DISCOURSES:

 BIOLOGICAL & GEOLOGICAL

 ESSAYS

 BY

 THOMAS H. HUXLEY

 1894

PREFACE

The contents of the present volume, with three exceptions, are eitherpopular lectures, or addresses delivered to scientific bodies with whichI have been officially connected. I am not sure which gave me the moretrouble. For I have not been one of those fortunate persons who are ableto regard a popular lecture as a mere _hors d'oeuvre_, unworthy of beingranked among the serious efforts of a philosopher; and who keep theirfame as scientific hierophants unsullied by attempts--at least of thesuccessful sort--to be understanded of the people. 

On the contrary, I found that the task of putting the truths learned inthe field, the laboratory and the museum, into language which, withoutbating a jot of scientific accuracy shall be generally intelligible, taxed such scientific and literary faculty as I possessed to theuttermost; indeed my experience has furnished me with no bettercorrective of the tendency to scholastic pedantry which besets all thosewho are absorbed in pursuits remote from the common ways of men, andbecome habituated to think and speak in the technical dialect of theirown little world, as if there were no other. 

If the popular lecture thus, as I believe, finds one moiety of itsjustification in the self-discipline of the lecturer, it surely finds theother half in its effect on the auditory. For though various sadlycomical experiences of the results of my own efforts have led me toentertain a very moderate estimate of the purely intellectual value oflectures; though I venture to doubt if more than one in ten of an averageaudience carries away an accurate notion of what the speaker has beendriving at; yet is that not equally true of the oratory of the hustings, of the House of Commons, and even of the pulpit?

Yet the children of this world are wise in their generation; and both thepolitician and the priest are justified by results. The living voice hasan influence over human action altogether independent of the intellectualworth of that which it utters. Many years ago, I was a guest at a greatCity dinner. A famous orator, endowed with a voice of rare flexibilityand power; a born actor, ranging with ease through every part, fromrefined comedy to tragic unction, was called upon to reply to a toast. The orator was a very busy man, a charming conversationalist and by nomeans despised a good dinner; and, I imagine, rose without having given athought to what he was going to say. The rhythmic roll of sound wasadmirable, the gestures perfect, the earnestness impressive; nothing waslacking save sense and, occasionally, grammar. When the speaker sat downthe applause was terrific and one of my neighbours was especiallyenthusiastic. So when he had quieted down, I asked him what the oratorhad said. And he could not tell me. 

That sagacious person John Wesley, is reported to have replied to someone who questioned the propriety of his adaptation of sacred words toextremely secular airs, that he did not see why the Devil should be leftin possession of all the best tunes. And I do not see why science shouldnot turn to account the peculiarities of human nature thus exploited byother agencies: all the more because science, by the nature of its being, cannot desire to stir the passions, or profit by the weaknesses, of humannature. The most zealous of popular lecturers can aim at nothing morethan the awakening of a sympathy for abstract truth, in those who do notreally follow his arguments; and of a desire to know more and better inthe few who do. 

At the same time it must be admitted that the popularization of science, whether by lecture or essay, has its drawbacks. Success in thisdepartment has its perils for those who succeed. The "people who fail"take their revenge, as we have recently had occasion to observe, byignoring all the rest of a man's work and glibly labelling him a morepopularizer. If the falsehood were not too glaring, they would say thesame of Faraday and Helmholtz and Kelvin. 

On the other hand, of the affliction caused by persons who think thatwhat they have picked up from popular exposition qualifies them fordiscussing the great problems of science, it may be said, as the Radicaltoast said of the power of the Crown in bygone days, that it "hasincreased, is increasing, and ought to be diminished. " The oddities of"English as she is spoke" might be abundantly paralleled by those of"Science as she is misunderstood" in the sermon, the novel, and theleading article; and a collection of the grotesque travesties ofscientific conceptions, in the shape of essays on such trifles as "theNature of Life" and the "Origin of All Things, " which reach me, from timeto time, might well be bound up with them. 

The tenth essay in this volume unfortunately brought me, I will not sayinto collision, but into a position of critical remonstrance with regardto some charges of physical heterodoxy, brought by my distinguishedfriend Lord Kelvin, against British Geology. As President of theGeological Society of London at that time (1869), I thought I mightventure to plead that we were not such heretics as we seemed to be; andthat, even if we were, recantation would not affect the question ofevolution. 

I am glad to see that Lord Kelvin has just reprinted his reply to myplea, [1] and I refer the reader to it. I shall not presume to questionanything, that on such ripe consideration, Lord Kelvin has to say uponthe physical problems involved. But I may remark that no one can haveasserted more strongly than I have done, the necessity of looking tophysics and mathematics, for help in regard to the earliest history ofthe globe. (See pp. 108 and 109 of this volume. )

[Footnote 1: _Popular Lectures and Addresses. _ II. Macmillan and Co. 1894. ]

And I take the opportunity of repeating the opinion, that, whether whatwe call geological time has the lower limit assigned to it by LordKelvin, or the higher assumed by other philosophers; whether the germs ofall living things have originated in the globe itself, or whether theyhave been imported on, or in, meteorites from without, the problem of theorigin of those successive Faunae and Florae of the earth, the existence ofwhich is fully demonstrated by paleontology remains exactly where it was. 

For I think it will be admitted, that the germs brought to us bymeteorites, if any, were not ova of elephants, nor of crocodiles; notcocoa-nuts nor acorns; not even eggs of shell-fish and corals; but onlythose of the lowest forms of animal and vegetable life. Therefore, sinceit is proved that, from a very remote epoch of geological time, the earthhas been peopled by a continual succession of the higher forms of animalsand plants, these either must have been created, or they have arisen byevolution. And in respect of certain groups of animals, the well-established facts of paleontology leave no rational doubt that they aroseby the latter method. 

In the second place, there are no data whatever, which justify thebiologist in assigning any, even approximately definite, period of time, either long or short, to the evolution of one species from another by theprocess of variation and selection. In the ninth of the following essays, I have taken pains to prove that the change of animals has gone on atvery different rates in different groups of living beings; that sometypes have persisted with little change from the paleozoic epoch tillnow, while others have changed rapidly within the limits of an epoch. In1862 (see below p. 303, 304) in 1863 (vol. II. , p. 461) and again in 1864(ibid. , p. 89-91) I argued, not as a matter of speculation, but, frompaleontological facts, the bearing of which I believe, up to that time, had not been shown, that any adequate hypothesis of the causes ofevolution must be consistent with progression, stationariness andretrogression, of the same type at different epochs; of different typesin the same epoch; and that Darwin's hypothesis fulfilled theseconditions. 

According to that hypothesis, two factors are at work, variation andselection. Next to nothing is known of the causes of the former process;nothing whatever of the time required for the production of a certainamount of deviation from the existing type. And, as respects selection, which operates by extinguishing all but a small minority of variations, we have not the slightest means of estimating the rapidity with which itdoes its work. All that we are justified in saying is that the rate atwhich it takes place may vary almost indefinitely. If the famous paint-root of Florida, which kills white pigs but not black ones, were abundantand certain in its action, black pigs might be substituted for white inthe course of two or three years. If, on the other hand, it was rare anduncertain in action, the white pigs might linger on for centuries. 

T. H. HUXLEY. 

HODESLEA, EASTBOURNE, _April, 1894. _

CONTENTS

I

ON A PIECE OF CHALK [1868](A Lecture delivered to the working men of Norwich during the meeting ofthe British Association. )

II

THE PROBLEMS OF THE DEEP SEA [1878]

III

ON SOME OF THE RESULTS OF THE EXPEDITION OF H. M. S. "CHALLENGER" [1875]

IV

YEAST [1871]

V

ON THE FORMATION OF COAL [1870](A Lecture delivered at the Philosophical Institute, Bradford. )

VI

ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS[1876](A Friday evening Lecture delivered at the Royal Institution. )

VII

A LOBSTER; OR, THE STUDY OF ZOOLOGY [1861](A Lecture delivered at the South Kensington Museum. )

VIII

BIOGENESIS AND ABIOGENESIS [1870](The Presidential Address to the Meeting of the British Association forthe Advancement of Science at Liverpool. )

IX

GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE [1862](Address to the Geological Society on behalf of the President by one ofthe Secretaries. )

X

GEOLOGICAL REFORM [1869](Presidential Address to the Geological Society. )

XI

PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION [1870](Presidential Address to the Geological Society. )

I

ON A PIECE OF CHALK

[1868]

If a well were sunk at our feet in the midst of the city of Norwich, thediggers would very soon find themselves at work in that white substancealmost too soft to be called rock, with which we are all familiar as"chalk. "

Not only here, but over the whole county of Norfolk, the well-sinkermight carry his shaft down many hundred feet without coming to the end ofthe chalk; and, on the sea-coast, where the waves have pared away theface of the land which breasts them, the scarped faces of the high cliffsare often wholly formed of the same material. Northward, the chalk may befollowed as far as Yorkshire; on the south coast it appears abruptly inthe picturesque western bays of Dorset, and breaks into the Needles ofthe Isle of Wight; while on the shores of Kent it supplies that long lineof white cliffs to which England owes her name of Albion. 

