extinction has incessantly recurred. At the presenttime improved breeds sometimes displace at an extraordinarily rapid rateolder breeds; as has recently occurred throughout England with pigs. TheLong-horn cattle in their native home were "suddenly swept away as if bysome murderous pestilence, " by the introduction of Short-horns. [934] What grand results have followed from the long-continued action ofmethodical and unconscious selection, checked and regulated to a certainextent by natural selection, is seen on every side of us. Compare the manyanimals and plants which are displayed at our exhibitions with theirparent-forms when these are known, or consult old historical records withrespect to their former state. Almost all our domesticated animals havegiven rise to numerous and distinct races, excepting those which cannot beeasily subjected to selection--such as cats, the cochineal insect, and thehive-bee, --and excepting those animals which are not much valued. Inaccordance with what we know of the process of selection, the formation ofour many races has been slow and gradual. The man who first observed andpreserved a pigeon with its oesophagus a little enlarged, its beak a littlelonger, or its tail a little more expanded than usual, never dreamed thathe had made the first step in the creation of the pouter, carrier, andfantail-pigeon. Man can create not only anomalous breeds, but others withtheir whole structure admirably co-ordinated for certain purposes, such asthe race-horse and dray-horse, or the greyhound. It is by no meansnecessary that each small change of structure throughout the body, leadingtowards excellence, should simultaneously arise and be selected. Althoughman seldom attends to differences in organs which are important under aphysiological point of view, yet he has so profoundly modified some breeds, that assuredly, if found wild, they would be ranked under distinct genera. The best proof of what selection has effected is perhaps afforded by thefact that whatever part or quality in any animal, and more especially inany plant, is most valued by man, that part or quality differs most in theseveral races. This result is well seen by comparing the amount ofdifference {427} between the fruits produced by the varieties of the samefruit-tree, between the flowers of the varieties in our flower-garden, between the seeds, roots, or leaves of our culinary and agriculturalplants, in comparison with the other and not valued parts of the sameplants. Striking evidence of a different kind is afforded by the factascertained by Oswald Heer, [935] namely, that the seeds of a large numberof plants, --wheat, barley, oats, peas, beans, lentils, poppies, --cultivatedfor their seed by the ancient Lake-inhabitants of Switzerland, were allsmaller than the seeds of our existing varieties. Rütimeyer has shown thatthe sheep and cattle which were kept by the earlier Lake-inhabitants werelikewise smaller than our present breeds. In the middens of Denmark, theearliest dog of which the remains have been found was the weakest; this wassucceeded during the Bronze age by a stronger kind, and this again duringthe Iron age by one still stronger. The sheep of Denmark during the Bronzeperiod had extraordinarily slender limbs, and the horse was smaller thanour present animal. [936] No doubt in these cases the new and larger breedswere generally introduced from foreign lands by the immigration of newhordes of men. But it is not probable that each larger breed, which in thecourse of time supplanted a previous and smaller breed, was the descendantof a distinct and larger species; it is far more probable that the domesticraces of our various animals were gradually improved in different parts ofthe great Europæo-Asiatic continent, and thence spread to other countries. This fact of the gradual increase in size of our domestic animals is allthe more striking as certain wild or half-wild animals, such as red-deer, aurochs, park-cattle, and boars, [937] have within nearly the same perioddecreased in size. The conditions favourable to selection by man are, --the closest attentionbeing paid to every character, --long-continued perseverance, --facility inmatching or separating animals, --and especially a large number being kept, so that the inferior individuals may be freely rejected or destroyed, andthe better ones preserved. When many are kept there will also be a {428}greater chance of the occurrence of well-marked deviations of structure. Length of time is all-important; for as each character, in order to becomestrongly pronounced, has to be augmented by the selection of successivevariations of the same nature, this can only be effected during a longseries of generations. Length of time will, also, allow any new feature tobecome fixed by the continued rejection of those individuals which revertor vary, and the preservation of those which inherit the new character. Hence, although some few animals have varied rapidly in certain respectsunder new conditions of life, as dogs in India and sheep in the WestIndies, yet all the animals and plants which have produced strongly markedraces were domesticated at an extremely remote epoch, often before the dawnof history. As a consequence of this, no record has been preserved of theorigin of our chief domestic breeds. Even at the present day new strains orsub-breeds are formed so slowly that their first appearance passesunnoticed. A man attends to some particular character, or merely matcheshis animals with unusual care, and after a time a slight difference isperceived by his neighbours;--the difference goes on being augmented byunconscious and methodical selection, until at last a new sub-breed isformed, receives a local name, and spreads; but, by this time, its historyis almost forgotten. When the new breed has spread widely, it gives rise tonew strains and sub-breeds, and the best of these succeed and spread, supplanting other and older breeds; and so always onwards in the march ofimprovement. When a well-marked breed has once been established, if not supplanted bystill improving sub-breeds, and if not exposed to greatly changedconditions of life, inducing further variability or reversion to long-lostcharacters, it may apparently last for an enormous period. We may inferthat this is the case from the high antiquity of certain races; but somecaution is necessary on this head, for the same variation may appearindependently after long intervals of time, or in distant places. We maysafely assume that this has occurred with the turnspit-dog which is figuredon the ancient Egyptian monuments, with the solid-hoofed swine[938]mentioned by Aristotle, with five-toed fowls {429} described by Columella, and certainly with the nectarine. The dogs represented on the Egyptianmonuments, about 2000 B. C. , show us that some of the chief breeds thenexisted, but it is extremely doubtful whether any are identically the samewith our present breeds. A great mastiff sculptured on an Assyrian tomb, 640 B. C. , is said to be the same with the dog still imported into the sameregion from Thibet. The true greyhound existed during the Roman classicalperiod. Coming down to a later period, we have seen that, though most ofthe chief breeds of the pigeon existed between two and three centuries ago, they have not all retained to the present day exactly the same character;but this has occurred in certain cases in which improvement was notdesired, for instance in the case of the Spot or the Indian ground-tumbler. De Candolle[939] has fully discussed the antiquity of various races ofplants; he states that the black-seeded poppy was known in the time ofHomer, the white-seeded sesamum by the ancient Egyptians, and almonds withsweet and bitter kernels by the Hebrews; but it does not seem improbablethat some of these varieties may have been lost and reappeared. One varietyof barley and apparently one of wheat, both of which were cultivated at animmensely remote period by the Lake-inhabitants of Switzerland, stillexist. It is said[940] that "specimens of a small variety of gourd which isstill common in the market of Lima were exhumed from an ancient cemetery inPeru. " De Candolle remarks that, in the books and drawings of the sixteenthcentury, the principal races of the cabbage, turnip, and gourd can berecognised; this might have been expected at so late a period, but whetherany of these plants are absolutely identical with our present sub-varietiesis not certain. It is, however, said that the Brussels sprout, a varietywhich in some places is liable to degeneration, has remained genuine formore than four centuries in the district where it is believed to haveoriginated. [941] * * * * * In accordance with the views maintained by me in this work and elsewhere, not only the various domestic races, but the {430} most distinct genera andorders within the same great class, --for instance, whales, mice, birds, andfishes--are all the descendants of one common progenitor, and we must admitthat the whole vast amount of difference between these forms of life hasprimarily arisen from simple variability. To consider the subject underthis point of view is enough to strike one dumb with amazement. But ouramazement ought to be lessened when we reflect that beings, almost infinitein number, during an almost infinite lapse of time, have often had theirwhole organisation rendered in some degree plastic, and that each slightmodification of structure which was in any way beneficial under excessivelycomplex conditions of life, will have been preserved, whilst each which wasin any way injurious will have been rigorously destroyed. And thelong-continued accumulation of beneficial variations will infallibly leadto structures as diversified, as beautifully adapted for various purposes, and as excellently co-ordinated, as we see in the animals and plants allaround us. Hence I have spoken of selection as the paramount power, whetherapplied by man to the formation of domestic breeds, or by nature to theproduction of species. I may recur to the metaphor given in a formerchapter: if an architect were to rear a noble and commodious edifice, without the use of cut stone, by selecting from the fragments at the baseof a precipice wedge-formed stones for his arches, elongated stones for hislintels, and flat stones for his roof, we should admire his skill andregard him as the paramount power. Now, the fragments of stone, thoughindispensable to the architect, bear to the edifice built by him the samerelation which the fluctuating variations of each organic being bear to thevaried and admirable structures ultimately acquired by its modifieddescendants. Some authors have declared that natural selection explains nothing, unlessthe precise cause of each slight individual difference be made clear. Now, if it were explained to a savage utterly ignorant of the art of building, how the edifice had been raised stone upon stone, and why wedge-formedfragments were used for the arches, flat stones for the roof, &c. ; and ifthe use of each part and of the whole building were pointed out, it wouldbe unreasonable if he declared that nothing had been {431} made clear tohim, because the precise cause of the shape of each fragment could not begiven. But this is a nearly parallel case with the objection that selectionexplains nothing, because we know not the cause of each individualdifference in the structure of each being. The shape of the fragments of stone at the base of our precipice may becalled accidental, but this is not strictly correct; for the shape of eachdepends on a long sequence of events, all obeying natural laws; on thenature of the rock, on the lines of deposition or cleavage, on the form ofthe mountain which depends on its upheaval and subsequent denudation, andlastly on the storm or earthquake which threw down the fragments. But inregard to the use to which the fragments may be put, their shape may bestrictly said to be accidental. And here we are led to face a greatdifficulty, in alluding to which I am aware that I am travelling beyond myproper province. An omniscient Creator must have foreseen every consequencewhich results from the laws imposed by Him. But can it be reasonablymaintained that the Creator intentionally ordered, if we use the words inany ordinary sense, that certain fragments of rock should assume certainshapes so that the builder might erect his edifice? If the various lawswhich have determined the shape of each fragment were not predetermined forthe builder's sake, can it with any greater probability be maintained thatHe specially ordained for the sake of the breeder each of the innumerablevariations in our domestic animals and plants;--many of these variationsbeing of no service to man, and not beneficial, far more often injurious, to the creatures themselves? Did He ordain that the crop and tail-feathersof the pigeon should vary in order that the fancier might make hisgrotesque pouter and fantail breeds? Did He cause the frame and mentalqualities of the dog to vary in order that a breed might be formed ofindomitable ferocity, with jaws fitted to pin down the bull for man'sbrutal sport? But if we give up the principle in one case, --if we do notadmit that the variations of the primeval dog were intentionally guided inorder that the greyhound, for instance, that perfect image of symmetry andvigour, might be formed, --no shadow of reason can be assigned for thebelief that variations, alike in nature and the result {432} of the samegeneral laws, which have been the groundwork through natural selection ofthe formation of the most perfectly adapted animals in the world, manincluded, were intentionally and specially guided. However much we may wishit, we can hardly follow Professor Asa Gray in his belief "that variationhas been led along certain beneficial lines, " like a stream "along definiteand useful lines of irrigation. " If we assume that each particularvariation was from the beginning of all time preordained, the plasticity oforganisation, which leads to many injurious deviations of structure, aswell as that redundant power of reproduction which inevitably leads to astruggle for existence, and, as a consequence, to the natural selection orsurvival of the fittest, must appear to us superfluous laws of nature. Onthe other hand, an omnipotent and omniscient Creator ordains everything andforesees everything. Thus we are brought face to face with a difficulty asinsoluble as is that of free will and predestination. * * * * * {433} INDEX. ABBAS Pacha, a fancier of fantailed pigeons, i. 206. ABBEY, Mr. , on grafting, ii. 147; on mignonette, ii. 237. ABBOTT, Mr. Keith, on the Persian tumbler pigeon, i. 150. ABBREVIATION of the facial bones, i. 73. ABORTION of organs, ii. 315-318, 397. ABSORPTION of minority in crossed races, ii. 87-89, 174. ACCLIMATISATION, ii. 305-315; of maize, i. 322. ACERBI, on the fertility of domestic animals in Lapland, ii. 112. _Achatinella_, ii. 53. _Achillea millefolium_, bud variation in, i. 408. _Aconitum napellus_, roots of, innocuous in cold climates, ii. 274. _Acorus calamus_, sterility of, ii. 170. ACOSTA, on fowls in South America at its discovery, i. 237. _Acropera_, number of seeds in, ii. 379. ADAM, Mr. , origin of _Cytisus Adami_, i. 390. ADAM, W. , on consanguineous marriages, ii. 123. ADAMS, Mr. , on hereditary diseases, ii. 7. ADVANCEMENT in scale of organisation, i. 8. _Ægilops triticoides_, observations of Fabre and Godron on, i. 313; increasing fertility of hybrids of, with wheat, ii. 110. _Æsculus flava_ and _rubicunda_, i. 392. _Æsculus pavia_, tendency of, to become double, ii. 168. _Æthusa cynapium_, ii. 337. AFFINITY, sexual elective, ii. 180. AFRICA, white bull from, i. 91; feral cattle in, i. 85; food-plants of savages of, i. 307-309; South, diversity of breeds of cattle in, i. 80; West, change in fleece of sheep in, i. 98. _Agave vivipara_, seeding of, in poor soil, ii. 169. AGE, changes in trees, dependent on, i. 387. AGOUTI, fertility of, in captivity, ii. 152. AGRICULTURE, antiquity of, ii. 243. _Agrostis_, seeds of, used as food, i. 309. AGUARA, i. 26. AINSWORTH, Mr. , on the change in the hair of animals at Angora, ii. 278. AKBAR Khan, his fondness for pigeons, i. 205; ii. 204. _Alauda arvensis_, ii. 154. ALBIN, on "Golden Hamburgh" fowls, i. 247; figure of the hook-billed duck, i. 277. ALBINISM, i. 111, ii. 17. ALBINO, negro, attacked by insects, ii. 229. ALBINOES, heredity of, ii. 9. ALBINUS, thickness of the epidermis on the palms of the hands in man, ii. 297. ALCO, i. 31, ii. 102. ALDROVANDI, on rabbits, i. 104; description of the nun pigeon, i. 156; on the fondness of the Dutch for pigeons in the seventeenth century, i. 205; notice of several varieties of pigeons, i. 207-210; on the breeds of fowls, i. 247; on the origin of the domestic duck, i. 278. ALEFIELD, Dr. , on the varieties of peas and their specific unity, i. 326; on the varieties of beans, i. 330. ALEXANDER the Great, his selection of Indian cattle, ii. 202. ALGÆ, retrogressive metamorphosis in, ii. 361; division of zoospores of, ii. 378. ALLEN, W. , on feral fowls, i. 237; ii. 33. ALLMAN, Professor, on a monstrous _Saxifraga geum_, ii. 166; on the development of the Hydroida, ii. 368. ALMOND, i. 337; antiquity of, ii. 429; bitter, not eaten by mice, ii. 232. _Alnus glutinosa_ and _incana_, hybrids of, ii. 130. ALPACA, selection of, ii. 208. _Althæa rosea_, i. 378, ii. 107. _Amaryllis_, ii. 139. _Amaryllis vittata_, effect of foreign pollen on, i. 400. AMAUROSIS, hereditary, ii. 9. AMERICA, limits within which no useful plants have been furnished by, i. 310; colours of feral horses in, i. 60-61; North, native cultivated plants of, i. 312; skin of feral pig from, i. 77; South, variations in cattle of, i. 88, 92. _Amygdalus persica_, i. 336-344, 374. {434} AMMON, on the persistency of colour in horses, ii. 21. _Anagallis arvensis_, ii. 190. ANALOGOUS variation, i. 409, ii. 348-352; in horses, i. 55; in the horse and ass, i. 64; in fowls, i. 243-246. _Anas boschas_, i. 277, ii. 40; skull of, figured, i. 282. _Anas moschata_, ii. 40. "ANCON" sheep of Massachusetts, i. 100, ii. 103. ANDALUSIAN fowls, i. 227. ANDALUSIAN rabbits, i. 105. ANDERSON, J. , on the origin of British sheep, i. 94; on the selection of qualities in cattle, ii. 196; on a one-eared breed of rabbits, i. 108; on the inheritance of characters from a one-eared rabbit and three-legged bitch, ii. 12; on the persistency of varieties of peas, i. 329; on the production of early peas by selection, ii. 201; on the varieties of the potato, i. 330-331; on crossing varieties of the melon, i. 399; on reversion in the barberry, i. 384. ANDERSON, Mr. , on the reproduction of the weeping ash by seed, ii. 19; on the cultivation of the tree pæony in China, ii. 205. ANDERSSON, Mr. , on the Damara, Bechuana, and Namaqua cattle, i. 88; on the cows of the Damaras, ii. 300; selection practised by the Damaras and Namaquas, ii. 207; on the use of grass-seeds and the roots of reeds as food in South Africa, i. 309. _Anemone coronaria_, doubled by selection, ii. 200. ANGINA pectoris, hereditary, occurring at a certain age, ii. 79. ANGLESEA, cattle of, i. 80. ANGOLA sheep, i. 95. ANGORA, change in hair of animals at, ii. 278; cats of, i. 45, 47; rabbits of, i. 106, 120. ANIMALS, domestication of, facilitated by fearlessness of man, i. 20; refusal of wild, to breed in captivity, ii. 149; compound, individual peculiarities of, reproduced by budding, i. 374; variation by selection in useful qualities of, ii. 220. ANNUAL plants, rarity of bud-variation in, i. 408. ANOMALIES in the osteology of the horse, i. 50. ANOMALOUS breeds of pigs, i. 75; of cattle, i. 89. _Anser albifrons_, characters of, reproduced in domestic geese, i. 288. _Anser ægyptiacus_, i. 282; ii. 68. _Anser canadensis_, ii. 157. _Anser cygnoides_, i. 237. _Anser ferus_, the original of the domestic goose, i. 287; fertility of cross of, with domestic goose, i. 288. ANSON, on feral fowls in the Ladrones, i. 238. ANTAGONISM between growth and reproduction, ii. 384. _Anthemis nobilis_, bud-variation in flowers of, i. 379; becomes single in poor soil, ii. 167. ANTHEROZOIDS, apparent independence of, in algæ, ii. 384. ANTHERS, contabescence of, ii. 165-166. ANTIGUA, cats of, i. 46; changed fleece of sheep in, i. 98. _Antirrhinum majus_, peloric, i. 365; ii. 59, 70, 166; double-flowered, ii. 167; bud-variation in, i. 381. ANTS, individual recognition of, ii. 251. APES, anthropomorphous, ii. 123. APHIDES, attacking pear-trees, ii. 231; development of, ii. 361-362. APOPLEXY, hereditary, occurring at a certain age, ii. 78. APPLE, i. 348-350; fruit of, in Swiss lake-dwellings, i. 317; rendered fastigate by heat in India, i. 361; bud-variation in the, i. 376; with dimidiate fruit, i. 392-393; with two kinds of fruit on the same branch, i. 392; artificial fecundation of, i. 401; St. Valéry, i. 401; ii. 166; reversion in seedlings of, ii. 31; crossing of varieties of, ii. 129; growth of the, in Ceylon, ii. 277; Winter Majetin, not attacked by _coccus_, ii. 231; flower-buds of, attacked by bullfinches, ii. 232; American, change of when grown in England, ii. 275. APRICOT, i. 344-345; glands on the leaves of, ii. 231; analogous variation in the, ii. 348. _Aquila fusca_, copulating in captivity, ii. 154. _Aquilegia vulgaris_, i. 365; ii. 330. ARAB boarhound, described by Harcourt, i. 17. _Arabis blepharophylla_ and _A. Soyeri, _ effects of crossing, i. 400. _Aralia trifoliata_, bud-variation in leaves of, i. 382. ARAUCARIAS, young, variable resistance of, to frost, ii. 309. ARCHANGEL pigeon, ii. 240. ARCTIC regions, variability of plants and shells of, ii. 256. _Aria vestita_, grafted on thorns, i. 387. ARISTOPHANES, fowls mentioned by, i. 246. ARISTOTLE, on solid-hoofed pigs, i. 75; domestic duck unknown to, i. 277; on the assumption of male characters by old hens, ii. 51. {435} ARNI, domestication of the, i. 82. ARREST of development, ii. 315-318. ARTERIES, increase of anastomosing branches of, when tied, ii. 230. ARU islands, wild pig of, i. 67. ARUM, Polynesian varieties of, ii. 256. _Ascaris_, number of eggs of, ii. 379. ASH, varieties of the, i. 360; weeping, i. 361; simple-leaved, i. 362; bud-variation in, i. 382; effects of graft upon the stock in the, i. 394; production of the blotched Breadalbane, _ibid. _; weeping, capricious reproduction of, by seed, ii. 19. _Asinus Burchellii_, i. 64. _Asinus hemionus_, ii. 43. _Asinus indicus_, ii. 42-43, 48. _Asinus quagga_, i. 64. _Asinus tæniopus_, ii. 41; the original of the domestic ass, i. 62. ASPARAGUS, increased fertility of cultivated, ii. 113. ASS, early domestication of the, i. 62; breeds of, _ibid. _; small size of, in India, _ibid. _; stripes of, i. 62-63; ii. 351; dislike of to cross water, i. 181; reversion in, ii. 41-43, 47; hybrid of the, with mare and zebra, ii. 42; prepotency of the, over the horse, ii. 67-68; crossed with wild ass, ii. 206; variation and selection of the, ii. 236. ASSYRIAN sculpture of a mastiff, i. 17. ASTERS, ii. 20, 316. ASTHMA, hereditary, ii. 8, 79. ATAVISM. _See_ Reversion. ATHELSTAN, his care of horses, ii. 203. ATKINSON, Mr. , on the sterility of the Tarroo silk-moth in confinement, ii. 157. AUBERGINE, ii. 91. AUDUBON, on feral hybrid ducks, i. 190; ii. 46; on the domestication of wild ducks on the Mississippi, i. 278; on the wild cock turkey visiting domestic hens, i. 292; fertility of _Fringilla ciris_ in captivity, ii. 154; fertility of _Columba migratoria_ and _leucocephala_ in captivity, ii. 155; breeding of _Anser canadensis_ in captivity, ii. 157. AUDUBON and Bachman, on the change of coat in _Ovis montana_, i. 99; sterility of _Sciurus cinerea_ in confinement, ii. 152. AURICULA, effect of seasonal conditions on the, ii. 273; blooming of, ii. 346. AUSTRALIA, no generally useful plants derived from, i. 310; useful plants of, enumerated by Hooker, i. 311. AUSTRIA, heredity of character in emperors of, ii. 65. AUTENRIETH, on persistency of colour in horses, ii. 21. AVA, horses of, i. 53. _Avena fatua_, cultivability of, i. 313. AYEEN Akbery, pigeons mentioned in the, i. 150, 155, 185, 205, 207, 208. AYRES, W. P. , on bud-variation in pelargoniums, i. 378. _Azalea indica_, bud-variation in, i. 377. AZARA, on the feral dogs of La Plata, i. 27; on the crossing of domestic with wild cats in Paraguay, i. 45; on hornlike processes in horses, i. 50; on curled hair in horses, i. 54; ii. 205, 325; on the colours of feral horses, i. 60, 61; ii. 259; on the cattle of Paraguay and La Plata, i. 82, 86, 89; ii. 250; on a hornless bull, ii. 205; on the increase of cattle in South America, ii. 119; on the growth of horns in the hornless cattle of Corrientes, ii. 39; on the "Niata" cattle, i. 90; on naked quadrupeds, ii. 279; on a race of black-skinned fowls in South America, i. 258; ii. 209; on a variety of maize, i. 321. BABINGTON, C. C. , on the origin of the plum, i. 345; British species of the genus _Rosa_, i. 366; distinctness of _Viola lutea_ and _tricolor_, i. 368. BACHMANN, Mr. , on the turkey, ii. 262. _See also_ Audubon. BADGER, breeding in confinement, ii. 151. "BAGADOTTEN-TAUBE, " i. 141. BAILY, Mr. , on the effect of selection on fowls, ii. 198; on Dorking fowls, ii. 238. BAIRD, S. , on the origin of the turkey, i. 292. BAKER, Mr. , on heredity in the horse, ii. 11; on the degeneration of the horse by neglect, ii. 239; orders of Henrys VII. And VIII. For the destruction of undersized mares, ii. 203. BAKEWELL, change in the sheep effected by, ii. 198. BALANCEMENT, ii. 342-344; of growth, law of, i. 274. BALDHEAD, pigeon, i. 151. BALDNESS, in man, inherited, ii. 73-74; with deficiency in teeth, ii. 326-327. BALLANCE, Mr. , on the effects of interbreeding on fowls, ii. 125; on variation in the eggs of fowls, i. 248. _Ballota nigra_, transmission of variegated leaves in, i. 383. BAMBOO, varieties of the, ii. 256. BANANA, variation of the, i. 372; ii. 256, 258; bud-variation in the, i. 377; sterility of the, ii. 268. BANTAM fowls, i. 230; Sebright, origin of, ii. 96; sterility of, ii. 101. BARB (Pigeon), i. 144-146, 210; ii. 227; {436} figure of, i. 145; figure of lower jaw of, i. 164. BARBS, of wheat, i. 314. BARBERRY, dark or red-leaved variety, i. 362; ii. 19; reversion in suckers of seedless variety, i. 384. BARBUT, J. , on the dogs of Guinea, i. 25; on the domestic pigeons in Guinea, i. 186; fowls not native in Guinea, i. 237. BARKING, acquisition of the habit of, by various dogs, i. 27. BARLEY, wild, i. 313; of the lake-dwellings, i. 317-318; ancient variety of, ii. 429. BARNES, Mr. , production of early peas by selection, ii. 201. BARNET, Mr. , on the intercrossing of strawberries, i. 351; dioeciousness of the Hautbois strawberry, i. 353; on the scarlet American strawberry, ii. 200. BARTH, Dr. , use of grass-seeds as food in Central Africa, i. 308. BARTLETT, A. D. , on the origin of "Himalayan" rabbits by intercrossing, i. 109; on the feral rabbits of Porto Santo, i. 114; on geese with reversed feathers on the head and neck, i. 288; on the young of the black-shouldered peacock, i. 290; on the breeding of the Felidæ in captivity, ii. 150. BARTRAM, on the black wolf-dog of Florida, i. 22. BATES, H. W. , refusal of wild animals to breed in captivity, ii. 150, 152; sterility of American monkeys in captivity, ii. 153; sterility of tamed guans, ii. 156. BATRACHIA, regeneration of lost parts in, ii. 15. BEACH, raised, in Peru, containing heads of maize, i. 320. BEAK, variability of, in fowls, i. 258; individual differences of, in pigeons, i. 160; correlation of, with the feet in pigeons, i. 171-174. BEALE, Lionel, on the contents of cells, ii. 370; on the multiplication of infectious atoms, ii. 378; on the origin of fibres, ii. 382. BEANS, i. 330; of Swiss lake-dwellings, i. 319; varieties of, produced by selection, ii. 218; French and scarlet, variable resistance of to frost, ii. 309, 314; superiority of native seed of, ii. 314; a symmetrical variation of scarlet, ii. 322; experiments on kidney, i. 330; with monstrous stipules and abortive leaflets, ii. 343. BEARD, pigeon, i. 151. BEARS, breeding in captivity, ii. 151. BEASLEY, J. , reversion in crossed cattle, ii. 41. BEATON, D. , effect of soil upon strawberries, i. 353; on varieties of pelargonium, i. 364, ii. 274, 311; bud-variation in _Gladiolus colvillii_, i. 382; cross between Scotch kail and cabbage, ii. 98; hybrid gladiolus, ii. 139; constant occurrence of new forms among seedlings, ii. 235; on the doubling of the compositæ, ii. 316. BECHUANA cattle, i. 88. BECK, Mr. , constitutional differences in pelargoniums, i. 364. BECKMANN, on changes in the odours of plants, ii. 274. BECKSTEIN, on the burrowing of wolves, i. 27; "Spitz" dog, i. 31; origin of the Newfoundland dog, i. 42; crossing of domestic and wild swine, i. 66; on the Jacobin pigeon, i. 154, 209; notice of swallow-pigeons, i. 156; on a fork-tailed pigeon, i. 157; variations in the colour of the croup in pigeons, i. 184; on the German dove-cot pigeon, i. 185; fertility of mongrel pigeons, i. 192; on hybrid turtle-doves, i. 193; on crossing the pigeon with _Columba oenas_, _C. Palumbus_, _Turtur risoria_, and _T. Vulgaris_, i. 193; development of spurs in the silk-hen, i. 256; on Polish fowls, i. 257, 264; on crested birds, i. 257; on the Canary-bird, i. 295, ii. 22, 161; German superstition about the turkey, i. 293; occurrence of horns in hornless breeds of sheep, ii. 30; hybrids of the horse and ass, ii. 68; crosses of tailless fowls, ii. 92; difficulty of pairing dove-cot and fancy pigeons, ii. 103; fertility of tame ferrets and rabbits, ii. 112; fertility of wild sow, _ibid. _; difficulty of breeding caged birds, ii. 154; comparative fertility of _Psittacus erithacus_ in captivity, ii. 155; on changes of plumage in captivity, ii. 158; liability of light-coloured cattle to the attacks of flies, ii. 229; want of exercise a cause of variability, ii. 257; effect of privation of light upon the plumage of birds, ii. 280; on a sub-variety of the monk-pigeon, ii. 350. BEDDOE, Dr. , correlation of complexion with consumption, ii. 335. BEDEGUAR gall, ii. 284. BEE, persistency of character of, ii. 236, 254; intercrossing, ii. 126; conveyance, of pollen of peas by, i. 329. BEE-OPHRYS, self-fertilisation of, ii. 91. BEECH, dark-leaved, i. 362, ii. 19; fern-leaved, reversion of, i. 382; weeping, non-production of by seed, ii. 19. BEECHEY, horses of Loochoo Islands, i. 53. BEET, i. 326; increase of sugar in, by selection, ii. 201. {437} _Begonia frigida_, singular variety of, i. 365; sterility of, ii. 166. BELGIAN rabbit, i. 106. BELL, T. , statement that white cattle have coloured ears, i. 85. BELL, W. , bud-variation in _Cistus tricuspis_, i. 377. BELLINGERI, observations on gestation in the dog, i. 30; on the fertility of dogs and cats, ii. 112. BELON, on high-flying pigeons in Paphlagonia, i. 209; varieties of the goose, i. 289. BENGUELA, cattle of, i. 88. BENNETT, Dr. G. , pigs of the Pacific islands, i. 70, 87; dogs of the Pacific islands, i. 87; varieties of cultivated plants in Tahiti, ii. 256. BENNETT, Mr. , on the fallow deer, ii. 103. BENTHAM, G. , number and origin of cultivated plants, i. 306; cereals all cultivated varieties, i. 312; species of the orange group, i. 334-335; distinctions of almond and peach, i. 338; British species of _Rosa_, i. 366; identity of _Viola lutea_ and _tricolor_, i. 368. _Berberis vulgaris_, i. 384, ii. 19. _Berberis Wallichii_, indifference of, to climate, ii. 164. BERJEAN, on the history of the dog, i. 16, 18. BERKELEY, G. F. , production of hen-cocks in a strain of game-fowls, i. 253. BERKELEY, M. J. , crossing of varieties of the pea, i. 397; effect of foreign pollen on grapes, i. 400; on hybrid plants, ii. 131; analogy between pollen of highly-cultivated plants and hybrids, ii. 268; on Hungarian kidney-beans, ii. 275; failure of Indian wheat in England, ii. 307; bud developed on the petal of a _Clarkia_, ii. 384. BERNARD, inheritance of disease in the horse, ii. 10. BERNARD, C. , independence of the organs of the body, ii. 368-369; special affinities of the tissues, ii. 380. BERNHARDI, varieties of plants with laciniated leaves, ii. 348. _Bernicla antarctica_, i. 288. BERTERO, on feral pigeons in Juan Fernandez, i. 190. _Betula alba_, ii. 18. BEWICK, on the British wild cattle, i. 84. BIBLE, reference to breeding studs of horses in, i. 54; references to domestic pigeons in the, i. 205; indications of selection of sheep in the, ii. 201; notice of mules in the, ii. 202. BIDWELL, Mr. , on self-impotence in _Amaryllis_, ii. 139. BIRCH, weeping, i. 387, ii. 18. BIRCH, Dr. S. , on the ancient domestication of the pigeon in Egypt, i. 205; notice of bantam fowls in a Japanese encyclopædia, i. 230, 247. BIRCH, Wyrley, on silver-grey rabbits, i. 109-110. BIRDS, sterility caused in, by change of conditions, ii. 153-157. BLADDER-NUT, tendency of the, to become double, ii. 168. BLAINE, Mr. , on wry-legged terriers, ii. 245. BLAINVILLE, origin and history of the dog, i. 15-16; variations in the number of teeth in dogs, i. 34; variations in the number of toes in dogs, i. 35; on mummies of cats, i. 43; on the osteology of solid-hoofed pigs, i. 75; on feral Patagonian and N. American pigs, i. 77. "BLASS-TAUBE, " i. 156. BLEEDING, hereditary, ii. 7, 8; sexual limitation of excessive, ii. 73. BLENDING of crossed races, time occupied by the, ii. 87. BLINDNESS, hereditary, ii. 9; at a certain age, ii. 78; associated with colour of hair, ii. 328. BLOODHOUNDS, degeneration of, caused by interbreeding, ii. 121. BLUMENBACH, on the protuberance of the skull in Polish fowls, i. 257; on the effect of circumcision, ii. 23; inheritance of a crooked finger, ii. 23; on badger-dogs and other varieties of the dog, ii. 220; on _Hydra_, ii. 293; on the "nisus formativus, " ii. 294. BLYTH, E. , on the Pariah dog, i. 24; hybrids of dog and jackal, i. 32; early domestication of cats in India, i. 43; origin of domestic cat, _ib. _; crossing of domestic and wild cats, i. 44; on Indian cats resembling _Felis chaus_, i. 45; on striped Burmese ponies, i. 58; on the stripes of the ass, i. 63; on Indian wild pigs, i. 66; on humped cattle, i. 79, 80; occurrence of _Bos frontosus_ in Irish crannoges, i. 81; fertile crossing of zebus and common cattle, i. 83; on the species of sheep, i. 94; on the fat-tailed Indian sheep, i. 96; origin of the goat, i. 101; on rabbits breeding in India, i. 112; number of tail-feathers in fantails, i. 146; Lotan tumbler pigeons, i. 150; number of tail-feathers in _Ectopistes_, i. 159; on _Columba affinis_, i. 183; pigeons roosting in trees, i. 181; on _Columba leuconota_, i. 182; on _Columba intermedia_ of Strickland, i. 184; variation in colour of croup in pigeons, i. 184-185, 197; voluntary domestication of rock-pigeons in India, i. 185; feral pigeons on the Hudson, i. 190; {438} occurrence of sub-species of pigeons, i. 204; notice of pigeon-fanciers in Delhi, &c. , i. 206; hybrids of _Gallus Sonneratii_ and the domestic hen, i. 234; supposed hybridity of _Gallus Temminckii_, i. 235; variations and domestication of _Gallus bankiva_, i. 235-236, 237; crossing of wild and tame fowls in Burmah, i. 236; restricted range of the larger gallinaceous birds, i. 237; feral fowls in the Nicobar islands, i. 238; black-skinned fowls occurring near Calcutta, i. 256; weight of _Gallus bankiva_, i. 272; degeneration of the turkey in India, i. 294, ii. 278; on the colour of gold-fish, i. 296; on the Ghor-Khur (_Asinus indicus_), ii. 42; on _Asinus hemionus_, ii. 43; number of eggs of _Gallus bankiva_, ii. 112; on the breeding of birds in captivity, ii. 157; co-existence of large and small breeds in the same country, ii. 279; on the drooping ears of the elephant, ii. 301; homology of leg and wing feathers, ii. 323. BOETHIUS on Scotch wild cattle, i. 85. BOITARD and Corbié, on the breeds of pigeons, i. 132; Lille pouter pigeon, i. 138; notice of a gliding pigeon, i. 156; variety of the pouter pigeon, i. 162; dove-cot pigeon, i. 185; crossing pigeons, i. 192-193, ii. 97, 126; sterility of hybrids of turtle-doves, i. 193; reversion of crossed pigeons, i. 197, ii. 40; on the fantail, i. 208, ii. 66; on the trumpeter, ii. 66; prepotency of transmission in silky fantail, ii. 67, 69; secondary sexual characters in pigeons, ii. 74; crossing of white and coloured turtle-doves, ii. 92; fertility of pigeons, ii. 112. BOMBYCIDÆ, wingless females of, ii. 299. _Bombyx hesperus_, ii. 304. _Bombyx Huttoni_, i. 302. _Bombyx mori_, i. 300-304. BONAFOUS, on maize, i. 320, 321. BONAPARTE, number of species of Columbidæ, i. 133; number of tail-feathers in pigeons, i. 158; size of the feet in Columbidæ, i. 174; on _Columba guinea_, i. 182; _Columba turricola_, _rupestris_, and _Schimperi_, i. 184. _Bonatea speciosa_, development of ovary of, i. 403. BONAVIA, Dr. , growth of cauliflowers in India, ii. 310. BONES, removal of portions of, ii. 296; regeneration of, ii. 294; growth and repair of, ii. 381-382. BONNET, on the salamander, ii. 15, 341, 358, 385; theory of reproduction, ii. 385. BORCHMEYER, experiments with the seeds of the weeping ash, ii. 19. BORECOLE, i. 323. BORELLI, on Polish fowls, i. 247. BORNEO, fowls of, with tail-bands, i. 235. BORNET, E. , condition of the ovary in hybrid _Cisti_, i. 389; self-impotence of hybrid _Cisti_, ii. 140. BORROW, G. , on pointers, i. 42. BORY de Saint-Vincent, on gold-fish, i. 297. _Bos_, probable origin of European domestic cattle from three species of, i. 83. _Bos frontosus_, i. 79, 81-82. _Bos indicus_, i. 79. _Bos longifrons_, i. 79, 81. _Bos primigenius_, i. 79-81, 119. _Bos sondaicus_, ii. 206. _Bos taurus_, i. 79. _Bos trochoceros_, i. 81. BOSC, heredity in foliage-varieties of the elm, i. 362. BOSSE, production of double flowers from old seed, ii. 167. BOSSI, on breeding dark-coloured silkworms, i. 302. BOUCHARDAT, on the vine disease, i. 334. BOUDIN, on local diseases, ii. 276; resistance to cold of dark-complexioned men, ii. 335. "BOULANS, " i. 137. "BOUTON d'Alep, " ii. 276. BOWEN, Prof. , doubts as to the importance of inheritance, ii. 3. BOWMAN, Mr. , hereditary peculiarities in the human eye, ii. 8-10; hereditary cataract, ii. 79. BRACE, Mr. , on Hungarian cattle, i. 80. _Brachycome iberidifolia_, ii. 261. BRACTS, unusual development of, in gooseberries, i. 355. BRADLEY, Mr. , effect of grafts upon the stock in the ash, i. 394; effect of foreign pollen upon apples, i. 401; on change of soil, ii. 146. "BRAHMA Pootras, " a new breed of fowls, i. 245. BRAIN, proportion of, in hares and rabbits, i. 126-129. BRANDT, origin of the goat, i. 101. _Brassica_, varieties of, with enlarged stems, ii. 348. _Brassica asperifolia_, ii. 343. _Brassica napus_, i. 325. _Brassica oleracea_, i. 323. _Brassica rapa_, i. 325, ii. 165. BRAUN, A. , bud-variation in the vine, i. 375; in the currant, i. 376; in _Mirabilis jalapa_, i. 382; in _Cytisus adami_, i. 388; on reversion in the foliage of trees, i. 382; spontaneous production of _Cytisus purpureo-elongatus_, i. 390; reversion of flowers by stripes and blotches, ii. 37; excess of nourishment a source of variability, ii. 257. {439} BRAZIL, cattle of, i. 88. BREAD-FRUIT, varieties of, ii. 256; sterility and variability of, ii. 262. BREE, W. T. , bud-variation in _Geranium pratense_ and _Centaurea cyanus_, i. 379; by tubers in the dahlia, i. 385; on the deafness of white cats with blue eyes, ii. 329. BREEDING, high, dependent on inheritance, ii. 3-4. BREEDS, domestic, persistency of, ii. 246, 428-429; artificial and natural, ii. 413-414; extinction of, ii. 425; of domestic cats, i. 45-47; of pigs produced by crossing, i. 78; of cattle, i. 86-87, 91-93; of goats, i. 101. BREHM, on _Columba amaliæ_, i. 183. BRENT, B. P. , number of mammæ in rabbits, i. 106; habits of the tumbler pigeon, i. 151; Laugher pigeon, i. 155; colouring of the kite tumbler, i. 160; crossing of the pigeon with _Columba oenas_, i. 193; mongrels of the trumpeter pigeon, ii. 66; close interbreeding of pigeons, ii. 126; opinion on Aldrovandi's fowls, i. 247; on stripes in chickens, i. 249-250; on the combs of fowls, i. 253; double-spurred Dorking fowls, i. 255; effect of crossing on colour of plumage in fowls, i. 258; incubatory instinct of mongrels between non-sitting varieties of fowls, ii. 44; origin of the domestic duck, i. 277; fertility of the hook-billed duck, _ibid. _; occurrence of the plumage of the wild duck in domestic breeds, i. 280; voice of ducks, i. 281; occurrence of a short upper mandible in crosses of hook-billed and common ducks, i. 281; reversion in ducks produced by crossing, ii. 40; variation of the canary-bird, i. 295; fashion in the canary, ii. 240; hybrids of canary and finches, ii. 45. BRICKELL, on raising nectarines from seed, i. 340; on the horses of North Carolina, ii. 300. BRIDGES, Mr. , on the dogs of Tierra del Fuego, i. 39; on the selection of dogs by the Fuegians, ii. 207. BRIDGMAN, W. K. , reproduction of abnormal ferns, i. 383, ii. 379. BRIGGS, J. J. , regeneration of portions of the fins of fishes, ii. 15. BROCA, P. , on the intercrossing of dogs, i. 31-32; on hybrids of hare and rabbit, i. 105; on the rumpless fowl, i. 259; on the character of half-castes, ii. 47; degree of fertility of mongrels, ii. 100; sterility of descendants of wild animals bred in captivity, ii. 160. BROCCOLI, i. 323; rudimentary flowers in, ii. 316; tenderness of, ii. 310. BROMEHEAD, W. , doubling of the Canterbury bell by selection, ii. 200. BROMFIELD, Dr. , sterility of the ivy and _Acorus calamus_, ii. 170. _Bromus secalinus_, i. 314. BRONN, H. G. , bud-variation in _Anthemis_, i. 379; effects of cross-breeding on the female, i. 404; on heredity in a one-horned cow, ii. 12, 13; propagation of a pendulous peach by seed, ii. 18; absorption of the minority in crossed races, ii. 88; on the crossing of horses, ii. 92; fertility of tame rabbits and sheep, ii. 112; changes of plumage in captivity, ii. 158; on the dahlia, ii. 261. BRONZE period, dog of, i. 18. BROWN, G. , variations in the dentition of the horse, i. 50. BROWN-SÉQUARD, Dr. , inheritance of artificially-produced epilepsy in the guinea-pig, ii. 24. _Brunswigia_, ii. 139. BRUSSELS Sprouts, i. 323, ii. 429. _Bubo maximus_, ii. 154. BUCKLAND, F. , on oysters, ii. 280; number of eggs in a codfish, ii. 379. BUCKLE, Mr. , doubts as to the importance of inheritance, ii. 3. BUCKLEY, Miss, carrier-pigeons roosting in trees, i. 181. BUCKMAN, Prof. , cultivation of _Avena fatua_, i. 313; cultivation of the wild parsnip, i. 326, ii. 201, 277; reversion in the parsnip, ii. 31. BUCKWHEAT, injurious to white pigs, when in flower, ii. 337. BUD and seed, close analogy of, i. 411. BUD-REVERSION, ii. 37. BUDS, adventitious, ii. 384. BUD-VARIATION, i. 373-411, ii. 254, 287-288, 291; contrasted with seminal reproduction, i. 373; peculiar to plants, i. 374; in the peach, i. 340, 374; in plums, i. 375; in the cherry, _ibid. _; in grapes, _ibid. _; in the gooseberry, currant, pear, and apple, i. 376; in the banana, camellia, hawthorn, _Azalea indica_, and _Cistus tricuspis_, i. 377; in the hollyhock and pelargonium, i. 378; in _Geranium pratense_ and the chrysanthemum, i. 379; in roses, i. 367, 379-381; in sweet williams, carnations, pinks, stocks, and snapdragons, i. 381; in wall-flowers, cyclamen, _Oenothera biennis_, _Gladiolus colvillii_, fuchsias, and _Mirabilis jalapa_, i. 382; in foliage of various trees, i. 382-384; in cryptogamic plants, i. 383; by suckers in _Phlox_ and barberry, i. 384; by tubers in the potato, _ibid. _; in the dahlia, i. 385; by bulbs in hyacinths, _Imatophyllum miniatum_, and tulips, i. 385; in _Tigridia conchiflora_, i. 386; {440} in _Hemerocallis_, _ibid. _; doubtful cases, i. 386-387; in _Cytisus Adami_, i. 387-394; probable in _Æsculus rubicunda_, i. 392; summary of observations on, 406. BUFFON, on crossing the wolf and dog, i. 32; increase of fertility by domestication, ii. 111; improvement of plants by unconscious selection, ii. 216; theory of reproduction, ii. 375. _Bulimus_, ii. 53. BULL, apparent influence of, on offspring, ii. 68. BULLACE, i. 345. BULLDOG, recent modifications of, i. 42. BULLFINCH, breeding in captivity, ii. 154; attacking flower-buds, ii. 232. BULT, Mr. , selection of pouter pigeons, ii. 197. "BÜNDTNERSCHWEIN, " i. 67. BUNTING, reed, in captivity, ii. 158. BURDACH, crossing of domestic and wild animals, i. 66; aversion of the wild boar to barley, ii. 303. BURKE, Mr. , inheritance in the horse, ii. 10. _Burlingtonia_, ii. 135. BURMAH, cats of, i. 47. BURMESE ponies, striped, i. 58, 59. BURNES, Sir A. , on the Karakool sheep, i. 98, ii. 278; varieties of the vine in Cabool, i. 333; hawks, trained in Scinde, ii. 153; pomegranates producing seed, ii. 168. BURTON Constable, wild cattle at, i. 84. "BURZEL-TAUBEN, " i. 150. BUSSORAH carrier, i. 141. _Buteo vulgaris_, copulation of, in captivity, ii. 154. BUTTERFLIES, polymorphic, ii. 399-400. BUZAREINGUES, Girou de, inheritance of tricks, ii. 6. CABANIS, pears grafted on the quince, ii. 239. CABBAGE, i. 323-326; varieties of, i. 323; unity of character in flowers and seeds of, i. 323-324; cultivated by ancient Celts, i. 324; classification of varieties of, _ibid. _; ready crossing of, _ibid. _, ii. 90, 91, 98, 130; origin of, i. 325; increased fertility of, when cultivated, ii. 113; growth of, in tropical countries, ii. 277. CABOOL, vines of, i. 333. CABRAL, on early cultivation in Brazil, i. 311. CACTUS, growth of cochineal on, in India, ii. 275. CÆSAR, _Bos primigenius_ wild in Europe in the time of, i. 81; notice of fowls in Britain, i. 246; notice of the importation of horses by the Celts, ii. 203. CAFFRE fowls, i. 230. CAFFRES, different kinds of cattle possessed by the, i. 88. "CÁGIAS, " a breed of sheep, i. 95. CALCEOLARIAS, i. 364; ii. 147; effects of seasonal conditions on, ii. 274; peloric flowers in, ii. 346. "CALONGOS, " a Columbian breed of cattle, i. 88. CALVER, Mr. , on a seedling peach producing both peaches and nectarines, i. 341. CALYX, segments of the, converted into carpels, ii. 392. CAMEL, its dislike to crossing water, i. 181. _Camellia_, bud-variations in, i. 377; recognition of varieties of, ii. 251; variety in, hardiness of, ii. 308. CAMERON, D. , on the cultivation of Alpine plants, ii. 163. CAMERONN, Baron, value of English blood in race-horses, ii. 11. _Campanula medium_, ii. 200. CANARY-BIRD, i. 295; conditions of inheritance in, ii. 22; hybrids of, ii. 45; period of perfect plumage in, ii. 77; diminished fertility of, ii. 161; standard of perfection in, ii. 195; analogous variation in, ii. 349. CANCER, heredity of, ii. 7, 8, 79. CANINE teeth, development of the, in mares, ii. 318. _Canis alopex_, i. 29. _Canis antarcticus_, i. 20. _Canis argentatus_, ii. 151. _Canis aureus_, i. 29. _Canis cancrivorus_, domesticated and crossed in Guiana, i. 23. _Canis cinereo-variegatus_, i. 29. _Canis fulvus_, i. 29. _Canis Ingæ_, the naked Peruvian dog, i. 23. _Canis latrans_, resemblance of, to the Hare Indian dog, i. 22; one of the original stocks, i. 26. _Canis lupaster_, i. 25. _Canis lupus_, var. _occidentalis_, resemblance of, to North American dogs, i. 21; crossed with dogs, i. 22; one of the original stocks, i. 26. _Canis mesomelas_, i. 25, 29. _Canis primævus_, tamed by Mr. Hodgson, i. 26. _Canis sabbar_, i. 25. _Canis simensis_, possible original of greyhounds, i. 33. _Canis thaleb_, i. 29. _Canis variegatus_, i. 29. CANTERBURY Bell, doubled by selection, ii. 200. CAPE of Good Hope, different kinds of cattle at the, i. 88; {441} no useful plants derived from the, i. 310. CAPERCAILZIE, breeding in captivity, ii. 156. _Capra ægagrus_ and _C. Falconeri_, probable parents of domestic goat, i. 101. CAPSICUM, i. 371. CARDAN, on a variety of the walnut, i. 356; on grafted walnuts, ii. 259-260. CARDOON, ii. 34. _Carex rigida_, local sterility of the, ii. 170. CARLIER, early selection of sheep, ii. 204. CARLISLE, Sir A. , inheritance of peculiarities, ii. 6, 8; of polydactylism, ii. 13. "CARME" pigeon, i. 156. CARNATION, bud-variation in, i. 381; variability of, i. 370; striped, produced by crossing red and white, i. 393; effect of conditions of life on the, ii. 273. CARNIVORA, general fertility of, in captivity, ii. 150. CAROLINE Archipelago, cats of, i. 47. CARP, ii. 236. CARPELS, variation of, in cultivated cucurbitaceæ, i. 359. CARPENTER, W. B. , regeneration of bone, ii. 294; production of double monsters, ii. 340; number of eggs in an _Ascaris_, ii. 379. _Carpinus betulus_, i. 362. _Carpophaga littoralis_ and _luctuosa_, i. 182. CARRIER pigeon, i. 139-142; English, i. 139-141; figured, i. 140; skull figured, i. 163; history of the, i. 211; Persian, i. 141; Bussorah, _ibid. _; Bagadotten, skull figured, i. 163; lower jaw figured, i. 165. CARRIÈRE, cultivation of the wild carrot, i. 326; intermediate form between the almond and the peach, i. 338; glands of peach-leaves, i. 343; bud-variation in the vine, i. 375; grafts of _Aria vestita_ upon thorns, i. 387; variability of hybrids of _Erythrina_, ii. 265. CARROT, wild, effects of cultivation on the, i. 326; reversion in the, ii. 31; run wild, ii. 33; increased fertility of cultivated, ii. 113; experiments on the, ii. 277; acclimatisation of the, in India, ii. 311. _Carthamus_, abortion of the pappus in, ii. 316. CARTIER, cultivation of native plants in Canada, i. 312. CARYOPHYLLACEÆ, frequency of contabescence in the, ii. 165. CASPARY, bud-variation in the moss-rose, i. 380; on the ovules and pollen of _Cytisus_, i. 388-389; crossing of _Cytisus purpureus_ and _C. Laburnum_, i. 389; trifacial orange, i. 391; differently-coloured flowers in the wild _Viola lutea, _ i. 408; sterility of the horse-radish, ii. 170. CASTELNAU, on Brazilian cattle, i. 88. CASTRATION, assumption of female characters caused by, ii. 51-52. _Casuarius bennettii_, ii. 156. CAT, domestic, i. 43-48; early domestication and probable origin of the, i. 43-44; intercrossing of with wild species, i. 44-45; variations of, i. 45-48; feral, i. 47, ii. 33; anomalous, i. 48; polydactylism in, ii. 14; black, indications of stripes in young, ii. 55; tortoiseshell, ii. 73; effects of crossing in, ii. 86; fertility of, ii. 111; difficulty of selection in, ii. 234, 236; length of intestines in, ii. 302; white with blue eyes, deafness of, ii. 329; with tufted ears, ii. 350. CATARACT, hereditary, ii. 9, 79. CATERPILLARS, effect of changed food on, ii. 280. CATLIN, G. , colour of feral horses in North America, i. 61. CATTLE, European, their probable origin from three original species, i. 79-82; humped, or Zebus, i. 79-80; intercrossing of, i. 83, 91-93; wild, of Chillingham, Hamilton, Chartley, Burton Constable, and Gisburne, i. 84, ii. 119; colour of feral, i. 84-85, ii. 102; British breeds of, i. 86-87; South African breeds of, i. 88; South American breeds of, i. 89, ii. 205; Niata, i. 89-91, ii. 205, 208, 332; effects of food and climate on, i. 91-92; effects of selection on, i. 92-93; Dutch-buttocked, ii. 8; hornless, production of horns in, ii. 29-30, 39; reversion in, when crossed, ii. 41; wildness of hybrid, ii. 45; short-horned, prepotency of, ii. 65; wild, influence of crossing and segregation on, ii. 86; crosses of, ii. 96, 104, 118; of Falkland islands, ii. 102; mutual fertility of all varieties of, ii. 110; effects of interbreeding on, ii. 117-119; effects of careful selection on, ii. 194, 199; naked, of Columbia, ii. 205; crossed with wild banteng in Java, ii. 206; with reversed hair in Banda Oriental, ii. 205; selection of trifling characters in, ii. 209; fashion in, ii. 210; similarity of best races of, ii. 241; unconscious selection in, ii. 214; effects of natural selection on anomalous breeds of, ii. 226-227; light-coloured, attacked by flies, ii. 229, 336; Jersey, rapid improvement of, ii. 234; effects of disuse of parts in, ii. 299; rudimentary horns in, ii. 315; supposed influence of humidity on the hair of, ii. 326; {442} white spots of, liable to disease, ii. 337; supposed analogous variation in, ii. 349; displacement of long-horned by short-horned, ii. 426. CAULIFLOWER, i. 323; free-seeding of, in India, ii. 310; rudimentary flowers in, ii. 316. CAVALIER pigeon, ii. 97. _Cavia aperea_, ii. 152. CAY (_Cebus azaræ_), sterility of, in confinement, ii. 153. _Cebus azaræ_, ii. 153. _Cecidomyia_, larval development of, ii. 283, 360, 367; and _Misocampus_, i. 5. CEDARS of Lebanon and Atlas, i. 364. CELERY, turnip-rooted, i. 336; run wild, ii. 33. CELL-THEORY, ii. 370. _Celosia cristata_, i. 365. CELSUS, on the selection of seed-corn, i. 318, ii. 203. CELTS, early cultivation of the cabbage by the, i. 324; selection of cattle and horses by the, ii. 202-203. _Cenchrus_, seeds of a, used as food, i. 309. _Centaurea cyanus_, bud-variation in, i. 379. CEPHALOPODA, spermatophores of, ii. 383. _Cerasus padus_, yellow-fruited, ii. 19. _Cercoleptes_, sterility of, in captivity, ii. 152. _Cercopithecus_, breeding of a species of, in captivity, ii. 153. CEREALS, i. 312-313; of the Neolithic period in Switzerland, i. 317; adaptation of, to soils, ii. 305. _Cereus_, ii. 38. _Cereus speciosissimus_ and _phyllanthus_, reversion in hybrids of, i. 392. _Cervus canadensis_, ii. 158. _Cervus dama_, ii. 120. CETACEA, correlation of dermal system and teeth in the, ii. 328. CEYLON, cats of, i. 46; pigeon-fancying in, i. 206. _Chamærops humilis_, crossed with date palm, i. 399. CHAMISSO, on seeding bread-fruit, ii. 168. CHANNEL islands, breeds of cattle in, i. 80. CHAPMAN, Professor, peach-trees producing nectarines, i. 341. CHAPUIS, F. , sexual peculiarities in pigeons, i. 162, ii. 74; effect produced by first male upon the subsequent progeny of the female, i. 405; sterility of the union of some pigeons, ii. 162. CHARACTERS, fixity of, ii. 239; latent, ii. 51-56, 399-400; continued divergence of, ii. 241; antagonistic, ii. 401. CHARDIN, abundance of pigeons in Persia, i. 205. CHARLEMAGNE, orders as to the selection of stallions, ii. 203. CHARTLEY, wild cattle of, i. 84. CHATÉ, reversion of the upper seeds in the pods of stocks, ii. 347-348. CHATIN, on _Ranunculus ficaria_, ii. 170. CHAUNDY, Mr. , crossed varieties of cabbage, ii. 130. CHEETAH, general sterility of, in captivity, ii. 151. _Cheiranthus cheiri_, i. 382. CHERRIES, i. 347-348; bud-variation in, i. 375; white Tartarian, ii. 230; variety of, with curled petals, ii. 232; period of vegetation of, changed by forcing, ii. 311. CHEVREUL, on crossing fruit-trees, ii. 129. CHICKENS, differences in characters of, i. 249-250; white, liable to gapes, ii. 228, 336. CHIGOE, ii. 275. CHILE, sheep of, i. 95. CHILLINGHAM cattle, identical with _Bos primigenius_, i. 81; characters of, i. 83-84. CHILOE, half-castes of, ii. 46. CHINA, cats of, with drooping ears, i. 47; horses of, i. 53; striped ponies of, i. 59; asses of, i. 62; notice of rabbits in, by Confucius, i. 103; breeds of pigeons reared in, i. 206; breeds of fowls of, in fifteenth century, i. 232, 247; goose of, i. 237. CHINCHILLA, fertility of, in captivity, ii. 152. CHINESE, selection practised by the, ii. 204-205; preference of the, for hornless rams, ii. 209; recognition of the value of native breeds by the, ii. 313. CHINESE, or Himalayan rabbit, i. 108. "CHIVOS, " a breed of cattle in Paraguay, i. 89. CHOUX-RAVES, i. 323. CHRIST, H. , on the plants of the Swiss Lake-dwellings, i. 309, 318; intermediate forms between _Pinus sylvestris_ and _montana_, i. 363. CHRYSANTHEMUM, i. 379. _Chrysotis festiva_, ii. 280. CINERARIA, effects of selection on the, ii. 200. CIRCASSIA, horses of, ii. 102. CIRCUMCISION, ii. 23. CIRRIPEDES, metagenesis in, ii. 366. _Cistus_, intercrossing and hybrids of, i. 336, 389, ii. 140. _Cistus tricuspis_, bud-variation in, i. 377. CITRONS, i. 334-335. "_Citrus aurantium fructu variabili_, " i. 336. _Citrus decumana_, i. 335. _Citrus lemonum_, i. 336. {443} _Citrus medica_, i. 335-336. CLEFT palate, inheritance of, ii. 24. CLEMENTE, on wild vines in Spain, i. 332. CLERMONT-TONNERRE, on the St. Valery apple, i. 401. CLAPHAM, A. , bud-variation in the hawthorn, i. 377. "CLAQUANT, " i. 138. "CLAQUERS" (pigeons), i. 156. CLARK, G. , on the wild dogs of Juan de Nova, i. 27; on striped Burmese and Javanese ponies, i. 59; breeds of goats imported into the Mauritius, i. 101; variations in the mammæ of goats, i. 102; bilobed scrotum of Muscat goat, _ibid. _ CLARK, H. J. , on fission and gemmation, ii. 359. CLARKE, R. T. , intercrossing of strawberries, i. 352. CLARKE, T. , hybridisation of stocks, i. 399, ii. 93. CLARKSON, Mr. , prize-cultivation of the gooseberry, i. 355. CLASSIFICATION, explained by the theory of natural selection, i. 11. CLIMATE, effect of, upon breeds of dogs, i. 37; on horses, i. 52, 53; on cattle, i. 91, 92; on the fleece of sheep, i. 98, 99; on seeds of wheat, i. 316; on cultivated cabbages, i. 325; adaptation of maize to, i. 322. CLIMATE and pasture, adaptation of breeds of sheep to, i. 96-97. CLIMATE and soil, effects of, upon strawberries, i. 353. CLINE, Mr. , on the skull in horned and hornless rams, ii. 333. CLOS, on sterility in _Ranunculus ficaria_, ii. 170. CLOTZSCH, hybrids of various trees, ii. 130. CLOVER, pelorism in, ii. 340. COATE, Mr. , on interbreeding pigs, ii. 122. COCCUS of apple trees, ii. 231. COCHIN fowls, i. 227, 250, 252, 260-261; occipital foramen of, figured, i. 261; section of skull of, figured, i. 263; cervical vertebra of, figured, i. 267. COCHINEAL, persistence of, ii. 236; preference of, for a particular cactus, ii. 275. _Cochlearia armoracia_, ii. 170. COCK, game, natural selection in, ii. 225; spur of, grafted on the comb, ii. 296; spur of, inserted into the eye of an ox, ii. 369; effect of castration upon the, ii. 51-52. COCK'S-COMB, varieties of the, i. 365. COCOONS, of silkworms, variations in, i. 302-303. CODFISH, bulldog, i. 89; number of eggs in the, ii. 379. _Coelogenys paca_, ii. 152. COLIN, prepotency of the ass over the horse, ii. 67-68; on cross-breeding, ii. 97; on change of diet, ii. 304. COLLINSON, Peter, peach-tree producing a nectarine, i. 340. COLORATION, in pigeons, an evidence of unity of descent, i. 195-197. COLOUR, correlation of, in dogs, i. 28-29; persistence of, in horses, i. 50; inheritance and diversity of, in horses, i. 55; variations of, in the ass, i. 62-63; of wild or feral cattle, i. 85; transmission of, in rabbits, i. 107; peculiarities of, in Himalayan rabbits, i. 111; influence of, ii. 227-230; correlation of, in head and limbs, ii. 324; correlated with constitutional peculiarities, ii. 335-338. COLOUR and odour, correlation of, ii. 325. COLOUR-BLINDNESS, hereditary, ii. 9; more common in men than in women, ii. 72-73; associated with inability to distinguish musical sounds, ii. 328. COLOURS, sometimes not blended by crossing, ii. 92. _Columba affinis_, Blyth, a variety of _C. Livia_, i. 183. _Columba amaliæ_, Brehm, a variety of _C. Livia_, i. 183. _Columba guinea_, i. 182. _Columba gymnocyclus_, Gray, a form of _C. Livia_, i. 184. _Columba gymnophthalmos_, hybrids of, with _C. Oenas_, i. 193; with _C. Maculosa_, i. 194. _Columba intermedia_, Strickland, a variety of _C. Livia_, i. 184. _Columba leucocephala_, ii. 155. _Columba leuconota_, i. 182, 195. _Columba littoralis_, i. 182. _Columba livia_, ii. 29, 40; the parent of domestic breeds of pigeons, i. 183; measurements of, i. 134; figured, i. 135; skull figured, i. 163; lower jaw figured, i. 164, 168; scapula figured, i. 167. _Columba luctuosa_, i. 182. _Columba migratoria_ and _leucocephala_, diminished fertility of, in captivity, ii. 155. _Columba oenas_, i. 183; crossed with common pigeon and _C. Gymnophthalmos_, i. 193. _Columba palumbus_, i. 193, ii. 350. _Columba rupestris_, i. 182, 184, 195. _Columba Schimperi_, i. 184. _Columba torquatrix_, ii. 350. _Columba turricola_, i. 184. COLUMBIA, cattle of, i. 88. COLUMBINE, double, i. 365, ii. 330. {444} COLUMBUS, on West Indian dogs, i. 23. COLUMELLA, on Italian shepherd's dogs, i. 23; on domestic fowls, i. 231, 247, ii. 202, 429; on the keeping of ducks, i. 277; on the selection of seed-corn, i. 318; on the benefits of change of soil to plants, ii. 146; on the value of native breeds, ii. 313. COLZA, i. 325. COMB, in fowls, variations of, i. 253-254; sometimes rudimentary, ii. 315. COMPENSATION, law of, i. 274. COMPENSATION of growth, ii. 342-344. COMPLEXION, connexion of, with constitution, ii. 335. COMPOSITÆ, double flowers of, i. 365, ii. 167, 316. CONCEPTION, earlier in Alderney and Zetland cows than in other breeds, i. 87. CONDITIONS of life, changed, effect of, ii. 418-419; on horses, i. 52; upon variation in pigeons, i. 212-213; upon wheat, i. 315-316; upon trees, i. 361; in producing bud-variation, i. 408; advantages of, ii. 145-148, 176-177; sterility caused by, ii. 148-165; conducive to variability, ii. 255-261, 394; accumulative action of, ii. 261-263; direct action of, ii. 271-292. CONDOR, breeding in captivity, ii. 154. CONFINEMENT, effect of, upon the cock, ii. 52. CONFUCIUS, on the breeding of rabbits in China, i. 103. CONOLLY, Mr. , on Angora goats, ii. 326. CONSTITUTIONAL differences in sheep, i. 96-97; in varieties of apples, i. 349-350; in pelargoniums, i. 364; in dahlias, i. 370. CONSTITUTIONAL peculiarities in strawberries, i. 353; in roses, i. 367. CONSUMPTION, hereditary, ii. 8; period of appearance of, ii. 77; correlated with complexion, ii. 335. CONTABESCENCE, ii. 165-166. _Convolvulus batatas_, ii. 169, 309. _Convolvulus tricolor_, bud-variation in, i. 408. COOPER, Mr. , improvement of vegetables by selection, ii. 204. COOPER, White, hereditary peculiarities of vision, ii. 9; association of affections of the eyes with those of other systems, ii. 328. CORALS, bud-variation in, i. 374; non-diffusion of cell-gemmules in, ii. 379. CORBIÉ. _See_ Boitard. CORNEA, opacity of, inherited, ii. 9. _Cornus mascula_, yellow-fruited, ii. 19. CORRELATION, ii. 319; of neighbouring parts, ii. 320; of change in the whole body and in some of its parts, ii. 321; of homologous parts, ii. 322-331; inexplicable, ii. 331-333; commingling of, with the effects of other agencies, ii. 333-335. CORRELATION of skull and limbs in swine, i. 73; of tusks and bristles in swine, i. 76; of multiplicity of horns and coarseness of wool in sheep, i. 95; of beak and feet in pigeons, i. 172-173; between nestling down and colour of plumage in pigeons, i. 194; of changes in silkworms, i. 304; in plants, ii. 219; in maize, i. 323; in pigeons, i. 167-171, 218; in fowls, i. 274-275. CORRESPONDING periods, inheritance at, ii. 75-80. CORRIENTES, dwarf cattle of, i. 89. CORRINGHAM, Mr. , influence of selection on pigs, ii. 198. CORSICA, ponies of, i. 52. "CORTBECK" (pigeon) of Aldrovandi, i. 209. _Corvus corone_ and _C. Cornix_, hybrids of, ii. 94. _Corydalis_, flower of, ii. 304. _Corydalis cava_, ii. 132-133. _Corydalis solida_, sterile when peloric, ii. 167. _Corydalis tuberosa_, peloric by reversion, ii. 58-59. _Corylus avellana_, i. 357. COSTA, A. , on shells transferred from England to the Mediterranean, ii. 280. "COUVE TRONCHUDA, " i. 323. COW, inheritance of loss of one horn in the, ii. 12, 23; amount of milk furnished by the, ii. 300; development of six mammæ in, ii. 317. COWSLIP, ii. 21, 182. CRACIDÆ, sterility of the, in captivity, ii. 156. CRANES, fertility of, in captivity, ii. 156. _Cratægus oxyacantha_, i. 363, ii. 18, 232, 258, 377. _Cratægus monogyna_, i. 364. _Cratægus sibirica_, i. 364. CRAWFURD, J. , Malasian cats, i. 47; horses of the Malay Archipelago, i. 49; horses of Japan, i. 53; occurrence of stripes in young wild pigs of Malacca, i. 76; on a Burmese hairy family with deficient teeth, ii. 77, 327; Japanese origin of the bantam, i. 230; game fowls of the Philippine islands, i. 232; hybrids of _Gallus varius_ and domestic fowl, i. 234; domestication of _Gallus bankiva_, i. 236; feral fowls in the Pellew islands, i. 238; history of the fowl, i. 246; history of the domestic duck, i. 277; domestication of the goose, i. 287; cultivated plants of New Zealand, i. 312; {445} breeding of tame elephants in Ava, ii. 150; sterility of _Goura coronata_ in confinement, ii. 155; geese of the Philippine islands, ii. 162. CREEPERS, a breed of fowls, i. 230. CRESTED fowl, i. 227; figured, i. 229. "CRÈVE-COEUR, " a French sub-breed of fowls, i. 229. CRISP, Dr. , on the brains of the hare and rabbit, i. 126. CROCKER, C. W. , singular form of _Begonia frigida_, i. 365-366, ii. 166; sterility in _Ranunculus ficaria_, ii. 170. CROCUS, ii. 165. CROSS-BREEDING, permanent effect of, on the female, i. 404. CROSSING, ii. 85-144, 173-192; a cause of uniformity, ii. 85-90, 173; occurs in all organised beings, ii. 90-92; some characters not blended by, ii. 92-95, 173; modifications and new races produced by, ii. 95-99; causes which check, ii. 100-109; domestication and cultivation favourable to, ii. 109-113, 189; beneficial effects of, ii. 114-131, 174-176; necessary in some plants, ii. 131-140, 175-176, 423; summary of subject of, ii. 140-144; of dogs with wolves in North America, i. 21-22; with _Canis cancrivorus_ in Guiana, i. 23; of dog with wolf, described by Pliny and others, i. 24; characters furnished by, brought out by reversion in the progeny, ii. 34-36; a direct cause of reversion, ii. 39-47, 48; a cause of variability, ii. 264-267. CRUSTACEA, macrourous, differences in the development of the, ii. 368. CRUSTACEAN with an antenna-like development of the eye-peduncle, ii. 391. CRYPTOGAMIC plants, bud-variation in, i. 383. CUBA, wild dogs of, i. 27. "CUCKOO, " sub-breeds of fowls, i. 244. CUCUMBER, variation in number of carpels of, i. 359; supposed crossing of varieties of the, i. 400. _Cucumis momordica_, i. 360. _Cucumis sativa_, i. 359. _Cucurbita_, dwarf, correlation of leaves in, ii. 330. _Cucurbita maxima_, i. 357, 359. _Cucurbita moschata_, i. 357, 359. _Cucurbita pepo_, i. 357, ii. 108; varieties of, i. 358; relation in size and number of fruit of, ii. 343. CUCURBITACEÆ, i. 357-360; supposed crossing of, i. 399; Naudin's observations on hybrids of, ii. 172; acclimatisation of, ii. 313. "CULBUTANTS" (pigeons), i. 150. CULTIVATION of plants, origin of, among savages, i. 309-310; fertility increased by, ii. 111-113. CUNIER, on hereditary night-blindness, ii. 9. CURRANTS, of Tierra del Fuego, i. 309; bud-variation in, i. 376. CURTIS, Mr. , bud-variation in the rose, i. 381. CUVIER, on the gestation of the wolf, i. 29; the odour of the jackal, an obstacle to domestication, i. 30; differences of the skull in dogs, i. 34; external characters of dogs, i. 35; elongation of the intestines in domestic pigs, i. 73, ii. 303; fertility of the hook-billed duck, i. 277; number of digits, ii. 13; hybrid of ass and zebra, ii. 42; breeding of animals in the Jardin des Plantes, ii. 149; sterility of predaceous birds in captivity, ii. 154; facility of hybridisation in confinement, ii. 160. CYANOSIS, affection of fingers in, ii. 332. CYCLAMEN, bud-variation in, i. 382. _Cynara cardunculus_, ii. 34. _Cynips fecundatrix_, ii. 283. _Cynocephalus hamadryas_, ii. 153. _Cyprinus auratus_, i. 296-297. _Cyrtanthus_, ii. 139. _Cyrtopodium_, ii. 134. _Cytisus Adami_, ii. 364; its bud-variation, i. 387-389, 406, ii. 37; seedlings from, i. 388; different views of its origin, i. 389-390; experiments in crossing _C. Purpureus_ and _laburnum_ to produce, i. 389; its production by M. Adam, i. 390; discussion of origin of, i. 396. _Cytisus alpino-laburnum_, ovules and pollen of, i. 389; origin of, i. 390. _Cytisus alpinus_, i. 388. _Cytisus laburnum_, i. 387, 389, 390, 396. _Cytisus purpureo-elongatus_, ovules and pollen of, i. 389; production of, i. 390. _Cytisus purpureus_, i. 387, 388, 389, 390, 396. DAHLBOM, effects of food on hymenoptera, ii. 281. DAHLIA, i. 369-370, ii. 147; bud-variation by tubers in the, i. 385; improvement of, by selection, ii. 216; steps in cultivation of, ii. 261; effect of conditions of life on, ii. 273; correlation of form and colour in, ii. 331. DAISY, hen and chicken, i. 365; Swan River, ii. 261. DALBRET, varieties of wheat, i. 314. DALIBERT, changes in the odours of plants, ii. 274. DALLY, Dr. , on consanguineous marriages, ii. 122. DALTONISM, hereditary, ii. 9. DAMARAS, cattle of, i. 88, ii. 207-208. {446} DAMSON, i. 347. DANDOLO, Count, on silkworms, i. 301. DANIELL, fertility of English dogs in Sierra Leone, ii. 161. DANISH Middens, remains of dogs in, i. 18. DAPPLING in horses, asses, and hybrids, i. 55. DARESTE. C. , on the skull of the Polish fowl, i. 262; on the production of monstrous chickens, ii. 289; co-existence of anomalies, ii. 331; production of double monsters, ii. 340. DARVILL, Mr. , heredity of good qualities in horses, ii. 11. DARWIN, C. , on _Lepus magellanicus_, i. 112; on the wild potato, i. 330; dimorphism in the polyanthus and primrose, ii. 21. DARWIN, Dr. , improvement of vegetables by selection, ii. 204. DARWIN, Sir F. , wildness of crossed pigs, ii. 45. D'ASSO, monogynous condition of the hawthorn in Spain, i. 364. _Dasyprocta aguti_, ii. 152. Date-palm, varieties of the, ii. 256; effect of pollen of, upon the fruit of _Chamærops_, i. 299. _Datura_, ii. 38; variability in, ii. 266. _Datura lævis_ and _stramonium_, reversion in hybrids of, i. 392. _Datura stramonium_, ii. 67. DAUBENTON, variations in the number of mammæ in dogs, i. 35; proportions of intestines in wild and domestic cats, i. 48, ii. 302. DAUDIN, on white rabbits, ii. 230. DAVY, Dr. , on sheep in the West Indies, i. 98. DAWKINS and Sandford, early domestication of _Bos longifrons_ in Britain, i. 81. DEAF-MUTES, non-heredity of, ii. 22. DEAFNESS, inheritance of, ii. 78. DEBY, wild hybrids of common and musk ducks, ii. 46. DE CANDOLLE, Alph. , number and origin of cultivated plants, i. 306-307, 371; regions which have furnished no useful plants, i. 310; wild wheat, i. 312-313; wild rye and oats, i. 313; antiquity of varieties of wheat, i. 316; apparent inefficacy of selection in wheat, i. 318; origin and cultivation of maize, i. 320, ii. 307; colours of seeds of maize, i. 321; varieties and origin of the cabbage, i. 324-325; origin of the garden-pea, i. 326; on the vine, i. 332, ii. 308; cultivated species of the orange group, i. 335; probable Chinese origin of the peach, i. 337; on the peach and nectarine, i. 340, 342; varieties of the peach, i. 342; origin of the apricot, i. 344; origin and varieties of the plum, i. 345; origin of the cherry, i. 347; varieties of the gooseberry, i. 354; selection practised with forest-trees, i. 361; wild fastigate oak, i. 361; dark-leaved varieties of trees, i. 362; conversion of stamens into pistils in the poppy, i. 365; variegated foliage, i. 366; heredity of white hyacinths, i. 371, ii. 20; changes in oaks dependent on age, i. 387; inheritance of anomalous characters, ii. 19; variation of plants in their native countries, ii. 256; deciduous bushes becoming evergreen in hot climates, ii. 305; antiquity of races of plants, ii. 429. DE CANDOLLE, P. , non-variability of monotypic genera, ii. 266; relative development of root and seed in _Raphanus sativus_, ii. 343. DECAISNE, on the cultivation of the wild carrot, i. 326; varieties of the pear, i. 350; inter-crossing of strawberries, i. 351; fruit of the apple, i. 401; sterility of _Lysimachia nummularia_, ii. 170; tender variety of the peach, ii. 308. DEER, assumption of horns by female, ii. 51; imperfect development of horns in a, on a voyage, ii. 158. DEER, fallow, ii. 103. DEERHOUND. Scotch, difference in size of the sexes of, ii. 73; deterioration of, ii. 121. DEGENERATION of high-bred races, under neglect, ii. 239. DE JONGHE, J. , on strawberries, i. 352, ii. 243; soft-barked pears, ii. 231; on accumulative variation, ii. 262; resistance of blossoms to frost, ii. 306. DELAMER, E. S. , on rabbits, i. 107, 112. _Delphinium ajacis_, ii. 21. _Delphinium consolida_, ii. 20-21. _Dendrocygna viduata_, i. 182, ii. 157. DENTITION, variations of, in the horse, i. 50. DEODAR, i. 364. DESMAREST, distribution of white on dogs, i. 29; cat from the Cape of Good Hope, i. 47; cats of Madagascar, i. 47; occurrence of striped young in Turkish pigs, i. 76; French breeds of cattle, i. 80; horns of goats, i. 102; on hornless goats, ii. 315. DESOR, E. , on the Anglo-Saxon race in America, ii. 276. DESPORTES, number of varieties of roses, i. 367. DEVAY, Dr. , singular case of albinism, ii. 17; on the marriage of cousins, ii. 122; on the effects of close interbreeding, ii. 143, 263. DEVELOPMENT and metamorphosis, ii. 388-389. DEVELOPMENT, arrests of, ii. 315-318. DEVELOPMENT, embryonic, ii. 366-368. {447} D'HERVEY-Saint-Denys, L. , on the ya-mi, or imperial rice of the Chinese, ii. 205. DHOLE, fertility of the, in captivity, ii. 151. DIABETES, occurrence of, in three brothers, ii. 17. _Dianthus_, contabescent plants of, ii. 165-166; hybrid varieties of, ii. 267. _Dianthus armeria_ and _deltoides_, hybrids of, ii. 98. _Dianthus barbatus_, i. 381. _Dianthus caryophyllus_, i. 381. _Dianthus japonicus_, contabescence of female organs in, ii. 166. DICHOGAMOUS plants, ii. 90. DICKSON, Mr. , on "running" in carnations, i. 381; on the colours of tulips, i. 386. _Dicotyles torquatus_ and _labiatus_, ii. 150. DIEFFENBACH, dog of New Zealand, i. 26; feral cats in New Zealand, i. 47; polydactylism in Polynesia, ii. 14. _Dielytra_, ii. 59. DIET, change of, ii. 303-304. _Digitalis_, properties of, affected by culture, ii. 274; poison of, ii. 380. DIGITS, supernumerary, ii. 57; analogy of, with embryonic conditions, ii. 16; fusion of, ii. 341. DIMORPHIC plants, ii. 166; conditions of reproduction in, ii. 181-184. DIMORPHISM, reciprocal, ii. 90. DINGO, i. 25; variation of, in colour, i. 28; half-bred, attempting to burrow, i. 28; attraction of foxes by a female, i. 31; variations of, in confinement, ii. 263. DIOECIOUSNESS of strawberries, i. 353. DISEASES, inheritance of, ii. 7-8; family uniformity of, ii. 57; inherited at corresponding periods of life, ii. 77-80; peculiar to localities and climates, ii. 276; obscure correlations in, ii. 331-332; affecting certain parts of the body, ii. 380; occurring in alternate generations, ii. 401. DISTEMPER, fatal to white terriers, ii. 227. DISUSE and use of parts, effects of, ii. 295-303, 352-353, 418-419; in the skeleton of rabbits, i. 124-128; in pigeons, i. 171-177; in fowls, i. 270-274; in ducks, i. 284-286; in the silk-moth, i. 300-304. DIVERGENCE, influence of, in producing breeds of pigeons, i. 220. DIXON, E. S. , on the musk duck, i. 182; on feral ducks, i. 190; on feral pigeons in Norfolk Island, i. 190; crossing of pigeons, i. 192; origin of domestic fowls, i. 230; crossing of _Gallus Sonneratii_ and common fowl, i. 234; occurrence of white in the young chicks of black fowls, i. 244; Paduan fowl of Aldrovandi, i. 247; peculiarities of the eggs of fowls, i. 248; chickens, i. 249-250; late development of the tail in Cochin cocks, i. 250; comb of lark-crested fowls, i. 256; development of webs in Polish fowls, i. 259; on the voice of fowls, i. 259; origin of the duck, i. 277; ducks kept by the Romans, i. 278; domestication of the goose, i. 287; gander frequently white, i. 288; breeds of turkeys, i. 293; incubatory instinct of mongrels of non-sitting races of fowls, ii. 44; aversion of the dove-cot pigeon to pair with fancy birds, ii. 103; fertility of the goose, ii. 112; general sterility of the guans in captivity, ii. 156; fertility of geese in captivity, ii. 157; white peafowl, ii. 332. DOBELL, H. , inheritance of anomalies of the extremities, ii. 14; non-reversion to a malformation, ii. 36. DOBRIZHOFFER, abhorrence of incest by the Abipones, ii. 123. DOGS, origin of, i. 15; ancient breeds of, i. 17, ii. 429; of neolithic, bronze and iron periods in Europe, i. 18-19, ii. 427; resemblance of to various species of canidæ, i. 21; of North America compared with wolves, i. 21-22; of the West Indies, South America, and Mexico, i. 23, 31; of Guiana, i. 23; naked dogs of Paraguay and Peru, _ibid. _ and 31; dumb, on Juan Fernandez, i. 27; of Juan de Nova, i. 27; of La Plata, i. 27; of Cuba, i. 27; of St. Domingo, i. 28; correlation of colour in, i. 28-29; gestation of, i. 29-30; hairless Turkish, i. 30, ii. 227; inter-crossing of different breeds of, i. 31; characters of different breeds of, discussed, i. 34-37; degeneration of European, in warm climates, i. 36, 38; ii. 278, 305; liability to certain diseases in different breeds of, i. 36 and _note_; causes of differences of breeds discussed, i. 37-43; catching fish and crabs in New Guinea and Tierra del Fuego, i. 39; webbing of the feet in, i. 39; influence of selection in producing different breeds of, i. 39, 43; retention of original habits by, i. 182; inheritance of polydactylism in, ii. 14; feral, ii. 33; reversion in fourth generation of, ii. 34; of the Pacific Islands, ii. 87, 220, 303; mongrel, ii. 92-93; comparative facility of crossing different breeds of, ii. 102; fertility of, ii. 111, 151; inter-breeding of, ii. 120-121; selection of, among the Greeks, ii. 202, 209; among savages, ii. 206-207; unconscious selection of, ii. 211-212; valued by the Fuegians, ii. 215; climatal changes in hair of, ii. 278; production of drooping ears in, ii. 301; {448} rejection of bones of game by, ii. 303; inheritance of rudiments of limbs in, ii. 315; development of fifth toe in, ii. 317; hairless, deficiency of teeth in, ii. 326; short-faced, teeth of, ii. 345; probable analogous variation in, ii. 349; extinction of breeds of, ii. 425. DOMBRAIN, H. H. , on the auricula, ii. 346-347. DOMESTICATION, essential points in, ii. 405-406; favourable to crossing, ii. 109-110; fertility increased by, ii. 111-113, 174. DOMESTICATED animals, origin of, ii. 160-161; occasional sterility of, under changed conditions, ii. 161-162. DONDERS, Dr. , hereditary hypermetropia, ii. 8. DORKING fowl, i. 227, 261; furcula of, figured, i. 268. DORMOUSE, ii. 152. DOUBLE FLOWERS, ii. 167-168, 171-172; produced by selection, ii. 200. DOUBLEDAY, H. , cultivation of the filbert pine strawberry, i. 354. DOUGLAS, J. , crossing of white and black game-fowls, ii. 92. DOWNING, Mr. , wild varieties of the hickory, i. 310; peaches and nectarines from seed, i. 339-340; origin of the Boston nectarine, i. 340; American varieties of the peach, i. 343; North American apricot, i. 344; varieties of the plum, i. 346; origin and varieties of the cherry, i. 347-348; "twin cluster pippins, " i. 349; varieties of the apple, i. 350; on strawberries, i. 351, 353; fruit of the wild gooseberry, i. 355; effects of grafting upon the seed, ii. 26; diseases of plum and peach trees, ii. 227-228; injury done to stone fruit in America by the "weevil, " ii. 231; grafts of the plum and peach, ii. 259; wild varieties of pears, ii. 260; varieties of fruit-trees suitable to different climates, ii. 306. _Draba sylvestris_, ii. 163. DRAGON, pigeon, i. 139, 141. "DRAIJER" (pigeon), i. 156. DRINKING, effects of, in different climates, ii. 289. DROMEDARY, selection of, ii. 205-206. DRUCE, Mr. , inter-breeding of pigs, ii. 121. DU CHAILLU, fruit-trees in West Africa, i. 309. DUCHESNE on _Fragaria vesca_, i. 351, 352, 353. DUFOUR, Léon, on _Cecidomyia_ and _Misocampus_, i. 5. DUCK, musk, retention of perching habit by the, i. 182; feral hybrid of, i. 190. DUCK, penguin, hybrid of, with Egyptian goose, ii. 68. DUCK, wild, difficulty of rearing, ii. 233; effects of domestication on, ii. 278. DUCKS, breeds of, i. 276-277; origin of, i. 277; history of, _ibid. _; wild, easily tamed, i. 278-279; fertility of breeds of, when crossed, i. 279; with the plumage of _Anas boschas_, i. 280; Malayan penguin, identical in plumage with English, i. 280; characters of the breeds of, i. 281-284; eggs of, i. 281; effects of use and disuse in, i. 284-286, ii. 298; feral, in Norfolk, i. 190; Aylesbury, inheritance of early hatching by, ii. 25; reversion in, produced by crossing, ii. 40; wildness of half-bred wild, ii. 45; hybrids of, with the musk duck, ii. 45-46; assumption of male plumage by, ii. 51; crossing of Labrador and penguin, ii. 97; increased fertility of, by domestication, ii. 112; general fertility of, in confinement, ii. 157; increase of size of, by care in breeding, ii. 199; change produced by domestication in, ii. 262. DUMÉRIL, Aug. , breeding of _Siredon_ in the branchiferous stage, ii. 384. DUN-coloured horses, origin of, i. 59. DUREAU de la Malle, feral pigs in Louisiana, ii. 33; feral fowls in Africa, _ibid. _; bud-variation in the pear, i. 376; production of mules among the Romans, ii. 110. _Dusicyon sylvestris_, i. 23. DUTCH rabbit, i. 107. DUTCH roller pigeon, i. 151. DUTROCHET, pelorism in the laburnum, ii. 346. DUVAL, growth of pears in woods in France, ii. 260. DUVAL-Jouve, on _Leersia oryzoides_, ii. 91. DUVERNOY, self-impotence in _Lilium candidum_, ii. 137. DZIERZON, variability in the characters and habits of bees, i. 298. EARLE, Dr. , on colour-blindness, ii. 72, 328. EARS, of fancy rabbits, i. 106; deficiency of, in breeds of rabbits, i. 108; rudimentary, in Chinese sheep, ii. 315; drooping, ii. 301; fusion of, ii. 341. EATON, J. M. , on fancy pigeons, i. 148, 153; variability of characters in breeds of pigeons, i. 161; reversion of crossed pigeons to coloration of _Columba livia_, i. 198; on pigeon-fancying, i. 206, 215-216; on tumbler-pigeons, i. 209, ii. 242; carrier-pigeon, i. 211; effects of interbreeding on pigeons, ii. 126; properties of pigeons, ii. 197-198; death of short-faced tumblers in the egg, ii. 226; {449} Archangel pigeon, ii. 240. ECHINODERMATA, metagenesis in, ii. 367. _Ectopistes_, specific difference in number of tail-feathers in, i. 159. _Ectopistes migratorius_, sterile hybrids of, with _Turtur vulgaris_, i. 193. EDENTATA, correlation of dermal system and teeth in the, ii. 328. EDGEWORTH, Mr. , use of grass-seeds as food in the Punjab, i. 309. EDMONSTON, Dr. , on the stomach in _Larus argentatus_ and the raven, ii. 302. EDWARDS and COLIN, on English wheat in France, ii. 307. EDWARDS, W. F. , absorption of the minority in crossed races, ii. 87. EDWARDS, W. W. , occurrence of stripes in a nearly thoroughbred horse, i. 57; in foals of racehorses, i. 59. EGGS, of fowls, characters of, i. 248; variations of, in ducks, i. 281; of the silkmoth, i. 301. EGYPT, ancient dogs of, i. 17-18; ancient domestication of the pigeon in, i. 204; absence of the fowl in ancient, i. 246. EGYPTIAN goose, hybrids of, with penguin duck, i. 282. EHRENBERG, Prof. , multiple origin of the dog, i. 16; dogs of Lower Egypt, i. 25; mummies of _Felis maniculata_, i. 43. ELEMENT, male, compared to a premature larva, ii. 384. ELEMENTS of the body, functional independence of the, ii. 368-371. ELEPHANT, its sterility in captivity, ii. 150. ELK, Irish, correlations in the, ii. 333-334. ELLIOT, Sir Walter, on striped horses, i. 58; Indian domestic and wild swine, i. 66; pigeons from Cairo and Constantinople, i. 132; fantail pigeons, i. 146; Lotan tumbler pigeons, i. 150; a pigeon uttering the sound _Yahu_, i. 155; _Gallus bankiva_ in Pegu, i. 236. ELLIS, Mr. , varieties of cultivated plants in Tahiti, ii. 256. ELM, nearly evergreen Cornish variety of the, i. 363, ii. 310; foliage-varieties of the, i. 362. ELM, weeping, i. 361; not reproduced by seed, ii. 19. _Emberiza passerina_, ii. 158. EMBRYOS, similarity of, i. 12; fusion of, ii. 339. ENGEL, on _Laurus sassafras_, ii. 274. ENGLAND, domestication of _Bos longifrons_ in, i. 81; selection of horses in, in mediæval times, ii. 203; laws against the early slaughter of rams in, ii. 203. EPHEMERIDÆ, development of the, ii. 366. _Epidendrum cinnabarinum_ and _E. Zebra_, ii. 134. EPILEPSY, hereditary, ii. 8, 78. ERDT, disease of the white parts of cattle, ii. 337. ERICACEÆ, frequency of contabescence in the, ii. 165. ERICHTHONIUS, an improver of horses by selection, ii. 202. ERMAN, on the fat-tailed Kirghisian sheep, i. 98, ii. 280; on the dogs of the Ostyaks, ii. 206. _Erodium_, ii. 59. _Erythrina Crista-galli_ and _E. Herbacea_, hybrids of, ii. 265. ESQUILANT, Mr. , on the naked young of dun-coloured pigeons, i. 170. ESQUIMAUX dogs, their resemblance to wolves, i. 21; selection of, ii. 206. EUDES-DESLONGCHAMPS, on appendages under the jaw of pigs, i. 75-76. _Euonymus Japonicus_, i. 383. EUROPEAN cultivated plants, still wild in Europe, i. 307. EVANS, Mr. , on the Lotan tumbler pigeon, i. 150. EVELYN, pansies grown in his garden, i. 368. EVEREST, R. , on the Newfoundland dog in India, i. 36, ii. 305; degeneration of setters in India, i. 38; Indian wild boars, i. 66. EWES, hornless, ii. 350. EXTINCTION of domestic races, i. 221. EYES, hereditary peculiarities of the, ii. 8-10; loss of, causing microphthalmia in children, ii. 24; modification of the structure of, by natural selection, ii. 222-223; fusion of, ii. 341. EYEBROWS, hereditary elongation of hairs in, ii. 8. EYELIDS, inherited peculiarities of the, ii. 8. EYTON, Mr. , on gestation in the dog, i. 30; variability in number of vertebræ in the pig, i. 74; individual sterility, ii. 162. _Faba vulgaris_, i. 330. FABRE, observations on _Ægilops triticoides, _ i. 313. _Fagus sylvatica_, ii. 19. FAIRWEATHER, Mr. , production of double flowers from old seed, ii. 167. _Falco albidus_, resumption of young plumage by, in captivity, ii. 158. _Falco ossifragus_, ii. 230. _Falco subbuteo_, copulating in captivity, ii. 154. _Falco tinnunculus_, breeding in captivity, ii. 154. {450} FALCONER, Dr. , sterility of English bulldogs in India, i, 38; resemblance between _Sivatherium_ and Niata cattle, i. 89; selection of the silkworm in India, i. 301; fastigate apple-trees in Calcutta, i. 361; reproduction of a supernumerary thumb after amputation, ii. 14; fertility of the dhole in captivity, ii. 151; fertility of English dogs in India, ii. 161; sterility of the tiger in captivity, ii. 151; turkeys at Delhi, ii. 161; on Indian cultivated plants, ii. 165; Thibet mastiff and goat, ii. 278. FALCONS, sterility of, in captivity, ii. 153. FALKLAND Islands, horses of the, i. 52-53, 61; feral pigs of the, i. 77; feral cattle of the, i. 82, 86; feral rabbits of the, i. 112. FALLOW deer, ii. 103, 120. FANTAIL pigeons, i. 146-148, ii. 227; figured, i. 147; furcula of, figured, i. 167; history of, i. 208; absence of oil-gland in, ii. 344. FAROE Islands, pigeons of the, i. 183. FASHION, influence of, in breeding, ii. 240. FASTIGATE trees, ii. 277, 348. FAUNAS, geographical differences, of, i. 10. "FAVOURITE" bull, ii. 65, 118. FEATHERS, homologous variation in, ii. 325. FEET, of pigeons, individual differences of, i. 160; correlations of external characters in, i. 170-171. FEET and beak, correlation of, in pigeons, i. 171-174. FELIDÆ, fertility of, in captivity, ii. 150. _Felis bubastes_, i. 43. _Felis caffra_, i. 44. _Felis caligulata_, i. 43. _Felis chaus_, i. 43-44. _Felis jubata_, ii. 151. _Felis lybica_, i. 44. _Felis maniculata_, i. 43. _Felis manul_, i. 45. _Felis ornata_, i. 45. _Felis sylvestris_, i. 44. _Felis torquata_, i. 45. FEMALE, affected by male element, ii. 365, 387-388. FEMALE flowers, in male panicle of maize, i. 321. FENNEL, Italian variety of, i. 326. FERAL cats, i. 47; cattle, i. 86; rabbits, i. 111-115; Guinea fowl, i. 294; animals and plants, reversion in, ii. 32-34, 47. FERGUSON, Mr. , supposed plurality of origin of domestic fowls, i. 231; chickens of black game-fowls, i. 244; relative size of eggs of fowls, i. 248; yolk of eggs of game-fowls, i. 249; early pugnacity of game-cocks, i. 250; voice of the Malay fowl, i. 259; effects