Were the thin soil which covers it all washed away, a curved band ofwhite chalk, here broader, and there narrower, might be followeddiagonally across England from Lulworth in Dorset, to Flamborough Head inYorkshire--a distance of over 280 miles as the crow flies. From this bandto the North Sea, on the east, and the Channel, on the south, the chalkis largely hidden by other deposits; but, except in the Weald of Kent andSussex, it enters into the very foundation of all the south-easterncounties. 

Attaining, as it does in some places, a thickness of more than a thousandfeet, the English chalk must be admitted to be a mass of considerablemagnitude. Nevertheless, it covers but an insignificant portion of thewhole area occupied by the chalk formation of the globe, much of whichhas the same general characters as ours, and is found in detachedpatches, some less, and others more extensive, than the English. Chalkoccurs in north-west Ireland; it stretches over a large part of France, --the chalk which underlies Paris being, in fact, a continuation of that ofthe London basin; it runs through Denmark and Central Europe, and extendssouthward to North Africa; while eastward, it appears in the Crimea andin Syria, and may be traced as far as the shores of the Sea of Aral, inCentral Asia. If all the points at which true chalk occurs werecircumscribed, they would lie within an irregular oval about 3, 000 milesin long diameter--the area of which would be as great as that of Europe, and would many times exceed that of the largest existing inland sea--theMediterranean. 

Thus the chalk is no unimportant element in the masonry of the earth'scrust, and it impresses a peculiar stamp, varying with the conditions towhich it is exposed, on the scenery of the districts in which it occurs. The undulating downs and rounded coombs, covered with sweet-grassed turf, of our inland chalk country, have a peacefully domestic and mutton-suggesting prettiness, but can hardly be called either grand orbeautiful. But on our southern coasts, the wall-sided cliffs, manyhundred feet high, with vast needles and pinnacles standing out in thesea, sharp and solitary enough to serve as perches for the warycormorant, confer a wonderful beauty and grandeur upon the chalkheadlands. And, in the East, chalk has its share in the formation of someof the most venerable of mountain ranges, such as the Lebanon. 

What is this wide-spread component of the surface of the earth? andwhence did it come?

You may think this no very hopeful inquiry. You may not unnaturallysuppose that the attempt to solve such problems as these can lead to noresult, save that of entangling the inquirer in vague speculations, incapable of refutation and of verification. If such were really thecase, I should have selected some other subject than a "piece of chalk"for my discourse. But, in truth, after much deliberation, I have beenunable to think of any topic which would so well enable me to lead you tosee how solid is the foundation upon which some of the most startlingconclusions of physical science rest. 

A great chapter of the history of the world is written in the chalk. Fewpassages in the history of man can be supported by such an overwhelmingmass of direct and indirect evidence as that which testifies to the truthof the fragment of the history of the globe, which I hope to enable youto read, with your own eyes, to-night. Let me add, that few chapters ofhuman history have a more profound significance for ourselves. I weigh mywords well when I assert, that the man who should know the true historyof the bit of chalk which every carpenter carries about in his breeches-pocket, though ignorant of all other history, is likely, if he will thinkhis knowledge out to its ultimate results, to have a truer, and thereforea better, conception of this wonderful universe, and of man's relation toit, than the most learned student who is deep-read in the records ofhumanity and ignorant of those of Nature. 

The language of the chalk is not hard to learn, not nearly so hard asLatin, if you only want to get at the broad features of the story it hasto tell; and I propose that we now set to work to spell that story outtogether. 

We all know that if we "burn" chalk the result is quicklime. Chalk, infact, is a compound of carbonic acid gas, and lime, and when you make itvery hot the carbonic acid flies away and the lime is left. By thismethod of procedure we see the lime, but we do not see the carbonic acid. If, on the other hand, you were to powder a little chalk and drop it intoa good deal of strong vinegar, there would be a great bubbling andfizzing, and, finally, a clear liquid, in which no sign of chalk wouldappear. Here you see the carbonic acid in the bubbles; the lime, dissolved in the vinegar, vanishes from sight. There are a great manyother ways of showing that chalk is essentially nothing but carbonic acidand quicklime. Chemists enunciate the result of all the experiments whichprove this, by stating that chalk is almost wholly composed of "carbonateof lime. "

It is desirable for us to start from the knowledge of this fact, thoughit may not seem to help us very far towards what we seek. For carbonateof lime is a widely-spread substance, and is met with under very variousconditions. All sorts of limestones are composed of more or less purecarbonate of lime. The crust which is often deposited by waters whichhave drained through limestone rocks, in the form of what are calledstalagmites and stalactites, is carbonate of lime. Or, to take a morefamiliar example, the fur on the inside of a tea-kettle is carbonate oflime; and, for anything chemistry tells us to the contrary, the chalkmight be a kind of gigantic fur upon the bottom of the earth-kettle, which is kept pretty hot below. 

Let us try another method of making the chalk tell us its own history. Tothe unassisted eye chalk looks simply like a very loose and open kind ofstone. But it is possible to grind a slice of chalk down so thin that youcan see through it--until it is thin enough, in fact, to be examined withany magnifying power that may be thought desirable. A thin slice of thefur of a kettle might be made in the same way. If it were examinedmicroscopically, it would show itself to be a more or less distinctlylaminated mineral substance, and nothing more. 

But the slice of chalk presents a totally different appearance whenplaced under the microscope. The general mass of it is made up of veryminute granules; but, imbedded in this matrix, are innumerable bodies, some smaller and some larger, but, on a rough average, not more than ahundredth of an inch in diameter, having a well-defined shape andstructure. A cubic inch of some specimens of chalk may contain hundredsof thousands of these bodies, compacted together with incalculablemillions of the granules. 

The examination of a transparent slice gives a good notion of the mannerin which the components of the chalk are arranged, and of their relativeproportions. But, by rubbing up some chalk with a brush in water and thenpouring off the milky fluid, so as to obtain sediments of differentdegrees of fineness, the granules and the minute rounded bodies may bepretty well separated from one another, and submitted to microscopicexamination, either as opaque or as transparent objects. By combining theviews obtained in these various methods, each of the rounded bodies maybe proved to be a beautifully-constructed calcareous fabric, made up of anumber of chambers, communicating freely with one another. The chamberedbodies are of various forms. One of the commonest is something like abadly-grown raspberry, being formed of a number of nearly globularchambers of different sizes congregated together. It is called_Globigerina_, and some specimens of chalk consist of little else than_Globigerinoe_ and granules. Let us fix our attention upon the_Globigerina_. It is the spoor of the game we are tracking. If we canlearn what it is and what are the conditions of its existence, we shallsee our way to the origin and past history of the chalk. 

A suggestion which may naturally enough present itself is, that thesecurious bodies are the result of some process of aggregation which hastaken place in the carbonate of lime; that, just as in winter, the rimeon our windows simulates the most delicate and elegantly arborescentfoliage--proving that the mere mineral water may, under certainconditions, assume the outward form of organic bodies--so this mineralsubstance, carbonate of lime, hidden away in the bowels of the earth, hastaken the shape of these chambered bodies. I am not raising a merelyfanciful and unreal objection. Very learned men, in former days, haveeven entertained the notion that all the formed things found in rocks areof this nature; and if no such conception is at present held to beadmissible, it is because long and varied experience has now shown thatmineral matter never does assume the form and structure we find infossils. If any one were to try to persuade you that an oyster-shell(which is also chiefly composed of carbonate of lime) had crystallizedout of sea-water, I suppose you would laugh at the absurdity. Yourlaughter would be justified by the fact that all experience tends to showthat oyster-shells are formed by the agency of oysters, and in no otherway. And if there were no better reasons, we should be justified, on likegrounds, in believing that _Globigerina_ is not the product of anythingbut vital activity. 

Happily, however, better evidence in proof of the organic nature of the_Globigerinoe_ than that of analogy is forthcoming. It so happens thatcalcareous skeletons, exactly similar to the _Globigerinoe_ of the chalk, are being formed, at the present moment, by minute living creatures, which flourish in multitudes, literally more numerous than the sands ofthe sea-shore, over a large extent of that part of the earth's surfacewhich is covered by the ocean. 

The history of the discovery of these living _Globigerinoe_, and of thepart which they play in rock building, is singular enough. It is adiscovery which, like others of no less scientific importance, hasarisen, incidentally, out of work devoted to very different andexceedingly practical interests. When men first took to the sea, theyspeedily learned to look out for shoals and rocks; and the more theburthen of their ships increased, the more imperatively necessary itbecame for sailors to ascertain with precision the depth of the watersthey traversed. Out of this necessity grew the use of the lead andsounding line; and, ultimately, marine-surveying, which is the recordingof the form of coasts and of the depth of the sea, as ascertained by thesounding-lead, upon charts. 

At the same time, it became desirable to ascertain and to indicate thenature of the sea-bottom, since this circumstance greatly affects itsgoodness as holding ground for anchors. Some ingenious tar, whose namedeserves a better fate than the oblivion into which it has fallen, attained this object by "arming" the bottom of the lead with a lump ofgrease, to which more or less of the sand or mud, or broken shells, asthe case might be, adhered, and was brought to the surface. But, howeverwell adapted such an apparatus might be for rough nautical purposes, scientific accuracy could not be expected from the armed lead, and toremedy its defects (especially when applied to sounding in great depths)Lieut. Brooke, of the American Navy, some years ago invented a mostingenious machine, by which a considerable portion of the superficiallayer of the sea-bottom can be scooped out and brought up from any depthto which the lead descends. In 1853, Lieut. Brooke obtained mud from thebottom of the North Atlantic, between Newfoundland and the Azores, at adepth of more than 10, 000 feet, or two miles, by the help of thissounding apparatus. The specimens were sent for examination to Ehrenbergof Berlin, and to Bailey of West Point, and those able microscopistsfound that this deep-sea mud was almost entirely composed of theskeletons of living organisms--the greater proportion of these being justlike the _Globigerinoe_ already known to occur in the chalk. 

Thus far, the work had been carried on simply in the interests ofscience, but Lieut. Brooke's method of sounding acquired a highcommercial value, when the enterprise of laying down the telegraph-cablebetween this country and the United States was undertaken. For it becamea matter of immense importance to know, not only the depth of the seaover the whole line along which the cable was to be laid, but the exactnature of the bottom, so as to guard against chances of cutting orfraying the strands of that costly rope. The Admiralty consequentlyordered Captain Dayman, an old friend and shipmate of mine, to ascertainthe depth over the whole line of the cable, and to bring back specimensof the bottom. In former days, such a command as this might have soundedvery much like one of the impossible things which the young Prince in theFairy Tales is ordered to do before he can obtain the hand of thePrincess. However, in the months of June and July, 1857, my friendperformed the task assigned to him with great expedition and precision, without, so far as I know, having met with any reward of that kind. Thespecimens or Atlantic mud which he procured were sent to me to beexamined and reported upon. [1]

[Footnote 1: See Appendix to Captain Dayman's _Deep-sea Soundings in theNorth Atlantic Ocean between Ireland and Newfoundland, made in H. M. S. "Cyclops_. " Published by order of the Lords Commissioners of theAdmiralty, 1858. They have since formed the subject of an elaborateMemoir by Messrs. Parker and Jones, published in the _PhilosophicalTransactions_ for 1865. ]

The result of all these operations is, that we know the contours and thenature of the surface-soil covered by the North Atlantic for a distanceof 1, 700 miles from east to west, as well as we know that of any part ofthe dry land. It is a prodigious plain--one of the widest and most evenplains in the world. If the sea were drained off, you might drive awaggon all the way from Valentia, on the west coast of Ireland, toTrinity Bay, in Newfoundland. And, except upon one sharp incline about200 miles from Valentia, I am not quite sure that it would even benecessary to put the skid on, so gentle are the ascents and descents uponthat long route. From Valentia the road would lie down-hill for about 200miles to the point at which the bottom is now covered by 1, 700 fathoms ofsea-water. Then would come the central plain, more than a thousand mileswide, the inequalities of the surface of which would be hardlyperceptible, though the depth of water upon it now varies from 10, 000 to15, 000 feet; and there are places in which Mont Blanc might be sunkwithout showing its peak above water. Beyond this, the ascent on theAmerican side commences, and gradually leads, for about 300 miles, to theNewfoundland shore. 

Almost the whole of the bottom of this central plain (which extends formany hundred miles in a north and south direction) is covered by a finemud, which, when brought to the surface, dries into a greyish whitefriable substance. You can write with this on a blackboard, if you are soinclined; and, to the eye, it is quite like very soft, grayish chalk. Examined chemically, it proves to be composed almost wholly of carbonateof lime; and if you make a section of it, in the same way as that of thepiece of chalk was made, and view it with the microscope, it presentsinnumerable _Globigerinoe_ embedded in a granular matrix. Thus this deep-sea mud is substantially chalk. I say substantially, because there are agood many minor differences; but as these have no bearing on the questionimmediately before us, --which is the nature of the _Globigerinoe_ of thechalk, --it is unnecessary to speak of them. 

_Globigerinoe_ of every size, from the smallest to the largest, areassociated together in the Atlantic mud, and the chambers of many arefilled by a soft animal matter. This soft substance is, in fact, theremains of the creature to which the _Globigerinoe_ shell, or ratherskeleton, owes its existence--and which is an animal of the simplestimaginable description. It is, in fact, a mere particle of living jelly, without defined parts of any kind--without a mouth, nerves, muscles, ordistinct organs, and only manifesting its vitality to ordinaryobservation by thrusting out and retracting from all parts of itssurface, long filamentous processes, which serve for arms and legs. Yetthis amorphous particle, devoid of everything which, in the higheranimals, we call organs, is capable of feeding, growing, and multiplying;of separating from the ocean the small proportion of carbonate of limewhich is dissolved in sea-water; and of building up that substance into askeleton for itself, according to a pattern which can be imitated by noother known agency. 

The notion that animals can live and flourish in the sea, at the vastdepths from which apparently living _Globigerinoe_; have been brought up, does not agree very well with our usual conceptions respecting theconditions of animal life; and it is not so absolutely impossible as itmight at first sight appear to be, that the _Globigcrinoe_ of theAtlantic sea-bottom do not live and die where they are found. 

As I have mentioned, the soundings from the great Atlantic plain arealmost entirely made up of _Globigerinoe_, with the granules which havebeen mentioned, and some few other calcareous shells; but a smallpercentage of the chalky mud--perhaps at most some five per cent. Of it--is of a different nature, and consists of shells and skeletons composedof silex, or pure flint. These silicious bodies belong partly to thelowly vegetable organisms which are called _Diatomaceoe_, and partly tothe minute, and extremely simple, animals, termed _Radiolaria_. It isquite certain that these creatures do not live at the bottom of theocean, but at its surface--where they may be obtained in prodigiousnumbers by the use of a properly constructed net. Hence it follows thatthese silicious organisms, though they are not heavier than the lightestdust, must have fallen, in some cases, through fifteen thousand feet ofwater, before they reached their final resting-place on the ocean floor. And considering how large a surface these bodies expose in proportion totheir weight, it is probable that they occupy a great length of time inmaking their burial journey from the surface of the Atlantic to thebottom. 

But if the _Radiolaria_ and Diatoms are thus rained upon the bottom ofthe sea, from the superficial layer of its waters in which they passtheir lives, it is obviously possible that the _Globigerinoe_ may besimilarly derived; and if they were so, it would be much more easy tounderstand how they obtain their supply of food than it is at present. Nevertheless, the positive and negative evidence all points the otherway. The skeletons of the full-grown, deep-sea _Globigerinoe_ are soremarkably solid and heavy in proportion to their surface as to seemlittle fitted for floating; and, as a matter of fact, they are not to befound along with the Diatoms and _Radiolaria_ in the uppermost stratum ofthe open ocean. It has been observed, again, that the abundance of_Globigerinoe_, in proportion to other organisms, of like kind, increaseswith the depth of the sea; and that deep-water _Globigerinoe_ are largerthan those which live in shallower parts of the sea; and such factsnegative the supposition that these organisms have been swept by currentsfrom the shallows into the deeps of the Atlantic. It therefore seems tobe hardly doubtful that these wonderful creatures live and die at thedepths in which they are found. [2]

[Footnote 2: During the cruise of H. M. S. _Bulldog_, commanded by SirLeopold M'Clintock, in 1860, living star-fish were brought up, clingingto the lowest part of the sounding-line, from a depth of 1, 260 fathoms, midway between Cape Farewell, in Greenland, and the Rockall banks. Dr. Wallich ascertained that the sea-bottom at this point consisted of theordinary _Globigerina_ ooze, and that the stomachs of the star-fisheswere full of _Globigerinoe_. This discovery removes all objections to theexistence of living _Globigerinoe_ at great depths, which are based uponthe supposed difficulty of maintaining animal life under such conditions;and it throws the burden of proof upon those who object to thesupposition that the _Globigerinoe_ live and die where they are found. ]

However, the important points for us are, that the living _Globigerinoe_are exclusively marine animals, the skeletons of which abound at thebottom of deep seas; and that there is not a shadow of reason forbelieving that the habits of the _Globigerinoe_ of the chalk differedfrom those of the existing species. But if this be true, there is noescaping the conclusion that the chalk itself is the dried mud of anancient deep sea. 