of interbreeding on fowls, ii. 124; selection in Cochin China fowls, ii. 196; on fashion in poultry, ii. 240. FERNANDEZ, on Mexican dogs, i. 23. FERNS, reproduction of abnormal forms of, by spores, i. 383; non-diffusion of cell-gemmules in, ii. 379. FERRETS, ii. 111, 151, 206. FERTILISATION, artificial, of the St. Valery apple, i. 350. FERTILITY, various degrees of, in sheep, i. 97; unlimited mutual, of breeds of pigeons, i. 192-194; comparative of mongrels and hybrids, ii. 100-101, 178-180; influence of nourishment on, ii. 111; diminished by close interbreeding, ii. 118, 175; reduced, of Chillingham wild cattle, ii. 119; of domesticated varieties when crossed, ii. 189. _Festuca_, species of, propagated by bulblets, ii. 170. FILBERTS, spared by tomtits, ii. 231. FILIPPI, on the breeding of branchiferous tritons, ii. 384. FINCHES, general sterility of, in captivity, ii. 154. FINNIKIN (pigeon), i. 156. FINNOCHIO, i. 326. FIR, Scotch, acclimatisation of, ii. 310. FISH, Mr. , advantage of change of soil to plants, ii. 147. FISHES, regeneration of portions of fins of, ii. 15; variability of, when kept in tanks, ii. 259; marine, living in fresh water, ii. 304; double monsters of, ii. 340. FISSION and gemmation, ii. 358. FITCH, Mr. , persistency of a variety of the pea, i. 329. FITTEST, survival of the, i. 6. FITZINGER, origin of sheep, i. 94; African maned sheep, i. 96. FIXEDNESS of character, conditions of, discussed, ii. 62-64. FLAX, found in the Swiss lake-dwellings, i. 317; climatal difference in products of, ii. 274. FLEECE, fineness of, in Austrian merinos, ii. 197. FLEISCHMANN, on German sheep crossed with merinos, ii. 88-89. "FLORENTINER-TAUBE, " i. 142-143. FLOUNDER, ii. 53. FLOURENS, crossing of wolf and dog, i. 32; prepotency of the jackal over the dog, ii. 67; hybrids of the horse and ass, ii. 68; breeding of monkeys in Europe, ii. 153. {451} FLOWER-GARDEN, earliest known, in Europe, ii. 217. FLOWERS, capricious transmission of colour-varieties in, ii. 20-21; tendency to uniformity in striped, ii. 70; scorching of, dependent on colour, ii. 229; change in, caused by conditions of life, ii. 273; rudimentary, ii. 316; relative position of, to the axis, ii. 345. FOETATION, abdominal, ii. 294. FOLEY, Mr. , wild varieties of pears, ii. 260. FOLIAGE, inherited peculiarities of, i. 362; variegation, of, i. 366; bud-variation in, i. 382-384. FOOD, influence of, on the pig, i. 72; on cattle, i. 91; excess of, a cause of variability, ii. 257. FORBES, D. , on Chilian sheep, i. 95; on the horses of Spain, Chili, and the Pampas, i. 52. _Formica rufa_, ii. 251. FORTUNE, R. , sterility of the sweet potato in China, ii. 169; development of axillary bulbs in the yam, _ibid. _ FOWL, common, breeds of, i. 225-230; supposed plurality of origin, i. 230; early history of, i. 231-233; causes of production of breeds of, i. 233; origin of from _Gallus bankiva_, i. 236-239, 245; feral, notices of, i. 237-238; reversion and analogous variation in, i. 239-246, ii. 35, 38, 39, 40, 349, 350; "cuckoo" sub-breeds of, i. 244; history of, i. 246-247; structural characters of, i. 247-250; sexual peculiarities of, i. 251-257, ii. 74; external differences of, i. 257-260; differences of breeds of, from _G. Bankiva_, i. 260; osteological characters of, i. 260-270; effects of disuse of parts in, i. 270-274, ii. 298; feral, i. 190, ii. 33; polydactylism in, ii. 14; fertility of, increased by domestication, ii. 112, 167; sterility of, under certain conditions, ii. 162; influence of selection on, ii. 196, 198, 209, 210; evils of close interbreeding of, ii. 124-125; crossing of, ii. 95, 96, 97; prepotency of transmission in, ii. 67; rudimentary organs in, ii. 315; crossing of non-sitting varieties of, ii. 43-44; homology of wing and leg feathers in, ii. 323; hybrids of, with pheasants and _Gallus Sonneratii_, ii. 45; black-skinned, ii. 209-210; black, preyed upon by the osprey in Iceland, ii. 230; five-toed, mentioned by Columella, ii. 429; rumpless, tailed chickens produced by, ii. 31; Dorking, crosses of, ii. 93; form of comb and colour of plumage in, ii. 238; game, crossing of white and black, ii. 92; five-spurred, ii. 391; Spanish, liable to suffer from frost, ii. 306; Polish, peculiarities of skull of, ii. 332-333. FOX, sterility of, in captivity, ii. 151. FOX, S. Bevan, races of bees, i. 298. FOX, W. Darwin, gestation of the dog, i. 30; "Negro" cat, i. 46; reversion of sheep in colour, ii. 30; period of gestation in the pig, i. 74; young of the Himalayan rabbit, i. 109; crossing of wild and domestic turkeys, i. 292; reversion in crossed musk ducks, ii. 40; spontaneous segregation of varieties of geese, ii. 104; effects of close interbreeding upon bloodhounds, ii. 121; deafness of white cats with blue eyes, ii. 329. FOXHOUNDS, i. 40, ii. 120. _Fragaria chiloensis_, i. 351. _Fragaria collina_, i. 351. _Fragaria dioica_ of Duchesne, i. 353. _Fragaria elatior_, i. 351. _Fragaria grandiflora_, i. 351. _Fragaria vesca_, i. 351. _Fragaria virginiana_, i. 351. _Fraxinus excelsior_, i. 360, 362, ii. 19. _Fraxinus lentiscifolia_, ii. 19. FRIESLAND cattle, probably descended from _Bos primigenius_, i. 81. FRILLBACK (pigeon), i. 155; Indian, i. 153. _Fringilla ciris_, ii. 154. _Fringilla spinus_, ii. 154. FRIZZLED fowls, i. 230; horses, i. 54. FROG, polydactylism in the, ii. 14. FRUIT, seedless, ii. 168. FRUIT-TREES, varieties of, occurring wild, i. 310. FRY, Mr. , on fertile hybrid cats, i. 44; on feral fowls in Ascension, i. 238. FUCHSIAS, origin of, i. 364; bud-variation in, i. 382. _Fuchsia coccinea_ and _fulgens_, twin seed produced by crossing, i. 391. FUEGIANS, their superstition about killing young water-fowl, i. 310; selection of dogs by the, ii. 207; their comparative estimation of dogs and old women, ii. 215; their power of distant vision, ii. 223. FUNGI, parasitic, ii. 284-285. FURCULA, characters and variations of the, in pigeons, i. 167; alteration of, by disuse, in pigeons, i. 175; characters of, in fowls, i. 268. FUSION of homologous parts, ii. 393. GAIT, inheritance of peculiarities of, ii. 6. GALAPAGOS Archipelago, its peculiar fauna and flora, i. 9. _Galeobdolon luteum_, pelorism in, ii. 59, 345. {452} GALLS, ii. 282-284. GALL-GNATS, ii. 283. GALL-LIKE excrescences not inherited, ii. 23. GALLINACEOUS birds, restricted range of large, i. 237; general fertility of in captivity, ii. 155. _Gallinula chloropus_, ii. 156. _Gallinula nesiotis_, i. 287. GALTON, Mr. , fondness of savages for taming animals, i. 20, ii. 160; cattle of Benguela, i. 88; on hereditary talent, ii. 7. GALLESIO, species of oranges, i. 334, 335, 336; hybridisation of oranges, i. 336; persistency of races in the peach, i. 339; supposed specific distinctions of peach and nectarine, i. 340; Bizzaria orange, i. 391; crossing of red and white carnations, i. 393; crossing of the orange and lemon, i. 399, ii. 365; effect of foreign pollen on maize, i. 400; spontaneous crossing of oranges, ii. 91; monstrosities a cause of sterility in plants, ii. 166; seeding of ordinarily seedless fruits, ii. 168; sterility of the sugar cane, ii. 169; tendency of male flowers to become double, ii. 171; effects of selection in enlarging fruit, &c. , ii. 217; variation of the orange tree in North Italy, ii. 256; naturalisation of the orange in Italy, ii. 309. _Gallus æneus_, a hybrid of _G. Varius_ and the domestic fowl, i. 235. _Gallus bankiva_, probable original of domestic fowls, i. 233, 236-239, 245; game-fowl, nearest to, i. 226; crossed with _G. Sonneratii_, i. 234; its character and habits, i. 235-236, ii. 109; differences of various breeds of fowls from, i. 260; occipital foramen of, figured, i. 261; skull of, figured, i. 262; cervical vertebra of, figured, i. 267; furcula of, figured, i. 268; reversion to, in crossed fowls, ii. 39-40; hybrid of, with _G. Varius_, i. 235, ii. 40; number of eggs of, ii. 112. _Gallus ferrugineus_, i. 226. _Gallus furcatus_, i. 234. _Gallus giganteus_, i. 235. _Gallus Sonneratii_, characters and habits of, i. 233; hybrids of, i. 234, ii. 45. _Gallus Stanleyi_, hybrids of, i. 234. _Gallus Temminckii_, probably a hybrid, i. 235. _Gallus varius_, character and habits of, i. 234; hybrids and probable hybrids of, i. 234-235. GAMBIER, Lord, his early cultivation of the pansy, i. 368. GAME-FOWL, i. 226, 250, 251, 252. GAPES, ii. 228. GARCILAZO de la Vega, annual hunts of the Peruvian Incas, ii. 207. GARNETT, Mr. , migratory propensities of hybrid ducks, ii. 45. GARROD, Dr. , on hereditary gout, ii. 7. GASPARINI, a genus of pumpkins, founded on stigmatic characters, i. 359. GAUDICHAUD, bud-variation in the pear, i. 376; apple tree with two kinds of fruit on branch, i. 392. GAUDRY, anomalous structure in the feet of horses, i. 50. GAY, on _Fragaria grandiflora_, i. 351; on _Viola lutea_ and _tricolor_, i. 368; on the nectary of _Viola grandiflora_, i. 369. GAYAL, domestication of the, i. 82. GAYOT, _see_ Moll. GÄRTNER, on the sterility of hybrids, i. 192, ii. 101; acquired sterility of varieties of plants when crossed, i. 358; sterility in transplanted plants, and in the lilac in Germany, ii. 164; mutual sterility of blue and red flowers of the pimpernel, ii. 190; supposed rules of transmission in crossing plants, ii. 68; on crossing plants, ii. 98, 127, 130, 131; on repeated crossing, ii. 267; absorption of one species by another, when crossed, ii. 88; crossing of varieties of the pea, i. 397; crossing maize, ii. 105; crossing of species of _Verbascum_, ii. 93, 105; reversion in hybrids, ii. 36, 49, 50; of _Cereus_, i. 392; of _Tropæolum majus_ and _minus_, i. 392; variability of hybrids, ii. 265; variable hybrids from one variable parent, ii. 270; graft hybrid produced by inosculation in the vine, i. 395; effect produced by grafts on the stock, i. 394, ii. 278; tendency of hybrid plants to produce double flowers, ii. 171; production of perfect fruit by sterile hybrids, ii. 172; sexual elective affinity, ii. 180; self-impotence in _Lobelia_, _Verbascum_, _Lilium_, and _Passiflora_, ii. 136-137; on the action of pollen, ii. 108; fertilisation of _Malva_, i. 402-403, ii. 363; prepotency of pollen, ii. 187; prepotency of transmission in species of _Nicotiana_, ii. 67; bud-variation in _Pelargonium zonale_, i. 375; in _Oenothera biennis_, i. 382; in _Achillæa millefolium_, i. 408; effect of manure on the fertility of plants, ii. 163; on contabescence, ii. 165-166; inheritance of plasticity, ii. 241; villosity of plants, ii. 277. GEESE (_anseres_) general fertility of, in captivity, ii. 157. GEGENBAUR, on the number of digits, ii. 13. GEMMATION and fission, ii. 358. {453} GEMMULES, or cell-gemmules, ii. 374, 378-381, 384. GENET, fertility of the, in captivity, ii. 151. GENERATION, alternate, ii. 361, 367, 390. GENERATION, sexual, ii. 359-364. GENIUS, inheritance of, ii. 7. _Gentiana amarella_, ii. 168. GEOFFROY Saint-Hilaire, production of monstrous chickens, ii. 289; "_Loi de l'affinité de soi pour soi_, " ii. 339; compensation of growth, ii. 342. GEOFFROY Saint-Hilaire, Isid. , origin of the dog, i. 66; barking of a jackal, i. 27; period of gestation and odour of the jackal, i. 30; anomalies in the teeth of dogs, i. 34; variations in the proportions of dogs, i. 35; webbed feet of Newfoundland dogs, i. 39; crossing of domestic and wild cats, i. 44; domestication of the arni, i. 82; supposed introduction of cattle into Europe from the East, _ibid. _; absence of interdigital pits in sheep, i. 95; origin of the goat, i. 101; feral geese, i. 190; ancient history of the fowl, i. 246; skull of the Polish fowl, i. 262; preference of the Romans for the liver of white geese, i. 289; polydactylism, ii. 12; assumption of male characters by female birds, ii. 51; supernumerary mammæ in women, ii. 58; development of a proboscis in the pig, _ibid. _; transmission and blending of characters in hybrids, ii. 94; refusal of animals to breed in captivity, ii. 149; on the Guinea pig, ii. 152; silkworms producing white cocoons, ii. 199; on the carp, ii. 236; on _Helix lactea_, ii. 280; on monstrosities, ii. 254; injury to the embryo a cause of monstrosity, ii. 269; alteration in the coat of horses in coal mines, ii. 278; length of the intestines in wild and tame animals, ii. 302-303; inheritance of rudimentary limbs in the dog, ii. 315; correlation in monstrosities, ii. 320; supernumerary digits in man, ii. 322; co-existence of anomalies, ii. 331; fusion of homologous parts, ii. 341-342; presence of hairs and teeth in ovarian tumours, ii. 370; development of teeth on the palate in the horse, ii. 391. GEOGRAPHICAL differences of faunas, i. 10. GEOLOGICAL succession of organisms, i. 11. _Geranium_, ii. 59. _Geranium phæum_ and _pyrenaicum_, ii. 258. _Geranium pratense_, i. 379. GERARD, asserted climatal change in Burgundian bees, i. 297. GERARDE, on varieties of the hyacinth, i. 370. GERSTÄCKER, on hive-bees, i. 299. GERVAIS, Prof. , origin of the dog, i. 16; resemblance of dogs and jackals, i. 24; taming of the jackal, i. 26; number of teeth in dogs, i. 34; breeds of dogs, i. 36; on tertiary horses, i. 51; biblical notices of horses, i. 55; species of _Ovis_, i. 94; wild and domestic rabbits, i. 103; rabbits from Mount Sinai and Algeria, i. 105; earless rabbits, i. 108; batrachia with doubled limbs, ii. 391. GESTATION, period of, in the dog, wolf, &c, i. 29-30; in the pig, i. 74; in cattle, i. 87, ii. 321; in sheep, i. 97. GESTURES, inheritance of peculiarities in, ii. 6. "GHOONDOOKS" a sub-breed of fowls, i. 229. GHOR-KHUR, ii. 42. GILES, Mr. , effect of cross-breeding in the pig, i. 404. GIRAFFE, co-ordination of structure of, ii. 221. GIRARD, period of appearance of permanent teeth in dogs, i. 35. GIROU de Buzareingues, inheritance in the horse, ii. 10; reversion by age in cattle, ii. 38; prepotency of transmission of character in sheep and cattle, ii. 66; on crossing gourds, ii. 108. GISBURNE, wild cattle at, i. 84. _Gladiolus_, i. 364; self-impotence of hybrids of, ii. 139. _Gladiolus colvillii_, bud-variation in, i. 382. GLANDS, compensatory development of, ii. 300. GLASTONBURY thorn, i. 364. GLENNY, Mr. , on the _Cineraria_, ii. 200. GLOEDE, F. , on strawberries, i. 353. GLOGER, on the wings of ducks, ii. 298. "GLOUGLOU" (pigeon), i. 154. _Gloxiniæ_, peloric, i. 365, ii. 167. GMELIN, on red cats, at Tobolsk, i. 47. GOAT, i. 101-102, ii. 33; polydactylism in the, ii. 14; sexual differences in horns of, ii. 73; valued by South Africans, ii. 207; Thibet, ii. 278; amount of milk and development of udders in the, ii. 300; hornless, rudimentary bony cores in, ii. 316; Angora, ii. 326. GODRON, odour of the hairless Turkish dog, i. 30; differences in the skull of dogs, i. 34; increase of breeds of horses, i. 51; crossing of domestic and wild swine, i. 66; on goats, i. 101-102; colour of the skin in fowls, i. 258; bees of north and south of France, i. 297; introduction of the silkworm into Europe, i. 300; variability in the silkworm, i. 304; supposed species of wheat, i. 312-314; on _Ægilops triticoides_, i. 313; variable presence of barbs in grasses, i. 314; {454} colours of the seeds of maize, i. 321; unity of character in cabbages, i. 323; correlation of colour and odour, i. 325; effect of heat and moisture on the cabbage, i. 325; on the cultivated species of _Brassica_, i. 325; on the Rouncival and sugar peas, i. 327; variation in the numbers of peas in the same pod, i. 328; wild vines in Spain, i. 332; on raising peaches from seed, i. 339; supposed specific distinctness of peach and nectarine, i. 340; nectarine producing peaches, i. 341; on the flower of _Corydalis_, i. 344; origin and variations of the plum, i. 345; origin of the cherry, i. 347; reversion of single-leaved strawberries, i. 353; five-leaved variety of _Fragaria collina_, i. 353; supposed immutability of specific characters, i. 358-359; varieties of _Robinia_, i. 361; permanency of the simple-leaved ash, i. 362; non-inheritance of certain mutilations, ii. 23; wild turnips, carrots, and celery, ii. 33; pre-potency of a goat-like ram, ii. 66; benefit of change of soil to plants, ii. 146; fertility of peloric flowers of _Corydalis solida_, ii. 167; seeding of ordinarily seedless fruit, ii. 168; sexual sterility of plants propagated by buds, &c. , ii. 169; increase of sugar in beet-root, ii. 201; effects of selection in enlarging particular parts of plants, ii. 217; growth of the cabbage in the tropics, ii. 277; rejection of bitter almonds by mice, ii. 232; influence of marshy pasture on the fleece of sheep, ii. 278; on the ears of ancient Egyptian pigs, ii. 301; primitive distinctness of species, ii. 415; solid hoofed swine, ii. 429. GOETHE, on compensation of growth, ii. 342. GOLDFISH, i. 296-297, ii. 236. GOMARA, on South American cats, i. 46. GONGORA, number of seeds in the, ii. 379. GOOSE, ancient domestication of, i. 287; sacred to Juno in Rome, _ibid. _; inflexibility of organisation of, i. 288; skull perforated in tufted, i. 288; characters of breeds and sub-breeds of, i. 288-289; variety of, from Sebastopol, i. 289, ii. 392; feral in La Plata, i. 190; Egyptian, hybrid of, with penguin duck, ii. 68; spontaneous segregation of varieties of, ii. 104; fertility of, increased by domestication, ii. 112; decreased fertility of, in Bogota, ii. 161; sterility of, in the Philippine Islands, ii. 162; selection of, ii. 204; white, preference of the Romans for the liver of, ii. 209; persistency of character in, ii. 254; Egyptian, change in breeding season of, ii. 304. GOOSEBERRY, i. 354-356; bud-variation in the, i. 376; Whitesmith's, ii. 232. GÖPPERT, on monstrous poppies, ii. 166. GOSSE, P. H. , feral dogs in Jamaica, i. 28; feral pigs of Jamaica, i. 77-78; feral rabbits of Jamaica, i. 112; on _Columba leucocephala_, i. 183; feral Guinea fowl in Jamaica, i. 190; reproduction of individual peculiarities by gemmation in a coral, i. 374; frequency of striped legs in mules, ii. 42. GOULD, Dr. , on hereditary hæmorrhage, ii. 7. GOULD, John, origin of the turkey, i. 292. _Goura coronata_ and _Victoriæ_, hybrids of, i. 194, ii. 155. GOURDS, i. 357; crossing of varieties of, ii. 108; ancient Peruvian variety of, ii. 429. GOUT, inheritance of, ii. 7; period of appearance of, ii. 77. GRABA, on the pigeon of the Faroe islands, i. 183. GRAFTING, ii. 147; effects of, ii. 259, 278; upon the stock, i. 394-395; upon the variability of trees, ii. 259; changes analogous to bud-variation produced by, i. 387, 389. GRAFT-HYBRIDS, i. 390-391, 394-397, ii. 364-365. GRAPES, bud-variation in, i. 375; cross of white and purple, i. 393; green, liable to disease, ii. 336; effect of foreign pollen on, i. 400. GRASSES, seeds of, used as food by savages, i. 307-309. GRAY, Asa, superior wild varieties of fruit-trees, i. 310; cultivated native plants of North America, i. 312, 357; non-variation of weeds, i. 317; supposed spontaneous crossing of pumpkins, i. 399; pre-ordination of variation, ii. 432; progeny of husked form of maize, i. 320; wild intermediate forms of strawberries, i. 352. GRAY, G. R. , on _Columba gymnocyclus_, i. 184. GRAY, J. E. , on _Sus pliciceps_, i. 70; on a variety of the gold-fish, i. 297; hybrids of the ass and zebra, ii. 42-43; on the breeding of animals at Knowsley, ii. 149; on the breeding of birds in captivity, ii. 157. GREENE, J. Reay, on the development of the echinodermata, ii. 367. GREENHOW, Mr. , on a Canadian web-footed dog, i. 39. GREENING, Mr. , experiments on _Abraxas grossulariata_, ii. 280. GREGSON, Mr. , experiments on _Abraxas grossulariata_, ii. 280. GREY, Sir George, preservation of seed-bearing plants by the Australian savages, i. 310; {455} detestation of incest by Australian savages, ii. 123. GREYHOUNDS, sculptured on Egyptian monuments, and in the Villa of Antoninus, i. 17; modern breed of, i. 41; crossed with the bulldog, by Lord Orford, ii. 95; co-ordination of structure of, due to selection, ii. 221-222; Italian, ii. 227. GREYNESS, inherited at corresponding periods of life, ii. 77. GRIEVE, Mr. , on early-flowering dahlias, i. 370. GRIGOR, Mr. , acclimatisation of the Scotch fir, ii. 310. GROOM-NAPIER, C. O. , on the webbed feet of the otter-hound, i. 40. "GROSSES-GORGES" (pigeons), i. 137. GROUND-TUMBLER, Indian, i. 150. GROUSE, fertility of, in captivity, ii. 156. GRÖNLAND, hybrids of _Ægilops_ and wheat, ii. 110. _Grus montigresia_, _cinerea_, and _Antigone_, ii. 156. GUANACOS, selection of, ii. 207. GUANS, general fertility of, in captivity, ii. 156. GUELDER-ROSE, ii. 185. GUELDERLAND fowls, i. 230. GUIANA, selection of dogs by the Indians of, ii. 206. GUINEA FOWL, i. 294; feral in Ascension, and Jamaica, i. 190, ii. 33; indifference of to change of climate, ii. 161. GUINEA pig, ii. 24, 152. GÜLDENSTADT, on the jackal, i. 25. GULL, herring, breeding in confinement, ii. 157. GULLS, general sterility of, in captivity, ii. 157. _Gulo_, sterility of, in captivity, ii. 152. GÜNTHER, A. , on tufted ducks and geese, i. 274; on the regeneration of lost parts in batrachia, ii. 15. GURNEY, Mr. , owls breeding in captivity, ii. 154; appearance of "black-shouldered" among ordinary peacocks, i. 291. HABIT, influence of, in acclimatisation, ii. 312-315. HABITS, inheritance of, ii. 395. HÄCKEL, on cells, ii. 370; on the double reproduction of medusæ, ii. 384; on inheritance, ii. 397. HACKLES, peculiarities of, in fowls, i. 254. HAIR, on the face, inheritance of, in man, ii. 4; peculiar lock of, inherited, ii. 5; growth of, under stimulation of skin, ii. 326; homologous variation of, ii. 325; development of, within the ears and in the brain, ii. 391. HAIR and teeth, correlation of, ii. 326-328. HAIRY family, corresponding period of inheritance in, ii. 77. HALF-CASTES, character of, ii. 46. HALF-LOP rabbits, figured and described, i. 107-108; skull of, i. 119. _Haliætus leucocephalus_, copulating in captivity, ii. 154. HALLAM, Col. , on a two-legged race of pigs, ii. 4. HAMBURGH fowl, i. 227, 261; figured, i. 228. HAMILTON, wild cattle of, i. 84. HAMILTON, Dr. , on the assumption of male plumage by the hen pheasant, ii. 51. HAMILTON, F. Buchanan, on the shaddock, i. 335; varieties of Indian cultivated plants, ii. 256. HANCOCK, Mr. , sterility of tamed birds, ii. 155-157. HANDWRITING, inheritance of peculiarities in, ii. 6. HANMER, Sir J. , on selection of flower seeds, ii. 204. HANSELL, Mr. , inheritance of dark yolks in duck's eggs, i. 281. HARCOURT, E. V. , on the Arab boar-hound, i. 17; aversion of the Arabs to dun-coloured horses, i. 55. HARDY, Mr. , effect of excess of nourishment on plants, ii. 257. HARE, hybrids of, with rabbit, i. 105; sterility of the, in confinement, ii. 152; preference of, for particular plants, ii. 232. HARE-LIP, inheritance of, ii. 24. HARLAN, Dr. , on hereditary diseases, ii. 7. HARMER, Mr. , on the number of eggs in a codfish, ii. 379. HARVEY, Mr. , monstrous red and white African bull, i. 91. HARVEY, Prof. , singular form of _Begonia frigida_, i. 365-366; effects of cross-breeding on the female, i. 404; monstrous saxifrage, ii. 166. HASORA wheat, i. 313. HAUTBOIS strawberry, i. 353. HAWKER, Col. , on call or decoy ducks, i. 281. HAWTHORN, varieties of, i. 360-364; pyramidal, i. 361; pendulous hybridised, ii. 18; changes of, by age, i. 364, 387; bud-variation in the, i. 377; flower buds of, attacked by bullfinches, ii. 232. HAYES, Dr. , character of Esquimaux dogs, i. 21-22. HAYWOOD, W. , on the feral rabbits of Porto Santo, i. 114. HAZEL, purple-leaved, i. 362, 395, ii. 330. HEAD of wild boar and Yorkshire pig, figured, i. 72. {456} HEAD and limbs, correlated variability of, ii. 323. HEADACHE, inheritance of, ii. 79. HEARTSEASE, i. 368-369; change produced in the, by transplantation, i. 386; reversion in, ii. 31, 47; effects of selection on, ii. 200; scorching of, ii. 229; effects of seasonal conditions on the, ii. 274; annual varieties of the, ii. 305. HEAT, effect of, upon the fleece of sheep, i. 98. HEBER, Bishop, on the breeding of the rhinoceros in captivity, ii. 150. HEBRIDES, cattle of the, i. 80; pigeons of the, i. 183. HEER, O. , on the plants of the Swiss lake-dwellings, i. 309, ii. 215, 427; on the cereals, i. 317-319; on the peas, i. 326; on the vine growing in Italy in the bronze age, i. 332. _Helix lactea_, ii. 280. _Hemerocallis fulva_ and _flava_, interchanging by bud-variation, i. 386. HEMLOCK yields no conicine in Scotland, ii. 274. HEMP, differences of, in various parts of India, ii. 165; climatal difference in products of, ii. 274. HEMPSEED, effect of, upon the colour of birds, ii. 280. HERMAPHRODITE flowers, occurrence of, in Maize, i. 321. HEN, assumption of male characters by the, ii. 51, 54; development of spurs in the, ii. 318. "HENNIES, " or hen-like male fowls, i. 252. HENRY, T. A. , a variety of the ash produced by grafting, i. 394; crossing of species of _Rhododendron_ and _Arabis_, i. 400. HENSLOW, Prof. , individual variation in wheat, i. 314; bud-variation in the Austrian bramble rose, i. 381; partial reproduction of the weeping ash by seed, ii. 19. HEPATICA, changed by transplantation, i. 386. HERBERT, Dr. , variations of _Viola grandiflora_, i. 368; bud-variation in camellias, i. 377; seedlings from reverted _Cytisus Adami_, i. 388; crosses of Swedish and other turnips, ii. 93; on hollyhocks, ii. 107; breeding of hybrids, ii. 131; self-impotence in hybrid hippeastrums, ii. 138-139; hybrid _Gladiolus_, ii. 139; on _Zephyranthes candida_, ii. 164; fertility of the crocus, ii. 165; on contabescence, ii. 165; hybrid _Rhododendron_, ii. 265. HERCULANEUM, figure of a pig found in, i. 67. HERON, Sir R. , appearance of "black-shouldered" among ordinary peacocks, i. 290-291; non-inheritance of monstrous characters by goldfish, i. 296; crossing of white and coloured Angora rabbits, ii. 92; crosses of solid-hoofed pigs, ii. 93. _Herpestes fasciatus_ and _griseus_, ii. 151. HEUSINGER, on the sheep of the Tarentino, ii. 227; on correlated constitutional peculiarities, ii. 337. HEWITT, Mr. , reversion in bantam cocks, i. 240; degeneration of silk fowls, i. 243; partial sterility of hen-like male fowls, i. 252; production of tailed chickens by rumpless fowls, i. 259; on taming and rearing wild ducks, i. 278-279, ii. 233, 262-263; conditions of inheritance in laced Sebright bantams, ii. 22; reversion in rumpless fowls, ii. 31; reversion in fowls by age, ii. 39; hybrids of pheasant and fowl, ii. 45, 68; assumption of male characters by female pheasants, ii. 51; development of latent characters in a barren bantam hen, ii. 54; mongrels from the silk-fowl, ii. 67; effects of close interbreeding on fowls, ii. 124-125; on feathered-legged bantams, ii. 323. HIBBERT, Mr. , on the pigs of the Shetland Islands, i. 70. HIGHLAND cattle, descended from _Bos longifrons_, i. 81. HILDEBRAND, Dr. , on the fertilisation of _Orchideæ_, i. 402-403; occasional necessary crossing of plants, ii. 90; on _Primula sinensis_ and _Oxalis rosea_, ii. 132; on _Corydalis cava_, ii. 132-133. HILL, R. , on the Alco, i. 31; feral rabbits in Jamaica, i. 112; feral peacocks in Jamaica, i. 190; variation of the Guinea fowl in Jamaica, i. 294; sterility of tamed birds in Jamaica, ii. 155, 157. HIMALAYA, range of gallinaceous birds in the, i. 237. HIMALAYAN rabbit, i. 107, 108-111; skull of, i. 120. HIMALAYAN sheep, i. 95. HINDMARSH, Mr. , on Chillingham cattle, i. 84. "HINKEL-TAUBE, " i. 142-143. HINNY and mule, difference of, ii. 67-68. _Hipparion_, anomalous resemblance to in horses, i. 50. _Hippeastrum_, hybrids of, ii. 138-139. HIVE-BEES, ancient domestication of, i. 297; breeds of, i. 298; smaller when produced in old combs, i. 297; variability in, i. 298; crossing of Ligurian and common, i. 299. "HOCKER-TAUBE, " i. 141. HOBBS, Fisher, on interbreeding pigs, ii. 121. HODGKIN, Dr. , on the attraction of foxes by a female Dingo, i. 31; {457} origin of the Newfoundland dog, i. 42; transmission of a peculiar lock of hair, ii. 5. HODGSON, Mr. , domestication of _Canis primævus_, i. 26; development of a fifth digit in Thibet mastiffs, i. 35; number of ribs in humped cattle, i. 79; on the sheep of the Himalaya, i. 95; presence of four mammæ in sheep, _ibid. _; arched nose in sheep, i. 96; measurements of the intestines of goats, i. 102; presence of interdigital pits in goats, _ibid. _; disuse a cause of drooping ears, ii. 301. HOFACKER, persistency of colour in horses, i. 51, ii. 21; production of dun horses from parents of different colours, i. 59; inheritance of peculiarities in handwriting, ii. 6; heredity in a one-horned stag, ii. 12; on consanguineous marriages, ii. 123. HOG, Red River, ii. 150. HOGG, Mr. , retardation of breeding in cows by hard living, ii. 112. HOLLAND, Sir H. , necessity of inheritance, ii. 2; on hereditary diseases, ii. 7; hereditary peculiarity in the eyelid, ii. 8; morbid uniformity in the same family, ii. 17; transmission of hydrocele through the female, ii. 52; inheritance of habits and tricks, ii. 395. HOLLY, varieties of the, i. 360, 362; bud-reversion in, i. 384; yellow-berried, ii. 19, 230. HOLLYHOCK, bud-variation in, i. 378; non-crossing of double varieties of, ii. 107; tender variety of the, ii. 310. HOMER, notice of Geese, i. 287; breeding of the horses of Æneas, ii. 202. HOMOLOGOUS parts, correlated variability of, ii. 322-331, 354-355; fusion of, ii. 393; affinity of, ii. 339-342. HOOFS, correlated with hair in variation, ii. 325. HOOK-BILLED DUCK, skull figured, i. 282. HOOKER, Dr. J. D. , forked shoulder-stripe in Syrian asses, i. 63; voice of the cock in Sikkim, i. 259; use of Arum-roots as food, i. 307; native useful plants of Australia, i. 311; wild walnut of the Himalayas, i. 356; variety of the plane tree, i. 362; production of _Thuja orientalis_ from seeds of _T. Pendula_, i. 362; singular form of _Begonia frigida_, i. 365; reversion in plants run wild, ii. 33; on the sugar-cane, ii. 169; on Arctic plants, ii. 256; on the oak grown at the Cape of Good Hope, ii. 274; on _Rhododendron ciliatum_, ii. 277; stock and mignonette, perennial in Tasmania, ii. 305. HOPKIRK, Mr. , bud-variation in the rose, i. 381; in _Mirabilis jalapa_, i. 382; in _Convolvulus tricolor_, i. 408. HORNBEAM, heterophyllous, i. 362. HORNED fowl, i. 229; skull figured, i. 265. HORNLESS cattle in Paraguay, i. 89. HORNS of sheep, i. 95; correlation of, with fleece in sheep, ii. 326; correlation of, with the skull, ii. 333; rudimentary in young polled cattle, ii. 315; of goats, i. 102. HORSES, in Swiss lake-dwellings, i. 49; different breeds of, in Malay Archipelago, i. 49; anomalies in osteology and dentition of, i. 50; mutual fertility of different breeds, i. 51; feral, i. 51; habit of scraping away snow, i. 53; mode of production of breeds of, i. 54; inheritance and diversity of colour in, i. 55; dark stripes in, i. 56-61, ii. 351; dun-coloured, origin of, i. 59; colours of feral, i. 60-61; effect of fecundation by a Quagga on the subsequent progeny of, i. 403-404; inheritance of peculiarities in, ii. 10-11; polydactylism in, ii. 14; inheritance of colour in, ii. 21; inheritance of exostoses in legs of, ii. 23; reversion in, ii. 33, 41; hybrids of, with ass and zebra, ii. 42; prepotency of transmission in the sexes of, ii. 65; segregation of, in Paraguay, ii. 102; wild species of, breeding in captivity, ii. 150; curly, in Paraguay, ii. 205, 325; selection of, for trifling characters, ii. 209; unconscious selection of, ii. 212-213; natural selection in Circassia, ii. 225; alteration of coat of, in coal-mines, ii. 278; degeneration of, in the Falkland Islands, ii. 278; diseases of, caused by shoeing, ii. 300; feeding on meat, ii. 305; white and white-spotted, poisoned by mildewed vetches, ii. 337; analogous variations in the colour of, ii. 349; teeth developed on palate of, ii. 391; of bronze period in Denmark, ii. 427. HORSE-CHESNUT, early, at the Tuileries, i. 362; tendency to doubleness in, ii. 168. HORSE-RADISH, general sterility of the, ii. 170. "HOUDAN, " a French sub-breed of fowls, i. 229. HOWARD, C. , on an Egyptian monument, i. 17; on crossing sheep, ii. 95, 120. HUC, on the Emperor Khang-hi, ii. 205; Chinese varieties of the bamboo, ii. 256. HUMBOLDT, A. , character of the Zambos, ii. 47; parrot speaking the language of an extinct tribe, ii. 154; on _Pulex penetrans_, ii. 275. HUMIDITY, injurious effect of, upon horses, i. 53. HUMPHREYS, Col. , on Ancon sheep, i. 100. HUNGARIAN cattle, i. 80. {458} HUNTER, John, period of gestation in the dog, i. 29; on secondary sexual characters, i. 179; fertile crossing of _Anser ferus_ and the domestic goose, i. 288; inheritance of peculiarities in gestures, voice, &c. , ii. 6; assumption of male characters by the human female, ii. 51; period of appearance of hereditary diseases, ii. 78; graft of the spur of a cock upon its comb, ii. 296; on the stomach of _Larus tridentatus_, ii. 302; double-tailed lizards, ii. 341. HUNTER, W. , evidence against the influence of imagination upon the offspring, ii. 264. HUTTON, Capt. , on the variability of the silk moth, i. 303; on the number of species of silkworms, i. 300; markings of silkworms, i. 302; domestication of the rock-pigeon in India, i. 185; domestication and crossing of _Gallus bankiva_, i. 236. HUTCHINSON, Col. , liability of dogs to distemper, i. 35. HUXLEY, Prof. , on the transmission of polydactylism, ii. 13; on unconscious selection, ii. 194; on correlation in the mollusca, ii. 320; on gemmation and fission, ii. 359; development of star-fishes, ii. 366. HYACINTHS, i. 370-371; bud-variation in, i. 385; graft-hybrid by union of half bulbs of, i. 395; white, reproduced by seed, ii. 20; red, ii. 229, 336; varieties of, recognisable by the bulb, ii. 251. HYACINTH, feather, ii. 185, 316. _Hyacinthus orientalis_, i. 370. _Hybiscus syriacus_, ii. 286. HYBRIDS, of hare and rabbit, i. 105; of various species of _Gallus_, i. 234-236; of almond, peach, and nectarine, i. 339; naturally produced, of species of _Cytisus_, i. 390; from twin-seed of _Fuchsia coccinea_ and _fulgens_, i. 391; reversion of, i. 392-394, ii. 36, 48-50; from mare, ass, and zebra, ii. 42; of tame animals, wildness of, ii. 44-46; female instincts of sterile male, ii. 52; transmission and blending of characters in, ii. 92-95; breed better with parent species than with each other, ii. 131; self-impotence in, ii. 138-140; readily produced in captivity, ii. 151. HYBRIDISATION, singular effects of, in oranges, i. 336; of cherries, i. 347; difficulty of, in _Cucurbitæ_, i. 358; of roses, i. 366. HYBRIDISM, ii. 178-191; the cause of a tendency to double flowers, ii. 171; in relation to pangenesis, ii. 385. HYBRIDITY in cats, i. 44-45; supposed of peach and nectarine, i. 342. _Hydra_, i. 374, ii. 293, 359. HYDRANGEA, colour of flowers of, influenced by alum, ii. 277. HYDROCELE, ii. 52. HYDROCEPHALUS, ii. 295. _Hypericum calycinum_, ii. 170. _Hypericum crispum_, ii. 227, 337. HYPERMETAMORPHOSIS, ii. 367. HYPERMETROPIA, hereditary, ii. 8. ICHTHYOPTERYGIA, number of digits in the, ii. 16. _Ilex aquifolium_, ii. 19. IMAGINATION, supposed effect of, on offspring, ii. 263. _Imatophyllum miniatum_, bud-variation in, i. 385. INCEST, abhorred by savages, ii. 123-124. INCUBATION, by crossed fowls of non-sitting varieties, ii. 43-44. INDIA, striped horses of, i. 58; pigs of, i. 66, 67, 76; breeding of rabbits in, i. 112; cultivation of pigeons in, i. 205-206. INDIVIDUAL variability in pigeons, i. 158-160. INGLEDEW, Mr. , cultivation of European vegetables in India, ii. 169. "INDISCHE Taube, " ii. 144. INHERITANCE, ii. 1-84, 371-373, 395, 397-402; doubts entertained of by some writers, ii. 3; importance of to breeders, 3-4; evidence of, derived from statistics of chances, 5; of peculiarities in man, 5-7, 12-16; of disease, 7-8, 17; of peculiarities in the eye, 8-10; of deviations from symmetry, 12; of polydactylism, 12-16; capriciousness of, 17-22, 27; of mutilations, 22-24; of congenital monstrosities, 24; causes of absence of, 24-26; by reversion or atavism, 28-61; its connexion with fixedness of character, 62-64; affected by prepotency of transmission of character, 65-71; limited by sex, 71-75; at corresponding periods of life, 75-80; summary of the subject of, 80-84; laws of, the same in seminal and bud varieties, i. 409; of characters in the horse, i. 10-11; in cattle, i. 87; in rabbits, i. 107; in the peach, i. 339; in the nectarine, i. 340; in plums, i. 347; in apples, i. 350; in pears, i. 351; in the pansy, i. 369; of primary characters of _Columba livia_ in crossed pigeons, i. 201; of peculiarities of plumage in pigeons, i. 160-161; of peculiarities of foliage in trees, i. 362; effects of, in varieties of the cabbage, i. 325. INSANITY, inheritance of, ii. 7, 78. INSECTS, regeneration of lost parts in, ii. 15, 294; agency of, in fecundation of larkspurs, ii. 21; effect of changed conditions upon, ii. 157; sterile neuter, ii. 186-187; {459} monstrosities in, ii. 269, 391. INSTINCTS, defective, of silkworms, i. 304. INTERBREEDING, close, ill effects of, ii. 114-131, 175. INTERCROSSING, of species, as a cause of variation, i. 188; natural, of plants, i. 336; of species of Canidæ and breeds of dogs, i. 31-33; of domestic and wild cats, i. 44-45; of breeds of pigs, i. 71, 78; of cattle, i. 83; of varieties of cabbage, i. 324; of peas, i. 326, 329-330; of varieties of orange, i. 336; of species of strawberries, i. 351-352; of _Cucurbitæ_, i. 357-358; of flowering plants, i. 364; of pansies, i. 368. INTERDIGITAL pits, in goats, i. 102. INTERMARRIAGES, close, ii. 122-123. INTESTINES, elongation of, in pigs, i. 73; relative measurements of parts of, in goats, i. 102; effects of changed diet on, ii. 302. _Ipomoea purpurea_, ii. 128. IRELAND, remains of _Bos frontosus_ and _longifrons_ found in, i. 81. IRIS, hereditary absence of the, ii. 9; hereditary peculiarities of colour of the, ii. 9-10. IRISH, ancient, selection practised by the, ii. 203. IRON period, in Europe, dog of, i. 18. ISLANDS, oceanic, scarcity of useful plants on, i. 311. ISLAY, pigeons of, i. 183. ISOLATION, effect of, in favour of selection, ii. 233-234. ITALY, vine growing in, during the bronze period, i. 332. IVY, sterility of, in the north of Europe, ii. 170. JACK, Mr. , effect of foreign pollen on grapes, i. 400. JACKAL, i. 24, 27, 30; hybrids of, with the dog, i. 32; prepotency of, over the dog, ii. 67. JACOBIN pigeon, i. 154, 208. JACQUEMET-BONNEFORT, on the mulberry, i. 334. JAGUAR, with crooked legs, i. 17. JAMAICA, feral dogs of, i. 28; feral pigs of, i. 77; feral rabbits of, i. 112. JAPAN, horses of, i. 53. JAPANESE pig (figured), i. 69. JARDINE, Sir W. , crossing of domestic and wild cats, i. 44. JARVES, J. , silkworm in the Sandwich islands, i. 301. JAVA, Fantail pigeon in, i. 148. JAVANESE ponies, i. 53, 59. JEMMY BUTTON, i. 309. JENYNS, L. , whiteness of ganders, i. 288; sunfish-like variety of the goldfish, i. 297. JERDON, J. C. , number of eggs laid by the pea-hen, ii. 112; origin of domestic fowl, i. 237. JERSEY, arborescent cabbages of, i. 323. JESSAMINE, i. 394. JEITTELES, Hungarian sheep-dogs, i. 24; crossing of domestic and wild cats, i. 44. JOHN, King, importation of stallions from Flanders by, ii. 203. JOHNSON, D. , occurrence of stripes on young wild pigs in India, i. 76. JORDAN, A. , on Vibert's experiments on the vine, i. 332; origin of varieties of the apple, i. 350; varieties of pears found wild in woods, ii. 260. JOURDAN, parthenogenesis in the silk moth, ii. 364. JUAN DE NOVA, wild dogs on, i. 27. JUAN FERNANDEZ, dumb dogs on, i. 27. _Juglans regia_, i. 356-357. JUKES, Prof. , origin of the Newfoundland dog, i. 42. JULIEN, Stanislas, early domestication of pigs in China, i. 68; antiquity of the domestication of the silk-worm in China, i. 300. JUMPERS, a breed of fowls, i. 230. JUNIPER, variations of the, i. 361, 364. _Juniperus suecica_, i. 361. _Jussiæa grandiflora_, ii. 170. JUSSIEU, A. De, structure of the pappus in _Carthamus_, ii. 316. KAIL, Scotch, reversion in, ii. 32. "KALA-PAR" pigeon, i. 142. KALES, i. 323. KALM, P. , on maize, i. 322, ii. 307; introduction of wheat into Canada, i. 315; sterility of trees growing in marshes and dense woods, ii. 170. "KALMI Lotan, " tumbler pigeon, i. 151. KANE, Dr. , on Esquimaux dogs, i. 21. KARAKOOL sheep, i. 98. KARKEEK, on inheritance in the horse, ii. 10. "KARMELITEN Taube, " i. 156. KARSTEN on _Pulex penetrans_, ii. 275. KATTYWAR horses, i. 58. KEELEY, R. , pelorism in _Galeobdolon luteum_, ii. 59. KERNER on the culture of Alpine plants, ii. 163. KESTREL, breeding in captivity, ii. 154. "KHANDÉSI, " i. 141. KHANG-HI, selection of a variety of rice by, ii. 205. KIANG, ii. 43. KIDD, on the canary bird, i. 77, ii. 275. KIDNEY Bean, i. 371; varieties of, ii. 256, 275. {460} KIDNEYS, compensatory development of the, ii. 300; fusion of the, ii. 341; shape of, in birds, influenced by the form of the pelvis, ii. 344. KING, Col. , domestication of rock doves from the Orkneys, i. 184, 185. KING, P. S. , on the Dingo, i. 21, 28. KIRBY and Spence, on the growth of galls, ii. 283. KIRGHISIAN sheep, i. 98. KITE, breeding in captivity, ii. 154. KLEINE, variability of bees, i. 298. KNIGHT, Andrew, on crossing horses of different breeds, i. 51; crossing varieties of peas, i. 326, ii. 129; persistency of varieties of peas, i. 329; origin of the peach, i. 338; hybridisation of the morello by the Elton cherry, i. 347; on seedling cherries, _ibid. _; variety of the apple not attacked by coccus, i. 349; intercrossing of strawberries, i, 351, 352; broad variety of the cock's comb, i. 365; bud variation in the cherry and plum, i. 375; crossing of white and purple grapes, i. 393; experiments in crossing apples, i. 402, ii. 129; hereditary disease in plants, ii. 11; on interbreeding, ii. 116; crossed varieties of wheat, ii. 130; necessity of intercrossing in plants, ii. 175; on variation, ii. 256, 257; effects of grafting, i. 387, ii. 278; bud-variation in a plum, ii. 289; compulsory flowering of early potatoes, ii. 343; correlated variation of head and limbs, ii. 323. KNOX, Mr. , breeding of the eagle owl in captivity, ii. 154. KOCH, degeneracy in the turnip, i. 325. KOHLRABI, i. 323. KÖLREUTER, reversion in hybrids, i. 392, ii. 36; acquired sterility of crossed varieties of plants, i. 358, ii. 101; absorption of _Mirabilis vulgaris_ by _M. Longiflora_, ii. 88; crosses of species of _Verbascum_, ii. 93, 107; on the hollyhock, ii. 107; crossing varieties of tobacco, ii. 108; benefits of crossing plants, ii. 130, 131, 175-176; self-impotence in _Verbascum_, ii. 136, 141; effects of conditions of growth upon fertility in _Mirabilis_, ii. 164; great development of tubers in hybrid plants, ii. 172; inheritance of plasticity, ii. 241; variability of hybrids of _Mirabilis_, ii. 265; repeated crossing a cause of variation, ii. 267-268; number of pollen-grains necessary for fertilization, ii. 363. "KRAUSESCHWEIN, " i. 67. KROHN, on the double reproduction of Medusæ, ii. 384. "KROPF-TAUBEN, " i. 137. LABAT, on the tusks of feral bears in the West Indies, i. 77; on French wheat grown in the West Indies, ii. 307; on the culture of the vine in the West Indies, ii. 308. LABURNUM, Adam's, see _Cytisus Adami_; oak-leaved, reversion of, i. 382; pelorism in the, ii. 346; Waterer's, i. 390. LACHMANN, on gemmation and fission, ii. 358. _Lachnanthes tinctoria_, ii. 227, 336. LACTATION, imperfect, hereditary, ii. 8; deficient, of wild animals in captivity, ii. 158. LADRONE islands, cattle of, i. 86. LAING, Mr. , resemblance of Norwegian and Devonshire cattle, i. 82. LAKE-DWELLINGS, sheep of, i. 94, ii. 427; cattle of, ii. 427; absence of the fowl in, i. 246; cultivated plants of, i. 309, ii. 427, 429; cereals of, i. 317-319; peas found in, i. 326; beans found in, i. 330. LAMARE-PIQUOT, observations on half-bred North American wolves, i. 22. LAMBERT, A. B. , on _Thuja pendula_ or _filiformis_, i. 362. LAMBERT family, ii. 4, 76. LAMBERTYE on strawberries, i. 351, 352; five-leaved variety of _Fragaria collina_, i. 353. LANDT, L. , on sheep in the Faroe islands, ii. 103. LA PLATA, wild dogs of, i. 27; feral cat from, i. 47. LARCH, ii. 310. LARKSPURS, insect agency necessary for the full fecundation of, ii. 21. _Larus argentatus_, ii. 157. _Larus tridactylus_, ii. 302. LASTERYE, merino sheep in different countries, i. 99. LATENT characters, ii. 51-56. LATHAM, on the fowl not breeding in the extreme north, ii. 161. _Lathyrus_, ii. 38. _Lathyrus aphaca_, ii. 343. _Lathyrus odoratus_, ii. 20, 91, 93, 311, 393. LA TOUCHE, J. D. , on a Canadian apple with dimidiate fruit, i. 392-393. "LATZ-TAUBE, " i. 154. LAUGHER pigeon, i. 155, 207. _Laurus sassafras_, ii. 274. LAWRENCE, J. , production of a new breed of fox-hounds, i. 40; occurrence of canines in mares, i. 50; on three-parts-bred horses, i. 54; on inheritance in the horse, ii. 10-11. LAWSON, Mr. , varieties of the potato, i. 330. LAXTON, Mr. , bud-variation in the gooseberry, i. 376; crossing of varieties of the pea, i. 397-398; {461} double-flowered peas, ii. 168. LAYARD, E. L. , resemblance of a Caffre dog to the Esquimaux breed, i. 25, ii. 286; crossing of the domestic cat with _Felis Caffra_, i. 44; feral pigeons in Ascension, i. 190; domestic pigeons of Ceylon, i. 206; on _Gallus Stanleyi_, i. 234; on black-skinned Ceylonese fowls, i. 256. LE COMPTE family, blindness inherited in, ii. 78. LECOQ, bud-variation in _Mirabilis jalapa_, i. 382; hybrids of _Mirabilis_, i. 393, ii. 169, 265; crossing in plants, ii. 127; fecundation of _Passiflora_, ii. 137; hybrid _Gladiolus_, ii. 139; sterility of _Ranunculus ficaria_, ii. 170; villosity in plants, ii. 277; double asters, ii. 316. LE COUTEUR, J. , varieties of wheat, i. 313-315; acclimatisation of exotic wheat in Europe, i. 315; adaptation of wheat to soil and climate, i. 316; selection of seed-corn, i. 318; on change of soil, ii. 147; selection of wheat, ii. 200; natural selection in wheat, ii. 233; cattle of Jersey, ii. 234. LEDGER, Mr. , on the Llama and Alpaca, ii. 208. LEE, Mr. , his early culture of the pansy, i. 368. _Leersia oryzoides_, ii. 91. LEFOUR, period of gestation in cattle, i. 87. LEGS, of fowls, effects of disuse on, i. 270-272; characters and variations of, in ducks, i. 284-288; fusion of, ii. 341. LEGUAT, cattle of the Cape of Good Hope, i. 88. LEHMANN, occurrence of wild double-flowered plants near a hot spring, ii. 168. LEIGHTON, W. A. , propagation of a weeping yew by seed, ii. 19. LEITNER, effects of the removal of anthers, ii. 167. LEMMING, ii. 152. LEMOINE, variegated _Symphytum_ and _Phlox_, i. 384. LEMON, i. 334, 335; orange fecundated by pollen of the, i. 399. LEMURS, hybrid, ii. 153. LEPORIDES, ii. 98-99, 152. LEPSIUS, figures of ancient Egyptian dogs, i. 17; domestication of pigeons in ancient Egypt, i. 204. _Leptotes_, ii. 134. _Lepus glacialis_, i. 111. _Lepus magellanicus_, i. 112. _Lepus nigripes_, i. 108. _Lepus tibetanus_, i. 111. _Lepus variabilis_, i. 111. LEREBOULLET, double monsters of fishes, ii. 340. LESLIE, on Scotch wild cattle, i. 85. LESSON, on _Lepus magellanicus_, i. 112. LEUCKART on the larva of Cecidomyidæ, ii. 360. LEWIS, G. , cattle of the West Indies, ii. 229. LHERBETTE and Quatrefages, on the horses of Circassia, ii. 102, 225. LIEBIG, differences in human blood, according to complexion, ii. 276. LIEBREICH, occurrence of pigmentary retinitis in deaf-mutes, ii. 328. LICHENS, sterility in, ii. 171. LICHTENSTEIN, resemblance of Bosjesman's dogs to _Canis mesomelas_, i. 25; Newfoundland dog at the Cape of Good Hope, i. 36. LILACS, ii. 164. LILIACEÆ, contabescence in, ii. 165. _Lilium candidum_, ii. 137. LIMBS, regeneration of, ii. 376-377. LIMBS and head, correlated variation of, ii. 323. LIME, effect of, upon shells of the mollusca, ii. 280. LIME tree, changes of by age, i. 364, 387. LIMITATION, sexual, ii. 71-75. LIMITATION, supposed, of variation, ii. 416. _Linaria_, pelorism in, ii. 58, 61, 346; peloric, crossed with the normal form, ii. 70; sterility of, ii. 166. _Linaria vulgaris_ and _purpurea_, hybrids of, ii. 94. LINDLEY, John, classification of varieties of cabbages, i. 324; origin of the peach, i. 338; influence of soil on peaches and nectarines, i. 340; varieties of the peach and nectarine, i. 343; on the New Town pippin, i. 349; freedom of the Winter Majetin apple from coccus, i. 349; production of monoecious Hautbois strawberries by bud-selection, i. 353; origin of the large tawny nectarine, i. 375; bud-variation in the gooseberry, i. 376; hereditary disease in plants, ii. 11; on double flowers, ii. 167; seeding of ordinarily seedless fruits, ii. 168; sterility of _Acorus calamus_, ii. 170; resistance of individual plants to cold, ii. 309. LINNÆUS, summer and winter wheat regarded as distinct species by, i. 315; on the single-leaved strawberry, i. 353; sterility of Alpine plants in gardens, ii. 163; recognition of individual reindeer by the Laplanders, ii. 251; growth of tobacco in Sweden, ii. 307. LINNET, ii. 158. _Linota cannabina_, ii. 158. {462} LINUM, ii. 165. LION, fertility of, in captivity, ii. 150, 151. LIPARI, feral rabbits of, i. 113. LIVINGSTONE, Dr. , striped young pigs on the Zambesi, i. 77; domestic rabbits at Loanda, i. 112; use of grass-seeds as food in Africa, i. 308; planting of fruit-trees by the Batokas, i. 309; character of half-castes, ii. 46; taming of animals among the Barotse, ii. 160; selection practised in South Africa, ii. 207, 209. LIVINGSTONE, Mr. , disuse a cause of drooping ears, ii. 301. LIZARDS, reproduction of tail in, ii. 294; with a double tail, ii. 341. LLAMA, selection of, ii. 208. LLOYD, Mr. , taming of the wolf, i. 26; English dogs in northern Europe, i. 36; fertility of the goose increased by domestication, i. 288; number of eggs laid by the wild goose, ii. 112; breeding of the capercailzie in captivity, ii. 156. LOANDA, domestic rabbits at, i. 112. _Loasa_, hybrid of two species of, ii. 98. _Lobelia_, reversion in hybrids of, ii. 392; contabescence in, ii. 166. _Lobelia fulgens_, _cardinalis_, and _syphilitica_, ii. 136. LOCKHART, Dr. , on Chinese pigeons, i. 206. LOCUST-TREE, ii. 274. LOISELEUR-DESLONGCHAMPS, originals of cultivated plants, i. 307; Mongolian varieties of wheat, i. 313; characters of the ear in wheat, i. 314; acclimatisation of exotic wheat in Europe, i. 315; effect of change of climate on wheat, i. 316; on the supposed necessity of the coincident variation of weeds and cultivated plants, i. 317; advantage of change of soil to plants, ii. 146. _Lolium temulentum_, variable presence of barbs in, i. 314. LONG-TAILED sheep, i. 94, 95. LOOCHOO islands, horses of, i. 53. LORD, J. K. , on Canis latrans, i. 22. "LORI RAJAH, " how produced, ii. 280. _Lorius garrulus_, ii. 280. "LOTAN, " tumbler pigeon, i. 150. LOUDON, J. W. , varieties of the carrot, i. 326; short duration of varieties of peas, i. 329; on the glands of peach-leaves, i. 343; presence of bloom on Russian apples, i. 349; origin of varieties of the apple, i. 350; varieties of the gooseberry, i. 354; on the nut tree, i. 357; varieties of the ash, i. 360; fastigate juniper (_J. Suecica_), i. 361; on _Ilex aquifolium ferox_, i. 362; varieties of the Scotch fir, i. 363; varieties of the hawthorn, _ibid. _; variation in the persistency of leaves on the elm and Turkish oak, i. 363; importance of cultivated varieties, _ibid. _; varieties of _Rosa spinosissima_, i. 367; variation of dahlias from the same seed, i. 370; production of Provence roses from seeds of the moss rose, i. 380; effect of grafting the purple-leaved upon the common hazel, i. 395; nearly evergreen Cornish variety of the elm, ii. 310. LOW, G. , on the pigs of the Orkney islands, i. 70. LOW, Prof. , pedigrees of greyhounds, ii. 3; origin of the dog, i. 10; burrowing instinct of a half-bred Dingo, i. 28; inheritance of qualities in horses, i. 51; comparative powers of English race-horses, Arabs, &c. , i. 54; British breeds of cattle, i. 80; wild cattle of Chartley, i. 84; effect of abundance of food on the size of cattle, i. 91; effects of climate on the skin of cattle, i. 92, ii. 326; on interbreeding, ii. 116; selection in Hereford cattle, ii. 214; formation of new breeds, ii. 244; on "sheeted" cattle, ii. 349. LOWE, Mr. , on hive bees, i. 299. LOWE, REV. Mr. , on the range of _Pyrus malus_ and _P. Acerba_, i. 348. "LOWTAN" tumbler pigeon, i. 150. _Loxia pyrrhula_, ii. 154. LUBBOCK, Sir J. , developments of the Ephemeridæ, ii. 366. LUCAS, P. , effects of cross-breeding on the female, i. 404; hereditary diseases, ii. 7, 78-79; hereditary affections of the eye, ii. 9-10; inheritance of anomalies in the human eye and in that of the horse, ii. 10, 11; inheritance of polydactylism, ii. 13; morbid uniformity in the same family, ii. 17; inheritance of mutilations, ii. 23; persistency of cross-reversion, ii. 35; persistency of character in breeds of animals in wild countries, ii. 64; prepotency of transmission, ii. 65, 68; supposed rules of transmission in crossing animals, ii. 68; sexual limitations of transmission of peculiarities, ii. 72-73; absorption of the minority in crossed races, ii. 88; crosses without blending of certain characters, ii. 92; on interbreeding, ii. 116; variability dependent on reproduction, ii. 250; period of action of variability, ii. 260; inheritance of deafness in cats, ii. 329; complexion and constitution, ii. 335. LUCAZE-DUTHIERS, structure and growth of galls, ii. 282-284. LUIZET, grafting of a peach-almond on a peach, i. 338. {463} LÜTKE, cats of the Caroline Archipelago, i. 47. LUXURIANCE, of vegetative organs, a cause of sterility in plants, ii. 168-171. LYONNET, on the scission of _Nais_, ii. 358. _Lysimachia nummularia_, sterility of, ii. 170. _Lythrum_, trimorphic species of, ii. 400. _Lythrum salicaria_, ii. 183; contabescence in, ii. 166. _Lytta vesicatoria_, affecting the kidneys, ii. 380. _Macacus_, species of, bred in captivity, ii. 153. MACAULAY, Lord, improvement of the English horse, ii. 213. MCCLELLAND, Dr. , variability of fresh-water fishes in India, ii. 259. MCCOY, Prof. , on the dingo, i. 26. MACFAYDEN, influence of soil in producing sweet or bitter oranges from the same seed, i. 335. MACGILLIVRAY, domestication of the rock-dove, i. 185; feral pigeons in Scotland, i. 190; number of vertebræ in birds, i. 266; on wild geese, i. 287; number of eggs of wild and tame ducks, ii. 112. MACKENZIE, Sir G. , peculiar variety of the potato, i. 330. MACKENZIE, P. , bud-variation in the currant, i. 376. MACKINNON, Mr. , horses of the Falkland islands, i. 52; feral cattle of the Falkland islands, i. 86. MACKNIGHT, C. , on interbreeding cattle, ii. 118. MACNAB, Mr. , on seedling weeping birches, ii. 18; non-production of the weeping beech by seed, ii. 19. MADAGASCAR, cats of, i. 47. MADDEN, H. , on interbreeding cattle, ii. 118. MADEIRA, rock pigeon of, i. 184. _Magnolia grandiflora_, ii. 308. MAIZE, its unity of origin, i. 320; antiquity of, _ibid. _; with husked grains said to grow wild, _ibid. _; variation of, i. 321; irregularities in the flowers of, i. 321; persistence of varieties, _ibid. _; adaptation of to climate, i. 322, ii. 307; acclimatisation of, ii. 313, 347; crossing of, i. 400, ii. 104-105; extinct Peruvian varieties of, ii. 425. MALAY fowl, i. 227. MALAY Archipelago, horses of, i. 53; short-tailed cats of, i. 47; striped young wild pigs of, i. 76; ducks of, i. 280. MALE, influence of, on the fecundated female, i. 397-406; supposed influence of, on offspring, ii. 68. MALE flowers, appearance of, among female flowers in maize, i. 321. MALFORMATIONS, hereditary, ii. 79. _Malva_, fertilisation of, i. 402, ii. 363. _Mamestra suasa_, ii. 157. MAMMÆ, variable in number in the pig, i. 74; rudimentary, occasional full development of, in cows, i. 87, ii. 317; four present in some sheep, i. 95; variable in number in rabbits, i. 106; latent functions of, in male animals, ii. 52, 317; supernumerary and inguinal, in women, ii. 57. MANGLES, Mr. , annual varieties of the heartsease, ii. 305. MANTELL, Mr. , taming of birds by the New Zealanders, ii. 161. MANU, domestic fowl noticed in the Institutes of, i. 246. MANURE, effect of, on the fertility of plants, ii. 163. MANX cats, i. 46, ii. 66. MARCEL de Serres, fertility of the ostrich, ii. 156. MARIANNE islands, varieties of _Pandanus_ in, ii. 256. MARKHAM, Gervase, on rabbits, i. 104, ii. 204. MARKHOR, probably one of the parents of the goat, i. 101. MARQUAND, cattle of the channel islands, i. 80. MARRIMPOEY, inheritance in the horse, ii. 10. MARROW, vegetable, i. 357. MARRYATT, Capt. , breeding of asses in Kentucky, ii. 237. MARSDEN, notice of _Gallus giganteus_, i. 235. MARSHALL, Mr. , voluntary selection of pasture by sheep, i. 96; adaptation of wheats to soil and climate, i. 316; "Dutch-buttocked" cattle, ii. 8; segregation of herds of sheep, ii. 103; advantage of change of soil to wheat and potatoes, ii. 146; fashionable change in the horns of cattle, ii. 210; sheep in Yorkshire, ii. 235. MARSHALL, Prof. , growth of the brain in microcephalous idiots, ii. 389. MARTENS, E. Von, on _Achatinella_, ii. 53. MARTIN, W. C. L. , origin of the dog, i. 16; Egyptian dogs, i. 18; barking of a Mackenzie River dog, i. 27; African hounds in the Tower menagerie, i. 32; on dun horses and dappled asses, i. 55; breeds of the horse, i. 49; wild horses, i. 51; Syrian breeds of asses, i. 62; asses without stripes, i. 63; effects of cross-breeding on the female in dogs, i. 404; striped legs of mules, ii. 42. MARTINS, defective instincts of silkworms, i. 304. MARTINS, C. , fruit trees of Stockholm, ii. 307. {464} MASON, W. , bud-variation in the ash, i. 382. MASTERS, Dr. , reversion in the spiral-leaved weeping willow, i. 383; on peloric flowers, ii. 58; pelorism in a clover, ii. 346; position as a cause of pelorism, ii. 345, 347. MASTERS, Mr. , persistence of varieties of peas, i. 329; reproduction of colour in hyacinths, ii. 20; on hollyhocks, ii. 107; selection of peas for seed, ii. 199-200; on _Opuntia leucotricha_, ii. 286; reversion by the terminal pea in the pod, ii. 347. MASTIFF, sculptured on an Assyrian monument, i. 17, ii. 429; Tibetan, i. 35-36, ii. 278. MATTHEWS, Patrick, on forest trees, ii. 237. _Matthiola annua_, i. 399, ii. 20. _Matthiola incana_, i. 381, 399. MAUCHAMP, merino sheep, i. 100. MAUDUYT, crossing of wolves and dogs in the Pyrenees, i. 24. MAUND, Mr. Crossed varieties of wheat, ii. 130. MAUPERTUIS, axiom of "least action, " i. 12. MAURITIUS, importation of goats into, i. 101. MAW, G. , correlation of contracted leaves and flowers in pelargoniums, ii. 330, 331. MAWZ, fertility of _Brassica rapa_, ii. 165. _Maxillaria_, self-fertilised capsules of, ii. 134; number of seeds in, ii. 379. _Maxillaria atro-rubens_, fertilisation of, by _M. Squalens_, ii. 133. MAYES, M. , self-impotence in _Amaryllis_, ii. 139. MECKEL, on the number of digits, ii. 13; correlation of abnormal muscles in the leg and arm, ii. 322. MEDUSÆ, development of, ii. 368, 384. MEEHAN, Mr. , comparison of European and American trees, ii. 281. _Meleagris mexicana_, i. 292. _Meles taxus_, ii. 151. MELONS, i. 359-360; mongrel, supposed to be produced from a twin-seed, i. 391; crossing of varieties of, i. 399, ii. 108, 129; inferiority of, in Roman times, ii. 216; changes in, by culture and climate, ii. 275; serpent, correlation of variations in, ii. 330; analogous variations in, ii. 349. MEMBRANES, false, ii. 294-295. MÉNÉTRIES, on the stomach of _Strix grallaria_, ii. 302. MENINGITIS, tubercular, inherited, ii. 78. METAGENESIS, ii. 366. METAMORPHOSIS, ii. 366. METAMORPHOSIS and development, ii. 388, 389. METZGER, on the supposed species of wheat, i. 312-313; tendency of wheat to vary, i. 315; variation of maize, i. 321-322; cultivation of American maize in Europe, i. 322, ii. 347; on cabbages, i. 323-325; acclimatisation of Spanish wheat in Germany, ii. 26; advantage of change of soil to plants, ii. 146; on rye, ii. 254; cultivation of different kinds of wheat, ii. 261. MEXICO, dog from, with tan spots on the eyes, i. 29; colours of feral horses in, i. 61. MEYEN, on sending of bananas, ii. 168. MICE, grey and white, colours of, not blended by crossing, ii. 92; rejection of bitter almonds by, ii. 232; naked, ii. 279. MICHAUX, F. , roan-coloured feral horses of Mexico, i. 61; origin of domestic turkey, i. 292; on raising peaches from seed, i. 339. MICHEL, F. , selection of horses in mediæval times, ii. 203; horses preferred on account of slight characters, ii. 209. MICHELY, effects of food on caterpillars, ii. 280; on _Bombyx hesperus_, ii. 304. MICROPHTHALMIA, associated with defective teeth, ii. 328. MIDDENS, Danish, remains of dogs in, i. 18, ii. 427. MIGNONETTE, ii. 237, 311. MILLET, i. 371. MILLS, J. , diminished fertility of mares when first turned out to grass, ii. 161. MILNE-EDWARDS, on the development of the crustacea, ii. 368. MILNE-EDWARDS, A. , on a crustacean with a monstrous eye-peduncle, ii. 391. _Milvus niger_, ii. 154. _Mimulus luteus_, ii. 128. MINOR, W. C. , gemmation and fission in the Annelida, ii. 358. _Mirabilis_, fertilisation of, ii. 363; hybrids of, ii. 131, 169, 265. _Mirabilis jalapa_, i. 382, 393. _Mirabilis longiflora_, ii. 88. _Mirabilis vulgaris_, ii. 88. _Misocampus_ and _Cecidomyia_, i. 5. MITCHELL, Dr. , effects of the poison of the rattlesnake, ii. 289. MITFORD, Mr. , notice of the breeding of horses by Erichthonius, ii. 202. MOCCAS Court, weeping oak at, ii. 18. MOGFORD, horses poisoned by fool's parsley, ii. 337. MÖLLER, L. , effects of food on insects, ii. 281. MOQUIN-TANDON, original form of maize, i. 320; variety of the double columbine, i. 365; {465} peloric flowers, ii. 58-59, 61; position as a cause of pelorism in flowers, ii. 345; tendency of peloric flowers to become irregular, ii. 70; on monstrosities, ii. 254; correlation in the axis and appendages of plants, ii. 321; fusion of homologous parts in plants, ii. 339, 341-342; on a bean with monstrous stipules and abortive leaflets, ii. 343; conversion of parts of flowers, ii. 392. MOLE, white, ii. 332. MOLL and Gayot, on cattle, i. 80, ii. 96, 210. MOLLUSCA, change in shells of, ii. 280. MONKE, Lady, culture of the pansy by, i. 368. MONKEYS, rarely fertile in captivity, ii. 153. MONNIER, identity of summer and winter wheat, i. 315. MONSTER, cyclopean, ii. 341. MONSTERS, double, ii. 339-340. MONSTROSITIES, occurrence of, in domesticated animals and cultivated plants, i. 366, ii. 254; due to persistence of embryonic conditions, ii. 57; occurring by reversion, ii. 57-60; a cause of sterility, ii. 166-167; caused by injury to the embryo, ii. 269. MONTEGAZZA, growth of a cock's-spur inserted into the eye of an ox, ii. 369. MONTGOMERY, E. , formation of cells, ii. 370. MOOR, J. H. , deterioration of the horse in Malasia, i. 53. MOORCROFT, Mr. , on Hasora wheat, i. 313; selection of white-tailed yaks, ii. 206; melon of Kaschmir, ii. 275; varieties of the apricot cultivated in Ladakh, i. 345; varieties of the walnut cultivated in Kaschmir, i. 356. MOORE, Mr. , on breeds of pigeons, i. 148, 156, 208, 209, 211. MOORUK, fertility of, in captivity, ii. 156. MORLOT, dogs of the Danish Middens, i. 18; sheep and horse of the bronze period, ii. 427. _Mormodes ignea_, ii. 53. MOROCCO, estimation of pigeons in, i. 205. MORREN, C. , on pelorism, ii. 58; in _Calceolaria_, ii. 346; non-coincidence of double flowers and variegated leaves, ii. 167. MORRIS, Mr. , breeding of the Kestrel in captivity, ii. 154. MORTON, Lord, effect of fecundation by a quagga on an Arab mare, i. 403-404. MORTON, Dr. , origin of the dog, i. 16; hybrid of zebra and mare, ii. 42. _Morus alba_, i. 334. MOSCOW, rabbits of, i. 106, 120; effects of cold on pear-trees at, ii. 307. MOSSES, sterility in, ii. 171; retrogressive metamorphosis in, ii. 361. MOSS-ROSE, probable origin of, from _Rosa centifolia_, i. 379; Provence roses produced from seeds of, i. 380. MOSTO, Cada, on the introduction of rabbits into Porto Santo, i. 113. MOTTLING of fruits and flowers, i. 400. MOUFFLON, i. 94. MOUNTAIN-ASH, ii. 230. MOUSE, Barbary, ii. 152. "MÖVEN-TAUBE, " i. 148. MOWBRAY, Mr. , on the eggs of game fowls, i. 248; early pugnacity of game cocks, i. 251; diminished fecundity of the pheasant in captivity, ii. 155. MOWBRAY, Mr. , reciprocal fecundation of _Passiflora alata_ and _racemosa_, ii. 137. MULATTOS, character of, ii. 46. MULBERRY, i. 334, ii. 256. MULE and hinny, differences in the, ii. 67-68. MULES, striped colouring of, ii. 42; obstinacy of, ii. 45; production of, among the Romans, ii. 110; noticed in the Bible, ii. 202. MÜLLER, Fritz, reproduction of orchids, ii. 134-135; development of crustacea, ii. 368; number of seeds in a _maxillaria_, ii. 379. MÜLLER, H. , on the face and teeth in dogs, i. 34, 73, ii. 345. MÜLLER, J. , production of imperfect nails after partial amputation of the fingers, ii. 15; tendency to variation, ii. 252; atrophy of the optic nerve consequent on destruction of the eye, ii. 297; on Janus-like monsters, ii. 340; on gemmation and fission, ii. 358; identity of ovules and buds, ii. 360; special affinities of the tissues, ii. 380. MÜLLER, Max, antiquity of agriculture, ii. 243. MULTIPLICITY of origin of pigeons, hypotheses of, discussed, i. 188-194. MUNIZ, F. , on Niata cattle, i. 90. MUNRO, R. , on the fertilisation of orchids, ii. 133; reproduction of _Passiflora alata_, ii. 138. "MURASSA" pigeon, i. 144. MURPHY, J. J. , the structure of the eye not producible by selection, ii. 222. _Mus alexandrinus_, ii. 87-88. _Musa sapientum_, _Chinensis_ and _Cavendishii_, i. 377. _Muscari comosum_, ii. 185, 316. MUSCLES, effects of use on, ii. 297. MUSK duck, feral hybrid of, with the common duck, i. 190. {466} MUSMON, female, sometimes hornless, i. 95. MUTILATIONS, inheritance or non-inheritance of, ii. 22-24, 397. MYATT, on a five-leaved variety of the strawberry, i. 353. MYOPIA, hereditary, ii. 8. MYRIAPODA, regeneration of lost parts in, ii. 15, 294. NAILS, growing on stumps of fingers, ii. 394. NAIS, scission of, ii. 358. NAMAQUAS, cattle of the, i. 88, ii. 207. NARCISSUS, double, becoming single in poor soil, ii. 167. NARVAEZ, on the cultivation of native plants in Florida, i. 312. _Nasua_, sterility of, in captivity, ii. 152. "NATAS, " or Niatas, a South American breed of cattle, i. 89-91. NATHUSIUS, H. Von, on the pigs of the Swiss lake-dwellings, i. 68; on the races of pigs, i. 65-68; convergence of character in highly-bred pigs, i. 73, ii. 241; causes of changes in the form of the pig's skull, i. 72-73; changes in breeds of pigs by crossing, i. 78; change of form in the pig, ii. 279; effects of disuse of parts in the pig, ii. 299; period of gestation in the pig, i. 74; appendages to the jaw in pigs, i. 76; on _Sus pliciceps_, i. 70; period of gestation in sheep, i. 97; on Niata cattle, i. 89; on short-horn cattle, ii. 118; on interbreeding, ii. 116; in the sheep, ii. 120; in pigs, ii. 122; unconscious selection in cattle and pigs, ii. 214; variability of highly selected races, ii. 238. NATO, P. , on the Bizzaria orange, i. 391. NATURAL selection, its general principles, i. 2-14. NATURE, sense in which the term is employed, i. 6. NAUDIN, supposed rules of transmission in crossing plants, ii. 68; on the nature of hybrids, ii. 48-49; essences of the species in hybrids, ii. 386, 401; reversion of hybrids, ii. 36, 49-50; reversion in flowers by stripes and blotches, ii. 37; hybrids of _Linaria vulgaris_ and _purpurea_, ii. 94; pelorism in _Linaria_, ii. 58, 346; crossing of peloric _Linaria_ with the normal form, ii. 70; variability in _Datura_, ii. 266; hybrids of _Datura lævis_ and _stramonium_, i. 392; prepotency of transmission of _Datura stramonium_ when crossed, ii. 67; on the pollen of _Mirabilis_ and of hybrids, i. 389; fertilisation of _Mirabilis_, ii. 363; crossing of _Chamærops humilis_ and the date palm, i. 399; cultivated Cucurbitaceæ, i. 357-360, ii. 108; rudimentary tendrils in gourds, ii. 316; dwarf _Cucurbitæ_, ii. 330; relation between the size and number of the fruit in _Cucurbita pepo_, ii. 343; analogous variation in _Cucurbitæ_, ii. 349; acclimatisation of Cucurbitaceæ, ii. 313; production of fruit by sterile hybrid Cucurbitaceæ, ii. 172; on the melon, i. 360, ii. 108, 275; incapacity of the cucumber to cross with other species, i. 359. NECTARINE, i. 336-344; derived from the peach, i. 337, 339-342; hybrids of, i. 339; persistency of characters in seedling, i. 340; origin of, _ibid. _; produced on peach trees, i. 340-341; producing peaches, i. 341; variation in, i. 342-343; bud-variation in, i. 374; glands in the leaves of the, ii. 231; analogous variation in, ii. 348. NECTARY, variations of, in pansies, i. 369. NEES, on changes in the odour of plants, ii. 274. "NEGRO" cat, i. 46. NEGROES, polydactylism in, ii. 14; selection of cattle practised by, ii. 207. NEOLITHIC period, domestication of _Bos longifrons_ and _primigenius_ in the, i. 81; cattle of the, distinct from the original species, i. 87; domestic goat in the, i. 101; cereals of the, i. 317. NERVE, optic, atrophy of the, ii. 297. NEUMEISTER, on the Dutch and German pouter pigeons, i. 138; on the Jacobin pigeon, i. 154; duplication of the middle flight feather in pigeons, i. 159; on a peculiarly coloured breed of pigeons, "Staarhalsige Taube, " i. 161; fertility of hybrid pigeons, i. 192; mongrels of the trumpeter pigeon, ii. 66; period of perfect plumage in pigeons, ii. 77; advantage of crossing pigeons, ii. 126. NEURALGIA, hereditary, ii. 79. NEW ZEALAND, feral cats of, i. 47; cultivated plants of, i. 311. NEWFOUNDLAND dog, modification of, in England, i. 42. NEWMAN, E. , sterility of Sphingidæ under certain conditions, ii. 158. NEWPORT, G. , non-copulation of _Vanessæ_ in confinement, ii. 157; regeneration of limbs in myriapoda, ii. 294; fertilisation of the ovule in batrachia, ii. 363. NEWT, polydactylism in the, ii. 14. NEWTON, A. , absence of sexual distinctions in the Columbidæ, i. 162; production of a "black-shouldered" pea-hen among the ordinary kind, i. 291; on hybrid ducks, ii. 157. NGAMI, Lake, cattle of, i. 88. "NIATA" cattle, i. 89-91; resemblance of to _Sivatherium_, i. 89; {467} prepotency of transmission of character by, ii. 66. "NICARD" rabbit, i. 107. NICHOLSON, Dr. , on the cats of Antigua, i. 46; on the sheep of Antigua, i. 98. _Nicotiana_, crossing of varieties and species of, ii. 108; prepotency of transmission of characters in species of, ii. 67; contabescence of female organs in, ii. 166. _Nicotiana glutinosa_, ii. 108. NIEBUHR, on the heredity of mental characteristics in some Roman families, ii. 65. NIGHT-BLINDNESS, non-reversion to, ii. 36. NILSSON, Prof. , on the barking of a young wolf, i. 27; parentage of European breeds of cattle, i. 80, 81; on _Bos frontosus_ in Scania, i. 81. NIND, Mr. , on the dingo, i. 39. "NISUS formativus, " i. 293, 294, 355. NITZSCH, on the absence of the oil-gland in certain Columbæ, i. 147. NON-INHERITANCE, causes of, ii. 24-26. "NONNAIN" pigeon, i. 154. NORDMANN, dogs of Awhasie, i. 25. NORMANDY, pigs of, with appendages under the jaw, i. 75. NORWAY, striped ponies of, i. 58. NOTT and Gliddon, on the origin of the dog, i. 16; mastiff represented on an Assyrian tomb, i. 17; on Egyptian dogs, i. 18; on the Hare-Indian dog, i. 22. _Notylia_, ii. 135. NOURISHMENT, excess of, a cause of variability, ii. 257. NUMBER, importance of, in selection, ii. 235. _Numida ptilorhyncha_, the original of the Guinea-fowl, i. 294. NUN pigeon, i. 155; known to Aldrovandi, i. 207. NUTMEG tree, ii. 237. OAK, weeping, i. 361, ii. 18, 241; pyramidal, i. 361; Hessian, i. 361; late-leaved, i. 363; variation in persistency of leaves of, i. 363; valueless as timber at the Cape of Good Hope, ii. 274; changes in, dependent on age, i. 387; galls of the, ii. 282. OATS, wild, i. 313; in the Swiss lake-dwellings, i. 319. OBERLIN, change of soil beneficial to the potato, ii. 146. ODART, Count, varieties of the vine, i. 333, ii. 278; bud-variation in the vine, i. 375. ODOUR and colour, correlation of, ii. 325. _Oecidium_, ii. 284. _Oenothera biennis_, bud-variation in, i. 382. OGLE, W. , resemblance of twins, ii. 252. OIL-GLAND, absence of, in fantail pigeons, i. 147, 160. OLDFIELD, Mr. , estimation of European dogs among the natives of Australia, ii. 215. OLEANDER, stock affected by grafting in the, i. 394. OLLIER, Dr. , insertion of the periosteum of a dog beneath the skin of a rabbit, ii. 369. _Oncidium_, reproduction of, ii. 133-135, 164. ONIONS, crossing of, ii. 90; white, liable to the attacks of fungi and disease, ii. 228, 336. _Ophrys apifera_, self-fertilisation of, ii. 91; formation of pollen by a petal in, ii. 392. _Opuntia leucotricha_, ii. 277. ORANGE, i. 334-336; crossing of, ii. 91; with the lemon, i. 399, ii. 365; naturalisation of, in Italy, ii. 308; variation of, in North Italy, ii. 256; peculiar variety of, ii. 331; Bizzaria, i. 391; trifacial, _ibid. _ ORCHIDS, reproduction of, i. 402, 403; ii. 133-135. ORFORD, Lord, crossing greyhounds with the bulldog, i. 41. ORGANISMS, origin of, i. 13. ORGANISATION, advancement in, i. 8. ORGANS, rudimentary and aborted, ii. 315-318; multiplication of abnormal, ii. 391. ORIOLE, assumption of hen-plumage by a male in confinement, ii. 158. ORKNEY islands, pigs of, i. 70; pigeons of, i. 184. ORTHOPTERA, regeneration of hind legs in the, ii. 294. _Orthosia munda_, ii. 157. ORTON, R. , on the effects of cross-breeding on the female, i. 404; on the Manx cat, ii. 66; on mongrels from the silk-fowl, ii. 67. OSBORNE, Dr. , inherited mottling of the iris, ii. 10. OSPREY, preying on Black-fowls, ii. 230. OSTEN-SACKEN, Baron, on American oak galls, ii. 282. OSTEOLOGICAL characters of pigs, i. 66, 67, 71-74; of rabbits, i. 115-130; of pigeons, i. 162-167; of ducks, i. 282-284. OSTRICH, diminished fertility of the, in captivity, ii. 156. OSTYAKS, selection of dogs by the, ii. 206. OTTER, ii. 151. "OTTER" sheep of Massachusetts, i. 100. OUDE, feral humped cattle in, i. 79. OUISTITI, breed in Europe, ii. 153. {468} OVARY, variation of, in _Cucurbita moschata_, i. 359; development of, independently of pollen, i. 403. _Ovis montana_, i. 99. OVULES and buds, identity of nature of, ii. 360. OWEN, Capt. , on stiff-haired cats at Mombas, i. 46. OWEN, Prof. R. , palæontological evidence as to the origin of dogs, i. 15; on _Bos longifrons_, i. 81; on the skull of the "Niata" cattle, i. 89, 90; on fossil remains of rabbits, i. 104; on the significance of the brain, i. 124; on the number of digits in the Ichthyopterygia, ii. 16; on metagenesis, ii. 366; theory of reproduction and parthenogenesis, ii. 375. OWL, eagle, breeding in captivity, ii. 154. OWL pigeon, i. 148; African, figured, i. 149; known in 1735, i. 209. _Oxalis_, trimorphic species of, ii. 400. _Oxalis rosea_, ii. 132. OXLEY, Mr. , on the nutmeg tree, ii. 237. OYSTERS, differences in the shells of, ii. 280. PACA, sterility of the, in confinement, ii. 152. PACIFIC islands, pigs of the, i. 70. PADUA, earliest known flower garden at, ii. 217. PADUAN fowl of Aldrovandi, i. 247. _Pæonia moutan_, ii. 205. PÆONY, tree, ancient cultivation of, in China, ii. 205. PAMPAS, feral cattle on the, i. 85. _Pandanus_, ii. 256. PANGENESIS, hypothesis of, ii. 357-404. _Panicum_, seeds of, used as food, i. 309; found in the Swiss lake-dwellings, i. 317. PANSY, i. 368-370. PAPPUS, abortion of the, in _Carthamus_, ii. 316. PAGET, on the Hungarian sheep dog, i. 24. PAGET, inheritance of cancer, ii. 7; hereditary elongation of hairs in the eyebrow, ii. 8; period of inheritance of cancer, ii. 79-80; on _Hydra_, ii. 293; on the healing of wounds, ii. 294; on the reparation of bones, _ibid. _; growth of hair near inflamed surfaces or fractures, ii. 295; on false membranes, _ibid. _; compensatory development of the kidney, ii. 300; bronzed skin in disease of supra-renal capsules, ii. 331; unity of growth and gemmation, ii. 359; independence of the elements of the body, ii. 369; affinity of the tissues for special organic substances, ii. 380. PALLAS, on the influence of domestication upon the sterility of intercrossed species, i. 31, 83, 193, ii. 109; hypothesis that variability is wholly due to crossing, i. 188, 374, ii. 250, 264; on the origin of the dog, i. 16; variation in dogs, i. 33; crossing of dog and jackal, i. 25; origin of domestic cats, i. 43; origin of Angora cat, i. 45; on wild horses, i. 52, 60; on Persian sheep, i. 94; on Siberian fat-tailed sheep, ii. 279; on Chinese sheep, ii. 315; on Crimean varieties of the vine, i. 333; on a grape with rudimentary seeds, ii. 316; on feral musk-ducks, ii. 46; sterility of Alpine plants in gardens, ii. 163; selection of white-tailed yaks, ii. 206. _Paradoxurus_, sterility of species of, in captivity, ii. 151. PARAGUAY, cats of, i. 46; cattle of, i. 89; horses of, ii. 102; dogs of, ii. 102; black-skinned domestic fowl of, i. 232. PARALLEL variation, ii. 348-352. PARAMOS, woolly pigs of, i. 78. PARASITES, liability to attacks of, dependent on colour, ii. 228. PARIAH dog, with crooked legs, i. 17; resembling the Indian wolf, i. 24. PARISET, inheritance of handwriting, ii. 6. PARKER, W. K. , number of vertebræ in fowls, i. 266. PARKINSON, Mr. , varieties of the hyacinth, i. 370. PARKYNS, Mansfield, on _Columba guinea_, i. 183. PARMENTIER, differences in the nidification of pigeons, i. 178; on white pigeons, ii. 230. PARROTS, general sterility of, in confinement, ii. 155; alteration of plumage of, ii. 280. PARSNIP, reversion in, ii. 31; influence of selection on, ii. 201; experiments on, ii. 277; wild, enlargement of roots of, by cultivation, i. 326. PARTHENOGENESIS, ii. 359, 364. PARTRIDGE, sterility of, in captivity, ii. 156. PARTURITION, difficult, hereditary, ii. 8. _Parus major_, ii. 231. _Passiflora_, self-impotence in species of, ii. 137-138; contabescence of female organs in, ii. 166. _Passiflora alata_, fertility of, when grafted, ii. 188. PASTURE and climate, adaptation of breeds of sheep to, i. 96, 97. PASTRANA, Julia, peculiarities in the hair and teeth of, ii. 328. PATAGONIA, crania of pigs from, i. 77. PATAGONIAN rabbit, i. 105. {469} PATERSON, R. , on the Arrindy silk moth, ii. 306. PAUL, W. , on the hyacinth, i. 370; varieties of pelargoniums, i. 378; improvement of pelargoniums, ii. 216. _Pavo cristatus_ and _muticus_, hybrids of, i. 290. _Pavo nigripennis_, i. 290-291. "PAVODOTTEN-TAUBE, " i. 141. PEACH, i. 336-344; derived from the almond, i. 337; stones of, figured, _ibid. _; contrasted with almonds, i. 338; double-flowering, i. 338-339, 343; hybrids of, i. 339; persistency of races of, _ibid. _; trees producing nectarines, i. 340-341; variation in, i. 342-343, ii. 256; bud-variation in, i. 374; pendulous, ii. 18; variation by selection in, ii. 218; peculiar disease of the, ii. 228; glands on the leaves of the, ii. 231; antiquity of the, ii. 308; increased hardiness of the, _ibid. _; varieties of, adapted for forcing, ii. 310; yellow-fleshed, liable to certain diseases, ii. 336. PEACH-ALMOND, i. 338. PEAFOWL, origin of, i. 290; japanned or black-shouldered, i. 290-291; feral, in Jamaica, i. 190; comparative fertility of, in wild and tame states, ii. 112, 268; white, ii. 332. PEARS, i. 350; bud-variation in, i. 376; reversion in seedling, ii. 31; inferiority of, in Pliny's time, ii. 215; winter nelis, attacked by aphides, ii. 231; soft-barked varieties of, attacked by wood-boring beetles, ii. 231; origination of good varieties of, in woods, ii. 260; Forelle, resistance of, to frost, ii. 306. PEAS, i. 326-330; origin of, 326; varieties of, 326-329; found in Swiss lake-dwellings, i. 317, 319, 326-329; fruit and seeds figured, i. 328; persistency of varieties, i. 329; intercrossing of varieties, i. 330, 397, ii. 129; effect of crossing on the female organs in, i. 398; double-flowered, ii. 168; maturity of, accelerated by selection, ii. 201; varieties of, produced by selection, ii. 218; thin-shelled, liable to the attacks of birds, ii. 231; reversion of, by the terminal seed in the pod, ii. 347. PECCARY, breeding of the, in captivity, ii. 150. PEDIGREES of horses, cattle, greyhounds, game-cocks, and pigs, ii. 3. PEGU, cats of, i. 47; horses of, i. 53. PELARGONIUMS, multiple origin of, i. 364; zones of, i. 366; bud-variation in, i. 378; variegation in, accompanied by dwarfing, i. 384; pelorism in, ii. 167, 345; by reversion, ii. 59; advantage of change of soil to, ii. 147; improvement of, by selection, ii. 216; scorching of, ii. 229; numbers of, raised from seed, ii. 235; effects of conditions of life on, ii. 274; stove-variety of, ii. 311; correlation of contracted leaves and flowers in, ii. 330-331. _Pelargonium fulgidum_, conditions of fertility in, ii. 164. "PELONES, " a Columbian breed of cattle, i. 88. PELORIC flowers, tendency of, to acquire the normal form, ii. 70; fertility or sterility of, ii. 166-167. PELORIC races of _Gloxinia speciosa_ and _Antirrhinum majus_, i. 365. PELORISM, ii. 58-60, 345-346. PELVIS, characters of, in rabbits, i. 122-123; in pigeons, i. 166; in fowls, i. 268; in ducks, i. 284. PEMBROKE cattle, i. 81. PENDULOUS trees, i. 361, ii. 348; uncertainty of transmission of, ii. 18-19. PENGUIN ducks, i. 280, 282; hybrid of the, with the Egyptian goose, i. 282. PENNANT, production of wolf-like curs at Fochabers, i. 37; on the Duke of Queensberry's wild cattle, i. 84. _Pennisetum_, seeds of, used as food in the Punjab, i. 309. _Pennisetum distichum_, seeds of, used as food in Central Africa, i. 308. PERCIVAL, Mr. , on inheritance in horses, ii. 10; on horn-like processes in horses, i. 50. _Perdix rubra_, occasional fertility of, in captivity, ii. 156. PERIOD of action of causes of variability, ii. 269. PERIOSTEUM of a dog, producing bone in a rabbit, ii. 369. PERIWINKLE, sterility of, in England, ii. 170. PERSIA, estimation of pigeons in, i. 205; carrier pigeon of, i. 141; tumbler pigeon of, i. 150; cats of, i. 45-47; sheep of, i. 94. _Persica intermedia_, i. 338. PERSISTENCE of colour in horses, i. 50; of generic peculiarities, i. 111. PERU, antiquity of maize in, i. 320; peculiar potato from, i. 331; selection of wild animals practised by the Incas of, ii. 207-208. "PERÜCKEN-TAUBE, " i. 154. PETALS, rudimentary, in cultivated plants, ii. 316; producing pollen, ii. 392. PETUNIAS, multiple origin of, i. 364; double-flowered, ii. 167. "PFAUEN-TAUBE, " i. 146. _Phacochoerus Africanus_, i. 76. _Phalænopsis_, pelorism in, ii. 346. PHALANGES, deficiency of, ii. 73. {470} _Phaps chalcoptera_, ii. 349. _Phaseolus multiflorus_, ii. 309, 322. _Phaseolus vulgaris_, ii. 309. _Phasianus pictus_, i. 275. _Phasianus Amherstiæ_, i. 275. PHEASANT, assumption of male plumage by the hen, ii. 51; wildness of hybrids of, with the common fowl, ii. 45; prepotency of the, over the fowl, ii. 68; diminished fecundity of the, in captivity, ii. 155. PHEASANTS, golden and Lady Amherst's, i. 275. PHEASANT-FOWLS, i. 244. PHILIPEAUX, regeneration of limbs in the salamander, ii. 376. PHILIPPAR, on the varieties of wheat, i. 314. PHILIPPINE Islands, named breeds of game fowl in the, i. 232. PHILLIPS, Mr. , on bud-variation in the potato, i. 385. _Phlox_, bud-variation by suckers in, i. 384. PHTHISIS, affection of the fingers in, ii. 332. PICKERING, Mr. , on the grunting voice of humped cattle, i. 79; occurrence of the head of a fowl in an ancient Egyptian procession, i. 246; seeding of ordinarily seedless fruits, ii. 168; extinction of ancient Egyptian breeds of sheep and oxen, ii. 425; on an ancient Peruvian gourd, ii. 429. PICOTEES, effect of conditions of life on, ii. 273. PICTET, A. , oriental names of the pigeon, i. 205. PICTET, Prof. , origin of the dog, i. 15; on fossil oxen, i. 81. PIEBALDS, probably due to reversion, ii. 37. PIGEAUX, hybrids of the hare and rabbit, ii. 99, 152. PIGEON à cravate, i. 148. PIGEON Bagadais, i. 142, 143. PIGEON coquille, i. 155. PIGEON cygne, i. 143. PIGEON heurté, i. 156. PIGEON Patu plongeur, i. 156. PIGEON Polonais, i. 144. PIGEON Romain, i. 142, 144. PIGEON tambour, i. 154. PIGEON Turc, i. 139. PIGEONS, origin of, i. 131-134, 180-204; classified table of breeds of, i. 136; pouter, i. 137-139; carrier, i. 139-142; runt, i. 142-144; barbs, i. 144-146; fantail, i. 146-148; turbit and owl, i. 148-149; tumbler, i. 150-153; Indian frill-back, i. 153; Jacobin, i. 154; trumpeter, i. 154; other breeds of, i. 155-157; differences of, equal to generic, i. 157-158; individual variations of, i. 158-160; variability of peculiarities characteristic of breeds in, i. 161; sexual variability in, i. 161-162; osteology of, i. 162-167; correlation of growth in, i. 167-171, ii. 321; young of some varieties naked when hatched, i. 170, ii. 332; effects of disuse in, i. 172-177; settling and roosting in trees, i. 181; floating in the Nile to drink, i. 181; Dovecot, i. 185-186; arguments for unity of origin of, i. 188-204; feral in various places, i. 190, ii. 33; unity of coloration in, i. 195-197; reversion of mongrel, to coloration of, _C. Livia_, i. 197-202; history of the cultivation of, i. 205-207; history of the principal races of, i. 207-212; mode of production of races of, i. 212-224; reversion in, ii. 29, 47; by age, ii. 38; produced by crossing in, ii. 40, 48; prepotency of transmission of character in breeds of, ii. 66-67; sexual differences in some varieties of, ii. 74; period of perfect plumage in, ii. 77; effect of segregation on, ii. 86; preferent pairing of, within the same breed, ii. 103; fertility of, increased by domestication, ii. 112, 155; effects of interbreeding and necessity of crossing, ii. 125-126; indifference of, to change of climate, ii. 161; selection of, ii. 195, 199, 204; among the Romans, ii. 202; unconscious selection of, ii. 211, 214; facility of selection of, ii. 234; white, liable to the attacks of hawks, ii. 230; effects of disuse of parts in, ii. 298; fed upon meat, ii. 304; effect of first male upon the subsequent progeny of the female, i. 405; homology of the leg and wing feathers in, ii. 323; union of two outer toes in feather-legged, _ibid. _; correlation of beak, limbs, tongue, and nostrils in, ii. 324; analogous variation in, ii. 349-350; permanence of breeds of, ii. 429. PIGS, of Swiss lake-dwellings, i. 67-68; types of, derived from _Sus scrofa_ and _Sus indica_, i. 66-67; Japanese (_Sus pliciceps_, Gray), figured, i. 69; of Pacific islands, i. 70, ii. 87; modifications, of skull in, i. 71-73; length of intestines in, i. 73, ii. 303; period of gestation of, i. 74; number of vertebræ and ribs in, i. 74; anomalous forms, i. 75-76; development of tusks and bristles in, i. 76; striped young of, i. 76-77; reversion of feral, to wild type, i. 77-78, ii. 33, 47; production and changes of breeds of, by intercrossing, i. 78; effects produced by the first male upon the subsequent progeny of the female, i. 404; two-legged race of, ii. 4; {471} polydactylism in, ii. 14; cross-reversion in, ii. 35; hybrid, wildness of, ii. 45; monstrous development of a proboscis in, ii. 57; disappearance of tusks in male under domestication, ii, 74; solid hoofed, ii. 429; crosses of, ii. 93, 95; mutual fertility of all varieties of, ii. 110; increased fertility by domestication, ii. 111; ill effects of close interbreeding in, ii. 121-122; influence of selection on, ii. 198; prejudice against certain colours in, ii. 210, 229, 336; unconscious selection of, ii. 214; black Virginian, ii. 227, 336; similarity of the best breeds of, ii. 241; change of form in, ii. 279; effects of disuse of parts in, ii. 299; ears of, ii. 301; correlations in, ii. 327; white, buck-wheat injurious to, ii. 337; tail of, grafted upon the back, ii. 369; extinction of the older races of, ii. 426. PIMENTA, ii. 91. PIMPERNEL, ii. 190. PINE-APPLE, sterility and variability of the, ii. 262. PINK, Chinese. 