In working over the soundings collected by Captain Dayman, I wassurprised to find that many of what I have called the "granules" of thatmud were not, as one might have been tempted to think at first, the morepowder and waste of _Globigerinoe_, but that they had a definite form andsize. I termed these bodies "_coccoliths_, " and doubted their organicnature. Dr. Wallich verified my observation, and added the interestingdiscovery that, not unfrequently, bodies similar to these "coccoliths"were aggregated together into spheroids, which lie termed"_coccospheres_. " So far as we knew, these bodies, the nature of which isextremely puzzling and problematical, were peculiar to the Atlanticsoundings. But, a few years ago, Mr. Sorby, in making a carefulexamination of the chalk by means of thin sections and otherwise, observed, as Ehrenberg had done before him, that much of its granularbasis possesses a definite form. Comparing these formed particles withthose in the Atlantic soundings, he found the two to be identical; andthus proved that the chalk, like the surroundings, contains thesemysterious coccoliths and coccospheres. Here was a further and mostinteresting confirmation, from internal evidence, of the essentialidentity of the chalk with modern deep-sea mud. _Globigerinoe_, coccoliths, and coccospheres are found as the chief constituents of both, and testify to the general similarity of the conditions under which bothhave been formed. [3]

[Footnote 3: I have recently traced out the development of the"coccoliths" from a diameter of 1/7000th of an inch up to their largestsize (which is about 1/1000th), and no longer doubt that they areproduced by independent organisms, which, like the _Globigerinoe_, liveand die at the bottom of the sea. ]

The evidence furnished by the hewing, facing, and superposition of thestones of the Pyramids, that these structures were built by men, has nogreater weight than the evidence that the chalk was built by_Globigerinoe_; and the belief that those ancient pyramid-builders wereterrestrial and air-breathing creatures like ourselves, is not betterbased than the conviction that the chalk-makers lived in the sea. But asour belief in the building of the Pyramids by men is not only grounded onthe internal evidence afforded by these structures, but gathers strengthfrom multitudinous collateral proofs, and is clinched by the totalabsence of any reason for a contrary belief; so the evidence drawn fromthe _Globigerinoe_ that the chalk is an ancient sea-bottom, is fortifiedby innumerable independent lines of evidence; and our belief in the truthof the conclusion to which all positive testimony tends, receives thelike negative justification from the fact that no other hypothesis has ashadow of foundation. 

It may be worth while briefly to consider a few of these collateralproofs that the chalk was deposited at the bottom of the sea. The greatmass of the chalk is composed, as we have seen, of the skeletons of_Globigerinoe_, and other simple organisms, imbedded in granular matter. Here and there, however, this hardened mud of the ancient sea reveals theremains of higher animals which have lived and died, and left their hardparts in the mud, just as the oysters die and leave their shells behindthem, in the mud of the present seas. 

There are, at the present day, certain groups of animals which are neverfound in fresh waters, being unable to live anywhere but in the sea. Suchare the corals; those corallines which are called _Polyzoa_; thosecreatures which fabricate the lamp-shells, and are called _Brachiopoda_;the pearly _Nautilus_, and all animals allied to it; and all the forms ofsea-urchins and star-fishes. Not only are all these creatures confined tosalt water at the present day; but, so far as our records of the past go, the conditions of their existence have been the same: hence, theiroccurrence in any deposit is as strong evidence as can be obtained, thatthat deposit was formed in the sea. Now the remains of animals of all thekinds which have been enumerated, occur in the chalk, in greater or lessabundance; while not one of those forms of shell-fish which arecharacteristic of fresh water has yet been observed in it. 

When we consider that the remains of more than three thousand distinctspecies of aquatic animals have been discovered among the fossils of thechalk, that the great majority of them are of such forms as are now metwith only in the sea, and that there is no reason to believe that any oneof them inhabited fresh water--the collateral evidence that the chalkrepresents an ancient sea-bottom acquires as great force as the proofderived from the nature of the chalk itself. I think you will now allowthat I did not overstate my case when I asserted that we have as stronggrounds for believing that all the vast area of dry land, at presentoccupied by the chalk, was once at the bottom of the sea, as we have forany matter of history whatever; while there is no justification for anyother belief. 

No less certain it is that the time during which the countries we nowcall south-east England, France, Germany, Poland, Russia, Egypt, Arabia, Syria, were more or less completely covered by a deep sea, was ofconsiderable duration. We have already seen that the chalk is, in places, more than a thousand feet thick. I think you will agree with me, that itmust have taken some time for the skeletons of animalcules of a hundredthof an inch in diameter to heap up such a mass as that. I have said thatthroughout the thickness of the chalk the remains of other animals arescattered. These remains are often in the most exquisite state ofpreservation. The valves of the shell-fishes are commonly adherent; thelong spines of some of the sea-urchins, which would be detached by thesmallest jar, often remain in their places. In a word, it is certain thatthese animals have lived and died when the place which they now occupywas the surface of as much of the chalk as had then been deposited; andthat each has been covered up by the layer of _Globigerina_ mud, uponwhich the creatures imbedded a little higher up have, in like manner, lived and died. But some of these remains prove the existence of reptilesof vast size in the chalk sea. These lived their time, and had theirancestors and descendants, which assuredly implies time, reptiles beingof slow growth. 

There is more curious evidence, again, that the process of covering up, or, in other words, the deposit of _Globigerina_ skeletons, did not go onvery fast. It is demonstrable that an animal of the cretaceous sea mightdie, that its skeleton might lie uncovered upon the sea-bottom longenough to lose all its outward coverings and appendages by putrefaction;and that, after this had happened, another animal might attach itself tothe dead and naked skeleton, might grow to maturity, and might itself diebefore the calcareous mud had buried the whole. 

Cases of this kind are admirably described by Sir Charles Lyell. Hespeaks of the frequency with which geologists find in the chalk afossilized sea-urchin, to which is attached the lower valve of a_Crania_. This is a kind of shell-fish, with a shell composed of twopieces, of which, as in the oyster, one is fixed and the other free. 

"The upper valve is almost invariably wanting, though occasionally foundin a perfect state of preservation in the white chalk at some distance. In this case, we see clearly that the sea-urchin first lived from youthto age, then died and lost its spines, which were carried away. Then theyoung _Crania_ adhered to the bared shell, grew and perished in its turn;after which, the upper valve was separated from the lower, before theEchinus became enveloped in chalky mud. "[4]

A specimen in the Museum of Practical Geology, in London, still furtherprolongs the period which must have elapsed between the death of the sea-urchin, and its burial by the _Globigerinoe_. For the outward face of thevalve of a _Crania_, which is attached to a sea-urchin, (_Micraster_), isitself overrun by an incrusting coralline, which spreads thence over moreor less of the surface of the sea-urchin. It follows that, after theupper valve of the _Crania_ fell off, the surface of the attached valvemust have remained exposed long enough to allow of the growth of thewhole coralline, since corallines do not live embedded in mud. [4]

[Footnote 4: _Elements of Geology_, by Sir Charles Lyell, Bart. F. B. S. , p. 23. ]

The progress of knowledge may, one day, enable us to deduce from suchfacts as these the maximum rate at which the chalk can have accumulated, and thus to arrive at the minimum duration of the chalk period. Supposethat the valve of the _Cronia_ upon which a coralline has fixed itself inthe way just described, is so attached to the sea-urchin that no part ofit is more than an inch above the face upon which the sea-urchin rests. Then, as the coralline could not have fixed itself, if the _Crania_ hadbeen covered up with chalk mud, and could not have lived had itself beenso covered, it follows, that an inch of chalk mud could not haveaccumulated within the time between the death and decay of the soft partsof the sea-urchin and the growth of the coralline to the full size whichit has attained. If the decay of the soft parts of the sea-urchin; theattachment, growth to maturity, and decay of the _Crania_; and thesubsequent attachment and growth of the coralline, took a year (which isa low estimate enough), the accumulation of the inch of chalk must havetaken more than a year: and the deposit of a thousand feet of chalk must, consequently, have taken more than twelve thousand years. 

The foundation of all this calculation is, of course, a knowledge of thelength of time the _Crania_ and the coralline needed to attain their fullsize; and, on this head, precise knowledge is at present wanting. Butthere are circumstances which tend to show, that nothing like an inch ofchalk has accumulated during the life of a _Crania_; and, on any probableestimate of the length of that life, the chalk period must have had amuch longer duration than that thus roughly assigned to it. 

Thus, not only is it certain that the chalk is the mud of an ancient sea-bottom; but it is no less certain, that the chalk sea existed during anextremely long period, though we may not be prepared to give a preciseestimate of the length of that period in years. The relative duration isclear, though the absolute duration may not be definable. The attempt toaffix any precise date to the period at which the chalk sea began, orended, its existence, is baffled by difficulties of the same kind. Butthe relative age of the cretaceous epoch may be determined with as greatease and certainty as the long duration of that epoch. 

You will have heard of the interesting discoveries recently made, invarious parts of Western Europe, of flint implements, obviously workedinto shape by human hands, under circumstances which show conclusivelythat man is a very ancient denizen of these regions. It has been provedthat the whole populations of Europe, whose existence has been revealedto us in this way, consisted of savages, such as the Esquimaux are now;that, in the country which is now France, they hunted the reindeer, andwere familiar with the ways of the mammoth and the bison. The physicalgeography of France was in those days different from what it is now--theriver Somme, for instance, having cut its bed a hundred feet deeperbetween that time and this; and, it is probable, that the climate wasmore like that of Canada or Siberia, than that of Western Europe. 

The existence of these people is forgotten even in the traditions of theoldest historical nations. The name and fame of them had utterly vanisheduntil a few years back; and the amount of physical change which has beeneffected since their day renders it more than probable that, venerable asare some of the historical nations, the workers of the chipped flints ofHoxne or of Amiens are to them, as they are to us, in point of antiquity. But, if we assign to these hoar relics of long-vanished generations ofmen the greatest age that can possibly be claimed for them, they are notolder than the drift, or boulder clay, which, in comparison with thechalk, is but a very juvenile deposit. You need go no further than yourown sea-board for evidence of this fact. At one of the most charmingspots on the coast of Norfolk, Cromer, you will see the boulder clayforming a vast mass, which lies upon the chalk, and must consequentlyhave come into existence after it. Huge boulders of chalk are, in fact, included in the clay, and have evidently been brought to the positionthey now occupy by the same agency as that which has planted blocks ofsyenite from Norway side by side with them. 

The chalk, then, is certainly older than the boulder clay. If you ask howmuch, I will again take you no further than the same spot upon your owncoasts for evidence. I have spoken of the boulder clay and drift asresting upon the chalk. That is not strictly true. Interposed between thechalk and the drift is a comparatively insignificant layer, containingvegetable matter. But that layer tells a wonderful history. It is full ofstumps of trees standing as they grew. Fir-trees are there with theircones, and hazel-bushes with their nuts; there stand the stools of oakand yew trees, beeches and alders. Hence this stratum is appropriatelycalled the "forest-bed. "

It is obvious that the chalk must have been upheaved and converted intodry land, before the timber trees could grow upon it. As the bolls ofsome of these trees are from two to three feet in diameter, it is no lessclear that the dry land thus formed remained in the same condition forlong ages. And not only do the remains of stately oaks and well-grownfirs testify to the duration of this condition of things, but additionalevidence to the same effect is afforded by the abundant remains ofelephants, rhinoceroses, hippopotamuses, and other great wild beasts, which it has yielded to the zealous search of such men as the Rev. Mr. Gunn. When you look at such a collection as he has formed, and bethinkyou that these elephantine bones did veritably carry their owners about, and these great grinders crunch, in the dark woods of which the forest-bed is now the only trace, it is impossible not to feel that they are asgood evidence of the lapse of time as the annual rings of the treestumps. 

Thus there is a writing upon the wall of cliffs at Cromer, and whoso runsmay read it. It tells us, with an authority which cannot be impeached, that the ancient sea-bed of the chalk sea was raised up, and remained dryland, until it was covered with forest, stocked with the great game thespoils of which have rejoiced your geologists. How long it remained inthat condition cannot be said; but "the whirligig of time brought itsrevenges" in those days as in these. That dry land, with the bones andteeth of generations of long-lived elephants, hidden away among thegnarled roots and dry leaves of its ancient trees, sank gradually to thebottom of the icy sea, which covered it with huge masses of drift andboulder clay. Sea-beasts, such as the walrus, now restricted to theextreme north, paddled about where birds had twittered among the topmosttwigs of the fir-trees. How long this state of things endured we knownot, but at length it came to an end. The upheaved glacial mud hardenedinto the soil of modern Norfolk. Forests grew once more, the wolf and thebeaver replaced the reindeer and the elephant; and at length what we callthe history of England dawned. 

Thus you have, within the limits of your own county, proof that the chalkcan justly claim a very much greater antiquity than even the oldestphysical traces of mankind. But we may go further and demonstrate, byevidence of the same authority as that which testifies to the existenceof the father of men, that the chalk is vastly older than Adam himself. The Book of Genesis informs us that Adam, immediately upon his creation, and before the appearance of Eve, was placed in the Garden of Eden. Theproblem of the geographical position of Eden has greatly vexed thespirits of the learned in such matters, but there is one point respectingwhich, so far as I know, no commentator has ever raised a doubt. This is, that of the four rivers which are said to run out of it, Euphrates andHiddekel are identical with the rivers now known by the names ofEuphrates and Tigris. But the whole country in which these mighty riverstake their origin, and through which they run, is composed of rocks whichare either of the same age as the chalk, or of later date. So that thechalk must not only have been formed, but, after its formation, the timerequired for the deposit of these later rocks, and for their upheavalinto dry land, must have elapsed, before the smallest brook which feedsthe swift stream of "the great river, the river of Babylon, " began toflow. 

Thus, evidence which cannot be rebutted, and which need not bestrengthened, though if time permitted I might indefinitely increase itsquantity, compels you to believe that the earth, from the time of thechalk to the present day, has been the theatre of a series of changes asvast in their amount, as they were slow in their progress. The area onwhich we stand has been first sea and then land, for at least fouralternations; and has remained in each of these conditions for a periodof great length. 

Nor have these wonderful metamorphoses of sea into land, and of land intosea, been confined to one corner of England. During the chalk period, or"cretaceous epoch, " not one of the present great physical features of theglobe was in existence. Our great mountain ranges, Pyrenees, Alps, Himalayas, Andes, have all been upheaved since the chalk was deposited, and the cretaceous sea flowed over the sites of Sinai and Ararat. Allthis is certain, because rocks of cretaceous, or still later, date haveshared in the elevatory movements which gave rise to these mountainchains; and may be found perched up, in some cases, many thousand feethigh upon their flanks. And evidence of equal cogency demonstrates that, though, in Norfolk, the forest-bed rests directly upon the chalk, yet itdoes so, not because the period at which the forest grew immediatelyfollowed that at which the chalk was formed, but because an immense lapseof time, represented elsewhere by thousands of feet of rock, is notindicated at Cromer. 

I must ask you to believe that there is no less conclusive proof that astill more prolonged succession of similar changes occurred, before thechalk was deposited. Nor have we any reason to think that the first termin the series of these changes is known. The oldest sea-beds preserved tous are sands, and mud, and pebbles, the wear and tear of rocks which wereformed in still older oceans. 

But, great as is the magnitude of these physical changes of the world, they have been accompanied by a no less striking series of modificationsin its living inhabitants. All the great classes of animals, beasts ofthe field, fowls of the air, creeping things, and things which dwell inthe waters, flourished upon the globe long ages before the chalk wasdeposited. Very few, however, if any, of these ancient forms of animallife were identical with those which now live. Certainly not one of thehigher animals was of the same species as any of those now in existence. The beasts of the field, in the days before the chalk, were not ourbeasts of the field, nor the fowls of the air such as those which the eyeof men has seen flying, unless his antiquity dates infinitely furtherback than we at present surmise. If we could be carried back into thosetimes, we should be as one suddenly set down in Australia before it wascolonized. We should see mammals, birds, reptiles, fishes, insects, snails, and the like, clearly recognizable as such, and yet not one ofthem would be just the same as those with which we are familiar, and manywould be extremely different. 

From that time to the present, the population of the world has undergoneslow and gradual, but incessant, changes. There has been no grandcatastrophe--no destroyer has swept away the forms of life of one period, and replaced them by a totally new creation: but one species has vanishedand another has taken its place; creatures of one type of structure havediminished, those of another have increased, as time has passed on. Andthus, while the differences between the living creatures of the timebefore the chalk and those of the present day appear startling, if placedside by side, we are led from one to the other by the most gradualprogress, if we follow the course of Nature through the whole series ofthose relics of her operations which she has left behind. It is by thepopulation of the chalk sea that the ancient and the modern inhabitantsof the world are most completely connected. The groups which are dyingout flourish, side by side, with the groups which are now the dominantforms of life. Thus the chalk contains remains of those strange flyingand swimming reptiles, the pterodactyl, the ichthyosaurus, and theplesiosaurus, which are found in no later deposits, but abounded inpreceding ages. The chambered shells called ammonites and belemnites, which are so characteristic of the period preceding the cretaceous, inlike manner die with it. 