322. PINKS, bud-variation in, i. 381; improvement of, ii. 216. _Pinus pumilio_, _Mughus_, and _nana_, varieties of _P. Sylvestris_, i. 363. _Pinus sylvestris_, i. 363, ii. 310; hybrids of, with _P. Nigricans_, ii. 130. PIORRY, on hereditary disease, ii. 7, 78. _Pistacia lentiscus_, ii. 274. PISTILS, rudimentary, in cultivated plants, ii. 316. PISTOR, sterility of some mongrel pigeons, i. 192; fertility of pigeons, ii. 112. _Pisum arvense_ and _sativum_, i. 326. PITYRIASIS versicolor, inheritance of, ii. 79. PLANCHON, G. , on a fossil vine, i. 332; sterility of _Jussiæa grandifiora_ in France, ii. 170. PLANE tree, variety of the, i. 362. PLANTIGRADE carnivora, general sterility of the, in captivity, ii. 151. PLANTS, progress of cultivation of, i. 305-312; cultivated, their geographical derivation, i. 311; crossing of, ii. 98, 99, 127; comparative fertility of wild and cultivated, ii. 112-113; self-impotent, ii. 131-140; dimorphic and trimorphic, ii. 132, 140; sterility of, from changed conditions, ii. 163-165; from contabescence of anthers, ii. 165-166; from monstrosities, ii. 166-167; from doubling of the flowers, ii. 167-168; from seedless fruit, ii. 168; from excessive development of vegetative organs, ii. 168-171; influence of selection on, ii. 199-201; variation by selection, in useful parts of, ii. 217-219; variability of, ii. 237; variability of, induced by crossing, ii. 265; direct action of change of climate on, ii. 277; change of period of vegetation in, ii. 304-305; varieties of, suitable to different climates, ii. 306; correlated variability of, ii. 330-331; antiquity of races of, ii. 429. PLASTICITY, inheritance of, ii. 241. PLATEAU, F. , on the vision of amphibious animals, ii. 223. _Platessa flesus_, ii. 53. PLATO, notice of selection in breeding dogs by, ii. 212. PLICA polonica, ii. 276. PLINY, on the crossing of shepherd's dogs with the wolf, i. 24; on Pyrrhus' breed of cattle, ii. 202; on the estimation of pigeons among the Romans, i. 205; pears described by, ii. 215. PLUM, i. 345-347; stones figured, i. 345; varieties of the, i. 345-346, ii. 219; bud-variation in the, i. 375; peculiar disease of the, ii. 227; flower-buds of, destroyed by bullfinches, ii. 232; purple-fruited, liable to certain diseases, ii. 336. PLUMAGE, inherited peculiarities of, in pigeons, i. 160-161; sexual peculiarities of, in fowls, i. 251-255. PLURALITY of races, Pouchet's views on, i. 2. _Poa_, seeds of, used as food, i. 308; species of, propagated by bulblets, ii. 170. PODOLIAN cattle, i. 80. POINTERS, modification of, i. 42; crossed with the foxhound, ii. 95. POIS sans parchemin, ii. 231. POITEAU, origin of _Cytisus Adami_, i. 390; origin of cultivated varieties of fruit-trees, ii. 260. POLISH fowl, i. 227, 250, 254, 256-257, 262; skull figured, i. 262; section of skull figured, i. 263; development of protuberance of skull, i. 250; furcula figured, i. 268. POLISH, or Himalayan rabbit, i. 108. POLLEN, ii. 363-364; action of, ii. 108; injurious action of, in some orchids, ii. 134-135; resistance of, to injurious treatment, ii. 164; prepotency of, ii. 187. POLLOCK, Sir F. , transmission of variegated leaves in _Ballota nigra_, i. 383; on local tendency to variegation, ii. 274. POLYANTHUS, ii. 21. POLYDACTYLISM, inheritance of, ii. 12-16; significance of, ii. 16-17. _Polyplectron_, i. 255. PONIES, most frequent on islands and mountains, i. 52; Javanese, i. 53. POOLE, Col. , on striped Indian horses, i. 58, 59; {472} on the young of _Asinus indicus_, ii. 43. POPLAR, Lombardy, i. 361. PÖPPIG, on Cuban wild dogs, i. 27. POPPY, found in the Swiss lake-dwellings, i. 317, 319; with the stamens converted into pistils, i. 365; differences of the, in different parts of India, ii. 165; monstrous, fertility of, ii. 166; black-seeded, antiquity of, ii. 429. PORCUPINE, breeding of, in captivity, ii. 152. PORCUPINE family, ii. 4, 76. _Porphyrio_, breeding of a species of, in captivity, ii. 156. PORTAL, on a peculiar hereditary affection of the eye, ii. 9. PORTO Santo, feral rabbits of, i. 112. _Potamochoerus penicillatus_, ii. 150. POTATO, i. 330-331; bud-variation by tubers in the, i. 384-385; graft-hybrid of, by union of half-tubers, i. 395; individual self-impotence in the, ii. 137; sterility of, ii. 169; advantage of change of soil to the, ii. 146; relation of tubers and flowers in the, ii. 343. POTATO, sweet, sterility of the, in China, ii. 169; varieties of the, suited to different climates, ii. 309. POUCHET, M. , his views on plurality of races, i. 2. POUTER pigeons, i. 137-139; furcula figured, i. 167; history of, i. 207. POWIS, Lord, experiments in crossing humped and English cattle, i. 83, ii. 45. POYNTER, Mr. , on a graft-hybrid rose, i. 396. PRAIRIE wolf, i. 22. PRECOCITY of highly-improved breeds, ii. 321. PREPOTENCY of pollen, ii. 187. PREPOTENCY of transmission of character, ii. 65, 174; in the Austrian emperors and some Roman families, ii. 65; in cattle, ii. 65-66; in sheep, ii. 66; in cats, _ibid. _; in pigeons, ii. 66-67; in fowls, ii. 67; in plants, _ibid. _; in a variety of the pumpkin, i. 358; in the jackal over the dog, ii. 67; in the ass over the horse, _ibid. _; in the pheasant over the fowl, ii. 68; in the penguin duck over the Egyptian goose, _ibid. _; discussion of the phenomena of, ii. 69-71. PRESCOTT, Mr. , on the earliest known European flower-garden, ii. 217. PRESSURE, mechanical, a cause of modification, ii. 344-345. PREVOST and Dumas, on the employment of several spermatozoids to fertilise one ovule, ii. 363. PRICE, Mr. , variations in the structure of the feet in horses, i. 50. PRICHARD, Dr. , on polydactylism in the negro, ii. 14; on the Lambert family, ii. 77; on an albino negro, ii. 229; on Plica polonica, ii. 276. PRIMROSE, ii. 21; double, rendered single by transplantation, ii. 167. _Primula_, intercrossing of species of, i. 336; contabescence in, ii. 166; hose and hose, i. 365; with coloured calyces, sterility of, ii. 166. _Primula sinensis_, reciprocally dimorphic, ii. 132. _Primula veris_, ii. 21, 109, 182. _Primula vulgaris_, ii. 21, 109. PRINCE, Mr. , on the intercrossing of strawberries, i. 352. _Procyon_, sterility of, in captivity, ii. 152. PROLIFICACY, increased by domestication, ii. 174. PROPAGATION, rapidity of, favourable to selection, ii. 297. PROTOZOA, reproduction of the, ii. 376. _Prunus armeniaca_, i. 344-345. _Prunus avium_, i. 347. _Prunus cerasus_, i. 347, 375. _Prunus domestica_, i. 345. _Prunus insititia_, i. 345-347. _Prunus spinosa_, i. 345. PRUSSIA, wild horses in, i. 60. _Psittacus erithacus_, ii. 155. _Psittacus macoa_, ii. 155. _Psophia_, general sterility of, in captivity, ii. 157. PTARMIGAN fowls, i. 228. _Pulex penetrans_, ii. 275. PUMPKINS, i. 357. PUNO ponies of the Cordillera, i. 52. PURSER, Mr. On _Cytisus Adami_, i. 389. PUSEY, Mr. , preference of hares and rabbits for common rye, ii. 232. PUTSCHE and Vertuch, varieties of the potato, i. 330. PUVIS, effects of foreign pollen on apples, i. 401; supposed non-variability of monotypic genera, ii. 266. _Pyrrhula vulgaris_, ii. 232; assumption of the hen-plumage by the male, in confinement, ii. 158. PYRRHUS, his breed of cattle, ii. 202. _Pyrus_, fastigate Chinese species of, ii. 277. _Pyrus acerba_, i. 348. _Pyrus aucuparia_, ii. 230. _Pyrus communis_, i. 350, 376. _Pyrus malus_, i. 348, 376. _Pyrus paradisiaca_, i. 348. _Pyrus præcox_, i. 348. QUAGGA, effect of fecundation by, on the subsequent progeny of a mare, i. 403-404. QUATREFAGES, A. De, on the burrowing of a bitch to litter, i. 77; {473} selection in the silkworm, i. 301; development of the wings in the silkmoth, i. 303, ii. 298; on varieties of the mulberry, i. 334; special raising of eggs of the silkmoth, ii. 197; on disease of the silkworm, ii. 228; on monstrosities in insects, ii. 269, 391; on the Anglo-Saxon race in America, ii. 276; on a change in the breeding season of the Egyptian goose, ii. 304; fertilisation of the _Teredo_, ii. 363; tendency to similarity in the best races, ii. 241; on his "_tourbillon vital_, " ii. 61; on the independent existence of the sexual elements, ii. 360. _Quercus cerris_, i. 363. _Quercus robur_ and _pedunculata_, hybrids of, ii. 130. QUINCE, pears grafted on the, ii. 259. RABBITS, domestic, their origin, i. 103-105; of Mount Sinai and Algeria, i. 105; breeds of, i. 105-111; Himalayan, Chinese, Polish, or Russian, i. 108-111, ii. 97; feral, i. 111-115; of Jamaica, i. 112; of the Falkland islands, i. 112; of Porto Santo, i. 112-115, ii. 103, 279; osteological characters of, i. 115-129; discussion of modifications in, i. 129-130; one-eared, transmission of peculiarity of, ii. 12; reversion in feral, ii. 33; in the Himalayan, ii. 41; crossing of white and coloured Angora, ii. 92; comparative fertility of wild and tame, ii. 111; high-bred, often bad breeders, ii. 121; selection of, ii. 204; white, liable to destruction, ii. 230; effects of disuse of parts in, ii. 298; skull of, affected by drooping ears, ii. 301; length of intestines in, ii. 303; correlation of ears and skull in, ii. 324-325; variations in skull of, ii. 350; periosteum of a dog producing bone in, ii. 369. RACE-HORSE, origin of, i. 54. RACES, modification and formation of, by crossing, ii. 95-99; natural and artificial, ii. 245; Pouchet's views on plurality of, i. 2; of pigeons, i. 207-212. RADISHES, i. 326; crossing of, ii. 90; varieties of, ii. 217-218. RADCLYFFE, W. F. , effect of climate and soil on strawberries, i. 354; constitutional differences in roses, i. 367. RADLKOFER, retrogressive metamorphosis in mosses and algæ, ii. 361. RAFFLES, Sir Stamford, on the crossing of Javanese cattle with _Bos sondaicus_, ii. 206. RAM, goat-like, from the Cape of Good Hope, ii. 66. RANCHIN, heredity of diseases, ii. 7. RANGE of gallinaceous birds on the Himalaya, i. 237. _Ranunculus ficaria_, ii. 170. _Ranunculus repens_, ii. 168. RAPE, i. 325. _Raphanus sativus_, ii. 343. RASPBERRY, yellow-fruited, ii. 230. RATTLESNAKE, experiments with poison of the, ii. 289. RAVEN, stomach of, affected by vegetable diet, ii. 302. RAWSON, A. , self-impotence in hybrids of _Gladiolus_, ii. 139-140. RÉ, Le Compte, on the assumption of a yellow colour by all varieties of maize, i. 321. RÉAUMUR, effect of confinement upon the cock, ii. 52; fertility of fowls in most climates, ii. 161. REED, Mr. , atrophy of the limbs of rabbits, consequent on the destruction of their nerves, ii. 297. REGENERATION of amputated parts in man, ii. 14; in the human embryo, ii. 15; in the lower vertebrata, insects, and myriapoda, _ibid. _ REINDEER, individuals recognised by the Laplanders, ii. 251. REGNIER, early cultivation of the cabbage by the Celts, i. 324. REISSEK, experiments in crossing _Cytisus purpureus_ and _laburnum_, i. 389; modification of a _Thesium_ by _Oecidium_, ii. 284. RELATIONS, characters of, reproduced in children, ii. 34. RENGGER, occurrence of jaguars with crooked legs in Paraguay, i. 17; naked dogs of Paraguay, i. 23, 31, ii. 93, 102; feral dogs of La Plata, i. 27; on the aguara, i. 26; cats of Paraguay, i. 46, ii. 86, 151; dogs of Paraguay, ii. 87; feral pigs of Buenos Ayres, i. 77; on the refusal of wild animals to breed in captivity, ii. 149; on _Dicotyles labiatus_, ii. 150; sterility of plantigrade carnivora in captivity, ii. 152; on _Cavia aperea_, ii. 152; sterility of _Cebus azaræ_ in captivity, ii. 153; abortions produced by wild animals in captivity, ii. 158. REPRODUCTION, sexual and asexual, contrasted, ii. 361; unity of forms of, ii. 383; antagonism of, to growth, ii. 384. _Reseda odorata_, ii. 237. RETINITIS, pigmentary, in deaf-mutes, ii. 328. REVERSION, ii. 28-29, 372-373, 396, 398-402; in pigeons, ii. 29; in cattle, ii. 29-30; in sheep, ii. 30; in fowls, ii. 31; in the heartsease, _ibid. _; in vegetables, _ibid. _; in feral animals and plants, ii. 32-34; to characters derived from a previous cross in man, dogs, pigeons, pigs, and fowls, ii. 34-35; {474} in hybrids, ii. 36; by bud-propagation in plants, ii. 36-38; by age in fowls, cattle, &c. , ii. 38-39; caused by crossing, ii. 39-51; explained by latent characters, ii. 51-56; producing monstrosities, ii. 57; producing peloric flowers, ii. 58-60; of feral pigs to the wild type, i. 77-78; of supposed feral rabbits to the wild type, i. 104, 111, 115; of pigeons, in coloration, when crossed, i. 197-202; in fowls, i. 239-246; in the silkworm, i. 302; in the pansy, i. 369; in a pelargonium, i. 378; in Chrysanthemums, i. 379; of varieties of the China rose in St. Domingo, i. 380; by buds in pinks and carnations, i. 381; of laciniated varieties of trees to the normal form, i. 382; in variegated leaves of plants, i. 383-384; in tulips, i. 386; of suckers of the seedless barberry to the common form, i. 384; by buds in hybrids of _Tropæolum_, i. 392; in plants, i. 409; of crossed peloric snapdragons, ii. 71; analogous variations due to, ii. 349-351. REYNIER, selection practised by the Celts, ii. 202-203. RHINOCEROS, breeding in captivity in India, ii. 150. _Rhododendron_, hybrid, ii. 265. _Rhododendron ciliatum_, ii. 277. _Rhododendron Dalhousiæ_, effect of pollen of _R. Nuttallii_ upon, i. 400. RHUBARB, not medicinal when grown in England, ii. 274. _Ribes grossularia_, i. 354-356, 376. _Ribes rubrum_, i. 376. RIBS, number and characters of, in fowls, i. 267; characters of, in ducks, i. 283-284. RICE, Imperial, of China, ii. 205; Indian varieties of, ii. 256; variety of, not requiring water, ii. 305. RICHARDSON, H. D. , on jaw-appendages in Irish pigs, i. 76; management of pigs in China, i. 68; occurrence of striped young in Westphalian pigs, i. 76; on crossing pigs, ii. 95; on interbreeding pigs, ii. 122; on selection in pigs, ii. 194. RICHARDSON, Sir John, observations on the resemblance between North American dogs and wolves, i. 21-22; on the burrowing of wolves, i. 27; on the broad feet of dogs, wolves, and foxes in North America, i. 40; on North American horses scraping away the snow, i. 53. _Ricinus_, annual in England, ii. 305. RIEDEL, on the "Bagadotte" pigeon, i. 141; on the Jacobin pigeon, i. 154; fertility of hybrid pigeons, i. 192. RINDERPEST, ii. 378. RISSO, on varieties of the orange, i. 336, ii. 308, 331. RIVERS, Lord, on the selection of greyhounds, ii. 235. RIVERS, Mr. , persistency of characters in seedling potatoes, i. 331; on the peach, i. 338, 339; persistency of races in the peach and nectarine, i. 339, 340; connexion between the peach and the nectarine, i. 340; persistency of character in seedling apricots, i. 344; origin of the plum, i. 345; seedling varieties of the plum, i. 346; persistency of character in seedling plums, i. 347; bud-variation in the plum, i. 375; plum, attacked by bullfinches, ii. 232; seedling apples with surface-roots, i. 349; variety of the apple found in a wood, ii. 260; on roses, i. 366-367; bud-variation in roses, i. 379-381; production of Provence roses from seeds of the moss-rose, i. 380; effect produced by grafting on the stock in jessamine, i. 394; in the ash, i. 394; on grafted hazels, i. 395; hybridisation of a weeping thorn, ii. 18; experiments with the seed of the weeping elm and ash, ii. 19; variety of the cherry with curled petals, ii. 232. RIVIÈRE, reproduction of _Oncidium Cavendishianum_, ii. 133. ROBERTS, Mr. , on inheritance in the horse, ii. 10. ROBERTSON, Mr. , on glandular-leaved peaches, i. 343. ROBINET, on the silkworm, i. 301-304, ii. 197. _Robinia_, ii. 274. ROBSON, Mr. , deficiencies of half-bred horses, ii. 11. ROBSON, Mr. , on the advantage of change of soil to plants, ii. 146-147; on the growth of the verbena, ii. 273; on broccoli, ii. 310. ROCK pigeon, measurements of the, i. 134; figured, i. 135. RODENTS, sterility of, in captivity, ii. 152. _Rodriguezia_, ii. 134, 135. RODWELL, J. , poisoning of horses by mildewed tares, ii. 337. ROHILCUND, feral humped cattle in, i. 79. ROLLE, F. , on the history of the peach, ii. 308. ROLLER-PIGEONS, Dutch, i. 151. ROLLESTON, Prof. , incisor teeth affected in form in cases of pulmonary tubercle, ii. 332. ROMANS, estimation of pigeons by, i. 205; breeds of fowls possessed by, i. 231, 247. {475} ROOKS, pied, ii. 77. _Rosa_, cultivated species of, i. 366. _Rosa devoniensis_, graft-hybrid produced by, on the white Banksian rose, i. 396. _Rosa indica_ and _centifolia_, fertile hybrids of, i. 366. _Rosa spinosissima_, history of the culture of, i. 367. ROSELLINI, on Egyptian dogs, i. 17. ROSES, i. 366-367; origin of, i. 364; bud-variation in, i. 379-381; Scotch, doubled by selection, ii. 200; continuous variation of, ii. 241; effect of seasonal conditions on, ii. 273; noisette, ii. 308; galls of, ii. 284. ROUENNAIS rabbit, i. 105. ROULIN, on the dogs of Juan Fernandez, i. 27; on South American cats, i. 46; striped young pigs, i. 77; feral pigs in South America, i. 78, ii. 33; on Columbian cattle, i. 88, ii. 205, 226; effects of heat on the hides of cattle in South America, i. 92; fleece of sheep in the hot valleys of the Cordilleras, i. 98; diminished fertility of these sheep, ii. 161; on black-boned South American fowls, i. 258; variation of the guinea-fowl in tropical America, i. 294; frequency of striped legs in mules, ii. 42; geese in Bogota, ii. 161; sterility of fowls introduced into Bolivia, ii. 162. ROY, M. , on a variety of _Magnolia grandiflora_, ii. 308. ROYLE, Dr. , Indian varieties of the mulberry, i. 334; on _Agave vivipara_, ii. 169; variety of rice not requiring irrigation, ii. 305; sheep from the Cape in India, ii. 306. _Rubus_, pollen of, ii. 268. RUDIMENTARY organs, i. 12, ii. 315-318. RUFZ de Lavison, extinction of breeds of dogs in France, ii. 425. RUMINANTS, general fertility of, in captivity, ii. 150. RUMPLESS fowls, i. 230. RUNTS, i. 142-144; history of, i. 210; lower jaws and skull figured, i. 164-165. RUSSIAN or Himalayan rabbit, i. 108. RÜTIMEYER, Prof. , dogs of the Neolithic period, i. 19; horses of Swiss lake-dwellings, i. 49; diversity of early domesticated horses i. 51; pigs of the Swiss lake-dwellings, i. 65, 67-68; on humped cattle, i. 80; parentage of European breeds of cattle, i. 80, 81, ii. 427; on "Niata" cattle, i. 89; sheep of the Swiss lake-dwellings, i. 94, ii. 427; goats of the Swiss lake-dwellings, i. 101; absence of fowls in the Swiss lake-dwellings, i. 246; on crossing cattle, ii. 98; differences in the bones of wild and domesticated animals, ii. 279; decrease in size of wild European animals, ii. 427. RYE, wild, De Candolle's observations on, i. 313; found in the Swiss lake-dwellings, i. 319; common, preferred by hares and rabbits, ii. 232; less variable than other cultivated plants, ii. 254. SABINE, Mr. , on the cultivation of _Rosa spinosissima_, i. 367; on the cultivation of the dahlia, i. 369-370, ii. 261; effect of foreign pollen on the seed-vessel in _Amaryllis vittata_, i. 400. ST. ANGE, influence of the pelvis on the shape of the kidneys in birds, ii. 344. ST. DOMINGO, wild dogs of, i. 28; bud-variation of dahlias in, i. 385. ST. HILAIRE, Aug. , milk furnished by cows in South America, ii. 300; husked form of maize, i. 320. ST. JOHN, C. , feral cats in Scotland, i. 47; taming of wild ducks, i. 278. ST. VALERY apple, singular structure of the, i. 350; artificial fecundation of the, i. 401. ST. VITUS' Dance, period of appearance of, ii. 77. SAGERET, origin and varieties of the cherry, i. 347-348; origin of varieties of the apple, i. 350; incapacity of the cucumber for crossing with other species, i. 359; varieties of the melon, i. 360; supposed twin-mongrel melon, i. 391; crossing melons, ii. 108, 129; on gourds, ii. 108; effects of selection in enlarging fruit, ii. 217; on the tendency to depart from type, ii. 241; variation of plants in particular soils, ii. 278. SALAMANDER, experiments on the, ii. 293, 341; regeneration of lost parts in the, ii. 15, 376, 385. _Salamandra cristata_, polydactylism in, ii. 14. SALISBURY, Mr. , on the production of nectarines by peach-trees, i. 341; on the dahlia, i. 369-370. _Salix_, intercrossing of species of, i. 336. _Salix humilis_, galls of, ii. 282, 283. SALLÉ, feral guinea-fowl in St. Domingo, i. 294. SALMON, early breeding of male, ii. 384. SALTER, Mr. , on bud-variation in pelargoniums, i. 378; in the Chrysanthemum, i. 379; transmission of variegated leaves by seed, i. 383; bud-variation by suckers in _Phlox_, i. 384; application of selection to bud-varieties of plants, i. 411; accumulative effect of changed conditions of life, ii. 262; on the variegation of strawberry leaves, ii. 274. SALTER, S. J. , hybrids of _Gallus Sonneratii_ and the common fowl, i. 234, ii. 45; {476} crossing of races or species of rats, ii. 87-88. SAMESREUTHER, on inheritance in cattle, ii. 10. SANDFORD. _See_ DAWKINS. SAP, ascent of the, ii. 296. _Saponaria calabrica_, ii. 20. SARDINIA, ponies of, i. 52. SARS, on the development of the hydroida, ii. 368. SATIATION of the stigma, i. 402-403. _Saturnia pyri_, sterility of, in confinement, ii. 157. SAUL, on the management of prize gooseberries, i. 356. SAUVIGNY, varieties of the goldfish, i. 296. SAVAGES, their indiscriminate use of plants as food, i. 307-310; fondness of, for taming animals, ii. 160. SAVI, effect of foreign pollen on maize, i. 400. _Saxifraga geum_, ii. 166. SAYZID MOHAMMED MUSARI, on carrier-pigeons, i. 141; on a pigeon which utters the sound "Yahu, " i. 155. SCANDEROONS (pigeons), i. 142, 143. SCANIA, remains of _Bos frontosus_ found in, i. 81. SCAPULA, characters of, in rabbits, i. 123; in fowls, i. 268; in pigeons, i. 167; alteration of, by disuse, in pigeons, i. 175. SCARLET fever, ii. 276. SCHAAFFHAUSEN, on the horses represented in Greek statues, ii. 213. SCHACHT, H. , on adventitious buds, ii. 384. SCHLEIDEN, excess of nourishment a cause of variability, ii. 257. SCHOMBURGK, Sir R. , on the dogs of the Indians of Guiana, i. 19, 23, ii. 206; on the musk duck, i. 182; bud-variation in the Banana, i. 377; reversion of varieties of the China rose in St. Domingo, i. 380; sterility of tame parrots in Guiana, ii. 155; on _Dendrocygna viduata_, ii. 157; selection of fowls in Guiana, ii. 209. SCHREIBERS, on _Proteus_, ii. 297. _Sciuropterus volucella_, ii. 152. _Sciurus palmarum_ and _cinerea_, ii. 152. SCLATER, P. L. , on _Asinus tæniopus_, i. 62, ii. 41; on _Asinus indicus_, ii. 42; striped character of young wild pigs, i. 70; osteology of _Gallinula nesiotis_, i. 287; on the black-shouldered peacock, i. 290; on the breeding of birds in captivity, ii. 157. SCHMERLING, Dr. , varieties of the dog, found in a cave, i. 19. SCOTCH fir, local variation of, i. 363. SCOTCH kail and cabbage, cross between, ii. 98. SCOTT, John, irregularities in the sex of the flowers of Maize, i. 321; bud-variation in _Imatophyllum miniatum_, i. 385; crossing of species of _Verbascum_, ii. 106-107; experiments on crossing _Primulæ_, ii. 109; reproduction of orchids, ii. 133; fertility of _Oncidium divaricatum_, ii. 164; acclimatisation of the sweet pea in India, ii. 311; number of seeds in _Acropera_ and _Gongora_, ii. 379. SCOTT, Sir W. , former range of wild cattle in Britain, i. 85. SCROPE, on the Scotch deerhound, ii. 73, 121. SEBRIGHT, Sir John, effects of close interbreeding in dogs, ii. 121; care taken by, in selection of fowls, ii. 197. _Secale cereale_, ii. 254. SEDGWICK, W. , effects of crossing on the female, i. 404; on the "Porcupine-man, " ii. 4; on hereditary diseases, ii. 7; hereditary affections of the eye, ii. 9, 78-79; inheritance of polydactylism and anomalies of the extremities, ii. 13-14; morbid uniformity in the same family, ii. 17; on deaf-mutes, ii. 22; inheritance of injury to the eye, ii. 24; atavism in diseases and anomalies of structure, ii. 34; non-reversion to night-blindness, ii. 36; sexual limitation of the transmission of peculiarities in man, ii. 72-73; on the effects of hard-drinking, ii. 289; inherited baldness with deficiency of teeth, ii. 326-327; occurrence of a molar tooth in place of an incisor, ii. 391; diseases occurring in alternate generations, ii. 401. SEDILLOT, on the removal of portions of bone, ii. 296. SEEDS, early selection of, ii. 204; rudimentary, in grapes, ii. 316; relative position of, in the capsule, ii. 345. SEEDS and buds, close analogies of, i. 411. SEEMANN, B. , crossing of the wolf and Esquimaux dog, i. 22. SELBY, P. J. , on the bud-destroying habits of the bullfinch, ii. 232. SELECTION, ii. 192-249; methodical, i. 214, ii. 194-210; by the ancients and semi-civilised people, ii. 201-210; of trifling characters, ii. 208-210; unconscious, i. 214, 217, ii. 174, 210-217; effects of, shown by differences in most valued parts, ii. 217-220; produced by accumulation of variability, ii. 220-223; natural, as affecting domestic productions, ii. 185-189, 224-233; as the origin of species, genera and other groups, ii. 429-432; circumstances favourable to, ii. 233-239; tendency of towards extremes, ii. 239-242; {477} possible limit of, ii. 242; influence of time on, ii. 243-244; summary of subject, ii. 246-249; effects of, in modifying breeds of cattle, i. 92, 93; in preserving the purity of breeds of sheep, i. 99-100; in producing varieties of pigeons, i. 213-218; in breeding fowls, i. 232-233; in the goose, i. 289; in the canary, i. 295; in the goldfish, i. 296; in the silkworm, i. 300-301; contrasted in cabbages and cereals, i. 323; in the white mulberry, i. 334; on gooseberries, i. 356; applied to wheat, i. 317-318; exemplified in carrots, &c. , i. 326; in the potato, i. 331; in the melon, i. 360; in flowering plants, i. 365; in the hyacinth, i. 371; applied to bud-varieties of plants, i. 411; illustrations of, ii. 421-428. SELECTION, sexual, ii. 75. SELF-IMPOTENCE in plants, ii. 131-140; in individual plants, ii. 136-138; of hybrids, ii. 174. SELWYN, Mr. , on the Dingo, i. 26. SELYS-LONGCHAMPS, on hybrid ducks, i. 190, ii. 46, 157; hybrid of the hook-billed duck and Egyptian goose, i. 282. SERINGE, on the St. Valery apple, i. 350. SERPENT Melon, i. 360. SERRES, Olivier de, wild poultry in Guiana, i. 237. SESAMUM, white-seeded, antiquity of the, ii. 429. _Setaria_, found in the Swiss lake-dwellings, i. 317. SETTERS, degeneration of, in India, i. 38; Youatt's remarks on, i. 41. SEX, secondary characters of, latent, ii. 51-52; of parents, influence of, on hybrids, ii. 267. SEXUAL characters, sometimes lost in domestication, ii. 74. SEXUAL limitation of characters, ii. 71-75. SEXUAL peculiarities, induced by domestication in sheep, i. 95; in fowls, i. 251-257; transfer of, i. 255-257. SEXUAL variability in pigeons, i. 161-162. SEXUAL selection, ii. 75. SHADDOCK, i. 335. SHAILER, Mr. , on the moss-rose, i. 379-380. SHANGHAI fowls, i. 227. SHANGHAI sheep, their fecundity, i. 97. SHAN ponies, striped, i. 58. SHEEP, disputed origin of, i. 94; early domestication of, i. 94; large-tailed, i. 94, 95, 98, ii. 279; variations in horns, mammæ and other characters of, i. 95; sexual characters of, induced by domestication, i. 95, 96; adaptation of, to climate and pasture, i. 96, 97; periods of gestation of, i. 97; effect of heat on the fleece of, i. 98-99, ii. 278; effect of selection on, i. 99-101; "ancon" or "otter" breeds of, i. 17, 92, 100; "Mauchamp-merino, " i. 100-101; cross of German and merino, ii. 85-89; black, of the Tarentino, ii. 227; Karakool, ii. 278; Jaffna, with callosities on the knees, ii. 302; Chinese, ii. 315; Danish, of the bronze period, ii. 427; polydactylism in, ii. 14; occasional production of horns in hornless breeds of, ii. 30; reversion of colour in, ii. 30; influence of male, on offspring, ii. 68; sexual differences in, ii. 73; influence of crossing or segregation on, ii. 86, 95-96, 102-103; interbreeding of, ii. 119-120; effect of nourishment on the fertility of, ii. 111-112; diminished fertility of, under certain conditions, ii. 161; unconscious selection of, ii. 213; natural selection in breeds of, ii. 224, 225, 227; reduction of bones in, ii. 242; individual differences of, ii. 251; local changes in the fleece of, in England, ii. 278; partial degeneration of, in Australia, ii. 278; with numerous horns, ii. 291; correlation of horns and fleece in, ii. 326; feeding on flesh, ii. 303; acclimatisation of, ii. 305-306; mountain, resistance of, to severe weather, ii. 312; white, poisoned by _Hypericum crispum_, ii. 337. SHEEP dogs resembling wolves, i. 24. SHELLS, sinistral and dextral, ii. 53. SHERIFF, Mr. New varieties of wheat, i. 315, 317; on crossing wheat, ii. 104-105; continuous variation of wheat, ii. 241. SIAM, cats of, i. 47; horses of, i. 53. SHIRLEY, E. P. , on the fallow-deer, ii. 103, 120. SHORT, D. , hybrids of the domestic cat and _Felis ornata_, i, 45. SIBERIA, northern range of wild horses in, i. 52. SICHEL, J. , on the deafness of white cats with blue eyes, ii. 329. SIDNEY, S. , on the pedigrees of pigs, ii. 3; on cross-reversion in pigs, ii. 35; period of gestation in the pig, i. 74; production of breeds of pigs by intercrossing, i. 78, 95; fertility of the pig, ii. 112; effects of interbreeding on pigs, ii. 121-122; on the colours of pigs, ii. 210, 229. SIEBOLD, on the sweet potato, ii. 309. SIEBOLD, von Carl, on parthenogenesis, ii. 364. _Silene_, contabescence in, ii. 166. SILK-FOWLS, i. 230, ii. 67, 69. {478} SILK-MOTH, Arrindy, ii. 306, 312; Tarroo, ii. 157. SILK-MOTHS, i. 300-304; domesticated species of, i. 300; history of, _ibid. _; causes of modification in, i. 300-301; differences presented by, i. 301-304; crossing of, ii. 98; disease in, ii. 228; effects of disuse of parts in, ii. 298; selection practised with, ii. 197, 199; variation of, ii. 236; parthenogenesis in, ii. 364. SILKWORMS, variations of, i. 301-302; yielding white cocoons, less liable to disease, ii. 336. SILVER-GREY rabbit, i. 108, 111, 120. SIMONDS, J. B. , period of maturity in various breeds of cattle, i. 87; differences in the periods of dentition in sheep, i. 96; on the teeth in cattle, sheep, &c. , ii. 322; on the breeding of superior rams, ii. 196. SIMON, on the raising of eggs of the silk-moth in China, ii. 197. SIMPSON, Sir J. , regenerative power of the human embryo, ii. 15. _Siredon_, breeding in the branchiferous stage, ii. 384. SISKIN, breeding in captivity, ii. 154. _Sivatherium_, resemblance of the, to Niata cattle, i. 89. SIZE, difference of, an obstacle to crossing, ii. 101. SKIN, and its appendages, homologous, ii. 325; hereditary affections of the, ii. 79. SKIRVING, R. S. , on pigeons settling on trees in Egypt, i. 181. SKULL, characters of the, in breeds of dogs, i. 34; in breeds of pigs, i. 71; in rabbits, i. 116-120, 127; in breeds of pigeons, i. 163-165; in breeds of fowls, i. 260-266; in ducks, i. 282-283. SKULL and horns, correlation of the, ii. 333. SKYLARK, ii. 154. SLEEMAN, on the Cheetah, ii. 151. SLOE, i. 345. SMALL-POX, ii. 378. SMITER (pigeon), i. 156. SMITH, Sir A. , on Caffrarian cattle, i. 88; on the use of numerous plants as food in South Africa, i. 307. SMITH, Colonel Hamilton, on the odour of the jackal, i. 30; on the origin of the dog, i. 16; wild dogs in St. Domingo, i. 28; on the Thibet mastiff and the alco, i. 28-29; development of the fifth toe in the hind feet of mastiffs, i. 35; differences in the skull of dogs, i. 34; history of the pointer, i. 42; on the ears of the dog, ii. 301; on the breeds of horses, i. 49; origin of the horse, i. 51; dappling of horses, i. 55; striped horses in Spain, i. 58; original colour of the horse, i. 60; on horses scraping away snow, i. 52; on _Asinus hemionus_, ii. 43; feral pigs of Jamaica, i. 77-78. SMITH, Sir J. E. , production of nectarines and peaches by the same tree, i. 340; on _Viola amoena_, i. 368; sterility of _Vinca minor_ in England, ii. 170. SMITH, J. , development of the ovary in _Bonatea speciosa_, by irritation of the stigma, i. 403. SMITH, N. H. , influence of the bull "Favourite" on the breed of Short-horn cattle, ii. 65. SMITH, W. , on the inter-crossing of strawberries, i. 352. SNAKE-RAT, ii. 87, 88. SNAKES, form of the viscera in, ii. 344. SNAPDRAGON, bud-variation in, i. 381; non-inheritance of colour in, ii. 21; peloric, crossed with the normal form, ii. 70, 93; asymmetrical variation of the, ii. 322. SOIL, adaptation of plums to, i. 346; influence of, on the zones of pelargoniums, i. 366; on roses, i. 367; on the variegation of leaves, i. 383; advantages of change of, ii. 146-148. SOIL and climate, effects of, on strawberries, i. 353. _Solanum_, non-intercrossing of species of, ii. 91. _Solanum tuberosum_, i. 330-331. SOLID-HOOFED pigs, i. 75. SOLOMON, his stud of horses, i. 55. SOMERVILLE, Lord, on the fleece of Merino sheep, i. 99; on crossing sheep, ii. 120; on selection of sheep, ii. 195; diminished fertility of Merino sheep brought from Spain, ii. 161. SOOTY fowls, i. 230, 256. SOTO, Ferdinand de, on the cultivation of native plants in Florida, i. 312. _Sorghum_, i. 371. SPAIN, hawthorn monogynous in, i. 364. SPALLANZANI, on feral rabbits in Lipari, i. 113; experiments on salamanders, ii. 15, 293, 385; experiments in feeding a pigeon with meat, ii. 304. SPANIELS, in India, i. 38; King Charles's, i. 41; degeneration of, caused by interbreeding, ii. 121. SPANISH fowls, i. 227, 250, 253; figured, i. 226; early development of sexual characters in, i. 250, 251; furcula of, figured, i. 268. SPECIES, difficulty of distinguishing from varieties, i. 4; conversion of varieties into, i. 5; origin of, by natural selection, ii. 414-415; by mutual sterility of varieties, ii. 185-189. {479} SPENCER, Lord, on selection in breeding, ii. 195. SPENCER, Herbert, on the "survival of the fittest, " i. 6; increase of fertility by domestication, ii. 111; on life, ii. 148, 177; changes produced by external conditions, ii. 281; effects of use on organs, ii. 295, 296; ascent of the sap in trees, ii. 296; correlation exemplified in the Irish elk, ii. 333-334; on "physiological units, " ii. 375; antagonism of growth and reproduction, ii. 384; formation of ducts in plants, ii. 300. SPERMATOPHORES of the cephalopoda, ii. 383. SPERMATOZOIDS, ii. 363-364; apparent independence of, in insects, ii. 384. SPHINGIDÆ, sterility of, in captivity, ii. 157. SPINOLA, on the injurious effect produced by flowering buckwheat on white pigs, ii. 337. SPITZ dog, i. 31. SPOONER, W. C. , cross-breeding of sheep, i. 100, ii. 95-96, 120; on the effects of crossing, ii. 96-97; on crossing cattle, ii. 118; individual sterility, ii. 162. SPORES, reproduction of abnormal forms by, i. 383. SPORTS, i. 373; in pigeons, i. 213. SPOT pigeon, i. 156, 207. SPRENGEL, C. K. , on dichogamous plants, ii. 90; on the hollyhock, ii. 107; on the functions of flowers, ii. 175. SPROULE, Mr. , inheritance of cleft-palate and hare-lip, ii. 24. SPURS, of fowls, i. 255; development of, in hens, ii. 318. SQUASHES, i. 357. SQUINTING, hereditary, ii. 9. SQUIRRELS, generally sterile in captivity, ii. 152. SQUIRRELS, flying, breeding in confinement, ii. 152. "STAARHALSIGE Taube, " i. 161. STAG, one-horned, supposed heredity of character in, ii. 12; degeneracy of, in the Highlands, ii. 208. STAMENS, occurrence of rudimentary, ii. 316; conversion of, into pistils, i. 365; into petals, ii. 392. _Staphylea_, ii. 168. STEENSTRUP, Prof. , on the dog of the Danish Middens, i. 18; on the obliquity of flounders, ii. 53. STEINAN, J. , on hereditary diseases, ii. 7, 79. STERILITY, in dogs, consequent on close confinement, i. 32; comparative, of crosses, ii. 103, 104; from changed conditions of life, ii. 148-165; occurring in the descendants of wild animals bred in captivity, ii. 160; individual, ii. 162; resulting from propagation by buds, cuttings, bulbs, &c. , ii. 169; in hybrids, ii. 178-180, 386, 410-411; in specific hybrids of pigeons, i. 193; as connected with natural selection, ii. 185-189. STERNUM, characters of the, in rabbits, i. 123; in pigeons, i. 167, 174-175; in fowls, i. 268, 273; effects of disuse on the, i. 174-175, 273. STEPHENS, J. F. , on the habits of the Bombycidæ, i. 303. STEWART, H. , on hereditary disease, ii. 79. STIGMA, variation of the, in cultivated Cucurbitaceæ, i. 359; satiation of the, i. 402-403. STOCKS, bud-variation in, i. 381; effect of crossing upon the colour of the seed of, i. 398-399; true by seed, ii. 20; crosses of, ii. 93; varieties of, produced by selection, ii. 219; reversion by the upper seeds in the pods of, ii. 347-348. STOCKHOLM, fruit-trees of, ii. 307. STOKES, Prof. , calculation of the chance of transmission of abnormal peculiarities in man, ii. 5. STOLONS, variations in the production of, by strawberries, i. 353. STOMACH, structure of the, affected by food, ii. 302. STONE in the bladder, hereditary, ii. 8, 79. STRAWBERRIES, i. 351-354; remarkable varieties of, i. 352-353; hautbois, dioecious, i. 353; selection in, ii. 200; mildew of, ii. 228; probable further modification of, ii. 243; variegated, effects of soil on, ii. 274. STRICKLAND, A. , on the domestication of _Anser ferus_, i. 287; on the colour of the bill and legs in geese, i. 288. _Strictoenas_, i. 183. STRIPES on young of wild swine, i. 76; of domestic pigs of Turkey, Westphalia, and the Zambesi, i. 76-77; of feral swine of Jamaica and New Granada, i. 77; of fruit and flowers, i. 400, ii. 37; in horses, i. 56-60; in the ass, i. 62-63; production of, by crossing species of Equidæ, ii. 42-43. _Strix grallaria_, ii. 302. _Strix passerina_, ii. 154. "STRUPP-TAUBE, " i. 155. STRUTHERS, Mr. , osteology of the feet in solid-hoofed pigs, i. 75; on polydactylism, ii. 13-14. STURM, prepotency of transmission of characters in sheep and cattle, ii. 66; absorption of the minority in crossed races, ii. 88; correlation of twisted horns and curled wool in sheep, ii. 326. {480} SUB-SPECIES, wild, of _Columba livia_ and other pigeons, i. 204. SUCCESSION, geological, of organisms, i. 11. SUCKERS, bud-variation by, i. 384. SUGAR cane, sterility of, in various countries, ii. 169; white, liability of, to disease, ii. 228, 336. SUICIDE, hereditary tendency to, ii. 7, 78. SULIVAN, Admiral, on the horses of the Falkland Islands, i. 53; wild pigs of the Falkland Islands, i. 77; feral cattle of the Falkland Islands, i. 86, 102; feral rabbits of the Falkland Islands, i. 112. SULTAN fowl, i. 228, 255. _Sus indica_, i. 65, 67-70, ii. 110. _Sus pliciceps_, i. 69 (figured). _Sus scrofa_, i. 65, 66, ii. 110. _Sus scrofa palustris_, i. 68. _Sus vittatus_, i. 67. SWALLOWS, a breed of pigeons, i. 156. SWAYNE, Mr. , on artificial crossing of varieties of the pea, i. 397. SWEET Peas, ii. 91; crosses of, ii. 93, 94; varieties of, coming true by seed, ii. 20; acclimatisation of, in India, ii. 311. SWEET William, bud-variation in, i. 381. SWINHOE, R. , on Chinese pigeons, i. 28, 206; on striped Chinese horses, i. 59. SWITZERLAND, ancient dogs of, i. 19; pigs of, in the Neolithic period, i. 67-68; goats of, i. 101. SYCAMORE, pale-leaved variety of the, ii. 330. SYKES, Colonel, on a Pariah dog with crooked legs, i. 17; on small Indian asses, i. 62; on _Gallus Sonneratii_, i. 233; on the voice of the Indian Kulm cock, i. 259; fertility of the fowl in most climates, ii. 161. SYMMETRY, hereditary departures from, ii. 12. _Symphytum_, variegated, i. 384. SYPHILIS, hereditary, ii. 332. SYRIA, asses of, i. 62. _Syringa persica_, _chinensis_, and _vulgaris_, ii. 164. TACITUS, on the care taken by the Celts in breeding animals, ii. 202. _Tagetes signata_, dwarf variety of, ii. 20. TAHITI, varieties of cultivated plants in, ii. 256. TAIL, occasional development of, in man, ii. 57; never curled in wild animals, ii. 301; rudimentary in Chinese sheep, ii. 315. TAIL-FEATHERS, numbers of, in breeds of pigeons, i. 158-159; peculiarities of, in cocks, i. 254-255; variability of, in fowls, i. 258; curled, in _Anas boschas_, and tame drakes, i. 280. TALENT, hereditary, ii. 7. TANKERVILLE, Earl of, on Chillingham cattle, i. 84, ii. 119. TANNER, Prof. , effects of disuse of parts in cattle, ii. 299. TAPIR, sterility of the, in captivity, ii. 150. TARGIONI-TOZZETTI, on cultivated plants, i. 306; on the vine, i. 332; varieties of the peach, i. 342; origin and varieties of the plum, i. 345; origin of the cherry, i. 347; origin of roses, i. 366. TARSUS, variability of the, in fowls, i. 259; reproduction of the, in a thrush, ii. 15. TARTARS, their preference for spiral-horned sheep, ii. 209. TAVERNIER, abundance of pigeons in Persia, i. 205. _Taxus baccata_, ii. 18. TEEBAY, Mr. , reversion in fowls, ii. 38. TEETH, number and position of, in dogs, i. 34; deficiency of, in naked Turkish dogs, i. 35; period of appearance of, in breeds of dogs, i. 35; precocity of, in highly bred animals, ii. 322; correlation of, with hair, ii. 326; double row of, with redundant hair, in Julia Pastrana, ii. 328; affected in form by hereditary syphilis and by pulmonary tubercle, ii. 332; fusion of, ii. 341; developed on the palate, ii. 391. TEGETMEIER, Mr. , on a cat with monstrous teeth, i. 48; on a swift-like pigeon, i. 157; naked young of some pigeons, i. 170; fertility of hybrid pigeons, i. 192; on white pigeons, ii. 230; reversion in crossed breeds of fowls, i. 239-244; chicks of the white silk-fowl, i. 249; development of the cranial protuberance in Polish fowls, i. 250; on the skull in the Polish fowl, i. 257, 262; on the intelligence of Polish fowls, i. 264; correlation of the cranial protuberance and crest in Polish fowls, i. 274; development of the web in the feet of Polish fowls, i. 259; early development of several peculiarities in Spanish cocks, i. 250; on the comb in Spanish fowls, i. 253; on the Spanish fowl, ii. 306; varieties of game-fowls, i. 252; pedigrees of game-fowls, ii. 3; assumption of female plumage by a game cock, i. 253; natural selection in the game cock, ii. 225; pugnacity of game hens, i. 256; length of the middle toe in Cochin fowls, i. 259; origin of the Sebright bantam, ii. 54; differences in the size of fowls, i. 257; effect of crossing in fowls, i. 258, ii. 96; effects of interbreeding in fowls, ii. 124-125; incubation by mongrels of non-sitting races of fowls, ii. 44; inverse correlation of crest and comb in fowls, i. 274; {481} occurrence of pencilled feathers in fowls, ii. 40; on a variety of the goose from Sebastopol, i. 289; on the fertility of the peahen, ii. 112; on the intercrossing of bees, ii. 126. TEMMINCK, origin of domestic cats, i. 43; origin of domestic pigeons, i. 180; on _Columba guinea_, i. 182; on _Columba leucocephala_, i. 183; asserted reluctance of some breeds of pigeons to cross, i. 192; sterility of hybrid turtle-doves, i. 193; variations of _Gallus bankiva_, i. 235; on a buff-coloured breed of Turkeys, i. 293; number of eggs laid by the peahen, ii. 112; breeding of Guans in captivity, ii. 156; behaviour of grouse in captivity, _ibid. _; sterility of the partridge in captivity, _ibid. _ TENDRILS in Cucurbitaceæ, i. 358, ii. 316. TENNENT, Sir J. E. , on the goose, i. 287; on the growth of the apple in Ceylon, ii. 277; on the Jaffna sheep, ii. 302. _Teredo_, fertilisation in, ii. 363. TERRIERS, wry-legged, ii. 245; white, subject to distemper, ii. 336. TESCHEMACHER, on a husked form of maize, i. 320. TESSIER, on the period of gestation of the dog, i. 29; of the pig, i. 74; in cattle, i. 87; experiments on change of soil, ii. 147. _Tetrao_, breeding of species of, in captivity, ii. 156. _Tetrapteryx paradisea_, ii. 156. _Teucrium campanulatum_, pelorism in, ii. 345. TEXAS, feral cattle in, i. 85. THEOGNIS, his notice of the domestic fowl, i. 246. THEOPHRASTUS, his notice of the peach, ii. 308. _Thesium_, ii. 284. THOMPSON, Mr. , on the peach and nectarine, i. 342; on the varieties of the apricot, i. 344; classification of varieties of cherries, i. 347-348; on the "Sister ribston-pippin, " i. 350; on the varieties of the gooseberry, i. 354, 