But, amongst these fading remainders of a previous state of things, aresome very modern forms of life, looking like Yankee pedlars among a tribeof Red Indians. Crocodiles of modern type appear; bony fishes, many ofthem very similar to existing species, almost supplant the forms of fishwhich predominate in more ancient seas; and many kinds of living shell-fish first become known to us in the chalk. The vegetation acquires amodern aspect. A few living animals are not even distinguishable asspecies, from those which existed at that remote epoch. The _Globigerina_of the present day, for example, is not different specifically from thatof the chalk; and the same maybe said of many other _Foraminifera_. Ithink it probable that critical and unprejudiced examination will showthat more than one species of much higher animals have had a similarlongevity; but the only example which I can at present give confidentlyis the snake's-head lampshell (_Terebratulina caput serpentis_), whichlives in our English seas and abounded (as _Terebratulina striata_ ofauthors) in the chalk. 

The longest line of human ancestry must hide its diminished head beforethe pedigree of this insignificant shell-fish. We Englishmen are proud tohave an ancestor who was present at the Battle of Hastings. The ancestorsof _Terebratulina caput serpentis_ may have been present at a battle of_Ichthyosauria_ in that part of the sea which, when the chalk wasforming, flowed over the site of Hastings. While all around has changed, this _Terebratulina_ has peacefully propagated its species fromgeneration to generation, and stands to this day, as a living testimonyto the continuity of the present with the past history of the globe. 

Up to this moment I have stated, so far as I know, nothing but well-authenticated facts, and the immediate conclusions which they force uponthe mind. But the mind is so constituted that it does not willingly restin facts and immediate causes, but seeks always after a knowledge of theremoter links in the chain of causation. 

Taking the many changes of any given spot of the earth's surface, fromsea to land and from land to sea, as an established fact, we cannotrefrain from asking ourselves how these changes have occurred. And whenwe have explained them--as they must be explained--by the alternate slowmovements of elevation and depression which have affected the crust ofthe earth, we go still further back, and ask, Why these movements?

I am not certain that any one can give you a satisfactory answer to thatquestion. Assuredly I cannot. All that can be said, for certain, is, thatsuch movements are part of the ordinary course of nature, inasmuch asthey are going on at the present time. Direct proof may be given, thatsome parts of the land of the northern hemisphere are at this momentinsensibly rising and others insensibly sinking; and there is indirect, but perfectly satisfactory, proof, that an enormous area now covered bythe Pacific has been deepened thousands of feet, since the presentinhabitants of that sea came into existence. Thus there is not a shadowof a reason for believing that the physical changes of the globe, in pasttimes, have been effected by other than natural causes. Is there any morereason for believing that the concomitant modifications in the forms ofthe living inhabitants of the globe have been brought about in otherways?

Before attempting to answer this question, let us try to form a distinctmental picture of what has happened in some special case. The crocodilesare animals which, as a group, have a very vast antiquity. They aboundedages before the chalk was deposited; they throng the rivers in warmclimates, at the present day. There is a difference in the form of thejoints of the back-bone, and in some minor particulars, between thecrocodiles of the present epoch and those which lived before the chalk;but, in the cretaceous epoch, as I have already mentioned, the crocodileshad assumed the modern type of structure. Notwithstanding this, thecrocodiles of the chalk are not identically the same as those which livedin the times called "older tertiary, " which succeeded the cretaceousepoch; and the crocodiles of the older tertiaries are not identical withthose of the newer tertiaries, nor are these identical with existingforms. I leave open the question whether particular species may havelived on from epoch to epoch. But each epoch has had its peculiarcrocodiles; though all, since the chalk, have belonged to the moderntype, and differ simply in their proportions, and in such structuralparticulars as are discernible only to trained eyes. 

How is the existence of this long succession of different species ofcrocodiles to be accounted for? Only two suppositions seem to be open tous--Either each species of crocodile has been specially created, or ithas arisen out of some pre-existing form by the operation of naturalcauses. Choose your hypothesis; I have chosen mine. I can find nowarranty for believing in the distinct creation of a score of successivespecies of crocodiles in the course of countless ages of time. Sciencegives no countenance to such a wild fancy; nor can even the perverseingenuity of a commentator pretend to discover this sense, in the simplewords in which the writer of Genesis records the proceedings of the fifthand six days of the Creation. 

On the other hand, I see no good reason for doubting the necessaryalternative, that all these varied species have been evolved from pre-existing crocodilian forms, by the operation of causes as completely apart of the common order of nature as those which have effected thechanges of the inorganic world. Few will venture to affirm that thereasoning which applies to crocodiles loses its force among otheranimals, or among plants. If one series of species has come intoexistence by the operation of natural causes, it seems folly to deny thatall may have arisen in the same way. 

A small beginning has led us to a great ending. If I were to put the bitof chalk with which we started into the hot but obscure flame of burninghydrogen, it would presently shine like the sun. It seems to me that thisphysical metamorphosis is no false image of what has been the result ofour subjecting it to a jet of fervent, though nowise brilliant, thoughtto-night. It has become luminous, and its clear rays, penetrating theabyss of the remote past, have brought within our ken some stages of theevolution of the earth. And in the shifting "without haste, but withoutrest" of the land and sea, as in the endless variation of the formsassumed by living beings, we have observed nothing but the naturalproduct of the forces originally possessed by the substance of theuniverse. 

II

THE PROBLEMS OF THE DEEP SEA

[1873]

On the 21st of December, 1872, H. M. S. _Challenger_, an eighteen guncorvette, of 2, 000 tons burden, sailed from Portsmouth harbour for athree, or perhaps four, years' cruise. No man-of-war ever left thatfamous port before with so singular an equipment. Two of the eighteensixty-eight pounders of the _Challenger's_ armament remained to enableher to speak with effect to sea-rovers, haply devoid of any respect forscience, in the remote seas for which she is bound; but the main-deckwas, for the most part, stripped of its war-like gear, and fitted up withphysical, chemical, and biological laboratories; Photography had its darkcabin; while apparatus for dredging, trawling, and sounding; forphotometers and for thermometers, filled the space formerly occupied byguns and gun-tackle, pistols and cutlasses. 

The crew of the _Challenger_ match her fittings. Captain Nares, hisofficers and men, are ready to look after the interests of hydrography, work the ship, and, if need be, fight her as seamen should; while thereis a staff of scientific civilians, under the general direction of Dr. Wyville Thomson, F. R. S. (Professor of Natural History in EdinburghUniversity by rights, but at present detached for duty _in partibus_), whose business it is to turn all the wonderfully packed stores ofappliances to account, and to accumulate, before the ship returns toEngland, such additions to natural knowledge as shall justify the labourand cost involved in the fitting out and maintenance of the expedition. 

Under the able and zealous superintendence of the Hydrographer, AdmiralRichards, every precaution which experience and forethought could devisehas been taken to provide the expedition with the material conditions ofsuccess; and it would seem as if nothing short of wreck or pestilence, both most improbable contingencies, could prevent the _Challenger_ fromdoing splendid work, and opening up a new era in the history ofscientific voyages. 

The dispatch of this expedition is the culmination of a series of suchenterprises, gradually increasing in magnitude and importance, which theAdmiralty, greatly to its credit, has carried out for some years past;and the history of which is given by Dr. Wyville Thomson in thebeautifully illustrated volume entitled "The Depths of the Sea, "published since his departure. 

"In the spring of the year 1868, my friend Dr. W. B. Carpenter, at thattime one of the Vice-Presidents of the Royal Society, was with me inIreland, where we were working out together the structure and developmentof the Crinoids. I had long previously had a profound conviction that theland of promise for the naturalist, the only remaining region where therewere endless novelties of extraordinary interest ready to the hand whichhad the means of gathering them, was the bottom of the deep sea. I hadeven had a glimpse of some of these treasures, for I had seen, the yearbefore, with Prof. Sars, the forms which I have already mentioned dredgedby his son at a depth of 300 to 400 fathoms off the Loffoten Islands. Ipropounded my views to my fellow-labourer, and we discussed the subjectmany times over our microscopes. I strongly urged Dr. Carpenter to usehis influence at head-quarters to induce the Admiralty, probably throughthe Council of the Royal Society, to give us the use of a vessel properlyfitted with dredging gear and all necessary scientific apparatus, thatmany heavy questions as to the state of things in the depths of theocean, which were still in a state of uncertainty, might be definitelysettled. After full consideration, Dr. Carpenter promised his hearty co-operation, and we agreed that I should write to him on his return toLondon, indicating generally the results which I anticipated, andsketching out what I conceived to be a promising line of inquiry. TheCouncil of the Royal Society warmly supported the proposal; and I givehere in chronological order the short and eminently satisfactorycorrespondence which led to the Admiralty placing at the disposal of Dr. Carpenter and myself the gunboat _Lightninq_, under the command of Staff-Commander May, R. N. , in the summer of 1868, for a trial cruise to theNorth of Scotland, and afterwards to the much wider surveys in H. M. S. _Porcupine_, Captain Calver, R. N. , which were made with the additionalassociation of Mr. Gwyn Jeffreys, in the summers of the years 1869 and1870. "[1]

[Footnote 1: The Depths of the Sea, pp. 49-50. ]

Plain men may be puzzled to understand why Dr. Wyville Thomson, not beinga cynic, should relegate the "Land of Promise" to the bottom of the deepsea, they may still more wonder what manner of "milk and honey" the_Challenger_ expects to find; and their perplexity may well rise to itsmaximum, when they seek to divine the manner in which that milk and honeyare to be got out of so inaccessible a Canaan. I will, therefore, endeavour to give some answer to these questions in an order the reverseof that in which I have stated them. 

Apart from hooks, and lines, and ordinary nets, fishermen have, from timeimmemorial, made use of two kinds of implements for getting at sea-creatures which live beyond tide-marks--these are the "dredge" and the"trawl. " The dredge is used by oyster-fishermen. Imagine a large bag, themouth of which has the shape of an elongated parallelogram, and isfastened to an iron frame of the same shape, the two long sides of thisrim being fashioned into scrapers. Chains attach the ends of the frame toa stout rope, so that when the bag is dragged along by the rope the edgeof one of the scrapers rests on the ground, and scrapes whatever ittouches into the bag. The oyster-dredger takes one of these machines inhis boat, and when he has reached the oyster-bed the dredge is tossedoverboard; as soon as it has sunk to the bottom the rope is paid outsufficiently to prevent it from pulling the dredge directly upwards, andis then made fast while the boat goes ahead. The dredge is thus draggedalong and scrapes oysters and other sea-animals and plants, stones, andmud into the bag. When the dredger judges it to be full he hauls it up, picks out the oysters, throws the rest overboard, and begins again. 

Dredging in shallow water, say ten to twenty fathoms, is an easyoperation enough; but the deeper the dredger goes, the heavier must behis vessel, and the stouter his tackle, while the operation of hauling upbecomes more and more laborious. Dredging in 150 fathoms is very hardwork, if it has to be carried on by manual labour; but by the use of thedonkey-engine to supply power, [2] and of the contrivances known as"accumulators, " to diminish the risk of snapping the dredge rope by therolling and pitching of the vessel, the dredge has been worked deeper anddeeper, until at last, on the 22nd of July, 1869, H. M. S. _Porcupine_being in the Bay of Biscay, Captain Calver, her commander, performed theunprecedented feat of dredging in 2, 435 fathoms, or 14, 610 feet, a depthnearly equal to the height of Mont Blanc. The dredge "was rapidly hauledon deck at one o'clock in the morning of the 23rd, after an absence of7-1/4 hours, and a journey of upwards of eight statute miles, " with ahundred weight and a half of solid contents. 

[Footnote 2: The emotional side of the scientific nature has itssingularities. Many persons will call to mind a certain philosopher'stenderness over his watch--"the little creature"--which was so singularlylost and found again. But Dr. Wyville Thomson surpasses the owner of thewatch in his loving-kindness towards a donkey-engine. "This little enginewas the comfort of our lives. Once or twice it was overstrained, and thenwe pitied the willing little thing, panting like an overtaxed horse. "]

The trawl is a sort of net for catching those fish which habitually liveat the bottom of the sea, such as soles, plaice, turbot, and gurnett. Themouth of the net may be thirty or forty feet wide, and one edge of itsmouth is fastened to a beam of wood of the same length. The two ends ofthe beam are supported by curved pieces of iron, which raise the beam andthe edge of the net which is fastened to it, for a short distance, whilethe other edge of the mouth of the net trails upon the ground. The closedend of the net has the form of a great pouch; and, as the beam is draggedalong, the fish, roused from the bottom by the sweeping of the net, readily pass into its mouth and accumulate in the pouch at its end. Afterdrifting with the tide for six or seven hours the trawl is hauled up, themarketable fish are picked out, the others thrown away, and the trawlsent overboard for another operation. 

More than a thousand sail of well-found trawlers are constantly engagedin sweeping the seas around our coast in this way, and it is to them thatwe owe a very large proportion of our supply of fish. The difficulty oftrawling, like that of dredging, rapidly increases with the depth atwhich the operation is performed; and, until the other day, it isprobable that trawling at so great a depth as 100 fathoms was somethingunheard of. But the first news from the _Challenger_ opens up newpossibilities for the trawl. 

Dr. Wyville Thomson writes ("Nature, " March 20, 1873):--

"For the first two or three hauls in very deep water off the coast ofPortugal, the dredge came up filled with the usual 'Atlantic ooze, 'tenacious and uniform throughout, and the work of hours, in sifting, gavethe very smallest possible result. We were extremely anxious to get someidea of the general character of the Fauna, and particularly of thedistribution of the higher groups; and after various suggestions formodification of the dredge, it was proposed to try the ordinary trawl. Wehad a compact trawl, with a 15-feet beam, on board, and we sent it downoff Cape St. Vincent at a depth of 600 fathoms. The experiment lookedhazardous, but, to our great satisfaction, the trawl came up all rightand contained, with many of the larger invertebrate, several fishes.... After the first attempt we tried the trawl several times at depths of1090, 1525, and, finally, 2125 fathoms, and always with success. "

To the coral-fishers of the Mediterranean, who seek the precious redcoral, which grows firmly fixed to rocks at a depth of sixty to eightyfathoms, both the dredge and the trawl would be useless. They, therefore, have recourse to a sort of frame, to which are fastened long bundles ofloosely netted hempen cord, and which is lowered by a rope to the depthat which the hempen cords can sweep over the surface of the rocks andbreak off the coral, which is brought up entangled in the cords. Asimilar contrivance has arisen out of the necessities of deep-seaexploration. 

In the course of the dredging of the _Porcupine_, it was frequently foundthat, while few objects of interest were brought up within the dredge, many living creatures came up sticking to the outside of the dredge-bag, and even to the first few fathoms of the dredge-rope. The mouth of thedredge doubtless rapidly filled with mud, and thus the things it shouldhave brought up were shut out. To remedy this inconvenience CaptainCalver devised an arrangement not unlike that employed by the coral-fishers. He fastened half a dozen swabs, such as are used for dryingdecks, to the dredge. A swab is something like what a birch-broom wouldbe if its twigs were made of long, coarse, hempen yarns. These draggedalong after the dredge over the surface of the mud, and entangled thecreatures living there--multitudes of which, twisted up in the strands ofthe swabs, were brought to the surface with the dredge. A furtherimprovement was made by attaching a long iron bar to the bottom of thedredge bag, and fastening large bunches of teased-out hemp to the end ofthis bar. These "tangles" bring up immense quantities of such animals ashave long arms, or spines, or prominences which readily become caught inthe hemp, but they are very destructive to the fragile organisms whichthey imprison; and, now that the trawl can be successfully worked at thegreatest depths, it may be expected to supersede them; at least, whereverthe ground is soft enough to permit of trawling. 

It is obvious that between the dredge, the trawl, and the tangles, thereis little chance for any organism, except such as are able to burrowrapidly, to remain safely at the bottom of any part of the sea which the_Challenger_ undertakes to explore. And, for the first time in thehistory of scientific exploration, we have a fair chance of learning whatthe population of the depths of the sea is like in the most widelydifferent parts of the world. 

And now arises the next question. The means of exploration being fairlyadequate, what forms of life may be looked for at these vast depths?

The systematic study of the Distribution of living beings is the mostmodern branch of Biological Science, and came into existence long afterMorphology and Physiology had attained a considerable development. Thisnaturally does not imply that, from the time men began to observe naturalphenomena, they were ignorant of the fact that the animals and plants ofone part of the world are different from those in other regions; or thatthose of the hills are different from those of the plains in the sameregion; or finally that some marine creatures are found only in theshallows, while others inhabit the deeps. Nevertheless, it was only afterthe discovery of America that the attention of naturalists was powerfullydrawn to the wonderful differences between the animal population of thecentral and southern parts of the new world and that of those parts ofthe old world which lie under the same parallels of latitude. So far backas 1667 Abraham Mylius, in his treatise "De Animalium origine etmigratione, populorum, " argues that, since there are innumerable speciesof animals in America which do not exist elsewhere, they must have beenmade and placed there by the Deity: Buffon no less forcibly insists uponthe difference between the Faunae of the old and new world. But the firstattempt to gather facts of this order into a whole, and to coordinatethem into a series of generalizations, or laws of GeographicalDistribution, is not a century old, and is contained in the "SpecimenZoologiae Geographicae Quadrupedum Domicilia et Migrationes sistens, "published, in 1777, by the learned Brunswick Professor, EberhardZimmermann, who illustrates his work by what he calls a "TabulaZoographica, " which is the oldest distributional map known to me. 