355. THOMPSON, William, on the pigeons of Islay, i. 184; feral pigeons in Scotland, i. 190; colour of the bill and legs in geese, i. 288; breeding of _Tetrao scotius_ in captivity, ii. 156; destruction of black-fowls by the osprey, ii. 230. THOMPSON, Prof. W. , on the obliquity of the flounder, ii. 53. THORNS, reconversion of, into branches, in pear trees, ii. 318. THORN, grafting of early and late, i. 363; Glastonbury, i. 364. THRUSH, asserted reproduction of the tarsus in a, ii. 15. _Thuja pendula_ or _filiformis_, a variety of _T. Orientalis_, i. 362. THURET, on the division of the zoospores of an alga, ii. 378. THWAITES, G. H. , on the cats of Ceylon, i. 46; on a twin seed of _Fuchsia coccinea_ and _fulgens_, i. 391. TIBURTIUS, experiments in rearing wild ducks, i. 278. TIGER, rarely fertile in captivity, ii. 150, 151. _Tigridia conchiflora_, bud-variation in, i. 386. TIME, importance of, in the production of races, ii. 243. TINZMANN, self-impotence in the potato, ii. 137. TISSUES, affinity of, for special organic substances, ii. 380. TITMICE, destructive to thin-shelled walnuts, i. 356; attacking nuts, i. 357; attacking peas, ii. 231. TOBACCO, crossing of varieties of, ii. 108; cultivation of in Sweden, ii. 307. TOBOLSK, red-coloured cats of, i. 47. TOES, relative length of, in fowls, i. 259; development of fifth in dogs, ii. 317. TOLLET, Mr. , his selection of cattle, ii. 199. TOMATO, ii. 91. TOMTITS. See _Titmice_. TONGUE, relation of, to the beak in pigeons, i. 168. TOOTH, occurrence of a molar, in place of an incisor, ii. 391. "TORFSCHWEIN, " i. 68. TRAIL, R. , on the union of half-tubers of different kinds of potatoes, i. 395. TREES, varieties of, suddenly produced, i. 361; weeping or pendulous, i. 361; fastigate or pyramidal, i. 361; with variegated or changed foliage, i. 362; early or late in leaf, i. 362-363; forest, non-application of selection to, ii. 237. "TREMBLEUR" (pigeons), i. 146. TREMBLEY, on reproduction in Hydra, ii. 359. "TREVOLTINI" silkworms, i. 301-302. _Trichosanthes anguina_, i. 360. TRICKS, inheritance of, ii. 6-7, 395. _Trifolium minus_ and _repens_, ii. 164. TRIMORPHIC plants, conditions of reproduction in, ii. 181-184. TRISTRAM, H. B. , selection of the dromedary, ii. 205-206. _Triticum dicoccum_, i. 319. _Triticum monococcum_, i. 319. _Triticum spelta_, i. 319. _Triticum turgidum_, i. 319. _Triticum vulgare_, wild in Asia, i. 312. {482} TRITON, breeding in the branchiferous stage, ii. 384. "TROMMEL-TAUBE, " i. 154. "TRONFO" pigeon, i. 144. _Tropæolum_, ii. 38. _Tropæolum minus_ and _majus_, reversion in hybrids of, i. 392. TROUBETZKOY, Prince, experiments with pear-trees at Moscow, ii. 307. TROUSSEAU, Prof. , pathological resemblance of twins, ii. 252. TRUMPETER pigeon, i. 154; known in 1735, i. 207. TSCHARNER, H. A. De, graft-hybrid produced by inosculation in the vine, i. 395. TSCHUDI, on the naked Peruvian dog, i. 23; extinct varieties of maize from Peruvian tombs, i. 320, ii. 425. TUBERS, bud-variation by, i. 384-385. TUCKERMAN, Mr. , sterility of _Carex rigida_, ii. 170. TUFTED ducks, i. 281. TULIPS, variability of, i. 370; bud-variation in, i. 385-386; influence of soil in "breaking, " i. 385. TUMBLER pigeon, i. 150-153; short-faced, figured, i. 152; skull figured, i. 163; lower jaw figured, i. 165; scapula and furcula figured, i. 167; early known in India, i. 207; history of, i. 209; sub-breeds of, i. 220; young unable to break the egg-shell, ii. 226; probable further modification of, ii. 242. "TÜMMLER" (pigeons), i. 150. TUMOURS, ovarian, occurrence of hairs and teeth in, ii. 370; polypoid, origin of, ii. 381. "TÜRKISCHE TAUBE, " i. 139. TURBIT (pigeon), i. 148. TURKEY, domestic, origin of, i. 292-293; crossing of with North American wild Turkey, i. 292-293; breeds of, i. 293; crested white cock, i. 293; wild, characters of, i. 293-294; degeneration of, in India, i. 294, ii. 278; failure of eggs of, in Delhi, ii. 161; feral on the Parana, i. 190; change produced in by domestication, ii. 262. TURKEY, striped young pigs in, i. 76. TURNER (pigeon), i. 156. TURNER, W. , on compensation in arteries and veins, ii. 300; on cells, ii. 370. TURNIPS, origin of, i. 325; reversion in, ii. 31; run wild, ii. 33; crosses of, ii. 93, 96; Swedish, preferred by hares, ii. 232; acclimatisation of, in India, ii. 311. TURNSPIT, on an Egyptian monument, i. 17; crosses of the, ii. 92. TURTLE-DOVE, white and coloured, crossing of, ii. 92. _Turtur auritus_, hybrids of, with _T. Cambayensis_ and _T. Suratensis_, i. 194. _Turtur risorius_, crossing of, with the common pigeon, i. 193; hybrid of, with _T. Vulgaris_, _ibid. _ _Turtur suratensis_, sterile hybrids of, with _T. Vulgaris_, i. 193; hybrids of, with _T. Auritus_, i. 194. _Turtur vulgaris_, crossing of, with the common pigeon, i. 193; hybrid of, with _T. Risorius_, _ibid. _; sterile hybrids of, with _T. Suratensis_ and _Ectopistes migratorius_, _ibid. _ TUSKS of wild and domesticated pigs, i. 76, 77. _Tussilago farfara_, variegated, i. 384. TWIN-SEED _Fuchsia coccinea_ and _fulgens_, i. 391. TYERMAN, B. , on the pigs of the Pacific islands, i. 70, ii. 87; on the dogs of the Pacific islands, ii. 87. TYLOR, Mr. , on the prohibition of consanguineous marriages, ii. 122-123. UDDERS, development of the, ii. 300. _Ulex_, double-flowered, ii. 167. _Ulmus campestris_ and _effusa_, hybrids of, ii. 130. UNIFORMITY of character, maintained by crossing, ii. 85-90. UNITS of the body, functional independence of the, ii. 368-371. UNITY or plurality of origin of organisms, i. 13. UPAS poison, ii. 380. UREA, secretion of, ii. 380. USE and disuse of parts, effects of, ii. 295-303, 352-353, 418-419; in rabbits, i. 124-128; in ducks, i. 284-286. UTILITY, considerations of, leading to uniformity, ii. 241. VALENTIN, experimental production of double monsters by, ii. 340. _Vallota_, ii. 139. VAN BECK, Barbara, a hairy-faced woman, ii. 4. VAN MONS on wild fruit-trees, i. 312, ii. 260; production of varieties of the vine, i. 333; correlated variability in fruit-trees, ii. 330; production of almond-like fruit by peach-seedlings, i. 339. _Vanessa_, species of, not copulating in captivity, ii. 157. VARIABILITY, i. 4, ii. 371-373, 394-397, 406-420; causes of, ii. 250-270; correlated, ii. 319-338, 353-355, 419-420; law of equable, ii. 351-352; necessity of, for selection, ii. 192; of selected characters, ii. 238-239; of multiple homologous parts, ii. 342. {483} VARIATION, laws of, ii. 293-356; continuity of, ii. 241; possible limitation of, ii. 242, 416-417; in domestic cats, i. 45-48; origin of breeds of cattle by, i. 88; in osteological characters of rabbits, i. 115-130; of important organs, i. 359; analogous or parallel, i. 348-352; in horses, i. 55; in the horse and ass, i. 64; in fowls, i. 243-246; in geese, i. 288; exemplified in the production of fleshy stems in cabbages, &c. , i. 326; in the peach, nectarine, and apricot, i. 342, 344; individual, in wheat, i. 314. VARIEGATION of foliage, i. 383, ii. 167-168. VARIETIES and species, resemblance of, i. 4, ii. 411-413; conversion of, into species, i. 5; abnormal, ii. 413; domestic, gradually produced, ii. 414. VARRO, on domestic ducks, i. 277; on feral fowls, ii. 33; crossing of the wild and domestic ass, ii. 206. VASEY, Mr. , on the number of sacral vertebræ in ordinary and humped cattle, i. 79; on Hungarian cattle, i. 80. VAUCHER, sterility of _Ranunculus ficaria_ and _Acorus calamus_, ii. 170. VEGETABLES, cultivated, reversion in, ii. 31-32; European, culture of, in India, ii. 168-169. VEITH, Mr. , on breeds of horses, i. 49. _Verbascum_, intercrossing of species of, i. 336, ii. 93, 105-107; reversion in hybrids of, i. 392; contabescent, wild plants of, ii. 165; villosity in, ii. 277. _Verbascum austriacum_, ii. 136. _Verbascum blattaria_, ii. 105-106. _Verbascum lychnitis_, ii. 105-106, 136. _Verbascum nigrum_, ii. 136. _Verbascum phoeniceum_, ii. 107, 137; variable duration of, ii. 305. _Verbascum thapsus_, ii. 106. VERBENAS, origin of, i. 364; white, liability of, to mildew, ii. 228, 336; scorching of dark, ii. 229, 336; effect of changed conditions of life on, ii. 273. VERLOT, on the darkleaved Barberry, i. 362; inheritance of peculiarities of foliage in trees, i. 362; production of _Rosa cannabifolia_ by bud-variation from _R. Alba_, i. 381; bud-variation in _Aralia trifoliata_, i. 382; variegation of leaves, i. 383; colours of tulips, i. 386; uncertainty of inheritance, ii. 18; persistency of white flowers, ii. 20; peloric flowers of _Linaria_, ii. 58; tendency of striped flowers to uniformity of colour, ii. 70; non-intercrossing of certain allied plants, ii. 91; sterility of _Primulæ_ with coloured calyces, ii. 166; on fertile proliferous flowers, _ibid. _; on the Irish yew, ii. 241; differences in the _Camellia_, ii. 251; effect of soil on the variegated strawberry, ii. 274; correlated variability in plants, ii. 330. _Verruca_, ii. 53, 400. VERTEBRÆ, characters of, in rabbits, i. 120-122; in ducks, i. 283-284; number and variations of, in pigeons, i. 165-166; number and characters of, in fowls, i. 266-268; variability of number of, in the pig, i. 74. VERTUCH, see Putsche. "VERUGAS, " ii. 276. VESPUCIUS, early cultivation in Brazil, i. 311. VIBERT'S experiments on the cultivation of the vine from seed, i. 332. _Viburnum opulus_, ii. 185, 316. _Vicia sativa_, leaflet converted into a tendril in, ii. 392. VICUNAS, selection of, ii. 207. VILLOSITY of plants, influenced by dryness, ii. 277. VILMORIN, cultivation of the wild carrot, i. 326, ii. 217; colours of tulips, i. 386; uncertainty of inheritance in balsams and roses, ii. 18; experiments with dwarf varieties of _Saponaria calabrica_ and _Tagetes signata_, ii. 20; reversion of flowers by stripes and blotches, ii. 37; on variability, ii. 262. _Vinca minor_, sterility in, ii. 170. VINE, i. 332-334; parsley-leaved, reversion of, i. 382; graft-hybrid produced by inosculation in the, i. 395; disease of, influenced by colour of grapes, ii. 228; influence of climate, &c. , on varieties of the, ii. 278; diminished extent of cultivation of the, ii. 308; acclimatisation of the, in the West Indies, ii. 313. _Viola_, species of, i. 368. _Viola lutea_, different coloured flowers in, i. 408. _Viola tricolor_, reversion in, ii. 31, 47. VIRCHOW, Prof. , blindness occurring in the offspring of consanguineous marriages, ii. 143; on the growth of bones, ii. 294, 381; on cellular prolification, ii. 295; independence of the elements of the body, ii. 369; on the cell-theory, ii. 370; presence of hairs and teeth in ovarian tumours, ii. 370; of hairs in the brain, ii. 391; special affinities of the tissues, ii. 380; origin of polypoid excrescences and tumours, ii. 381. VIRGIL on the selection of seed-corn, i. 318, ii. 203; of cattle and sheep, ii. 202. VIRGINIAN islands, ponies of, i. 52. _Virgularia_, ii. 378. VISION, hereditary peculiarities of, ii. 8-9; {484} in amphibious animals, ii. 223; varieties of, ii. 300; affections of organs of, correlated with other peculiarities, ii. 328. _Vitis vinifera_, i. 332-334, 375. _Viverra_, sterility of species of, in captivity, ii. 151. VOGEL, varieties of the date palm, ii. 256. VOGT, on the indications of stripes on black kittens, ii. 55. VOICE, differences of, in fowls, i. 259; peculiarities of, in ducks, i. 281; inheritance of peculiarities of, ii. 6. VOLZ, on the history of the dog, i. 16; ancient history of the fowl, i. 246; domestic ducks unknown to Aristotle, i. 277; Indian cattle sent to Macedonia by Alexander, ii. 202; mention of mules in the Bible, ii. 202; history of the increase of breeds, ii. 244. VON BERG on _Verbascum phoeniceum_, ii. 305. VOORHELM, G. , his knowledge of hyacinths, i. 371, ii. 251. VROLIK, Prof. , on polydactylism, ii. 12; on double monsters, ii. 340; influence of the shape of the mother's pelvis on her child's head, ii. 344. WADERS, behaviour of, in confinement, ii. 156. WAHLENBERG, on the propagation of Alpine plants by buds, runners, bulbs, &c. , ii. 169. "WAHLVERWANDTSCHAFT" of Gärtner, ii. 180. WALES, white cattle of, in the 10th century, i. 85. WALKER, A. , on intermarriage, i. 404; on the inheritance of polydactylism, ii. 13. WALKER, D. , advantage of change of soil to wheat, ii. 146. WALLACE, A. R. , on a striped Javanese horse, i. 59; on the conditions of life of feral animals, ii. 32; artificial alteration of the plumage of birds, ii. 280; on polymorphic butterflies, ii. 399-400; on reversion, ii. 415; on the limit of change, ii. 417. WALLACE, Dr. , on the sterility of Sphingidæ hatched in autumn, ii. 158. WALLACHIAN sheep, sexual peculiarities in the horns of, i. 96. WALLFLOWER, bud-variation in, i. 382. WALLICH, Dr. , on _Thuja pendula_ or _filiformis_, i. 362. WALNUTS, i. 356-357; thin-shelled, attacked by tomtits, ii. 231; grafting of, ii. 259. WALSH, B. D. , on galls, ii. 282, 283; his "Law of equable variability, " ii. 351-352. WALTHER, F. L. , on the history of the dog, i. 16; on the intercrossing of the zebu and ordinary cattle, i. 83. WARING, Mr. , on individual sterility, ii. 162. WART hog, i. 76. WATERER, Mr. , spontaneous production of _Cytisus alpino-laburnum_, i. 390. WATER melon, i. 357. WATERHOUSE, G. R. , on the winter-colouring of _Lepus variabilis_, i. 111. WATERTON, C. , production of tailless foals, i. 53; on taming wild ducks, i. 278; on the wildness of half-bred wild ducks, ii. 45; assumption of male characters by a hen, ii. 51. WATSON, H. C. , on British wild fruit-trees, i. 312; on the non-variation of weeds, i. 317; origin of the plum, i. 345; variation in _Pyrus malus_, i. 348; on _Viola amoena_ and _tricolor_, i. 368; on reversion in Scotch kail, ii. 32; fertility of _Draba sylvestris_ when cultivated, ii. 163; on generally distributed British plants, ii. 285. WATTLES, rudimentary, in some fowls, ii. 315. WATTS, Miss, on Sultan fowls, i. 228. WEBB, James, interbreeding of sheep, ii. 120. WEBER, effect of the shape of the mother's pelvis on her child's head, ii. 344. WEEDS, supposed necessity for their modification, coincidently with cultivated plants, i. 317. WEEPING varieties of trees, i. 361. WEEPING habit of trees, capricious inheritance of, ii. 18-19. WEEVIL, injury done to stone-fruit by, in North America, ii. 231. WELSH cattle, descended from _Bos longifrons_, i. 81. WEST Indies, feral pigs of, i. 77; effect of climate of, upon sheep, i. 98. WESTERN, Lord, change effected by, in the sheep, ii. 198. WESTPHALIA, striped young pigs in, i. 76. WESTWOOD, J. O. , on peloric flowers of _Calceolaria_, ii. 346. WHATELY, Archbishop, on grafting early and late thorns, i. 363. WHEAT, specific unity or diversity of, i. 312-313, 316-317; Hasora, i. 313; presence or absence of barbs in, i. 314; Godron on variations in, _ibid. _; varieties of, i. 314-315; effects of soil and climate on, i. 316; deterioration of, _ibid. _; crossing of varieties of, _ibid. _, ii. 96, 104-105, 130; in the Swiss lake-dwellings, i. 317-319; selection applied to, i. 318, ii. 200; increased fertility of hybrids of, with _Ægilops_, ii. 110; advantage of change of soil to, ii. 146; {485} differences of, in various parts of India, ii. 165; continuous variation in, ii. 200; red, hardiness of, ii. 229, 336; Fenton, ii. 232; natural selection in, ii. 233; varieties of, found wild, ii. 260; effects of change of climate on, ii. 307; ancient variety of, ii. 429. WHITBY, Mrs. , on the markings of silkworms, i. 302; on the silkmoth, i. 303. WHITE, Mr. , reproduction of supernumerary digits after amputation, ii. 14; time occupied in the blending of crossed races, ii. 87. WHITE, Gilbert, vegetable diet of dogs, ii. 303. WHITE and white-spotted animals, liability of, to disease, ii. 336-337. WHITE flowers, most truly reproduced by seed, ii. 20. WICHURA, Max, on hybrid willows, ii. 50, 131, 267; analogy between the pollen of old-cultivated plants, and of hybrids, ii. 268. WICKING, Mr. , inheritance of the primary characters of _Columba livia_ in cross-bred pigeons, i. 201; production of a white head in almond tumblers, ii. 199. WICKSTED, Mr. , on cases of individual sterility, ii. 162. WIEGMANN, spontaneous crossing of blue and white peas, i. 397; crossing of varieties of cabbage, ii. 130; on contabescence, ii. 165. WIGHT, Dr. , sexual sterility of plants propagated by buds, &c. , ii. 169. WILDE, Sir W. R. , occurrence of _Bos frontosus_ and _longifrons_ in Irish crannoges, i. 81; attention paid to breeds of animals by the ancient Irish, ii. 203. WILDMAN, on the dahlia, ii. 216, 273. WILDNESS of the progeny of crossed tame animals, ii. 44-46. WILKES, Capt. , on the taming of pigeons among the Polynesians, ii. 161. WILKINSON, J. , on crossed cattle, ii. 104. WILLIAMS, Mr. , change of plumage in a Hamburgh hen, i. 258. WILLIAMS, Mr. , intercrossing of strawberries, i. 352. WILLIAMSON, Capt. , degeneration of dogs in India, i. 37; on small Indian asses, i. 62. WILLIAMSON, Rev. W. , doubling of _Anemone coronaria_ by selection, ii. 200. WILLOWS, weeping, i. 361; reversion of spiral-leaved weeping, i. 383; hybrids of, ii. 267; galls of, ii. 282-283. WILLOUGHBY, F. , notice of spot pigeons, i. 156; on a fantail pigeon, i. 208; on tumbler pigeons, i. 209; on the turbit, i. 209; on the barb and carrier pigeons, i. 211; on the hook-billed duck, i. 277. WILMOT, Mr. , on a crested white Turkey cock, i. 293; reversion of sheep in colour, ii. 30. WILSON, B. O. , fertility of hybrids of humped and ordinary cattle in Tasmania, i. 83. WILSON, Dr. , prepotency of the Manx over the common cat, ii. 66. WILSON, James, origin of dogs, i. 16. WILSON, Mr. , on prepotency of transmission in sheep, ii. 69; on the breeding of bulls, ii. 196. WINGS, proportionate length of, in different breeds of pigeons, i. 175-176; of fowls, effects of disuse on, i. 270-272; characters and variations of, in ducks, i. 284-286; diminution of, in birds of small islands, i. 286-287. WING-FEATHERS, number of, in pigeons, i. 159; variability of, in fowls, i. 258. WOLF, recent existence of, in Ireland, i. 16; barking of young, i. 27; hybrids of, with the dog, i. 32. WOLF-DOG, black, of Florida, i. 22. WOLVES, North American, their resemblance to dogs of the same region, i. 21-22; burrowing of, i. 27. WOODBURY, Mr. , crossing of the Ligurian and common hive bees, i. 299, ii. 126; variability of bees, i. 298. WOODWARD, S. P. , on Arctic Mollusca, ii. 256. WOOD, Willoughby, on Mr. Bates' cattle, ii. 118. WOOLER, W. A. , on the young of the Himalayan rabbit, i. 109; persistency of the coloured calyx in a crossed Polyanthus, i. 365. WORRARA poison, ii. 380. WOUNDS, healing of, ii. 294. WRIGHT, J. , production of crippled calves by shorthorned cattle, ii. 118; on selection in cattle, ii. 194; effect of close interbreeding on pigs, ii. 121-122; deterioration of game cocks by close interbreeding, ii. 124. WRIGHT, Strethill, on the development of the hydroida, ii. 368. WYMAN, Dr. , on Niata cattle, and on a similar malformation in the codfish, i. 89; on Virginian pigs, ii. 227. XENOPHON, on the colours of hunting dogs, ii. 209. XIMENES, Cardinal, regulations for the selection of rams, ii. 204. "YAHOO, " the name of the pigeon in Persia, i. 155. YAKS, domestication of, i. 82; selection of white-tailed, ii. 206, 209. {486} YAM, development of axillary bulbs in the, ii. 169. YARRELL, Mr. , deficiency of teeth in hairless dogs, i. 34, ii. 326; on ducks, i. 279, ii. 262; characters of domestic goose, resembling those of _Anser albifrons_, i. 288; whiteness of ganders, i. 288; variations in goldfish, i. 296-297; assumption of male plumage by the hen-pheasant, ii. 51; effect of castration upon the cock, ii. 51-52; breeding of the skylark in captivity, ii. 154; plumage of the male linnet in confinement, ii. 158; on the dingo, ii. 263. YELLOW fever, in Mexico, ii. 276. YEW, fastigate, ii. 241. YEW, Irish, hardy in New York, ii. 309. YEW, weeping, i. 361; propagation of, by seed, ii. 18-19. YOLK, variations of, in the eggs of ducks, i. 281. YOUATT, Mr. , history of the dog, i. 16-17; variations of the pulse in breeds of dogs, i. 35; liability to disease in dogs, i. 35, ii. 227; inheritance of goître in dogs, ii. 10; on the greyhound, i. 34, 41; on King Charles' spaniels, i. 41; on the setter, i. 41; on breeds of horses, i. 49; variation in the number of ribs in the horse, i. 50; inheritance of diseases in the horse, ii. 10, 11; introduction of Eastern blood into English horses, ii. 212-213; on white Welsh cattle, i. 85, ii. 209; improvement of British breeds of cattle, i. 93; rudiments of horns in young hornless cattle, ii. 55, 315; on crossed cattle, ii. 104, 119; on Bakewell's long-horned cattle, ii. 118; selection of qualities in cattle, ii. 196; degeneration of cattle by neglect, ii. 239; on the skull in hornless cattle, ii. 333; disease of white parts of cattle, ii. 337; displacement of long-horned by short-horned cattle, ii. 426; on Angola sheep, i. 95; on the fleece of sheep, i. 99; correlation of horns and fleece in sheep, i. 95; adaptation of breeds of sheep to climate and pasture, i. 96; horns of Wallachian sheep, i. 96; exotic sheep in the Zoological Gardens, i. 96-97, ii. 305; occurrence of horns in hornless breeds of sheep, ii. 30; on the colour of sheep, ii. 30; on interbreeding sheep, ii. 120; on Merino rams in Germany, ii. 196; effect of unconscious selection on sheep, ii. 213; reversion of Leicester sheep on the Lammermuir Hills, ii. 224; on many-horned sheep, ii. 326; reduction of bone in sheep, ii. 242; persistency of character in breeds of animals in mountainous countries, ii. 64; on interbreeding, ii. 116; on the power of selection, ii. 194-195; slowness of production of breeds, ii. 244; passages in the Bible relating to the breeding of animals, ii. 201-202. YOUNG, J. , on the Belgian rabbit, i. 106. YULE, Capt. , on a Burmese hairy family, ii. 77, 327. ZAMBESI, striped young pigs on the, i. 77. ZAMBOS, character of the, ii. 47. ZANO, J. G. , introduction of rabbits into Porto Santo by, i. 112. _Zea Mays_, i. 320. ZEBU, i. 79; domestication of the, i. 82; fertile crossing of, with European cattle, i. 83, ii. 110. ZEBRA, hybrids of, with the ass and mare, ii. 42. _Zephyranthes candida_, ii. 164. _Zinnia_, cultivation of, ii. 261. ZOLLINGER on Malayan penguin ducks, i. 280. ZOOSPORE, division of, in Algæ, ii. 378. "ZOPF-TAUBE, " i. 154. THE END. LONDON: PRINTED BY W. CLOWES AND SONS, DUKE STREET, STAMFORD STREET, ANDCHARING CROSS. * * * * * NOTES [1] 'Medical Notes and Reflections, ' 3rd edit. , 1855, p. 267. [2] Mr. Buckle, in his grand work on 'Civilisation, ' expresses doubts onthe subject owing to the want of statistics. _See_ also Mr. Bowen, Professor of Moral Philosophy, in 'Proc. American Acad. Of Sciences, ' vol. V. P. 102 [3] For greyhounds, _see_ Low's 'Domest. Animals of the British Islands, '1845, p. 721. For game-fowls, _see_ 'The Poultry Book, ' by Mr. Tegetmeier, 1866, p. 123. For pigs, _see_ Mr. Sidney's edit. Of 'Youatt on the Pig, '1860, pp. 11, 22. [4] 'The Stud Farm, ' by Cecil, p. 39. [5] 'Philosophical Transactions, ' 1755, p. 23. I have seen only second-handaccounts of the two grandsons. Mr. Sedgwick, in a paper to which I shallhereafter often refer, states that _four_ generations were affected, and ineach the males alone. [6] Barbara Van Beck, figured, as I am informed by the Rev. W. D. Fox, inWoodburn's 'Gallery of Rare Portraits, ' 1816, vol. Ii. [7] 'Proc. Zoolog. Soc. , ' 1833, p. 16 [8] Hofacker, 'Ueber die Eigenschaften, ' &c. , 1828, s. 34. Report byPariset in 'Comptes Rendus, ' 1847, p. 592. [9] Hunter, as quoted in Harlan's 'Med. Researches, ' p. 530. Sir A. Carlisle, 'Phil. Transact. , ' 1814, p. 94. [10] Girou de Buzareignues, 'De la Génération, ' p. 282. [11] 'Macmillan's Magazine, ' July and August, 1865. [12] The works which I have read and found most useful are Dr. ProsperLucas's great work, 'Traité de l'Hérédité Naturelle, ' 1847. Mr. W. Sedgwick, in 'British and Foreign Medico-Chirurg. Review, ' April and July, 1861, and April and July, 1863: Dr. Garrod on Gout is quoted in thesearticles. Sir Henry Holland, 'Medical Notes and Reflections, ' 3rd edit. , 1855. Piorry, 'De l'Hérédité dans les Maladies, ' 1840. Adams, 'APhilosophical Treatise on Hereditary Peculiarities, ' 2nd edit. , 1815. Essayon 'Hereditary Diseases, ' by Dr. J. Steinan, 1843. _See_ Paget, in 'MedicalTimes, ' 1857, p. 192, on the Inheritance of Cancer; Dr. Gould, in 'Proc. OfAmerican Acad. Of Sciences, ' Nov. 8, 1853, gives a curious case ofhereditary bleeding in four generations. Harlan, 'Medical Researches, ' p. 593. [13] Marshall, quoted by Youatt in his work on Cattle, p. 284. [14] 'Philosoph. Transact. , ' 1814, p. 94. [15] 'Medical Notes and Reflections, ' 3rd edit. , p. 33. [16] This affection, as I hear from Mr. Bowman, has been ably described andspoken of as hereditary by Dr. Dondera, of Utrecht, whose work waspublished in English by the Sydenham Society in 1864. [17] Quoted by Mr. Herbert Spencer, 'Principles of Biology, ' vol. I. P. 244. [18] 'British and Foreign Medico-Chirurg. Review, 'April, 1861, p. 482-6;'l'Héréd. Nat. , ' tom. I. Pp. 391-408. [19] Dr. Osborne, Pres. Of Royal College of Phys. In Ireland, publishedthis case in the 'Dublin Medical Journal' for 1835. [20] These various statements are taken from the following works andpapers:--Youatt on 'The Horse, ' pp. 35, 220. Lawrence, 'The Horse, ' p. 30. Karkeek, in an excellent paper in 'Gard. Chronicle, ' 1853, p. 92. Mr. Burke, in 'Journal of R. Agricul. Soc. Of England, ' vol. V. P. 511. 'Encyclop. Of Rural Sports, ' p. 279. Girou de Buzareignues, 'Philosoph. Phys. , ' p. 215. _See_ following papers in 'The Veterinary:' Roberts, invol. Ii. P. 144; M. Marrimpoey, vol. Ii. P. 387; Mr. Karkeek, vol. Iv. P. 5; Youatt on Goître in Dogs, vol. V. P. 483; Youatt, in vol. Vi. Pp. 66, 348, 412; M. Bernard, vol. Xi. P. 539; Dr. Samesreuther, on Cattle, in vol. Xii. P. 181; Percivall, in vol. Xiii. P. 47. With respect to blindness inhorses, _see_ also a whole row of authorities in Dr. P. Lucas's great work, tom. I. P. 399. Mr. Baker, in 'The Veterinary, ' vol. Xiii. P. 721, gives astrong case of hereditary imperfect vision and of jibbing. [21] Knight on 'The Culture of the Apple and Pear, ' p. 31. Lindley's'Horticulture, ' p. 180. [22] These statements are taken from the following works in order:--Youatton 'The Horse, ' p. 48; Mr. Darvill, in 'The Veterinary, ' vol. Viii. P. 50. With respect to Robson, _see_ 'The Veterinary, ' vol. Iii. P. 580; Mr. Lawrence on 'The Horse, ' 1829, p. 9; 'The Stud Farm, ' by Cecil, 1851; BaronCameronn, quoted in 'The Veterinary, ' vol x. P. 500. [23] 'Recreations in Agriculture and Nat. Hist. , ' vol. I. P. 68. [24] 'Ueber die Eigenschaften, ' &c. , 1828, s. 107. [25] Bronn's 'Geschichte der Natur, ' band ii. S. 132. [26] Vrolik has discussed this point at full length in a work published inDutch, from which Mr. Paget has kindly translated for me passages. _See_, also, Isidore Geoffroy St. Hilaire's 'Hist. Des Anomalies, ' 1832, tom. I. P. 684. [27] 'Edinburgh New Phil. Journal, ' July, 1863. [28] Some great anatomists, as Cuvier and Meckel, believe that the tubercleone side of the hinder foot of the tailless Batrachians represents a sixthdigit. Certainly, when the hinder foot of a toad, as soon as it firstsprouts from the tadpole, is dissected, the partially ossified cartilage ofthis tubercle resembles under the microscope, in a remarkable manner, adigit. But the highest authority on such subjects, Gegenbaur (Untersuchung. Zur vergleich. Anat. Der Wirbelthiere: Carpus et Tarsus, 1864, s. 63), concludes that this resemblance is not real, only superficial. [29] For these several statements, _see_ Dr. Struthers, in work cited, especially on intermissions in the line of descent. Prof. Huxley, 'Lectureson our Knowledge of Organic Nature, ' 1863, p. 97. With respect toinheritance, _see_ Dr. Prosper Lucas, 'L'Hérédité Nat. , ' tom. I. P. 325. Isid. Geoffroy, 'Anom. , ' tom. I. P. 701. Sir A. Carlisle, in 'Phil. Transact. , ' 1814, p. 94. A. Walker, on 'Intermarriage, ' 1838, p. 140, givesa case of five generations; as does Mr. Sedgwick, in 'Brit. And ForeignMedico-Chirurg. Review, ' April, 1863, p. 462. On the inheritance of otheranomalies in the extremities, _see_ Dr. H. Dobell, in vol. Xlvi. Of'Medico-Chirurg. Transactions, ' 1863; also Mr. Sedgwick, in op. Cit. , April, 1863, p. 460. With respect to additional digits in the negro, _see_Prichard, 'Physical History of Mankind. ' Dr. Dieffenbach ('Journ. RoyalGeograph. Soc. , ' 1841, p. 208) says this anomaly is not uncommon with thePolynesians of the Chatham Islands. [30] 'The Poultry Chronicle, ' 1854, p. 559. [31] The statements in this paragraph are taken from Isidore Geoffroy St. Hilaire, 'Hist. Des Anomalies, ' tom. I. Pp. 688-693. [32] As quoted by Carpenter, 'Princ. Of Comp. Physiology, ' 1854, p. 480. [33] Müller's 'Phys. , ' Eng. Translat. , vol. I. 1838, p. 407. A thrush, however, was exhibited before the British Association at Hull, in 1853, which had lost its tarsus, and this member, it was asserted, had beenthrice reproduced: I presume it was lost each time by disease. [34] 'Monthly Journal of Medical Science, ' Edinburgh, 1848, new series, vol. Ii. P. 890. [35] 'An Essay on Animal Reproduction, ' trans. By Dr. Maty, 1769, p. 79. [36] Bonnet, 'Oeuvres d'Hist. Nat. , ' tom. V. , part i. , 4to. Edit. , 1781, pp. 343, 350, 353. [37] So with insects, the larvæ reproduce lost limbs, but, except in oneorder, the mature insect has no such power. But the Myriapoda, whichapparently represent the larvæ of true insects, have, as Newport has shown, this power until their last moult. _See_ an excellent discussion on thiswhole subject by Dr. Carpenter in his 'Princ. Comp. Phys. , ' 1854, p. 479. [38] Dr. Günther, in Owen's 'Anatomy of Vertebrates, ' vol. I. , 1866, p. 567. Spallanzani has made similar observations. [39] 'On the Anatomy of Vertebrates, ' 1866, p. 170: with respect to thepectoral fins of fishes, pp. 166-168. [40] 'Medical Notes and Reflections, ' 1839, pp. 24, 34. _See_, also, Dr. P. Lucas, 'l'Héréd. Nat. , ' tom. Ii. P. 33. [41] 'Du Danger des Mariages Consanguins, ' 2nd edit. , 1862, p. 103. [42] 'British and Foreign Medico-Chirurg. Review, ' July, 1863, pp. 183, 189. [43] Verlot, 'La Production des Variétés, ' 1865, p. 32. [44] Loudon's 'Gard. Mag. , ' vol. Xii. , 1836, p. 368. [45] Verlot, 'La Product. Des Variétés, ' 1865, p. 94. [46] Bronn's 'Geschichte der Natur, ' b. Ii. S. 121. [47] Rev. W. A. Leighton, 'Flora of Shropshire, ' p. 497; and Charlesworth's'Mag. Of Nat. Hist. , ' vol. I, 1837, p. 30. [48] Verlot, op. Cit. , p. 93. [49] For these several statements, _see_ Loudon's 'Gard. Magazine, ' vol. X. , 1834, pp. 408, 180; and vol. Ix. , 1833, p. 597. [50] These statements are taken from Alph. De Candolle, 'Bot. Géograph. , 'p. 1083. [51] Verlot, op. Cit. , p. 38. [52] Op. Cit. , p. 59. [53] Alph. De Candolle, 'Géograph. Bot. , ' p. 1082. [54] _See_ 'Cottage Gardener, ' April 10, 1860, p. 18, and Sept. 10, 1861, p. 456; 'Gard. Chron. , ' 1845, p. 102. [55] Darwin, in 'Journal of Proc. Linn. Soc. Bot. , ' 1862, p. 94. [56] Hofacker, 'Ueber die Eigenschaften, ' &c. , s. 10. [57] Bechstein, 'Naturgesch. Deutschlands, ' b. Iv. S. 462. Mr. Brent, agreat breeder of canaries, informs me that he believes that thesestatements are correct. [58] 'The Poultry Book, ' by W. B. Tegetmeier, 1866, p. 245. [59] 'British and Foreign Med. -Chirurg. Review, ' July, 1861, pp. 200-204. Mr. Sedgwick has given such full details on this subject, with amplereferences, that I need refer to no other authorities. [60] 'De l'Espèce, ' tom. Ii. , 1859, p. 299. [61] 'Philosoph. Magazine, ' vol. Iv. , 1799, p. 5. [62] This last case is quoted by Mr. Sedgwick in 'British and ForeignMedico-Chirurg. Review, ' April, 1861, p. 484. For Blumenbach, _see_above-cited paper. _See_, also, Dr. P. Lucas, 'Traité de l'Héréd. Nat. , 'tom. Ii. P. 492. Also 'Transact. Lin. Soc. , ' vol. Ix. P. 323. Some curiouscases are given by Mr. Baker in 'The Veterinary, ' vol. Xiii. P. 723. Another curious case is given in the 'Annales des Scienc. Nat. , ' 1stseries, tom. Xi. P. 324. [63] 'Proc. Royal Soc. , ' vol. X. P. 297. [64] Mr. Sproule, in 'British Medical Journal, ' April 18, 1863. [65] Downing, 'Fruits of America, ' p. 5; Sageret, 'Pom. Phys. , ' pp. 43, 72. [66] Youatt on Sheep, pp. 20, 234. The same fact of loose hornsoccasionally appearing in hornless breeds has been observed in Germany:Bechstein, 'Naturgesch. Deutschlands, ' b. I. S. 362. [67] Youatt on Cattle, pp. 155, 174. [68] Youatt on Sheep, 1838, pp. 17, 145. [69] I have been informed of this fact through the Rev. W. D. Fox, on theexcellent authority of Mr. Wilmot: _see_, also, remarks on this subject inan original article in the 'Quarterly Review, ' 1849, p. 395. [70] Youatt, pp. 19, 234. [71] 'The Poultry Book, ' by Mr. Tegetmeier, 1866, p. 231. [72] Loudon's 'Gard. Mag. , ' vol. X. , 1834, p. 396: a nurseryman, with muchexperience on this subject, has likewise assured me that this sometimesoccurs. [73] 'Gardener's Chron. , ' 1855, p. 777. [74] Ibid. , 1862, p. 721. [75] _See_ some excellent remarks on this subject by Mr. Wallace, 'JournalProc. Linn. Soc. , ' 1858, vol. Iii. P. 60. [76] Dureau de la Malle, in 'Comptes Rendus, ' tom. Xli. , 1855, p. 807. Fromthe statements above given, the author concludes that the wild pigs ofLouisiana are not descended from the European _Sus scrofa_. [77] Capt. W. Allen, in his 'Expedition to the Niger, ' states that fowlshave run wild on the island of Annobon, and have become modified in formand voice. The account is so meagre and vague that it did not appear to meworth copying; but I now find that Dureau de la Malle ('Comptes Rendus, 'tom. Xli. , 1855, p. 690) advances this as a good instance of reversion tothe primitive stock, and as confirmatory of a still more vague statement inclassical times by Varro. [78] 'Flora of Australia, ' 1859, Introduct. , p. Ix. [79] 'De l'Espèce, ' tom. Ii. Pp. 54, 58, 60. [80] Mr. Sedgwick gives many instances in the 'British and ForeignMed. -Chirurg. Review, ' April and July, 1863, pp. 448, 188. [81] In his edit. Of 'Youatt on the Pig, ' 1860, p. 27. [82] Dr. P. Lucas, 'Héréd. Nat. , ' tom. Ii. Pp. 314, 892: _see_ a goodpractical article on this subject in 'Gard. Chronicle, ' 1856, p. 620. Icould add a vast number of references, but they would be superfluous. [83] Kölreuter gives cases in his 'Dritte Fortsetzung, ' 1766, s. 53, 59;and in his well-known 'Memoirs on Lavatera and Jalapa. ' Gärtner, 'Bastarderzeugung, ' s. 437, 441, &c. Naudin, in his 'Recherches surl'Hybridité, Nouvelles Archives du Muséum, ' tom. I. P. 25. [84] Quoted by Mr. Sedgwick in 'Med. -Chirurg. Review, ' April, 1861, p. 485. Dr. H. Dobell, in 'Med. -Chirurg. Transactions, ' vol. Xlvi. , gives ananalogous case, in which, in a large family, fingers with thickened jointswere transmitted to several members during five generations; but when theblemish once disappeared it never reappeared. [85] Verlot, 'Des Variétés, ' 1865, p. 63. [86] 'Nouvelles Archives du Muséum, ' tom. I. P. 25. Alex. Braun (in his'Rejuvenescence, ' Ray Soc. , 1853, p. 315) apparently holds a similaropinion. [87] Mr. Teebay, in 'The Poultry Book, ' by Mr. Tegetmeier, 1866, p. 72. [88] Quoted by Hofacker, 'Ueber die Eigenschaften, ' &c. , s. 98. [89] 'Essais Hist. Nat. Du Paraguay, ' tom. Ii. 1801, p. 372. [90] These facts are given on the high authority of Mr. Hewitt, in 'ThePoultry Book, ' by Mr. Tegetmeier, 1866, p. 248. [91] 'The Poultry Book, ' by Tegetmeier, 1866, p. 97. [92] 'Gardener's Chron. And Agricultural Gazette, ' 1866, p. 528. [93] Ibid. , 1860, p. 343. [94] Sclater, in 'Proc. Zoolog. Soc. , ' 1862, p. 163. [95] 'History of the Horse, ' p. 212. [96] 'Mém. Présentés par divers Savans à l'Acad. Royale, ' tom. Vi. 1835, p. 338. [97] 'Letters from Alabama, ' 1859, p. 280. [98] 'Hist. Nat. Des Mammifères, ' 1820, tom. I. [99] 'Philosoph. Transact. , ' 1821, p. 20. [100] Sclater, in 'Proc. Zoolog. Soc. , ' 1862, p. 163: this species is theGhor-Khur of N. W. India, and has often been called the Hemionus of Pallas. _See_, also, Mr. Blyth's excellent paper in 'Journ. Of Asiatic Soc. OfBengal, ' vol. Xxviii. , 1860, p. 229. [101] Another species of wild ass, the true _A. Hemionus_ or _Kiang_, whichordinarily has no shoulder-stripes, is said occasionally to have them; andthese, as with the horse and ass, are sometimes double: _see_ Mr. Blyth, inthe paper just quoted, and in 'Indian Sporting Review, ' 1856, p. 320; andCol. Hamilton Smith, in 'Nat. Library, Horses, ' p. 318; and 'Dict. Class. D'Hist. Nat. , ' tom. Iii. P. 563. [102] Figured in the 'Gleanings from the Knowsley Menageries, ' by Dr. J. E. Gray. [103] Cases of both Spanish and Polish hens sitting are given in the'Poultry Chronicle, ' 1855, vol. Iii. P. 477. [104] 'The Poultry Book, ' by Mr. Tegetmeier, 1866, pp. 119, 163. Theauthor, who remarks on the two negatives ('Journ. Of Hort. , ' 1862, p. 325), states that two broods were raised from a Spanish cock and Silver-pencilledHamburgh hen, neither of which are incubators, and no less than seven outof eight hens in these two broods "showed a perfect obstinacy in sitting. "The Rev. E. S. Dixon ('Ornamental Poultry, ' 1848, p. 200) says thatchickens reared from a cross between Golden and Black Polish fowls, are"good and steady birds to sit. " Mr. B. P. Brent informs me that he raisedsome good sitting hens by crossing Pencilled Hamburgh and Polish breeds. Across-bred bird from a Spanish non-incubating cock and Cochin incubatinghen is mentioned in the 'Poultry Chronicle, ' vol. Iii. P. 13, as an"exemplary mother. " On the other hand, an exceptional case is given in the'Cottage Gardener, ' 1860, p. 388, of a hen raised from a Spanish cock andblack Polish hen which did not incubate. [105] 'The Poultry Book, ' by Tegetmeier, 1866, pp. 165, 167. [106] 'Natural History Review, ' 1863, April, p. 277. [107] 'Essays on Natural History, ' p. 197. [108] As stated by Mr. Orton, in his 'Physiology of Breeding, ' p. 12. [109] M. E. De Selys-Longchamps refers ('Bulletin Acad. Roy. De Bruxelles, 'tom. Xii. No. 10) to more than seven of these hybrids shot in Switzerlandand France. M. Deby asserts ('Zoologist, ' vol. V. , 1845-46, p. 1254) thatseveral have been shot in various parts of Belgium and Northern France. Audubon ('Ornitholog. Biography, ' vol. Iii. P. 168), speaking of thesehybrids, says that, in North America, they "now and then wander off andbecome quite wild. " [110] 'Journal of Researches, ' 1845, p. 71. [111] 'Expedition to the Zambesi, ' 1865, pp. 25, 150. [112] Dr. P. Broca, on 'Hybridity in the Genus Homo, ' Eng. Translat. , 1864, p. 39. [113] 'Nouvelles Archives du Muséum, ' tom. I. P. 151. [114] 'Bastarderzeugung, ' s. 582, 438, &c. [115] 'Die Bastardbefruchtung ... Der Weiden, ' 1865, s. 23. For Gärtner'sremarks on this head, _see_ 'Bastarderzeugung, ' s. 474, 582. [116] Yarrell, 'Phil. Transact. , ' 1827, p. 268; Dr. Hamilton, in 'Proc. Zoolog. Soc. , ' 1862, p. 23. [117] 'Archiv. Skand. Beiträge zur Naturgesch. , ' viii. S. 397-413. [118] In his 'Essays on Nat. Hist. , ' 1838. Mr. Hewitt gives analogous caseswith hen-pheasants in 'Journal of Horticulture, ' July 12, 1864, p. 37. Isidore Geoffroy Saint Hilaire, in his 'Essais de Zoolog. Gén. ' (suites àBuffon, 1842, pp. 496-513), has collected such cases in ten different kindsof birds. It appears that Aristotle was well aware of the change in mentaldisposition in old hens. The case of the female deer acquiring horns isgiven at p. 513. [119] 'Cottage Gardener, ' 1860, p. 379. [120] 'Art de faire Eclorre, ' &c. , 1749, tom. Ii. P. 8. [121] Sir H. Holland, 'Medical Notes and Reflections, ' 3rd edit. , 1855, p. 31. [122] Prof. Thomson on Steenstrup's Views on the Obliquity of Flounders:'Annals and Mag. Of Nat. Hist. , ' May, 1865, p. 361. [123] Dr. E. Von Martens, in 'Annals and Mag. Of Nat. Hist. , ' March, 1866, p. 209. [124] Darwin, 'Balanidæ, ' Ray Soc. , 1854, p. 499: _see_ also the appendedremarks on the apparently capricious development of the thoracic limbs onthe right and left sides in the higher crustaceans. [125] Mormodes ignea: Darwin, 'Fertilization of Orchids, ' 1862, p. 251. [126] 'Journal of Horticulture, ' July, 1864, p. 38. I have had theopportunity of examining these remarkable feathers through the kindness ofMr. Tegetmeier. [127] 'The Poultry Book, ' by Mr. Tegetmeier, 1866, p. 241. [128] Carl Vogt, 'Lectures on Man, ' Eng. Translat. , 1864, p. 411. [129] On Cattle, p. 174. [130] Isid. Geoffroy St. Hilaire, 'Des Anomalies, ' tom. Iii. P. 353. Withrespect to the mammæ in women, _see_ tom. I. P. 710. [131] 'Natural Hist. Review, ' April, 1863, p. 258. _See_ also his Lecture, Royal Institution, March 16, 1860. On same subject, _see_ Moquin-Tandon, 'Eléments de Tératologie, ' 1841, pp. 184, 352. [132] Verlot, 'Des Variétés, ' 1865, p. 89; Naudin, 'Nouvelles Archives duMuséum, ' tom. I. P. 137. [133] In his discussion on some curious peloric calceolarias, quoted in'Journal of Horticulture, ' Feb. 24, 1863, p. 152. [134] For other cases of six divisions in peloric flowers of the Labiatæand Scrophulariaceæ, _see_ Moquin-Tandon, 'Tératologie, ' p. 192. [135] Moquin-Tandon, 'Tératologie, ' p. 186. [136] _See_ Youatt on Cattle, pp. 92, 69, 78, 88, 163: also Youatt onSheep, p. 325. Also Dr. Lucas, 'L'Héréd. Nat. , ' tom. Ii. P. 310. [137] 'Héréd. Nat. , ' tom. Ii. Pp. 112-120. [138] Sir H. Holland, 'Chapters on Mental Physiology, ' 1852, p. 234. [139] 'Gardener's Chronicle, ' 1860, p. 270. [140] Mr. N. H. Smith, Observations on Breeding, quoted in 'Encyclop. OfRural Sports, ' p. 278. [141] Quoted by Bronn, 'Geschichte der Natur, ' b. Ii. S. 170. _See_ Sturm, 'Ueber Racen, ' 1825, s. 104-107. For the niata cattle, _see_ my 'Journal ofResearches, ' 1845, p. 146. [142] Lucas, 'l'Hérédité Nat. , ' tom. Ii. P. 112. [143] Mr. Orton, 'Physiology of Breeding, ' 1855, p. 9. [144] Boitard and Corbié, 'Les Pigeons, ' 1824, p. 224. [145] 'Les Pigeons, pp. 168, 198. [146] 'Das Ganze, ' &c. , 1837, s. 39. [147] 'The Pigeon Book, ' p. 46. [148] 'Physiology of Breeding, ' p. 22; Mr. Hewitt, in 'The Poultry Book, ' byTegetmeier, 1866, p. 224. [149] Boitard and Corbié, 'Les Pigeons, ' 1824, p. 226. [150] 'Bastarderzeugung, ' s. 256, 290, &c. Naudin ('Nouvelles Archives duMuséum, ' tom. I. P. 149) gives a striking instance of prepotency in _Daturastramonium_ when crossed with two other species. [151] Flourens, 'Longévité Humaine, ' p. 144, on crossed jackals. Withrespect to the difference between the mule and the hinny, I am aware thatthis has generally been attributed to the sire and dam transmitting theircharacters differently; but Colin, who has given in his 'Traité Phys. Comp. , ' tom. Ii. Pp. 537-539, the fullest description which I have met withof these reciprocal hybrids, is strongly of opinion that the asspreponderates in both crosses, but in an unequal degree. This is likewisethe conclusion of Flourens, and of Bechstein in his 'NaturgeschichteDeutschlands, ' b. I. S. 294. The tail of the hinny is much more like thatof the horse than is the tail of the mule, and this is generally accountedfor by the males of both species transmitting with greater power this partof their structure; but a compound hybrid which I saw in the ZoologicalGardens, from a mare by a hybrid ass-zebra, closely resembled its mother inits tail. [152] Mr. Hewitt, who has had such great experience in raising thesehybrids, says ('Poultry Book, ' by Mr. Tegetmeier, 1866, pp. 165-167) thatin all, the head was destitute of wattles, comb, and ear-lappets; and allclosely resembled the pheasant in the shape of the tail and general contourof the body. These hybrids were raised from hens of several breeds by acock-pheasant; but another hybrid, described by Mr. Hewitt, was raised froma hen-pheasant by a silver-laced Bantam cock, and this possessed arudimental comb and wattles. [153] 'L'Héréd. Nat. , ' tom. Ii. Book ii. Ch. I. [154] 'Bastarderzeugung, ' s. 264-266. Naudin ('Nouvelles Archives duMuséum, ' tom. I. P. 148) has arrived at a similar conclusion. [155] 'Cottage Gardener, ' 1856, pp. 101, 137. [156] _See_ some remarks on this head with respect to sheep by Mr. Wilson, in 'Gardener's Chronicle, ' 1863, p. 15. [157] Verlot, 'Des Variétés, ' 1865, p. 66. [158] Moquin-Tandon, 'Tératologie, ' p. 191. [159] 'Nouvelles Archives du Muséum, ' tom. I. P. 137. [160] 'L'Héréd. Nat. , ' tom. Ii. Pp. 137-165. _See_, also, Mr. Sedgwick'sfour memoirs, immediately to be referred to. [161] On Sexual Limitation in Hereditary Diseases, 'Brit. And For. Med. -Chirurg. Review, ' April, 1861, p. 477; July, p. 198; April, 1863, p. 44; and July, p. 159. [162] W. Scrope, 'Art of Deer Stalking, ' p. 354. [163] Boitard and Corbié, 'Les Pigeons, ' p. 173; Dr. F. Chapuis, 'Le PigeonVoyageur Belge, ' 1865, p. 87. [164] Prichard, 'Phys. Hist. Of Mankind, ' 1851, vol. I. P. 349. [165] 'Embassy to the Court of Ava, ' vol. I. P. 320. The third generationis described by Capt. Yule in his 'Narrative of the Mission to the Court ofAva, ' 1855, p. 94. [166] 'Das Ganze der Taubenzucht, ' 1837, s. 21, tab. I. , fig. 4; s. 24, tab. Iv. , fig. 2. [167] Kidd's 'Treatise on the Canary, ' p. 18. [168] Charlesworth, 'Mag. Of Nat. Hist. , ' vol. I. , 1837, p. 167. [169] Dr. Prosper Lucas, 'Héréd. Nat. , ' tom. Ii. P. 713. [170] 'L'Héréd. Dans les Maladies, ' 1840, p. 135. For Hunter, _see_Harlan's 'Med. Researches, ' p. 530. [171] 'L'Héréd. Nat. , ' tom. Ii. P. 850. [172] Sedgwick, 'Brit. And For. Med. -Chirurg. Review, ' April 1861, p. 485. I have seen three accounts, all taken from the same original authority(which I have not been able to consult), and all differ in the details! butas they agree in the main facts, I have ventured to quote this case. [173] Prosper Lucas, 'Héréd. Nat. , ' tom. I. P. 400. [174] Sedgwick, idem, July, 1861, p. 202. [175] Piorry, p. 109; Prosper Lucas, tom. Ii. P. 759. [176] Prosper Lucas, tom. Ii. P. 748. [177] Prosper Lucas, tom. Ii. Pp. 678, 700, 702; Sedgwick, idem, April, 1863, p. 449, and July, 1863, p. 162; Dr. J. Steinan, 'Essay on HereditaryDisease, ' 1843, pp. 27, 34. [178] These cases are given by Mr. Sedgwick, on the authority of Dr. H. Stewart, in 'Med. -Chirurg. Review, ' April, 1863, pp. 449, 477. [179] 'Héréd. Nat. , ' tom. Ii. P. 852. [180] Communications to the Board of Agriculture, vol. I. P. 367. [181] 'Review of Reports, North of England, ' 1808, p. 200. [182] 'Säugethiere von Paraguay, ' 1830, s. 212. [183] Rengger, 'Säugethiere, ' &c. , s. 154. [184] White, 'Regular Gradation in Man, ' p. 146. [185] Dr. W. F. Edwards, in his 'Charactères Physiolog. Des RacesHumaines, ' p. 23, first called attention to this subject, and ablydiscussed it. [186] Rev. D. Tyerman, and Bennett, 'Journal of Voyages, ' 1821-1829, vol. I. P. 300. [187] Mr. S. J. Salter, 'Journal Linn. Soc. , ' vol. Vi. , 1862, p. 71. [188] Sturm, 'Ueber Racen, &c. , ' 1825, s. 107. Bronn, 'Geschichte derNatur. , ' b. Ii. S. 170, gives a table of the proportions of blood aftersuccessive crosses. Dr. P. Lucas, 'l'Hérédité Nat. , ' tom. Ii. P. 308. [189] 'Bastarderzeugung, ' s. 463, 470. [190] 'Nova Acta Petrop. , ' 1794, p. 393: _see_ also previous volume. [191] As quoted in the 'True Principles of Breeding, ' by C. H. Macknightand Dr. H. Madden, 1865, p. 11. [192] With respect to plants, an admirable essay on this subject (DieGeschlechter-Vertheilung bei den Pflanzen: 1867) has lately been publishedby Dr. Hildebrand, who arrives at the same general conclusions as I havedone. [193] 'Teoria della Riproduzione Vegetal, ' 1816, p. 12. [194] Verlot, 'Des Variétés, ' 1865, p. 72. [195] Duval-Jouve, 'Bull. Soc. Bot. De France, ' tom. X. , 1863, p. 194. [196] Extract of a letter from Sir R. Heron, 1838, given me by Mr. Yarrell. With respect to mice, _see_ 'Annal. Des Sc. Nat. , ' tom. I. P. 180; and Ihave heard of other similar cases. For turtle-doves, Boitard and Corbié, 'Les Pigeons, ' &c. , p. 238. For the Game fowl, 'The Poultry Book, ' 1866, p. 128. For crosses of tailless fowls, _see_ Bechstein, 'Naturges. Deutsch. 'b. Iii. S. 403. Bronn, 'Geschichte der Natur, ' b. Ii. S. 170, givesanalogous facts with horses. On the hairless condition of crossed SouthAmerican dogs, _see_ Rengger, 'Säugethiere von Paraguay, ' s. 152: but I sawin the Zoological Gardens mongrels, from a similar cross, which werehairless, quite hairy, or hairy in patches, that is, piebald with hair. Forcrosses of Dorking and other fowls, _see_ 'Poultry Chronicle, ' vol. Ii. P. 355. About the crossed pigs, extract of letter from Sir R. Heron to Mr. Yarrell. For other cases, _see_ P. Lucas, 'Héréd. Nat. , ' tom. I. P. 212. [197] 'Internat. Hort. And Bot. Congress of London, ' 1866. [198] 'Bastarderzeugung, ' s. 307. Kölreuter ('Dritte Fortsetszung, ' s. 34, 39), however, obtained intermediate tints from similar crosses in the genusVerbascum. With respect to the turnips, _see_ Herbert's 'Amaryllidaceæ, '1837, p. 370. [199] 'Nouvelles Archives du Muséum, ' tom. I. P. 100. [200] Richardson, 'Pigs, ' 1847, pp. 37, 42; S. Sidney's edition of 'Youatton the Pig, ' 1860, p. 3. [201] _See_ Mr. W. C. Spooner's excellent paper on Cross-Breeding, 'JournalRoyal Agricult. Soc. , ' vol. Xx. , part ii. : _see_ also an equally goodarticle by Mr. Ch. Howard, in 'Gardener's Chronicle, ' 1860, p. 320. [202] 'Gardener's Chronicle, ' 1857, pp. 649, 652. [203] 'Bulletin de la Soc. D'Acclimat. , ' 1862, tom. Ix. P. 463. _See_ also, for other cases, MM. Moll and Gayot, 'Du Boeuf, ' 1860, p. Xxxii. [204] 'Poultry Chronicle, ' vol. Ii. , 1854, p. 36. [205] 'The Poultry Book, ' by W. B. Tegetmeier, 1866, p. 58. [206] 'Gardener's Chronicle, ' 1852, p. 765. [207] Spooner, in 'Journal Royal Agricult. Soc. , ' vol. Xx. , part ii. [208] _See_ Colin's 'Traité de Phys. Comp. Des Animaux Domestiques, ' tom. Ii. P. 536, where this subject is well treated. [209] 'Les Pigeons, ' p. 37. [210] Vol. I. , 1854, p. 101. [211] 'Cottage Gardener, ' 1856, p. 110. [212] 'Bastarderzeugung, ' s. 553. [213] Dr. Pigeaux, in 'Bull. Soc. D'Acclimat. , ' tom. Iii. , July 1866, asquoted in 'Annals and Mag. Of Nat. Hist. , ' 1867, vol. Xx. P. 75. [214] 'Journal de Physiolog. , ' tom. Ii. , 1859, p. 385. [215] Dec. 1863, p. 484. [216] On the Varieties of Wheat, p. 66. [217] Rengger, 'Säugethiere von Paraguay, ' s. 336. [218] _See_ a memoir by MM. Lherbette and De Quatrefages, in 'Bull. Soc. D'Acclimat. , ' tom. Viii. , July, 1861, p. 312. [219] For the Norfolk sheep, _see_ Marshall's 'Rural Economy of Norfolk, 'vol. Ii. P. 133. _See_ Rev. L. Landt's 'Description of Faroe, ' p. 66. Forthe ancon sheep, _see_ 'Phil. Transact. , ' 1813, p. 90. [220] White's 'Nat. Hist. Of Selbourne, ' edited by Bennett, p. 39. Withrespect to the origin of the dark-coloured deer, _see_ 'Some Account ofEnglish Deer Parks, ' by E. P. Shirley, Esq. [221] 'The Dovecote, ' by the Rev. E. S. Dixon, p. 155; Bechstein, 'Naturgesch. Deutschlands, ' Band iv. , 1795, s. 17. [222] 'Cattle, ' p. 202. [223] Mr. J. Wilkinson, in 'Remarks addressed to Sir J. Sebright, ' 1820, p. 38. [224] 'Gardener's Chronicle, ' 1858, p. 771. [225] 'Bastarderzeugung, ' s. 87, 169. _See_ also the Table at the end ofvolume. [226] 'Bastarderzeugung, ' s. 87, 577. [227] 'Kenntniss der Befruchtung, ' s. 137; 'Bastarderzeugung, ' s. 92, 181. On raising the two varieties from seed _see_ s. 307. [228] 'Bastarderzeugung, ' s. 216. [229] The following facts, given by Kölreuter in his 'Dritte Fortsetzung, 's. 34, 39, appear at first sight strongly to confirm Mr. Scott's andGärtner's statements; and to a certain limited extent they do so. Kölreuterasserts, from innumerable observations, that insects incessantly carrypollen from one species and variety of Verbascum to another; and I canconfirm this assertion; yet he found that the white and yellow varieties of_Verbascum lychnitis_ often grew wild mingled together: moreover, hecultivated these two varieties in considerable numbers during four years inhis garden, and they kept true by seed; but when he crossed them, theyproduced flowers of an intermediate tint. Hence it might have thought thatboth varieties must have a stronger elective affinity for the pollen oftheir own variety than for that of the other; this elective affinity, I mayadd, of each species for its own pollen (Kölreuter, 'Dritte Forts. , ' s. 39, and Gärtner, 'Bastarderz. , ' _passim_) being a perfectly well-ascertainedpower. But the force of the foregoing facts is much lessened by Gärtner'snumerous experiments, for, differently from Kölreuter, he never once got('Bastarderz. , ' s. 307) an intermediate tint when he crossed the yellow andwhite flowered varieties of Verbascum. So that the fact of the white andyellow varieties keeping true to their colour by seed does not prove thatthey were not mutually fertilised by the pollen carried by insects from oneto the other. [230] 'Amaryllidaceæ, ' 1837, p. 366. Gärtner has made a similarobservation. [231] Kölreuter first observed this fact. 'Mém. De l'Acad. St. Petersburg, 'vol. Iii. P. 197. _See_ also C. K. Sprengel, 'Das Entdeckte Geheimniss, ' s. 345. [232] Namely, Barbarines, Pastissons, Giraumous: 'Annal. Des Sc. Nat. , 'tom. Xxx. , 1833, pp. 398 and 405. [233] 'Mémoire sur les Cucurbitaceæ, ' 1826, pp. 46, 55. [234] 'Annales des Se. Nat. , ' 4th series, tom. Vi. M. Naudin considersthese forms as undoubtedly varieties of _Cucurbita pepo_. [235] 'Mém. Cucurb. , ' p. 8. [236] 'Zweite Forts. , ' s. 53, namely, Nicotiana major vulgaris; (2)perennis; (3) Transylvanica; (4) a sub-var. Of the last; (5) major latifol. Fl. Alb. [237] Kölreuter was so much struck with this fact that he suspected that alittle pollen of _N. Glutinosa_ in one of his experiments might haveaccidentally got mingled with that of _var. Perennis_, and thus aided itsfertilising power. But we now know conclusively from Gärtner('Bastarderz. , ' s. 34, 431) that two kinds of pollen never act _conjointly_on a third species; still less will the pollen of a distinct species, mingled with a plant's own pollen, if the latter be present in sufficientquantity, have any effect. The sole effect of mingling two kinds of pollenis to produce in the same capsule seeds which yield plants, some takingafter the one and some after the other parent. [238] Mr. Scott has made some observations on the absolute sterility of apurple and white primrose (_Primula vulgaris_) when fertilised by pollenfrom the primrose ('Journal of Proc. Of Linn. Soc. , ' vol. Viii. , 1864, p. 98); but these observations require confirmation. I raised a number ofpurple-flowered long-styled seedlings from seed kindly sent me by Mr. Scott, and, though they were all some degree sterile, they were much morefertile with pollen taken from the common primrose than with their ownpollen. Mr. Scott has likewise described a red equal-styled cowslip (_P. Veris_, idem, p. 106), which was found by him to be highly sterile whencrossed with the common cowslip; but this was not the case with severalequal-styled red seedlings raised by me from his plant. This variety of thecowslip presents the remarkable peculiarity of combining male organs inevery respect like those of the short-styled form, with female organsresembling in function and partly in structure those of the long-styledform; so that we have the singular anomaly of the two forms combined in thesame flower. Hence it is not surprising that these flowers should bespontaneously self-infertile in a high degree. [239] 'Act. Acad. St. Petersburg, ' 1780, part ii. , pp. 84, 100. [240] 'Annales des Sc. Nat. , ' tom. Xxi. (1st series), p. 61. [241] 'Bull. Bot. Soc. De France, ' Dec. 27th, 1861, tom. Viii. P. 612. [242] Quoted by Isid. Geoffroy St. Hilaire, 'Hist. Naturelle Générale, 'tom. Iii. P. 476. Since this MS. Has been sent to press a full discussionon the present subject has appeared in Mr. Herbert Spencer's 'Principles ofBiology, ' vol. Ii. 1867, p. 457 _et seq. _ [243] For cats and dogs, &c. , _see_ Bellingeri, in 'Annal. Des Sc. Nat. , '2nd series, Zoolog. , tom. Xii. P. 155. For ferrets, Bechstein, 'Naturgeschichte Deutschlands, ' Band i. , 1801, s. 786, 795. For rabbits, ditto, s. 1123, 1131; and Bronn's 'Geschichte der Natur, ' B. Ii. S. 99. Formountain sheep, ditto, s. 102. For the fertility of the wild sow, _see_Bechstein's 'Naturgesch. Deutschlands, ' B. I. , 1801, s. 534; for thedomestic pig, Sidney's edit. Of Youatt on the Pig, 1860, p. 62. Withrespect to Lapland, _see_ Acerbi's 'Travels to the North Cape, ' Eng. Translat. , vol. Ii. P. 222. About the Highland cows, _see_ Hogg on Sheep, p. 263. [244] For the eggs of _Gallus bankiva_, _see_ Blyth, in 'Annals and Mag. OfNat. Hist. , 2nd series, vol. I. , 1848, p. 456. For wild and tame ducks, Macgillivray, 'British Birds, ' vol. V. P. 37; and 'Die Enten, ' s. 87. Forwild geese, L. Lloyd, 'Scandinavian Adventures, ' vol. Ii. 1854, p. 413; andfor tame geese, 'Ornamental Poultry, ' by Rev. E. S. Dixon, p. 139. On thebreeding of pigeons, Pistor, 'Das Ganze der Taubenzucht, ' 1831, s. 46; andBoitard and Corbié, 'Les Pigeons, ' p. 158. With respect to peacocks, according to Temminck ('Hist. Nat. Gén. Des Pigeons, ' &c. , 1813, tom. Ii. P. 41), the hen lays in India even as many as twenty eggs; but according toJerdon and another writer (quoted in Tegetmeier's 'Poultry Book, ' 1866, pp. 280, 282), she there lays only from four to nine or ten eggs: in Englandshe is said, in the 'Poultry Book, ' to lay five or six, but another writersays from eight to twelve eggs. [245] 'The Art of Improving the Breed, &c. , ' 1809, p. 16. [246] For Andrew Knight, _see_ A. Walker, on 'Intermarriage, ' 1838, p. 227. Sir J. Sebright's Treatise has just been quoted. [247] 'Cattle, ' p. 199. [248] Nathusius, 'Ueber Shorthorn Rindvieh, ' 1857, s. 71: _see_ also'Gardener's Chronicle, ' 1860, p. 270. Many analogous cases are given in apamphlet recently published by Mr. C. Macknight and Dr. H. Madden, 'On theTrue Principles of Breeding;' Melbourne, Australia, 1865. [249] Mr. Willoughby Wood, in 'Gardener's Chronicle, ' 1855, p. 411; and1860, p. 270. _See_ the very clear tables and pedigrees given in Nathusius''Rindvieh, ' s. 72-77. [250] Mr. Wright, 'Journal of Royal Agricult. Soc. , ' vol. Vii. , 1846, p. 204. [251] Youatt on Cattle, p. 202. [252] Report British Assoc. , Zoolog. Sect. , 1838. [253] Azara, 'Quadrupèdes du Paraguay, ' tom. Ii. Pp. 354, 368. [254] For the case of the Messrs. Brown, _see_ 'Gard. Chronicle, ' 1855, p. 26. For the Foscote flock, 'Gard. Chron. , ' 1860, p. 416. For the Naz flock, 'Bull. De la Soc. D'Acclimat. , ' 1860, p. 477. [255] Nathusius, 'Rindvieh, ' s. 65; Youatt on Sheep, p. 495. [256] 'Gard. Chronicle, ' 1861, p. 631. [257] Lord Somerville, 'Facts on Sheep and Husbandry, ' p. 6. Mr. Spooner, in 'Journal of Royal Agricult. Soc. Of England, ' vol. Xx. , part ii. _See_also an excellent paper on the same subject in 'Gard. Chronicle, ' 1860, p. 321, by Mr. Charles Howard. [258] 'Some Account of English Deer Parks, ' by Evelyn P. Shirley, 1867. [259] 'The Art of Improving the Breed, ' &c. , p. 13. With respect to Scotchdeer-hounds, _see_ Scrope's 'Art of Deer Stalking, ' pp. 350-353. [260] 'Cottage Gardener, ' 1861, p. 327. [261] Sidney's edit. Of Youatt on the Pig, 1860, p. 30; p. 33, quotationfrom Mr. Druce; p. 29, on Lord Western's case. [262] 'Journal, Royal Agricult. Soc. Of England, ' 1846, vol. Vii. P. 205. [263] 'Ueber Rindvieh, ' &c. , s. 78. [264] Sidney on the Pig, p. 36. _See_ also note, p. 34. Also Richardson onthe Pig, 1847, p. 26. [265] Dr. Dally has published an excellent article (translated in the'Anthropolog. Review, ' May, 1864, p. 65), criticising all writers who havemaintained that evil follows from consanguineous marriages. No doubt onthis side of the question many advocates have injured their cause byinaccuracies: thus it has been stated (Devay, 'Du Danger des Mariages, '&c. , 1862, p. 141) that the marriages of cousins have been prohibited bythe legislature of Ohio; but I have been assured, in answer to inquiriesmade in the United States, that this statement is a mere fable. [266] _See_ his most interesting work on the 'Early History of Man, ' 1865, chap. X. [267] On Consanguinity in Marriage, in the 'Fortnightly Review, ' 1865, p. 710; Hofacker, 'Ueber die Eigenschaften, ' &c. [268] Sir G. Grey's 'Journal of Expeditions into Australia, ' vol. Ii. P. 243; and Dobrizhoffer, 'On the Abipones of South America. ' [269] 'The Art of Improving the Breed, ' p. 13. [270] 'The Poultry Book, ' by W. B. Tegetmeier, 1866, p. 245. [271] 'Journal Royal Agricult. Soc. ' 1846, vol. Vii. P. 205; _see_ alsoFerguson on the Fowl, pp. 83, 317; _see_ also 'The Poultry Book, ' byTegetmeier, 1866, p. 135, with respect to the extent to which cock-fightersfound that they could venture to breed in-and-in, viz. , occasionally a henwith her own son; "but they were cautious not to repeat the in-and-inbreeding. " [272] 'The Poultry Book, ' by W. B. Tegetmeier, 1866, p. 79. [273] 'The Poultry Chronicle, ' 1854, vol. I. P. 43. [274] 'The Poultry Book, ' by W. B. Tegetmeier, 1866, p. 79. [275] 'The Poultry Chronicle, ' vol. I. P. 89. [276] 'The Poultry Book, ' 1866, p. 210. [277] Ibid, 1866, p. 167; and 'Poultry Chronicle, ' vol. Iii. , 1855, p. 15. [278] 'A Treatise on Fancy Pigeons, ' by J. M. Eaton, p. 56. [279] 'The Pigeon Book, ' p. 46. [280] 'Das Ganze der Taubenzucht, ' 1837, s. 18. [281] 'Les Pigeons, ' 1824, p. 35. [282] 'Proc. Entomolog. Soc. , ' Aug. 6th, 1860, p. 126. [283] 'Journal of Horticulture, ' 1861, pp. 39, 77, 158; and 1864, p. 206. [284] 'Beiträge zur Kenntniss der Befruchtung, ' 1844, s. 366. [285] 'Amaryllidaceæ, ' p. 371. [286] 'De la Fécondation, ' 2nd edit. , 1862, p. 79. [287] 'Mémoire sur les Cucurbitacées, ' pp. 36, 28, 30. [288] Loudon's 'Gard. Mag. , ' vol. Viii. , 1832, p. 52. [289] 'Transact. Hort. Soc. , ' vol. I. P. 25. [290] 'Annal. Des Sc. Nat. , ' 3rd series, Bot. , tom. Vi. P. 189. [291] 'Philosophical Transactions, ' 1799, p. 200. [292] 'Ueber die Bastarderzeugung, ' 1828, s. 32, 33. For Mr. Chaundy'scase, _see_ Loudon's 'Gard. Mag. , ' vol. Vii. , 1831, p. 696. [293] 'Gardener's Chron. , ' 1846, p. 601. [294] 'Philosoph. Transact. , ' 1799, p. 201. [295] Quoted in 'Bull. Bot. Soc. France, ' vol. Ii. , 1855, p. 327. [296] Gärtner, 'Bastarderzeugung, ' s. 259, 518, 526 _et seq. _ [297] 'Fortsetzung, ' 1763, s. 29; 'Dritte Fortsetzung, ' s. 44, 96; 'Act. Acad. St. Petersburg, ' 1782, part ii. , p. 251; 'Nova Acta, ' 1793, pp. 391, 394; 'Nova Acta, ' 1795, pp. 316, 323. [298] 'Die Bastardbefruchtung, ' &c. , 1865, s. 31, 41, 42. [299] Max Wichura fully accepts this view ('Bastardbefruchtung, ' s. 43), asdoes the Rev. M. J. Berkeley, in 'Journal of Hort. Soc. , ' Jan. 1866, p. 70. [300] 'Bastarderzeugung, ' s. 394, 526, 528. [301] Kölreuter, ' Nova Acta, ' 1795, p. 316. [302] Gärtner, 'Bastarderzeugung, ' s. 430. [303] 'Botanische Zeitung, ' Jan. 1864, s. 3. [304] 'Monatsbericht Akad. Wissen, ' Berlin, 1866, s. 372. [305] International Hort. Congress, London, 1866. [306] 'Proc. Bot. Soc. Of Edinburgh, ' May, 1863: these observations aregiven in abstract, and others are added, in the 'Journal of Proc. Of Linn. Soc. , ' vol. Viii. Bot. , 1864, p. 162. [307] Prof. Lecoq, 'De la Fécondation, ' 2nd edit. , 1862, p. 76. [308] 'Bastarderzeugung, ' s. 64, 357. [309] Idem, s. 357. [310] 'Zweite Fortsetzung, ' s. 10; 'Dritte Fort. , ' s. 40. [311] Duvernoy, quoted by Gärtner, 'Bastarderzeugung, ' s. 334. [312] 'Gardner's Chronicle, ' 1846, p. 183. [313] 'Transact. Hort. Soc. , ' vol. Vii. , 1830, p. 95. [314] Prof. Lecoq, 'De la Fécondation, ' 1845, p. 70; Gärtner, 'Bastarderzeugung, ' s. 64. [315] 'Gardener's Chron. ' 1866, p. 1068. [316] 'Journal of Proc. Of Linn. Soc. , ' vol. Viii. , 1864, p. 168. [317] 'Amaryllidaceæ, ' 1837, p. 371; 'Journal of Hort. Soc. , ' vol. Ii. , 1847, p. 19. [318] Loudon's 'Gardener's Magazine, ' vol. Xi. , 1835, p. 260. [319] 'Gardener's Chronicle, ' 1850, p. 470. [320] 'Journal Hort. Soc. , vol. V. P. 135. The seedlings thus raised weregiven to the Hort. Soc. ; but I find, on inquiry, that they unfortunatelydied the following winter. [321] Mr. D. Beaton, in 'Journal of Hort. , ' 1861, p. 453. Lecoq, however('De la Fécond. , ' 1862, p. 369), states that this hybrid is descended from_G. Psittacinus_ and _cardinalis_; but this is opposed to Herbert'sexperience, who found that the former species could not be crossed. [322] This is the conclusion of Prof. Devay, 'Du Danger des MariagesConsang. , ' 1862, p. 97. Virchow quotes, in the 'Deutsche Jahrbücher, ' 1863, s. 354, some curious evidence on half the cases of a peculiar form ofblindness occurring in the offspring from near relations. [323] For England, _see_ below. For Germany, _see_ Metzger, 'Getreidearten, ' 1841, s. 63. For France, Loiseleur-Deslongchamps ('Consid. Sur les Céreales, ' 1843, p. 200) gives numerous references on this subject. For Southern France, _see_ Godron, 'Florula Juvenalis, ' 1854, p. 28. [324] 'A general Treatise of Husbandry, ' vol. Iii. P. 58. [325] 'Gardener's Chronicle and Agricult. Gazette, ' 1858, p. 247; and forthe second statement, idem, 1850, p. 702. On this same subject, _see_ alsoRev. D. Walker's 'Prize Essay of Highland Agricult. Soc. , ' vol. Ii. P. 200. Also Marshall's 'Minutes of Agriculture, ' November, 1775. [326] Oberlin's 'Memoirs, ' Eng. Translat. , p. 73. For Lancashire, _see_Marshall's 'Review of Reports, ' 1808, p. 295. [327] 'Cottage Gardener, ' 1856, p. 186. For Mr. Robson's subsequentstatements, _see_ 'Journal of Horticulture, ' Feb. 18, 1866, p. 121. For Mr. Abbey's remarks on grafting, &c. , idem, July 18, 1865, p. 44. [328] 'Mém. De l'Acad. Des Sciences, ' 1790, p. 209. [329] 'On the Varieties of Wheat, ' p. 52. [330] Mr. Spencer has fully and ably discussed this whole subject in his'Principles of Biology, ' 1864, vol. Ii. Ch. X. In the first edition of my'Origin of Species, ' 1859, p. 267, I spoke of the good effects from slightchanges in the conditions of life and from cross-breeding, and of the evileffects from great changes in the conditions and from crossing widelydistinct forms, as a series of facts "connected together by some common butunknown bond, which is essentially related to the principle of life. " [331] 'Essais de Zoologie Générale, ' 1841, p. 256. [332] Du Rut, 'Annales du Muséum, ' 1807, tom. Ix. P. 120. [333] 'Säugethiere von Paraguay, ' 1830, s. 49, 106, 118, 124, 201, 208, 249, 265, 327. [334] 'The Naturalist on the Amazons, ' 1863, vol. I. Pp. 99, 193; vol. Ii. P. 113. [335] 'Embassy to the Court of Ava, ' vol. I. P. 534. [336] 'Journal, ' vol. I. P. 213. [337] 'Säugethiere, ' s. 327. [338] On the Breeding of the larger Felidæ, 'Proc. Zoolog. Soc. , ' 1861, p. 140. [339] Sleeman's 'Rambles in India, ' vol. Ii. P. 10. [340] Wiegmann's 'Archif für Naturgesch. , ' 1837, s. 162. [341] Rengger, 'Säugethiere, ' &c. , s. 276. On the parentage of theguinea-pig, _see_ also Isid. Geoffroy St. Hilaire, 'Hist. Nat. Gén. ' [342] Although the existence of the _Leporides_, as described by Dr. Broca('Journal de Phys. , ' tom. Ii. P. 370), is now positively denied, yet Dr. Pigeaux ('Annals and Mag. Of Nat. Hist. , ' vol. Xx. , 1867, p. 75) affirmsthat the hare and rabbit have produced hybrids. [343] 'Quadrupeds of North America, ' by Audubon and Bachman, 1846, p. 268. [344] Loudon's 'Mag. Of Nat. Hist. , ' vol. Ix. , 1836, p. 571; Audubon andBachman's 'Quadrupeds of North America, ' p. 221. [345] Flourens, 'De l'Instinct, ' &c. , 1845, p. 88. [346] _See_ 'Annual Reports Zoolog. Soc. , ' 1855, 1858, 1863, 1864; 'Times'newspaper, Aug. 10th, 1847; Flourens, 'De l'Instinct, ' p. 85. [347] 'Säugethiere, ' &c. , s. 34, 49. [348] Art. Brazil, 'Penny Cyclop. , ' p. 363. [349] 'The Naturalist on the River Amazon, ' vol. I. P. 99. [350] 'Encyclop. Of Rural Sports, ' p. 691. [351] According to Sir A. Burnes ('Cabool, ' &c. , p. 51), eight species areused for hawking in Scinde. [352] Loudon's 'Mag. Of Nat. Hist. , ' vol. Vi. , 1833, p. 110. [353] F. Cuvier, 'Annal. Du Muséum, ' tom. Ix. P. 128. [354] 'The Zoologist, ' vol. Vii. -viii. , 1849-50, p. 2648. [355] Knox, 'Ornithological Rambles in Sussex, ' p. 91. [356] 'The Zoologist, ' vol. Vii. -viii. , 1849-50, p. 2566; vol. Ix. -x. , 1851-2, p. 3207. [357] Bechstein, 'Naturgesch. Der Stubenvögel, ' 1840, s. 20. [358] 'Ornithological Biography, ' vol. V. P. 517. [359] A case is recorded in 'The Zoologist, ' vol. I. -ii. , 1843-45, p. 453. For the siskin breeding, vol. Iii. -iv. , 1845-46, p. 1075. Bechstein, 'Stubenvögel, ' s. 139, speaks of bullfinches making nests, but rarelyproducing young. [360] Yarrell's 'Hist. British Birds, ' 1839, vol. I. P. 412. [361] Loudon's 'Mag. Of Nat. History, ' vol. Ix. , 1836, p. 347. [362] 'Mémoires du Muséum d'Hist. Nat. , ' tom. X. P. 314: five cases ofparrots breeding in France are here recorded. _See_, also, 'Report Brit. Assoc. Zoolog. , ' 1843. [363] 'Stubenvögel, ' s. 105, 83. [364] Dr. Hancock remarks ('Charlesworth's Mag. Of Nat. Hist. , ' vol. Ii. , 1838, p. 492), "it is singular that, amongst the numerous useful birds thatare indigenous to Guiana, none are found to propagate among the Indians;yet the common fowl is reared in abundance throughout the country. " [365] 'A Week at Port Royal, ' 1855, p. 7. [366] Audubon, 'American Ornithology, ' vol. V. Pp. 552, 557. [367] Moubray on Poultry, 7th edit. , p. 133. [368] Temminck, 'Hist. Nat. Gén. Des Pigeons, ' &c. , 1813, tom. Iii. Pp. 288, 382; 'Annals and Mag. Of Nat. Hist. , ' vol. Xii. , 1843, p. 453. Otherspecies of partridge have occasionally bred; as the red-legged (_P. Rubra_), when kept in a large court in France (_see_ 'Journal de Physique, 'tom. Xxv. P. 294), and in the Zoological Gardens in 1856. [369] Rev. E. S. Dixon, 'The Dovecote, ' 1851, pp. 243-252. [370] Temminck, 'Hist. Nat. Gén. Des Pigeons, ' &c. , tom. Ii. Pp. 456, 458;tom. Iii. Pp. 2, 13, 47. [371] Bates, 'The Naturalist on the Amazons, ' vol. I. P. 193; vol. Ii. P. 112. [372] Temminck, 'Hist. Nat. Gén. , ' &c. , tom. Iii. P. 125. For _Tetraourogallus_, _see_ L. Lloyd, 'Field Sports of North of Europe, ' vol. I. Pp. 287, 314; and 'Bull. De la Soc. D'Acclimat. , ' tom. Vii. , 1860, p. 600. For_T. Scoticus_, Thompson, 'Nat. Hist. Of Ireland, ' vol. Ii. , 1850, p. 49. For _T. Cupido_, 'Boston Journal of Nat. Hist. , ' vol. Iii. P. 199. [373] Marcel de Serres, 'Annales des Sci. Nat. , ' 2nd series, Zoolog. , tom. Xiii. P. 175. [374] Dr. Hancock, in 'Charlesworth's Mag. Of Nat. Hist. ' vol. Ii. , 1838, p. 491; R. Hill, 'A Week at Port Royal, ' p. 8; 'Guide to the ZoologicalGardens, ' by P. L. Sclater, 1859, pp. 11, 12; 'The Knowsley Menagerie, ' byDr. Gray, 1846, pl. Xiv. ; E. Blyth, 'Report Asiatic Soc. Of Bengal, ' May, 1855. [375] Prof. Newton, in 'Proc. Zoolog. Soc. , ' 1860, p. 336. [376] 'The Dovecote and Aviary, ' p. 428. [377] 'Ornithological Biography, ' vol. Iii. P. 9. [378] 'Geograph. Journal, ' vol. Xiii. , 1844, p. 32. [379] Loudon's 'Mag. Of Nat. Hist. , ' vol. V. , 1832, p. 153. [380] 'Zoologist, ' vols. V. -vi. , 1847-48, p. 1660. [381] 'Transact. Entomolog. Soc. , ' vol. Iv. , 1845, p. 60. [382] 'Transact. Linn. Soc. , ' vol. Vii. P. 40. [383] _See_ an interesting paper by Mr. Newman, in the 'Zoologist, ' 1857, p. 5764; and Dr. Wallace, in 'Proc. Entomolog. Soc. , ' June 4th, 1860, p. 119. [384] Yarrell's 'British Birds, ' vol. I. P. 506; Bechstein, 'Stubenvögel, 's. 185; 'Philosoph. Transact. , ' 1772, p. 271. Bronn ('Geschichte derNatur, ' Band ii. S. 96) has collected a number of cases. For the case ofthe deer, _see_ 'Penny Cyclop. , ' vol. Viii. P. 350. [385] 'Journal de Physiologie, ' tom. Ii. P. 347. [386] For additional evidence on this subject, _see_ F. Cuvier, in 'Annalesdu Muséum, ' tom. Xii. P. 119. [387] Numerous instances could be given. Thus Livingstone ('Travels, ' p. 217) states that the King of the Barotse, an inland tribe which never hadany communication with white men, was extremely fond of taming animals, andevery young antelope was brought to him. Mr. Galton informs me that theDamaras are likewise fond of keeping pets. The Indians of South Americafollow the same habit. Capt. Wilkes states that the Polynesians of theSamoan Islands tamed pigeons; and the New Zealanders, as Mr. Mantellinforms me, kept various kinds of birds. [388] For analogous cases with the fowl, _see_ Réaumur, 'Art de faireEclorre, ' &c. , 1749, p. 243; and Col. Sykes, in 'Proc. Zoolog. Soc. , ' 1832, &c. With respect to the fowl not breeding in northern regions, _see_Latham's 'Hist. Of Birds, ' vol. Viii. , 1823, p. 169. [389] 'Mém. Par divers Savans, Acad. Des Sciences, ' tom. Vi. , 1835, p. 347. [390] Youatt on Sheep, p. 181. [391] J. Mills, 'Treatise on Cattle, ' 1776, p. 72. [392] Bechstein, 'Stubenvögel, ' s. 242. [393] Crawfurd's 'Descriptive Dict. Of the Indian Islands, ' 1856, p. 145. [394] 'Bull. De la Soc. Acclimat. , tom. Ix. , 1862, pp. 380, 384. [395] For pigeons, _see_ Dr. Chapuis, 'Le Pigeon Voyageur Belge, ' 1865, p. 66. [396] 'Swedish Acts, ' vol. I. , 1739, p. 3. Pallas makes the same remark inhis Travels (Eng. Translat. ), vol. I. P. 292. [397] A. Kerner, 'Die Cultur der Alpenflanzen, ' 1864, s. 139; Watson's'Cybele Britannica, ' vol. I. P. 131; Mr. D. Cameron, also, has written onthe culture of Alpine plants in 'Gard. Chronicle, ' 1848, pp. 253, 268, andmentions a few which seed. [398] 'Beiträge zur Kenntniss der Befruchtung, ' 1844, s. 333. [399] 'Nova Acta Petrop. , ' 1793, p. 391. [400] 'Cottage Gardener, ' 1856, pp. 44, 109. [401] Dr. Herbert, 'Amaryllidaceæ, ' p. 176. [402] Gärtner, 'Beiträge zur Kenntniss, ' &c. , s. 560, 564. [403] 'Gardener's Chronicle, ' 1844, p. 215; 1850, p. 470. [404] 'Beiträge zur Kenntniss, ' &c. , s. 252, 333. [405] 'Journal of Hort. Soc. , ' vol. Ii. 1847, p. 83. [406] 'Beiträge zur Kenntniss, ' &c. , s. 117 _et seq. _; Kölreuter, 'ZweiteFortsetzung, ' s. 10, 121; 'Dritte Fortsetzung, ' s. 57. Herbert, 'Amaryllidaceæ, ' p. 355. Wiegmann, 'Ueber die Bastarderzeugung, ' s. 27. [407] 'Bastarderzeugung, ' s. 356. [408] 'Teoria della Riproduzione, ' 1816, p. 84; 'Traité du Citrus, ' 1811, p. 67. [409] Mr. C. W. Crocker, in 'Gard. Chronicle, ' 1861, p. 1092. [410] Verlot, 'Des Variétés, ' 1865, p. 80. [411] Verlot, idem, p. 88. [412] Prof. Allman, Brit. Assoc. , quoted in the 'Phytologist, ' vol. Ii. P. 483. Prof. Harvey, on the authority of Mr. Andrews, who discovered theplant, informed me that this monstrosity could be propagated by seed. Withrespect to the poppy, _see_ Prof. Goeppert, as quoted in 'Journal ofHorticulture, ' July 1st, 1863, p. 171. [413] 'Comptes Rendus, ' Dec. 19th, 1864, p. 1039. [414] 'Gardener's Chronicle, ' 1866, p. 681. [415] 'Theory of Horticulture, ' p. 333. [416] Mr. Fairweather, in 'Transact. Hort. Soc. , ' vol. Iii. P. 406; Bosse, quoted by Bronn, 'Geschichte der Natur, ' B. Ii. S. 77. On the effects ofthe removal of the anthers, _see_ Mr. Leitner, in Silliman's 'NorthAmerican Journ. Of Science, ' vol. Xxiii. P. 47; and Verlot, 'Des Variétés, '1865, p. 84. [417] Lindley's 'Theory of Horticulture, ' p. 333. [418] 'Gardener's Chronicle, ' 1865, p. 626; 1866, pp. 290, 730; and Verlot, 'Des Variétés, ' p. 75. [419] 'Gardener's Chronicle, ' 1843, p. 628. In this article I suggested thefollowing theory on the doubleness of flowers. [420] Quoted by Gärtner, 'Bastarderzeugung, ' s. 567. [421] 'Gardener's Chronicle, ' 1866, p. 901. [422] Lindley, 'Theory of Horticulture, ' p. 175-179; Godron, 'De l'Espèce, 'tom. I. P. 106: Pickering, 'Races of Man;' Gallesio, 'Teoria dellaRiproduzione, ' 1816, p. 101-110. Meyen ('Reise um Erde, ' Th. Ii. S. 214)states that at Manilla one variety of the banana is full of seeds; andChamisso (Hooker's 'Bot. Misc. , ' vol. I. P. 310) describes a variety of thebread-fruit in the Mariana Islands with small fruit, containing seeds whichare frequently perfect. Burnes, in his 'Travels in Bokhara, ' remarks on thepomegranate seeding in Mazenderan, as a remarkable peculiarity. [423] Ingledew, in 'Transact. Of Agricult. And Hort. Soc. Of India, ' vol. Ii. [424] 'De la Fécondation, ' 1862, p. 308. [425] Hooker's 'Bot. Misc. , ' vol. I. P. 99; Gallesio, 'Teoria dellaRiproduzione, ' p. 110. [426] 'Transact. Linn. Soc. , ' vol. Xvii. P. 563. [427] Godron, 'De l'Espèce, ' tom. Ii. P. 106; Herbert on Crocus, in'Journal of Hort. Soc. , ' vol. I. , 1846, p. 254. --Dr. Wight, from what hehas seen in India, believes in this view; 'Madras Journal of Lit. AndScience, ' vol. Iv. , 1836, p. 61. [428] Wahlenberg specifies eight species in this state on the Lapland Alps:_see_ Appendix to Linnæus' 'Tour in Lapland, ' translated by Sir J. E. Smith, vol. Ii. Pp. 274-280. [429] 'Travels in North America, ' Eng. Translat. , vol. Iii. P. 175. [430] With respect to the ivy and Acorus, _see_ Dr. Bromfield in the'Phytologist, ' vol. Iii. P. 376. _See_ also Lindley and Vaucher on theAcorus. [431] 'Annal. Des Sc. Nat. , ' 3rd series, Zool. , tom. Iv. P. 280. Prof. Decaisne refers also to analogous cases with mosses and lichens near Paris. [432] Mr. Tuckerman, in Silliman's 'American Journal of Science, ' vol. Xlv. P. 41. [433] Sir J. E. Smith, 'English Flora, ' vol. I. P. 339. [434] G. Planchon, 'Flora de Montpellier, ' 1864, p. 20. [435] On the non-production of seeds in England _see_ Mr. Crocker, in'Gardener's Weekly Magazine, ' 1852, p. 70; Vaucher, 'Hist. Phys. Plantesd'Europe, ' tom. I. P. 33; Lecoq, 'Géograph. Bot. De l'Europe, ' tom. Iv. P. 466; Dr. D. Clos, in 'Annal. Des Sc. Nat. , ' 3rd series, Bot. , tom. Xvii. , 1852, p. 129: this latter author refers to other analogous cases. On thenon-production of pollen by this Ranunculus _see_ Chatin, in 'ComptesRendus, ' June 11th, 1866. [436] 'Bastarderzeugung, ' s. 565. Kölreuter ('Dritte Fortsetzung, ' s. 73, 87, 119) also shows that when two species, one single and the other double, are crossed, the hybrids are apt to be extremely double. [437] 'Teoria della Riproduzione Veg. , ' 1816, p. 73. [438] 'Bastarderzeugung, ' s. 573. [439] Ibid. , s. 527. [440] 'Transactions Phil. Soc. , ' 1799, p. 202. For Kölreuter, _see_ 'Mém. De l'Acad. De St. Pétersbourg, ' tom. Iii. , 1809 (published 1811), p. 197. In reading C. K. Sprengel's remarkable work, 'Das entdeckte Geheimniss, '&c. , 1793, it is curious to observe how often this wonderfully acuteobserver failed to understand the full meaning of the structure of theflowers which he has so well described, from not always having before hismind the key to the problem, namely, the good derived from the crossing ofdistinct individual plants. [441] This abstract was published in the fourth edition (1866) of my'Origin of Species;' but as this edition will be in the hands of but fewpersons, and as my original observations on this point have not as yet beenpublished in detail, I have ventured here to reprint the abstract. [442] The term _unconscious selection_ has been objected to as acontradiction: but _see_ some excellent observations on this head by Prof. Huxley ('Nat. Hist. Review, ' Oct. 1864, p. 578), who remarks that when thewind heaps up sand-dunes it sifts and _unconsciously selects_ from thegravel on the beach grains of sand of equal size. [443] Sheep, 1838, p. 60. [444] Mr. J. Wright on Shorthorn Cattle, in 'Journal of Royal Agricult. Soc. , ' vol. Vii. Pp. 208, 209. [445] H. D. Richardson on Pigs, 1817, p. 44. [446] 'Journal of R. Agricult. Soc. , ' vol. I. P. 24. [447] Sheep, pp. 520, 319. [448] Loudon's 'Mag. Of Nat. Hist. , ' vol. Viii. , 1835, p. 618. [449] 'A Treatise on the Art of Breeding the Almond Tumbler, ' 1851, p. 9. [450] 'Recreations in Agriculture, ' vol. Ii. P. 409. [451] Youatt on Cattle, pp. 191, 227. [452] Ferguson, 'Prize Poultry, ' 1854, p. 208. [453] Wilson, in 'Transact. Highland Agricult. Soc. , ' quoted in 'Gard. Chronicle, ' 1844, p. 29. [454] Simmonds, quoted in 'Gard. Chronicle, ' 1855, p. 637. And for thesecond quotation, _see_ Youatt on Sheep, p. 171. [455] Robinet, 'Vers à Soie, ' 1848, p. 271. [456] Quatrefages, 'Les Maladies du Ver à Soie, ' 1859, p. 101. [457] M. Simon, in 'Bull. De la Soc. D'Acclimat. , ' tom. Ix. , 1862, p. 221. [458] 'The Poultry Chronicle, ' vol. I. , 1854, p. 607. [459] J. M. Eaton, 'A Treatise on Fancy Pigeons, ' 1852, p. Xiv. , and 'ATreatise on the Almond Tumbler, ' 1851, p. 11. [460] 'Journal Royal Agricultural Soc. , ' vol. Vi. P. 22. [461] 'Poultry Chronicle, ' vol. Ii. , 1855, p. 596. [462] Isid. Geoffroy St. Hilaire, 'Hist. Nat. Gén. , ' tom. Iii. P. 254. [463] 'Gardener's Chronicle, ' 1850, p. 198. [464] 'Transact. Hort. Soc. , ' vol. Vi. P. 152. [465] 'Journal of Horticulture, ' 1862, p. 369. [466] 'Transact. Hort. Soc. , ' vol. Iv. P. 381. [467] 'Transact. Hort. Soc. , ' vol. Iv. P. 285. [468] Rev. W. Bromehead, in 'Gard. Chronicle, ' 1857, p. 550. [469] 'Gard. Chronicle, ' 1862, p. 721. [470] Dr. Anderson, in 'The Bee, ' vol. Vi. P. 96; Mr. Barnes, in 'Gard. Chronicle, ' 1844, p. 476. [471] Godron, 'De l'Espèce, ' 1859, tom. Ii. P. 69; 'Gard. Chronicle, ' 1854, p. 258. [472] On Sheep, p. 18. [473] Volz, 'Beiträge zur Kulturgeschichte, ' 1852, s. 47. [474] Mitford's 'History of Greece, ' vol. I. P. 73. [475] Dr. Dally, translated in 'Anthropological Review, ' May 1864, p. 101. [476] Volz, 'Beiträge, ' &c. , 1852, s. 80. [477] 'History of the World, ' ch. 45. [478] 'Gardener's Chronicle, ' 1848, p. 323. [479] Reynier, 'De l'Economie des Celtes, ' 1818, pp. 487, 503. [480] Le Couteur on Wheat, p. 15. [481] Michel, 'Des Haras, ' 1861, p. 84. [482] Sir W. Wilde, an 'Essay on Unmanufactured Animal Remains, ' &c. , 1860, p. 11. [483] Col. Hamilton Smith, 'Nat. Library, ' vol. Xii. , Horses, pp. 135, 140. [484] Michel, 'Des Haras, ' p. 90. [485] Mr. Baker, 'History of the Horse, ' Veterinary, vol. Xiii. P. 423. [486] M. L'Abbé Carlier, in 'Journal de Physique, ' vol. Xxiv. , 1784, p. 181: this memoir contains much information on the ancient selection ofsheep; and is my authority for rams not being killed young in England. [487] 'Gardener's Chronicle, ' 1843, p. 389. [488] Communications to Board of Agriculture, quoted in Dr. Darwin's'Phytologia, ' 1800, p. 451. [489] 'Mémoire sur les Chinois, ' 1786, tom. Xi. P. 55; tom. V. P. 507. [490] 'Recherches sur l'Agriculture des Chinois, ' par L. D'Hervey-Saint-Denys, 1850, p. 229. With respect to Khang-hi, _see_ Huc's'Chinese Empire, ' p. 311. [491] Anderson, in 'Linn. Transact. , ' vol. Xii. P. 253. [492] 'Mém. De l'Acad. ' (divers savans), tom. Vi. , 1835, p. 333. [493] 'Des Quadrupèdes du Paraguay, ' 1801, tom. Ii. P. 333, 371. [494] 'The Great Sahara, ' by the Rev. H. B. Tristram, 1860, p. 238. [495] Pallas, 'Act. Acad. St. Petersburg, ' 1777, p. 249; Moorcroft andTrebeck, 'Travels in the Himalayan Provinces, ' 1841. [496] Quoted from Raffles, in the 'Indian Field, ' 1859, p. 196; for Varro, _see_ Pallas, _ut supra_. [497] Erman's 'Travels in Siberia, ' Eng. Translat. , vol. I. P. 453. [498] _See_ also 'Journal of R. Geograph. Soc. , ' vol. Xiii. Part i. P. 65. [499] Livingstone's 'First Travels, ' pp. 191, 439, 565; _see_ also'Expedition to the Zambesi, ' 1865, p. 465, for an analogous case respectinga good breed of goats. [500] Andersson's 'Travels in South Africa, ' pp. 232, 318, 319. [501] Dr. Vavasseur, in 'Bull. De la Soc. D'Acclimat. , ' tom. Viii. , 1861, p. 136. [502] 'The Natural History of Dee Side, ' 1855, p. 476. [503] 'Bull. De la Soc. D'Acclimat. , ' tom. Vii. , 1860, p. 457. [504] 'Cattle, ' p. 48. [505] Livingstone's Travels, p. 576; Andersson, 'Lake Ngami, ' 1856, p. 222. With respect to the sale in Kaffraria, _see_ 'Quarterly Review, ' 1860, p. 139. [506] 'Mémoire sur les Chinois' (by the Jesuits), 1786, tom. Xi. P. 57. [507] F. Michel, 'Des Haras, ' pp. 47, 50. [508] Col. Hamilton Smith, Dogs, in 'Nat. Lib. , ' vol. X. P. 103. [509] Azara, 'Quadrupèdes du Paraguay, ' tom. Ii. P. 324. [510] Sidney's edit. Of Youatt, 1860, pp. 24, 25. [511] 'Rural Economy of Yorkshire, ' vol. Ii. P. 182. [512] Moll et Gayot, 'Du Boeuf, ' 1860, p. 547. [513] 'The India Sporting Review, ' vol. Ii. P. 181; 'The Stud Farm, ' byCecil, p. 58. [514] 'The Horse, ' p. 22. [515] 'History of England, ' vol. I. P. 316. [516] 'Uber Beständigkeit der Arten. ' [517] Youatt on Sheep, p. 315. [518] 'Ueber Shorthorn Rindvieh, ' 1857, s. 51. [519] Low, 'Domesticated Animals, ' 1845, p. 363. [520] 'Quarterly Review, ' 1849, p. 392. [521] H. Von Nathusius, 'Vorstudien ... Schweineschædel, ' 1864, s. 140. [522] _See_ also Dr. Christ, in 'Rütimeyer's Pfahlbauten, ' 1861, s. 226. [523] The passage is given 'Bull. Soc. D'Acclimat. , ' 1858, p. 11. [524] 'Journal of Horticulture, ' 1862, p. 394. [525] 'Gardener's Chronicle, ' 1857, p. 85. [526] _See_ Mr. Wildman's address to the Floricult. Soc. , in 'Gardener'sChronicle, ' 1843, p. 86. [527] 'Journal of Horticulture, ' Oct. 24th, 1865, p. 239. [528] Prescott's 'Hist. Of Mexico, ' vol. Ii. P. 61. [529] Sageret, 'Pomologie Physiologique, ' 1830, p. 47; Gallesio, 'Teoriadella Riproduzione, ' 1816, p. 88; Godron, 'De l'Espèce, ' 1859, tom. Ii. Pp. 63, 67, 70. In my tenth and eleventh chapters I have given details on thepotato; and I can confirm similar remarks with respect to the onion. I havealso shown how far Naudin concurs in regard to the varieties of the melon. [530] Godron, 'De l'Espèce, ' tom. Ii. P. 27. [531] 'The Anthropological Treatises of Blumenbach, ' 1865, p. 292. [532] Mr. J. J. Murphy in his opening address to the Belfast Nat. Hist. Soc. , as given in the Belfast Northern Whig, Nov. 19, 1866. Mr. Murphy herefollows the line of argument against my views previously and morecautiously given by the Rev. C. Pritchard, Pres. Royal Astronomical Soc. , in his sermon (Appendix, p. 33) preached before the British Association atNottingham, 1866. [533] On the Vision of Fishes and Amphibia, translated in 'Annals and Mag. Of Nat. Hist. , ' vol. Xviii. , 1866, p. 469. [534] Fourth edition, 1866, p. 215. [535] Quoted by Youatt on Sheep, p. 325. _See_ also Youatt on Cattle, pp. 62, 69. [536] MM. Lherbette and De Quatrefages, in 'Bull. Soc. Acclimat. , ' tom. Viii. , 1861, p. 311. [537] 'The Poultry Book, ' 1866, p. 123. [538] Youatt on Sheep, p. 312. [539] 'Treatise on the Almond Tumbler, ' 1851, p. 33. [540] Dr. Heusinger, 'Wochenschrift für die Heilkunde, ' Berlin, 1846, s. 279. [541] Youatt on the Dog, p. 232. [542] 'The Fruit-trees of America, ' 1845, p. 270: for peaches, p. 466. [543] 'Proc. Royal Soc. Of Arts and Sciences of Mauritius, ' 1852, p. Cxxxv. [544] 'Gardener's Chronicle, ' 1856, p. 379. [545] Quatrefages, 'Maladies Actuelles du Ver à Soie, ' 1859, pp. 12, 214. [546] 'Gardener's Chronicle, ' 1851, p. 595. [547] 'Journal of Horticulture, ' 1862, p. 476. [548] 'Gardener's Chronicle, ' 1852, pp. 435, 691. [549] Bechstein, 'Naturgesch. Deutschlands, ' 1801, B. I. S. 310. [550] Prichard, 'Phys. Hist. Of Mankind, ' 1851, vol. I. P. 224. [551] G. Lewis's 'Journal of Residence in West Indies, ' 'Home and Col. Library, ' p. 100. [552] Sidney's edit. Of Youatt on the Pig, p. 24. [553] 'Journal of Horticulture, ' 1862, pp. 476, 498; 1865, p. 460. Withrespect to the heartsease, 'Gardener's Chronicle, ' 1863, p. 628. [554] 'Des Jacinthes, de leur Culture, ' 1768, p. 53: on wheat, 'Gardener'sChronicle, ' 1846, p. 653. [555] W. B. Tegetmeier, 'The Field, ' Feb. 25, 1865. With respect to blackfowls, _see_ a quotation in Thompson's 'Nat. Hist. Of Ireland, ' 1849, vol. I. P. 22. [556] 'Bull. De la Soc. D'Acclimat. , ' tom. Vii. 1860, p. 359. [557] 'Transact. Hort. Soc. , ' vol. I. 2nd series, 1835, p. 275. Forraspberries, _see_ 'Gard. Chronicle, ' 1855, p. 154, and 1863, p. 245. [558] 'Gardener's Chronicle, ' 1843, p. 806. [559] Ibid. , 1850, p. 732. [560] Ibid. , 1860, p. 956. [561] J. De Jonghe, in 'Gard. Chronicle, ' 1860, p. 120. [562] Downing, 'Fruit-trees of North America, ' pp. 266, 501: in regard tothe cherry, p. 198. [563] 'Gardener's Chronicle, ' 1849, p. 755. [564] 'Journal of Horticulture, ' Sept. 26th, 1865, p. 254; _see_ otherreferences given in chap. X. [565] Mr. Selby, in 'Mag. Of Zoology and Botany, ' Edinburgh, vol. Ii. , 1838, p. 393. [566] The Reine Claude de Bavay, 'Journal of Horticulture, ' Dec. 27, 1864, p. 511. [567] Mr. Pusey, in 'Journal of R. Agricult. Soc. , vol. Vi. P. 179. ForSwedish turnips, _see_ 'Gard. Chron. , ' 1847, p. 91. [568] Godron, 'De l'Espèce, ' tom. Ii. P. 98. [569] 'Gardener's Chron. , ' 1866, p. 732. [570] 'Gardener's Chronicle, ' 1862, pp. 820, 821. [571] 'On the Varieties of Wheat, ' p. 59. [572] Mr. Hewitt and others, in 'Journal of Hort. , ' 1862, p. 773. [573] 'Encyclop. Of Rural Sports, ' p. 405. [574] Col. Le Couteur, 'Journal Roy. Agricult. Soc. , ' vol. Iv. P. 43. [575] 'Gardener's Chronicle, ' 1845, p. 273. [576] 'Journal of Horticulture, ' 1862, p. 157. [577] 'Cottage Gardener, ' 1860, p. 368. [578] 'A Review of Reports, ' 1808, p. 406. [579] 'Gardener's Chronicle, ' 1853, p. 45. [580] Isidore Geoffroy St. Hilaire, 'Hist. Nat. Gén. , ' tom. Iii. P. 49. Onthe Cochineal Insect, p. 46. [581] Capt. Marryat, quoted by Blyth in 'Journ. Asiatic Soc. Of Bengal, 'vol. Xxviii. P. 229. [582] Mr. Oxley, 'Journal of the Indian Archipelago, ' vol. Ii. , 1848, p. 645. [583] Mr. Abbey, in 'Journal of Horticulture, ' Dec. 1, 1863, p. 430. [584] 'On Naval Timber, ' 1831, p. 107. [585] Mr. Baily, in 'The Poultry Chronicle, ' vol. Ii. , 1854, p. 150. Alsovol. I. P. 342; vol. Iii. P. 245. [586] 'Cottage Gardener, ' 1855, December, p. 171; 1856, January, pp. 248, 323. [587] 'Ueber Shorthorn Rindvieh, ' 1857, s. 51. [588] 'The Veterinary, ' vol. Xiii. P. 720. For the Glamorganshire cattle, _see_ Youatt on Cattle, p. 51. [589] J. M. Eaton, 'A Treatise on Fancy Pigeons, ' p. 82; Ferguson, on 'Rareand Prize Poultry, ' p. 162; Mr. Brent, in 'Cottage Gardener, ' Oct. 1860. P. 13. [590] 'Die Racen des Schweines, ' 1860, s. 48. [591] _See_ some good remarks on this head by M. De Quatrefages, 'Unité del'Espèce Humaine, ' 1861, p. 119. [592] Verlot, 'Des Variétés, ' 1865, p. 94. [593] Mr. Patrick Sheriff, in 'Gard. Chronicle, ' 1858, p. 771. [594] 'Pomologie Physiolog. , ' 1830, p. 106. [595] Youatt on Sheep, p. 521. [596] 'A Treatise on the Almond Tumbler, ' p. I. [597] M. J. De Jonghe, in 'Gard. Chron. , ' 1858, p. 173. [598] Max. Müller, 'Science of Language, ' 1861, p. 223. [599] Youatt on Cattle, pp. 116, 128. [600] 'Domesticated Animals, ' p. 188. [601] Volz, 'Beiträge zur Kulturgeschichte, ' 1852, s. 99 _et passim_. [602] Blaine, 'Encyclop. Of Rural Sports, ' p. 213. [603] 'Des Jacinthes, ' &c. , Amsterdam, 1768, p. 43; Verlot, 'Des Variétés, '&c. , p. 86. On the reindeer, _see_ Linnæus, 'Tour in Lapland, ' translatedby Sir J. E. Smith, vol. I. P. 314. The statement in regard to Germanshepherds is given on the authority of Dr. Weinland. [604] Müller's 'Physiology, ' Eng. Translation, vol. Ii. P. 1662. Withrespect to the similarity of twins in constitution, Dr. William Ogle hasgiven me the following extract from Professor Trousseau's Lectures('Clinique Médicale, ' tom. I. P. 523), in which a curious case isrecorded:--"J'ai donné mes soins à deux frères jumeaux, tous deux siextraordinairement ressemblants qu'il m'était impossible de lesreconnaître, à moins de les voir l'un à côté de l'autre. Cette ressemblancephysique s'étendait plus loin: ils avaient, permettez-moi l'expression, unesimilitude pathologique plus remarquable encore. Ainsi l'un d'eux que jevoyais aux néothermes à Paris malade d'une ophthalmie rhumatismale medisait, 'En ce moment mon frère doit avoir une ophthalmie comme la mienne;'et comme je m'étais récrié, il me montrait quelques jours après une lettrequ'il venait de recevoir de ce frère alors à Vienne, et qui lui écrivait eneffet--'J'ai mon ophthalmie, tu dois avoir la tienne. ' Quelque singulierque ceci puisse paraître, le fait non est pas moins exact: on ne me l'a pasraconté, je l'ai vu, et j'en ai vu d'autres analogues dans ma pratique. Cesdeux jumeaux étaient aussi tous deux asthmatiques, et asthmatiques à uneffroyable degré. Originaires de Marseille, ils n'ont jamais pu demeurerdans cette ville, où leurs intérêts les appelaient souvent, sans être prisde leurs accès; jamais ils n'en éprouvaient à Paris. Bien mieux, il leursuffisait de gagner Toulon pour être guéris de leurs attaques deMarseilles. Voyageant sans cesse et dans tous pays pour leurs affaires, ilsavaient remarqué que certaines localités leur étaient funestes, que dansd'autres ils étaient exempts de tout phénomène d'oppression. " [605] Isid. Geoffroy St. Hilaire, 'Hist. Des Anomalies, ' tom. Iii. P. 352;Moquin Tandon, 'Tératologie Végétale, ' 1841, p. 115. [606] Metzger, 'Die Getreidearten, ' 1841, s. 39. [607] On the date-palm, _see_ Vogel, 'Annals and Mag. Of Nat. Hist. , ' 1854, p. 460. On Indian varieties, Dr. F. Hamilton, 'Transact. Linn. Soc. , ' vol. Xiv. P. 296. On the varieties cultivated in Tahiti, _see_ Dr. Bennett, inLoudon's 'Mag. Of N. Hist. , ' vol. V. , 1832, p. 484. Also Ellis, 'PolynesianResearches, ' vol. I. Pp. 375, 370. On twenty varieties of the Pandanus andother trees in the Marianne Island, _see_ 'Hooker's Miscellany, ' vol. I. P. 308. On the bamboo in China, _see_ Huc's 'Chinese Empire, ' vol. Ii. P. 307. [608] 'Treatise on the Culture of the Apple, ' &c. , p. 3. [609] Gallesio, 'Teoria della Riproduzione Veg. , ' p. 125. [610] _See_ Dr. Hooker's Memoir on Arctic Plants in 'Linn. Transact. , ' vol. Xxiii, part ii. Mr. Woodward, and a higher authority cannot be quoted, speaks of the Arctic mollusca (in his 'Rudimentary Treatise, ' 1856, p. 355)as remarkably subject to variation. [611] Bechstein, in his 'Naturgeschichte der Stubenvögel, ' 1840, s. 238, has some good remarks on this subject. He states that his canary-birdsvaried in colour, though kept on uniform food. [612] 'The Plant, ' by Schleiden, translated by Henfrey, 1848, p. 169. _See_also Alex. Braun, in 'Bot. Memoirs, ' Ray. Soc. , 1853, p. 313. [613] Messrs. Hardy and Son, of Maldon, in 'Gard. Chronicle, ' 1856, p. 458. [614] 'Quadrupèdes du Paraguay, ' 1801, tom. Ii. P. 319. [615] McClelland on Indian Cyprinidæ, 'Asiatic Researches, ' vol. Xix. Partii. , 1839, pp. 266, 268, 313. [616] Quoted by Sageret, 'Pom. Phys. , ' 1830, p. 43. [617] 'The Fruits of America, ' 1845, p. 5. [618] M. Cardan, in 'Comptes Rendus, ' Dec. 1848, quoted in 'Gard. Chronicle, ' 1849, p. 101. [619] M. Alexis Jordan mentions four excellent pears found in woods inFrance, and alludes to others ('Mém. Acad. De Lyon, ' tom. Ii. 1852, p. 159). Poiteau's remark is quoted in 'Gardener's Mag. , ' vol. Iv. , 1828, p. 385. _See_ 'Gard. Chronicle, ' 1862, p. 335, for another case of a newvariety of the pear found in a hedge in France. Also for another case, _see_ Loudon's 'Encyclop. Of Gardening, ' p. 901. Mr. Rivers has given mesimilar information. [620] Duval, 'Hist. Du Poirier, ' 1849, p. 2. [621] I infer that this is the fact from Van Mons' statement ('ArbresFruitiers, ' 1835, tom. I. P. 446) that he finds in the woods seedlingsresembling all the chief cultivated races of both the pear and apple. VanMons, however, looked at these wild varieties as aboriginal species. [622] Downing, 'Fruit-trees of North America, ' p. 422; Foley, in 'Transact. Hort. Soc. , ' vol. Vi. P. 412. [623] 'Gard. Chronicle, ' 1847, p. 244. [624] 'Gardener's Chronicle, ' 1841, p. 383; 1850, p. 700; 1854, p. 650. [625] 'Die Getreidearten, ' 1843, s. 66, 116, 117. [626] Sabine, in 'Hort. Transact. , ' vol. Iii. P. 225; Bronn, 'Geschichteder Natur, ' b. Ii. S. 119. [627] 'Journal of Horticulture, ' 1861, p. 112; on Zinnia, 'Gardener'sChronicle, ' 1860, p. 852. [628] 'The Chrysanthemum, its History, &c. , ' 1865, p. 3. [629] 'Gardener's Chron. , ' 1855, p. 54; 'Journal of Horticulture, ' May 9, 1865, p. 363. [630] Quoted by Verlot, 'Des Variétés, ' &c. , 1865, p. 28. [631] 'Examination of the Characteristics of Genera and Species:'Charleston, 1855, p. 14. [632] Mr Hewitt, 'Journal of Hort. , ' 1863, p. 39. [633] Devay, 'Mariages Consanguins, ' pp. 97, 125. In conversation I havefound two or three naturalists of the same opinion. [634] Müller has conclusively argued against this belief, 'Elements ofPhys. , ' Eng. Translat. , vol. Ii. , 1842, p. 1405. [635] 'Act. Acad. St. Petersburg, ' 1780, part ii. P. 84, &c. [636] 'Bastarderzeugung, ' s. 249, 255, 295. [637] 'Nova Acta, St. Petersburg, ' 1794, p. 378; 1795, pp. 307, 313, 316;1787, p. 407. [638] 'De la Fécondation, ' 1862, p. 311. [639] 'Amaryllidaceæ, ' 1837, p. 362. [640] Abstracted in 'Gard. Chronicle, ' 1860, p. 1081. [641] This was the opinion of the elder De Candolle, as quoted in 'Dic. Class. D'Hist. Nat. , ' tom. Viii. P. 405. Puvis, in his work, 'De laDégénération, ' 1837, p. 37, has discussed this same point. [642] 'Comptes Rendus, ' Novembre 21, 1864, p. 838. [643] 'Nova Acta, St. Petersburg, ' 1794, p. 391. [644] 'Bastarderzeugung, ' s. 507, 516, 572. [645] 'Die Bastardbefruchtung, ' &c. , 1865, s. 24. [646] 'Bastarderzeugung, ' s. 452, 507. [647] 'Die Bastardbefruchtung, ' s. 56. [648] 'Bastarderzeugung, ' s. 423. [649] 'Dritte Fortsetzung, ' &c. , 1766, s. 85. [650] 'Die Bastardbefruchtung, ' &c. , 1865, s. 92; _see_ also the Rev. M. J. Berkeley on the same subject, in 'Journal of Royal Hort. Soc. , ' 1866, p. 80. [651] Dr. P. Lucas has given a history of opinion on this subject: 'Héréd. Nat. , ' 1847, tom. I. P. 175. [652] 'Hist. Des Anomalies, ' tom. Iii. P. 499. [653] Idem. , tom. Iii. Pp. 392, 502. [654] _See_ his interesting work, 'Métamorphoses de l'Homme, ' &c. , 1862, p. 129. [655] 'Dritte Fortsetzung, ' &c. , s. 123; 'Bastarderzeugung, ' s. 249. [656] 'Gardener's Chronicle, ' 1853, p. 183. [657] Mr. Wildman, 'Floricultural Soc. , ' Feb. 7, 1843, reported in 'Gard. Chron. , ' 1843, p. 86. [658] Mr. Robson, in 'Journal of Horticulture, ' Feb. 13th, 1866, p. 122. [659] 'Journal of Horticulture, ' 1861, p. 24. [660] Ibid. , 1862, p. 83. [661] 'Gard. Chron. , ' 1845, p. 660. [662] Ibid. , 1863, p. 628. [663] 'Journal of Hort. , ' 1861, pp. 64, 309. [664] 'Des Variétés, ' &c. , p. 76. [665] Engel, 'Sur les Prop. Médicales des Plantes, ' 1860, pp. 10, 25. Onchanges in the odours of plants, _see_ Dalibert's Experiments, quoted byBeckman, 'Inventions, ' vol. Ii. P. 344; and Nees, in Ferussac, 'Bull. DesSc. Nat. , ' 1824, tom. I. P. 60. With respect to the rhubarb, &c. , _see_also 'Gardener's Chronicle, ' 1849, p. 355; 1862, p. 1123. [666] Hooker, 'Flora Indica, ' p. 32. [667] Naudin, 'Annales des Sc. Nat. , ' 4th series, Bot. , tom. Xi. , 1859, p. 81. 'Gardener's Chronicle, ' 1859, p. 464. [668] Moorcroft's 'Travels, ' &c. , vol. Ii. P. 143. [669] 'Gardener's Chronicle, ' 1861, p. 1113. [670] Royle, 'Productive Resources of India, ' p. 59. [671] 'Personal Narrative, ' Eng. Translat. , vol. V. P. 101. This statementhas been confirmed by Karsten ('Beitrag zur Kenntniss der Rhynchoprion:'Moscow, 1864. S. 39), and by others. [672] 'Organic Chemistry, ' Eng. Translat. , 1st edit. , p. 369. [673] Prichard, 'Phys. Hist. Of Mankind, ' 1851, vol. I. P. 155. [674] Darwin, 'Journal of Researches, ' 1845, p. 434. [675] These statements on disease are taken from Dr. Boudin's 'Géographieet de Statistique Médicales, ' 1857, tom. I. P. Xliv. And lii. ; tom. Ii. P. 315. [676] E. Desor, quoted in the 'Anthrop. Rev. , ' 1863, p. 180. For muchconfirmatory evidence, _see_ Quatrefages, 'Unité de l'Espèce Humaine, '1861, p. 131. [677] 'Ceylon, ' by Sir J. E. Tennent, vol. I. , 1859, p. 89. [678] Godron, 'De l'Espèce, ' tom. Ii. P. 52. [679] 'Journal of Horticultural Soc. , ' vol. Vii. , 1852, p. 117. [680] 'Journal of Hort. Soc. , ' vol. I. P. 160. [681] _See_ Lecoq on the Villosity of Plants, 'Geograph. Bot. , ' tom. Iii. Pp. 287, 291; Gärtner, 'Bastarderz. , ' s. 261; Mr. Musters, on the Opuntia, in 'Gard. Chronicle, ' 1846, p. 444. [682] 'Pom. Phys. , ' p. 136. [683] 'Ampelographie, ' 1849, p. 19. [684] Gärtner, 'Bastarderz. , ' s. 606, has collected nearly all recordedfacts. Andrew Knight (in 'Transact. Hort. Soc. , ' vol. Ii. P. 160) goes sofar as to maintain that few varieties are absolutely permanent in characterwhen propagated by buds or grafts. [685] Mr. Blyth, in 'Annals and Mag. Of Nat. Hist. , ' vol. Xx. , 1847, p. 391. [686] 'Natural History Review, ' 1862, p. 113. [687] 'Journal of Roy. Geographical Soc. , ' vol. Ix. , 1839, p. 275. [688] 'Travels in Bokhara, ' vol. Iii. P. 151. [689] _See_ also, on the influence of marshy pastures on the wool, Godron, 'L'Espèce, ' tom. Ii. P. 22. [690] Isidore Geoffroy St. Hilaire, 'Hist. Nat. Gén. , ' tom. Iii. P. 438. [691] Azara has made some good remarks on this subject, 'Quadrupèdes duParaguay, ' tom. Ii. P. 337. _See_ an account of a family of naked miceproduced in England, 'Proc. Zoolog. Soc. , ' 1856, p. 38. [692] 'Die Fauna der Pfahlbauten, ' 1861, s. 15. [693] 'Schweinschædel, ' 1864, s. 99. [694] 'Travels in Siberia, ' Eng. Translat. , vol. I. P. 228. [695] A. R. Wallace, 'Travels on the Amazon and Rio Negro, ' p. 294. [696] 'Naturgeschichte der Stubenvögel, ' 1840, s. 262, 308. [697] 'Hist. Nat. Gén. , ' tom. Iii. P. 402. [698] 'Bull. De la Soc. Imp. D'Acclimat. , ' tom. Viii. P. 351. [699] _See_ an account of Mr. Gregson's experiments on the _Abraxusgrossulariata_, 'Proc. Entomolog. Soc. , ' Jan. 6th, 1862: these experimentshave been confirmed by Mr. Greening, in 'Proc. Of the Northern Entomolog. Soc. , ' July 28th, 1862. For the effects of food on caterpillars, see acurious account by M. Michely, in 'Bull. De la Soc. Imp. D'Acclimat. , ' tom. Viii. P. 563. For analogous facts from Dahlbom on Hymenoptera, _see_Westwood's 'Modern Class. Of Insects, ' vol. Ii. P. 98. _See_ also Dr. L. Möller, 'Die Abhängigkeit der Insecten, ' 1867, s. 70. [700] 'The Principles of Biology, ' vol. Ii. 1866. The present chapters werewritten before I had read Mr. Herbert Spencer's work, so that I have notbeen able to make so much use of it as I should otherwise probably havedone. [701] 'Proc. Acad. Nat. Soc. Of Philadelphia, ' Jan. 28th, 1862. [702] _See_ Mr. B. D. Walsh's excellent papers in 'Proc. Entomolog. Soc. Philadelphia, ' Dec. 1866, p. 284. With respect to the willow, _see_ idem, 1864, p. 546. [703] _See_ his admirable Histoire des Galles, in 'Annal. Des Sc. Nat. Bot. , ' 3rd series, tom. Xix. , 1853, p. 273. [704] Kirby and Spence's 'Entomology, ' 1818, vol. I. P. 450;Lucaze-Duthiers, idem, p. 284. [705] 'Proc. Entomolog. Soc. Philadelphia, ' 1864, p. 558. [706] Mr. B. D. Walsh, idem, p. 633; and Dec. 1866, p. 275. [707] Mr. B. D. Walsh, idem, 1864, p. 545, 411, 495; and Dec. 1866, p. 278. _See_ also Lucaze-Duthiers. [708] Lucaze-Duthiers, idem, pp. 325, 328. [709] 'Linnæa, ' vol. Xvii. , 1843; quoted by Dr. M. T. Masters, RoyalInstitution, March 16th, 1860. [710] Hewett C. Watson, 'Cybele Britannica, ' vol. I. , 1847, p. 11. [711] 'Gardener's Chronicle, ' 1857, p. 629. [712] 'Mémoire sur la Production Artificielle des Monstrosités, ' 1862, pp. 8-12; 'Recherches sur les Conditions, &c. , chez les Monstres, ' 1863, p. 6. An abstract is given of Geoffroy's Experiments by his son, in his 'Vie, Travaux, &c. , ' 1847, p. 290. [713] Paget, 'Lectures on Surgical Pathology, ' 1853, vol. I. P. 483. [714] 'Researches upon the Venom of the Rattle-snake, ' Jan. 1861, by Dr. Mitchell, p. 67. [715] Mr. Sedgwick, in 'British and Foreign Medico-Chirurg. Review, ' July1863, p. 175. [716] 'An Essay on Generation, ' Eng. Translat. , p. 18; Paget, 'Lectures onSurgical Pathology, ' 1853, vol. I. P. 209. [717] 'An Essay on Animal Reproduction, ' Eng. Translat. , 1769, p. 79. [718] Carpenter's 'Principles of Comp. Physiology, ' 1854, p. 479. [719] Charlesworth's 'Mag. Of Nat. Hist. , ' vol. I. , 1837, p. 145. [720] Paget, 'Lectures on Surgical Pathology, ' vol. I. P. 239. [721] Quoted by Carpenter, 'Comp. Phys. , ' p. 479. [722] Paget, 'Lectures, ' &c. , p. 257. [723] These cases are given by Blumenbach in his 'Essay on Generation, ' pp. 52, 54. [724] 'Cellular Pathology, ' trans. By Dr. Chance, 1860, pp. 27, 441. [725] Paget, 'Lectures on Pathology, ' vol. I. , 1853, p. 357. [726] Paget, idem, p. 150. [727] 'The Principles of Biology, ' vol. Ii. , 1866, chap. 3-5. [728] 'Lectures on Pathology, ' 1853, vol. I. P. 71. [729] 'Comptes Rendus, ' Sept. 26th, 1864, p. 539. [730] 'The Principles of Biology, ' vol. Ii. P. 243. [731] Idem, vol. Ii. P. 269. [732] Idem, vol. Ii. P. 273. [733] Paget, 'Lectures on Pathology, ' vol. Ii. P. 209. [734] Müller's 'Phys. , ' Eng. Translat. , pp. 54, 791. Prof. Reed has given('Physiological and Anat. Researches, ' p. 10) a curious account of theatrophy of the limbs of rabbits after the destruction of the nerve. [735] Quoted by Lecoq, in 'Geograph. Bot. , ' tom. I. , 1854, p. 182. [736] 'Das Abändern der Vögel, ' 1833, s. 74. [737] Nathusius, 'Die Racen des Schweines, ' 1860, s. 53, 57; 'Vorstudien... Schweineschædel, ' 1864, s. 103, 130, 133. [738] 'Journal of Agriculture of Highland Soc. , ' July, 1860, p. 321. [739] 'Principles of Biology, ' vol. Ii. P. 263. [740] 'Natural History Review, ' vol. Iv. , Oct. 1864, p. 617. [741] 'Lectures on Surgical Pathology, ' 1853, vol. I. P. 27. [742] Andersson, 'Travels in South Africa, ' p. 318. For analogous cases inSouth America, _see_ Aug. St. Hilaire, 'Voyage dans le Province de Goyaz, 'tom. I. P. 71. [743] Brickell's 'Nat. Hist. Of North Carolina, ' 1739, p. 53. [744] Livingstone, quoted by Youatt on Sheep, p. 142. Hodgson, in 'Journalof Asiatic Soc. Of Bengal, ' vol. Xvi. , 1847, p. 1006, &c. &c. [745] 'Naturalist Library, ' Dogs, vol. Ii. 1840, p. 104. [746] 'De l'Espèce, ' tom. I. , 1859, p. 367. [747] 'Ceylon, ' by Sir J. E. Tennent, 1859, vol. Ii. P. 531. [748] For the foregoing statements, _see_ Hunter's 'Essays andObservations, ' 1861, vol. Ii. P. 329; Dr. Edmondston, as quoted inMacgillivray's 'British Birds, ' vol. V. P. 550; Menetries, as quoted inBronn's 'Geschichte der Natur, ' B. Ii. S. 110. [749] These statements on the intestines are taken from Isidore GeoffroySt. Hilaire, 'Hist. Nat. Gén. , ' tom. Iii. Pp. 427, 441. [750] Gilbert White, 'Nat. Hist. Selbourne, ' 1825, vol. Ii. P. 121. [751] Burdach, 'Traité de Phys. , ' tom. Ii. P. 267, as quoted by Dr. P. Lucas, 'L'Héréd. Nat. , ' tom. I. P. 388. [752] This and several other cases are given by Colin, 'Physiologie Comp. Des Animaux Dom. , ' 1854, tom. I. P. 426. [753] M. Michely de Cayenne, in 'Bull. Soc. D'Acclimat. , ' tom. Viii. , 1861, p. 563. [754] Quatrefages, 'Unité de l'Espèce Humaine, ' 1861, p. 79. [755] 'Flora, ' 1835, B. Ii. P. 504. [756] Alph. De Candolle, 'Géograph. Bot. , ' tom. Ii. P. 1078. [757] Royle, 'Illustrations of the Botany of the Himalaya, ' p. 19. [758] 'Gardener's Chronicle, ' 1850, pp. 204, 219. [759] Rev. R. Everest, 'Journal As. Soc. Of Bengal, ' vol. Iii. P. 19. [760] Youatt on Sheep, 1838, p. 491. [761] Royle, 'Prod. Resources of India, ' p. 153. [762] Tegetmeier, 'Poultry Book, ' 1866, p. 102. [763] Dr. R. Paterson, in a paper communicated to Bot. Soc. Of Canada, quoted in the 'Reader, ' 1863. Nov. 13th. [764] _See_ remarks by Editor in 'Gard. Chronicle, ' 1848, p. 5. [765] 'Gard. Chronicle, ' 1860, p. 938. Remarks by Editor and quotation fromDecaisne. [766] J. De Jonghe, of Brussels, in 'Gard. Chronicle, ' 1857, p. 612. [767] Ch. Martius, 'Voyage Bot. Côtes Sept. De la Norvège, ' p. 26. [768] 'Journal de l'Acad. Hort. De Gand, ' quoted in 'Gard. Chron. , ' 1859, p. 7. [769] 'Gard. Chronicle, ' 1851, p. 396. [770] Idem. , 1862, p. 235. [771] On the authority of Labat, quoted in 'Gard. Chron. , ' 1862, p. 235. [772] MM. Edwards and Colin, 'Annal. Des Sc. Nat. , ' 2nd series, Bot. , tom. V. P. 22. [773] 'Géograph. Bot. , ' p. 337. [774] 'Swedish Acts, ' Eng. Translat. , 1739-40, vol. I. Kalm, in his'Travels, ' vol. Ii. P. 166, gives an analogous case with cotton-plantsraised in New Jersey from Carolina seed. [775] De Candolle, 'Géograph. Bot. , ' p. 339. [776] 'Gard. Chronicle, ' 1862, p. 235. [777] Gallesio, 'Teoria della Riproduzione Veg. , ' 1816, p. 125; and 'Traitédu Citrus, ' 1811, p. 359. [778] 'Essai sur l'Hist. Des Orangers, ' 1813, p. 20, &c. [779] Alph. De Candolle, 'Géograph. Bot. , ' p. 882. [780] 'Ch. Darwin's Lehre von der Entstehung, ' &c. , 1862, s. 87. [781] Decaisne, quoted in 'Gard. Chronicle, ' 1865, p. 271. [782] For the magnolia, _see_ Loudon's 'Gard. Mag. , ' vol. Xiii. , 1837, p. 21. For camellias and roses, _see_ 'Gard. Chron. , ' 1860, p. 384. For theyew, 'Journal of Hort. , ' March 3rd, 1863, p. 174. For sweet potatoes, _see_Col. Von Siebold, in 'Gard. Chron. , ' 1855, p. 822. [783] The Editor, 'Gard. Chron. , ' 1861, p. 239. [784] Loudon's 'Gard. Mag. , ' vol. Xii. , 1836, p. 378. [785] 'Gardeners Chron. , ' 1865, p. 699. [786] 'Arboretum et Fruticetum, ' vol. Iii. P. 1376. [787] Mr. Robson, in 'Journal of Horticulture, ' 1861, p. 23. [788] Dr. Bonavia, 'Report of the Agri. -Hort. Soc. Of Oudh, ' 1866. [789] 'Cottage Gardener, ' 1860, April, 24th, p. 57. [790] 'Gardener's Chronicle, ' 1841, p. 291. [791] Mr. Beaton, in 'Cottage Gardener, ' March 20th, 1860, p. 377. QueenMab will also stand stove heat, _see_ 'Gard. Chronicle, ' 1845, p. 226. [792] 'Gardener's Chronicle, ' 1841, p. 439. [793] Quoted by Asa Gray, in 'Am. Journ. Of Sci. , ' 2nd series, Jan. 1865, p. 106. [794] For China, _see_ 'Mémoire sur les Chinois, ' tom, xi. , 1786, p. 60. Columella is quoted by Carlier, in 'Journal de Physique, ' tom. Xxiv. 1784. [795] Messrs. Hardy and Son, in 'Gard. Chronicle, ' 1856, p. 589. [796] Isid. Geoffroy St. Hilaire, 'Hist. Nat. Des Anomalies, ' 1836, tom. Ii. Pp. 210, 223, 224, 395; 'Philosoph. Transact. , ' 1775, p. 313. [797] Pallas, quoted by Youatt on Sheep, p. 25. [798] Youatt on Cattle, 1834, p. 174. [799] 'Encyclop. Méthod. , ' 1820, p. 483: _see_ p. 500, on the Indian zebucasting its horns. Similar cases in European cattle were given in the thirdchapter. [800] Pallas, 'Travels, ' Eng. Translat. , vol. I. P. 243. [801] Mr. Beaton, in 'Journal of Horticulture, ' May 21, 1861, p. 133. [802] Lecoq, 'De la Fécondation, ' 1862, p. 233. [803] 'Annales du Muséum, ' tom. Vi. P. 319. [804] 'Hist. Des Anomalies, ' tom. Iii. P. 392. Prof. Huxley applies thesame principle in accounting for the remarkable, though normal, differencesin the arrangement of the nervous system in the Mollusca, in his greatpaper on the Morphology of the Cephalous Mollusca, in 'Phil. Transact. , '1853, p. 56. [805] 'Eléments de Tératologie Veg. , ' 1841, p. 113. [806] Prof. J. B. Simonds, on the Age of the Ox, Sheep, &c. , quoted in'Gard. Chronicle, ' 1854, p. 588. [807] 'Hist. Des Anomalies, ' tom. I. P. 674. [808] Quoted by Isid. Geoffroy, idem, tom. I. P. 635. [809] 'The Poultry Book, ' by W. B. Tegetmeier, 1866, p. 250. [810] A. Walker on Intermarriage, 1838, p. 160. [811] 'The Farrier and Naturalist, ' vol. I. , 1828, p. 456. [812] Godron, 'Sur l'Espèce, ' tom. Ii. P. 217. [813] 'Quadrupèdes du Paraguay, ' tom. Ii. P. 333. [814] On Sheep, p. 142. [815] 'Ueber Racen, Kreuzungen, &c. , ' 1825, s. 24. [816] Quoted from Conolly, in 'The Indian Field, ' Feb. 1859, vol. Ii. P. 266. [817] 'Domesticated Animals of the British Islands, ' pp. 307, 368. [818] 'Proceedings Zoolog. Soc. , ' 1833, p. 113. [819] Sedgwick, 'Brit. And Foreign Medico-Chirurg. Review, ' April 1863, p. 453. [820] 'Gard. Chronicle, ' 1849, p. 205. [821] 'Embassy to the Court of Ava, ' vol. I. P. 320. [822] 'Narrative of a Mission to the Court of Ava in 1855, ' p. 94. [823] Those statements are taken from Mr. Sedgwick, in the 'Medico-Chirurg. Review, ' July 1861, p. 198; April 1863, pp. 455 and 458. Liebreich isquoted by Professor Devay, in his 'Mariages Consanguins, ' 1862, p. 116. [824] Loudon's 'Mag. Of Nat. Hist. , ' vol. I. , 1829, pp. 66, 178. _See_ alsoDr. P. Lucas, 'L'Héréd. Nat. , ' tom. I. P. 428, on the inheritance ofdeafness in cats. [825] 'Annales des Sc. Nat. ' Zoolog. , 3rd series, 1847, tom. Viii. P. 239. [826] 'Gardener's Chron. , ' 1864, p. 1202. [827] Verlot gives several other instances, 'Des Variétés, ' 1865, p. 72. [828] 'Arbres Fruitiers, ' 1836, tom. Ii. Pp. 204, 226. [829] 'Annales du Muséum, ' tom. Xx. P. 188. [830] 'Gardener's Chron. , ' 1843, p. 877. [831] Ibid. , 1845, p. 102. [832] 'Hist. Des Anomalies, ' tom. Iii. P. 402. _See_ also M. CamilleDareste, 'Recherches sur les Conditions, ' &c. , 1863, pp. 16, 48. [833] Rev. E. S. Dixon, 'Ornamental Poultry, ' 1848, p. 111; IsidoreGeoffroy, 'Hist. Anomalies, ' tom. I. P. 211. [834] 'On the Breeding of Domestic Animals, ' 1829, p. 6. [835] Youatt on Cattle, 1834, p. 283. [836] Mr. Herbert Spencer ('Principles of Biology, ' 1864, vol. I. Pp. 452, 468) takes a different view; and in one place remarks: "We have seen reasonto think that, as fast as essential faculties multiply, and as fast as thenumber of organs that co-operate in any given function increases, indirectequilibration through natural selection becomes less and less capable ofproducing specific adaptations; and remains fully capable only ofmaintaining the general fitness of constitution to conditions. " This viewthat natural selection can do little in modifying the higher animalssurprises me, seeing that man's selection has undoubtedly effected muchwith our domesticated quadrupeds and birds. [837] Dr. Prosper Lucas apparently disbelieves in any such connexion, 'L'Héréd. Nat. , ' tom. Ii. Pp. 88-94. [838] 'British Medical Journal, ' 1862, p. 433. [839] Boudin, 'Geograph. Médicale, ' tom. I. P. 406. [840] This fact and the following cases, when not stated to the contrary, are taken from a very curious paper by Prof. Heusinger, in 'Wochenschriftfür Heilkunde, ' May 1846, s. 277. [841] Mr. Mogford, in the 'Veterinarian, ' quoted in 'The Field, ' Jan. 22, 1861, p. 545. [842] 'Edinburgh Veterinary Journal, ' Oct. 1860, p. 347. [843] 'Hist. Des Anomalies, ' 1832, tom. I. Pp. 22, 537-556; tom. Iii. P. 462. [844] 'Comptes Rendus, ' 1855, pp. 855, 1029. [845] Carpenter's 'Comp. Phys. , ' 1854, p. 480; _see_ also Camille Dareste, 'Comptes Rendus, ' March 20th, 1865, p. 562. [846] 'Elements of Physiology, ' Eng. Translat, vol. I. , 1838, p. 412. Withrespect to Vrolik, _see_ Todd's 'Cyclop. Of Anat. And Phys. , ' vol. Iv. , 1849-52, p. 973. [847] 'Tératologie Vég. , ' 1841, livre iii. [848] 'Hist. Des Anomalies, ' tom. Iii. Pp. 4, 5, 6. [849] 'Tératologie Vég. , ' p. 156. _See_ also my paper on climbing plants in'Journal of Linn. Soc. Bot. , ' vol. Ix. , 1865, p. 114. [850] 'Mémoires du Muséum, ' &c. , tom. Viii. P. 178. [851] Loudon's 'Encyclop. Of Gardening, ' p. 829. [852] Prichard, 'Phys. Hist. Of Mankind, ' 1851, vol. I. P. 324. [853] 'Annales des Sc. Nat. , ' 1st series, tom. Xix. P. 327. [854] 'Comptes Rendus, ' Dec. 1864, p. 1039. [855] Ueber Fötale Rachites, 'Würzburger Medicin. Zeitschrift, ' 1860, B. I. S. 265. [856] 'Tératologie Vég. , ' p. 192. Dr. M. Masters informs me that he doubtsthe truth of this conclusion; but the facts to be given seem to besufficient to establish it. [857] 'Journal of Horticulture, ' July 2nd, 1861, p. 253. [858] It would be worth trial to fertilise with the same pollen the centraland lateral flowers of the pelargonium, and of some other highly cultivatedplants, protecting them of course from insects: then to sow the seedseparately, and observe whether the one or the other lot of seedlingsvaried the most. [859] Quoted in 'Journal of Horticulture, ' Feb. 24, 1863, p. 152. [860] 'Gardener's Chronicle, ' 1866, p. 612. For the Phalænopsis, _see_idem, 1867, p. 211. [861] Mémoires ... Des Végétaux, ' 1837, tom. Ii. P. 170. [862] 'Journal of Horticulture, ' July 23, 1861, p. 311. [863] 'Nouvelles Archives du Muséum, ' tom. I. P. 137. [864] Hugo von Mohl, 'The Vegetable Cell, ' Eng. Tr. , 1852, p. 76. [865] The Rev. H. H. Dombrain, in 'Journal of Horticulture, ' 1861, June4th, p. 174; and June 25th, p. 234; 1862, April 29th, p. 83. [866] 'Transact. Linn. Soc. , ' vol. Xxiii. , 1861, p. 360. [867] 'Die Getreidearten, ' 1843, s. 208, 209. [868] 'Gardener's Chronicle, ' 1850, p. 198. [869] Quoted in 'Gardener's Chron. , ' 1866, p. 74. [870] 'Ueber den Begriff der Pflanzenart, ' 1834, s. 14. [871] 'Domesticated Animals, ' 1845, p. 351. [872] Bechstein, 'Naturgeschichte Deutschlands, ' Band iv. , 1795, s. 31. [873] 'Proc. Entomolog. Soc. Of Philadelphia, ' Oct. 1863, p. 213. [874] Quoted by Paget, 'Lectures on Pathology, ' 1853, p. 159. [875] Dr. Lachmann, also, observes ('Annals and Mag. Of Nat. History, ' 2ndseries, vol. Xix. , 1857, p. 231) with respect to infusoria, that "fissationand gemmation pass into each other almost imperceptibly. " Again, Mr. W. C. Minor ('Annals and Mag. Of Nat. Hist. , ' 3rd series, vol. Xi. P. 328) showsthat with Annelids the distinction that has been made between fission andbudding is not a fundamental one. _See_ Bonnet, 'Oeuvres d'Hist. Nat. , 'tom. V. , 1781, p. 339, for remarks on the budding-out of the amputatedlimbs of Salamanders. _See_, also, Professor Clark's work 'Mind in Nature, 'New York, 1865, pp. 62, 94. [876] Paget, 'Lectures on Pathology, ' 1853, p. 158. [877] Idem, pp. 152, 164. [878] On the Asexual Reproduction of Cecydomyide Larvæ, translated in'Annals and Mag. Of Nat. Hist. , ' March 1866, pp. 167, 171. [879] _See_ some excellent remarks on this head by Quatrefages, in 'Annalesdes Sc. Nat. , ' Zoolog. , 3rd series, 1850, p. 138. [880] 'Annals and Mag. Of Nat. Hist. , ' 2nd series, vol. Xx. , 1857, pp. 153-455. [881] 'Annales des Sc. Nat. , ' 3rd series, 1850, tom. Xiii. [882] 'Transact. Phil. Soc. , ' 1851, pp. 196, 208, 210; 1853, p. 245, 247. [883] 'Beitrage zur Kenntniss, ' &c. , 1844, s. 345. [884] 'Nouvelles Archives du Muséum, ' tom. I. P. 27. [885] As quoted by Sir J. Lubbock in 'Nat. Hist. Review, ' 1862, p. 345. [886] 'Transact. Linn. Soc. , ' vol. Xxiv. , 1863, p. 62. [887] 'Parthenogenesis, ' 1849, pp. 25-26. Prof. Huxley has some excellentremarks ('Medical Times, ' 1856, p. 637) on this subject, in reference tothe development of star-fishes, and shows how curiously metamorphosisgraduates into gemmation or zoid-formation, which is in fact the same asmetagenesis. [888] Prof. J. Reay Greene, in Günther's 'Record of Zoolog. Lit. , ' 1865, p. 625. [889] Fritz Müller's 'Für Darwin, ' 1864, s. 65, 71. The highest authorityon crustaceans, Prof. Milne Edwards, insists ('Annal. Des Sci. Nat. , ' 2ndseries, Zoolog. , tom. Iii. P. 322) on their metamorphoses differing even inclosely allied genera. [890] Prof. Allman, in 'Annals and Mag. Of Nat. Hist. , ' 3rd series, vol. Xiii. , 1864, p. 348; Dr. S. Wright, idem, vol. Viii. , 1861, p. 127. _See_also p. 358 for analogous statements by Sars. [891] 'Tissus Vivants, ' 1866, p. 22. [892] 'Cellular Pathology, ' translat. By Dr. Chance, 1860, pp. 14, 18, 83, 460. [893] Paget, 'Surgical Pathology, ' vol. I. , 1853, pp. 12-14. [894] Idem, p. 19. [895] Mantegazza, quoted in 'Popular Science Review, ' July 1865, p. 522. [896] 'De la Production Artificielle des Os, ' p. 8. [897] Isidore Geoffroy St. Hilaire, 'Hist. Des Anomalies, ' tom. Ii. Pp. 549, 560, 562; Virchow, idem, p. 484. [898] For the most recent classification of cells, _see_ Ernst Häckel's'Generelle Morpholog. , ' Band ii. , 1866, s. 275. [899] 'The Structure and Growth of Tissues, ' 1865, p. 21, &c. [900] Dr. W. Turner, 'The present Aspect of Cellular Pathology, ' 'EdinburghMedical Journal, ' April, 1863. [901] This term is used by Dr. E. Montgomery ('On the Formation ofso-called Cells in Animal Bodies, ' 1867, p. 42), who denies that cells arederived from other cells by a process of growth, but believes that theyoriginate through certain chemical changes. [902] Prof. Huxley has called my attention to the views of Buffon andBonnet. The former ('Hist. Nat. Gén. , ' edit. Of 1749, tom. Ii. Pp. 54, 62, 329, 333, 420, 425) supposes that organic molecules exist in the foodconsumed by every living creature; and that these molecules are analogousin nature with the various organs by which they are absorbed. When theorgans thus become fully developed, the molecules being no longer requiredcollect and form buds or the sexual elements. If Buffon had assumed thathis organic molecules had been formed by each separate unit throughout thebody, his view and mine would have been closely similar. Bonnet ('Oeuvres d'Hist. Nat. , ' tom. V. , part i. , 1781, 4to edit. , p. 334)speaks of the limbs having germs adapted for the reparation of all possiblelosses; but whether these germs are supposed to be the same with thosewithin the buds and sexual organs is not clear. His famous but now explodedtheory of _emboîtement_ implies that perfect germs are included withingerms in endless succession, pre-formed and ready for all succeedinggenerations. According to my view, the germs or gemmules of each separatepart were not originally pre-formed, but are continually produced at allages during each generation, with some handed down from precedinggenerations. Prof. Owen remarks ('Parthenogenesis, ' 1849, pp. 5-8), "Not all the progenyof the primary impregnated germ-cell are required for the formation of thebody in all animals: certain of the derivative germ-cells may remainunchanged and become included in that body which has been composed of theirmetamorphosed and diversely combined or confluent brethren: so included, any derivative germ-cell, or the nucleus of such, may commence and repeatthe same processes of growth by imbibition, and of propagation byspontaneous fission, as those to which itself owed its origin;" &c. By theagency of these germ-cells Prof. Owen accounts for parthenogenesis, forpropagation by self-division during successive generations, and for therepairs of injuries. His view agrees with mine in the assumed transmissionand multiplication of his germ-cells, but differs fundamentally from minein the belief that the primary germ-cell was formed within the ovarium ofthe female and was fertilised by the male. My gemmules are supposed to beformed, quite independently of sexual concourse, by each separate cell orunit throughout the body, and to be merely aggregated within thereproductive organs. Lastly, Mr. Herbert Spencer ('Principles of Biology, ' vol. I. , 1863-4, chaps. Iv. And viii. ) has discussed at considerable length what hedesignates as physiological units. These agree with my gemmules in beingsupposed to multiply and to be transmitted from parent to child; the sexualelements are supposed to serve merely as their vehicles; they are theefficient agents in all the forms of reproduction and in the repairs ofinjuries; they account for inheritance, but they are not brought to bear onreversion or atavism, and this is unintelligible to me; they are supposedto possess polarity, or, as I call it, affinity; and apparently they arebelieved to be derived from each separate part of the whole body. Butgemmules differ from Mr. Spencer's physiological units, inasmuch as acertain number, or mass of them, are, as we shall see, requisite for thedevelopment of each cell or part. Nevertheless I should have concluded thatMr. Spencer's views were fundamentally the same with mine, had it not beenfor several passages which, as far as I understand them, indicate somethingquite different. I will quote some of these passages from pp. 254-256. "Inthe fertilised germ we have two groups of physiological units, slightlydifferent in their structures. "... "It is not obvious that change in theform of the part, caused by changed action, involves such change in thephysiological units throughout the organism, that these, when groups ofthem are thrown off in the shape of reproductive centres, will unfold intoorganisms that have this part similarly changed in form. Indeed, whentreating of Adaptation, we saw that an organ modified by increase ordecrease of function can but slowly so react on the system at large as tobring about those correlative changes required to produce a newequilibrium; and yet only when such new equilibrium has been established, can we expect it to be _fully_ expressed in the modified physiologicalunits of which the organism is built--only then can we count on a completetransfer of the modification to descendants. "... "That the change in theoffspring must, other things equal, be in the same direction as the changein the parent, we may dimly see is implied by the fact, that the changepropagated throughout the parental system is a change towards a new stateof equilibrium--a change tending to bring the actions of all organs, reproductive included, into harmony with these new actions. " [903] M. Philipeaux ('Comptes Rendus, ' Oct. 1, 1866, p. 576, and June, 1867) has lately shown that when the entire fore-limb, including thescapula, is extirpated, the power of regrowth is lost. From this heconcludes that it is necessary for regrowth that a small portion of thelimb should be left. But as in the lower animals the whole body may bebisected and both halves be reproduced, this belief does not seem probable. May not the early closing of a deep wound, as in the case of theextirpation of the scapula, prevent the formation or protrusion of thenascent limb? [904] 'Annal. Des Sc. Nat. , ' 3rd series, Bot. , tom. Xiv. , 1850, p. 244. [905] _See_ some very interesting papers on this subject by Prof. LionelBeale, in 'Medical Times and Gazette, ' Sept. 9th, 1865, pp. 273, 330. [906] Third Report of the R. Comm. On the Cattle Plague, as quoted in'Gard. Chronicle, ' 1866, p. 446. [907] In a cod-fish, weighing 20 lb. , Mr. F. Buckland ('Land and Water, '1867, p. 57) calculated the above number of eggs. In another instance, Harmer ('Phil. Transact. , ' 1767, p. 280) found 3, 681, 760 eggs. For theAscaris, _see_ Carpenter's 'Comp. Phys. , ' 1854, p. 590. Mr. J. Scott, ofthe Royal Botanic Garden of Edinburgh, calculated, in the same manner as Ihave done for some British orchids ('Fertilisation of Orchids, ' p. 344), the number of seeds in a capsule of an Acropera, and found the number to be371, 250. Now this plant produces several flowers on a raceme and manyracemes during a season. In an allied genus, Gongora, Mr. Scott has seentwenty capsules produced on a single raceme: ten such racemes on theAcropera would yield above seventy-four millions of seed. I may add thatFritz Müller informs me that he found in a capsule of a Maxillaria, inSouth Brazil, that the seed weighed 42½ grains: he then arranged half agrain of seed in a narrow line, and by counting a measured length found thenumber in the half-grain to be 20, 667, so that in the capsule there musthave been 1, 756, 440 seeds! The same plant sometimes produces half-a-dozencapsules. [908] 'Annals and Mag. Of Nat. Hist. , ' 3rd series, vol. Viii. , 1861, p. 490. [909] Paget, 'Lectures on Pathology, ' p. 27; Virchow, 'Cellular Pathology, 'translat. By Dr. Chance, pp. 123, 126, 294; Claude Bernard, 'Des TissusVivants, ' pp. 177, 210, 337; Müller's 'Physiology, ' Eng. Translat. , p. 290. [910] Virchow, 'Cellular Pathology, ' trans. By Dr. Chance, 1860, pp. 60, 162, 245, 441, 454. [911] Idem, pp. 412-426. [912] _See_ Rev. J. M. Berkeley, in 'Gard. Chron. , ' April 28th, 1866, on abud developed on the petal of the Clarkia. _See_ also H. Schacht, 'Lehrbuchder Anat. , ' &c. , 1859, Theile ii. S. 12, on adventitious buds. [913] Mr. Herbert Spencer ('Principles of Biology, ' vol. Ii. P. 430) hasfully discussed the antagonism between growth and reproduction. [914] The male salmon is known to breed at a very early age. The Triton andSiredon, whilst retaining their larval branchiæ, according to Filippi andDuméril ('Annals and Mag. Of Nat. Hist. , ' 3rd series, 1866, p. 157), arecapable of reproduction. Ernst Häckel has recently ('Monatsbericht Akad. Wiss. Berlin, ' Feb. 2nd, 1865) observed the surprising case of a medusa, with its reproductive organs active, which produces by budding a widelydifferent form of medusa; and this latter also has the power of sexualreproduction. Krohn has shown ('Annals and Mag. Of Nat. Hist. , ' 3rd series, vol. Xix. , 1862, p. 6) that certain other medusæ, whilst sexually mature, propagate by gemmæ. [915] _See_ his excellent discussion on this subject in 'Nouvelles Archivesdu Muséum, ' tom. I. P. 151. [916] Various physiologists have insisted on this distinction betweengrowth and development. Prof. Marshall ('Phil. Transact. , ' 1864, p. 544)gives a good instance in microcephalous idiots, in which the braincontinues to grow after having been arrested in its development. [917] 'Compte Rendu, ' Nov. 14, 1864, p. 800. [918] As previously remarked by Quatrefages, in his 'Metamorphoses del'Homme, ' &c. , 1862, p. 129. [919] Günther's 'Zoological Record, ' 1864, p. 279. [920] Sedgwick, in 'Medico-Chirurg. Review, ' April 1863, p. 454. [921] Isid. Geoffroy St. Hilaire, 'Hist. Des Anomalies, ' tom. I. , 1832, pp. 435, 657; and tom. Ii. P. 560. [922] Virchow, 'Cellular Pathology, ' 1860, p. 66. [923] Moquin-Tandon, 'Tératologie Veg. , ' 1841, pp. 218, 220, 353. For thecase of the pea, _see_ 'Gardener's Chron. , ' 1866, p. 897. [924] Müller's 'Physiology, ' Eng. Translat. , vol. I. P. 407. [925] _See_ some remarks to this effect by Sir H. Holland in his 'MedicalNotes, ' 1839, p. 32. [926] This is the view taken by Prof. Häckel, in his 'GenerelleMorphologie' (B. Ii. S. 171), who says: "Lediglich die partielle Identitätder specifischconstituirten Materie im elterlichen und im kindlichenOrganismus, die Theilung dieser Materie bei der Fortpflanzung, ist dieUrsache der Erblichkeit. " [927] In these remarks I, in fact, follow Naudin, who speaks of theelements or essences of the two species which are crossed. See hisexcellent memoir in the 'Nouvelles Archives du Muséum, ' tom. I. P. 151. [928] Godron, 'De l'Espèce, ' 1859, tom. Ii. P. 44, &c. [929] Journal Proc. Linn. Soc. , 1858, vol. Iii. P. 60. [930] 'The Quarterly Journal of Science, ' Oct. 1867, p. 486. [931] M. Rufz de Lavison, in 'Bull. Soc. Imp. D'Acclimat. , ' Dec. 1862, p. 1009. [932] 'Races of Man, ' 1850, p. 315. [933] 'Travels in Peru, ' Eng. Translat. , p. 177. [934] Youatt on Cattle, 1834, p 200: on Pigs; _see_ 'Gard. Chronicle, '1854, p. 410. [935] 'Die Pflanzen der Pfahlbauten, ' 1865. [936] Morlot, 'Soc. Vaud. Des Scien. Nat, ' Mars 1860, p. 298. [937] Rütimeyer, 'Die Fauna der Pfahlbauten, ' 1861, s. 30. [938] Godron, 'De l'Espèce, ' tom. I. , 1859, p. 368. [939] 'Géographie Botan. , ' 1855, p. 989. [940] Pickering, 'Races of Man, ' 1850, p. 318. [941] 'Journal of a Horticultural Tour, ' by a Deputation of the CaledonianHist. Soc. , 1823, p. 293. * * * * * Corrections made to printed original. p. Iii. "APPEARANCE WITH ADVANCING AGE": 'ARPEARANCE' in original. p. Vi. "SLIGHT CHANGES SUFFICIENT": 'SUFFICENT' in original. p. 61. "bearing in mind what has been said": 'bearnig' in original. p. 78. "not attached to any particular period": 'particuliar' in original. p. 243. "it permits innumerable individuals to be born": 'permitts' inoriginal. p. 294. "liable to complete absorption": 'absortion' in original. p. 297. "found that when the animal was compelled ... ": 'found than ... ' inoriginal. p. 318. "branches in a rudimentary condition": 'rudimentry' in original. p. 384. "force themselves into a minute orifice": 'into' was printed onnext line in original, after 'must'.