In regard to matters of fact, Zimmermann's chief aim is to show thatamong terrestrial mammals, some occur all over the world, while othersare restricted to particular areas of greater or smaller extent; and thatthe abundance of species follows temperature, being greatest in warm andleast in cold climates. But marine animals, he thinks, obey no such law. The Arctic and Atlantic seas, he says, are as full of fishes and otheranimals as those of the tropics. It is, therefore, clear that cold doesnot affect the dwellers in the sea as it does land animals, and that thismust be the case follows from the fact that sea water, "propter variasquas continet bituminis spiritusque particulas, " freezes with much moredifficulty than fresh water. On the other hand, the heat of theEquatorial sun penetrates but a short distance below the surface of theocean. Moreover, according to Zimmermann, the incessant disturbance ofthe mass of the sea by winds and tides, so mixes up the warm and the coldthat life is evenly diffused and abundant throughout the ocean. 

In 1810, Risso, in his work on the Ichthyology of Nice, laid thefoundation of what has since been termed "bathymetrical" distribution, ordistribution in depth, by showing that regions of the sea bottom ofdifferent depths could be distinguished by the fishes which inhabit them. There was the _littoral region_ between tide marks with its sand-eels, pipe fishes, and blennies: the _seaweed region_, extending from low-water-mark to a depth of 450 feet, with its wrasses, rays, and flat fish;and the _deep-sea region_, from 450 feet to 1500 feet or more, withits file-fish, sharks, gurnards, cod, and sword-fish. 

More than twenty years later, M. M. Audouin and Milne Edwards carried outthe principle of distinguishing the Faunae of different zones of depthmuch more minutely, in their "Recherches pour servir à l'HistoireNaturelle du Littoral de la France, " published in 1832. 

They divide the area included between highwater-mark and lowwater-mark ofspring tides (which is very extensive, on account of the great rise andfall of the tide on the Normandy coast about St. Malo, where theirobservations were made) into four zones, each characterized by itspeculiar invertebrate inhabitants. Beyond the fourth region theydistinguish a fifth, which is never uncovered, and is inhabited byoysters, scallops, and large starfishes and other animals. Beyond thisthey seem to think that animal life is absent. [3]

[Footnote 3: "Enfin plus has encore, c'est-à-dire alors loin des côtes, le fond des eaux ne paraît plus être habité, du moms dans nos mers, paraucun de ces animaux" (1. C. Tom. I. P. 237). The "ces animaux" leavesthe meaning of the authors doubtful. ]

Audouin and Milne Edwards were the first to see the importance of thebearing of a knowledge of the manner in which marine animals aredistributed in depth, on geology. They suggest that, by this means, itwill be possible to judge whether a fossiliferous stratum was formed uponthe shore of an ancient sea, and even to determine whether it wasdeposited in shallower or deeper water on that shore; the association ofshells of animals which live in different zones of depth will prove thatthe shells have been transported into the position in which they arefound; while, on the other hand, the absence of shells in a deposit willnot justify the conclusion that the waters in which it was formed weredevoid of animal inhabitants, inasmuch as they might have been only toodeep for habitation. 

The new line of investigation thus opened by the French naturalists wasfollowed up by the Norwegian, Sars, in 1835, by Edward Forbes, in our owncountry, in 1840, [4] and by Oersted, in Denmark, a few years later. Thegenius of Forbes, combined with his extensive knowledge of botany, invertebrate zoology, and geology, enabled him to do more than any of hiscompeers, in bringing the importance of distribution in depth intonotice; and his researches in the Aegean Sea, and still more hisremarkable paper "On the Geological Relations of the existing Fauna andFlora of the British Isles, " published in 1846, in the first volume ofthe "Memoirs of the Geological Survey of Great Britain, " attracteduniversal attention. 

[Footnote 4: In the paper in the _Memoirs of the Survey_ cited furtheron, Forbes writes:--

"In an essay 'On the Association of Mollusca on the British Coasts, considered with reference to Pleistocene Geology, ' printed in [the_Edinburgh Academic Annual_ for] 1840, I described the mollusca, asdistributed on our shores and seas, in four great zones or regions, usually denominated 'The Littoral zone, ' 'The region of Laminariae, ' 'Theregion of Coral-lines, ' and 'The region of Corals. ' An extensive seriesof researches, chiefly conducted by the members of the committeeappointed by the British Association to investigate the marine geology ofBritain by means of the dredge, have not invalidated this classification, and the researches of Professor Lovén, in the Norwegian and Lapland seas, have borne out their correctness The first two of the regions abovementioned had been previously noticed by Lamoureux, in his account of thedistribution (vertically) of sea-weeds, by Audouin and Milne Edwards intheir _Observations on the Natural History of the coast of France_, andby Sars in the preface to his _Beskrivelser og Jagttayelser_. "]

On the coasts of the British Islands, Forbes distinguishes four zones orregions, the Littoral (between tide marks), the Laminarian (betweenlowwater-mark and 15 fathoms), the Coralline (from 15 to 50 fathoms), andthe Deep sea or Coral region (from 50 fathoms to beyond 100 fathoms). But, in the deeper waters of the Aegean Sea, between the shore and a depthof 300 fathoms, Forbes was able to make out no fewer than eight zones oflife, in the course of which the number and variety of forms graduallydiminished until, beyond 300 fathoms, life disappeared altogether. Henceit appeared as if descent in the sea had much the same effect on life, asascent on land. Recent investigations appear to show that Forbes wasright enough in his classification of the facts of distribution in depthas they are to be observed in the Aegean; and though, at the time hewrote, one or two observations were extant which might have warned himnot to generalize too extensively from his Aegean experience, his owndredging work was so much more extensive and systematic than that of anyother naturalist, that it is not wonderful he should have felt justifiedin building upon it. Nevertheless, so far as the limit of the range oflife in depth goes, Forbes' conclusion has been completely negatived, andthe greatest depths yet attained show not even an approach to a "zero oflife":--

"During the several cruises of H. M. Ships _Lightning_ and _Porcupine_ inthe years 1868, 1869, and 1870, " says Dr. Wyville Thomson, "fifty-sevenhauls of the dredge were taken in the Atlantic at depths beyond 500fathoms, and sixteen at depths beyond 1, 000 fathoms, and, in all cases, life was abundant. In 1869, we took two casts in depths greater than2, 000 fathoms. In both of these life was abundant; and with the deepestcast, 2, 435 fathoms, off the month of the Bay of Biscay, we took living, well-marked and characteristic examples of all the five invertebrate sub-kingdoms. And thus the question of the existence of abundant animal lifeat the bottom of the sea has been finally settled and for all depths, forthere is no reason to suppose that the depth anywhere exceeds betweenthree and four thousand fathoms; and if there be nothing in theconditions of a depth of 2, 500 fathoms to prevent the full development ofa varied Fauna, it is impossible to suppose that even an additionalthousand fathoms would make any great difference. "[5]

[Footnote 5: _The Depths of the Sea_, p. 30. Results of a similar kind, obtained by previous observers, are stated at length in the sixthchapter, pp. 267-280. The dredgings carried out by Count Pourtales, underthe authority of Professor Peirce, the Superintendent of the UnitedStates Coast Survey, in the years 1867, 1868, and 1869, are particularlynoteworthy, and it is probably not too much to say, in the words ofProfessor Agassiz, "that we owe to the coast survey the first broad andcomprehensive basis for an exploration of the sea bottom on a largescale, opening a new era in zoological and geological research. "]

As Dr. Wyville Thomson's recent letter, cited above, shows, the use ofthe trawl, at great depths, has brought to light a still greaterdiversity of life. Fishes came up from a depth of 600 to more than 1, 000fathoms, all in a peculiar condition from the expansion of the aircontained in their bodies. On their relief from the extreme pressure, their eyes, especially, had a singular appearance, protruding like greatglobes from their heads. Bivalve and univalve mollusca seem to be rare atthe greatest depths; but starfishes, sea urchins and other echinoderms, zoophytes, sponges, and protozoa abound. 

It is obvious that the _Challenger_ has the privilege of opening a newchapter in the history of the living world. She cannot send down herdredges and her trawls into these virgin depths of the great oceanwithout bringing up a discovery. Even though the thing itself may beneither "rich nor rare, " the fact that it came from that depth, in thatparticular latitude and longitude, will be a new fact in distribution, and, as such, have a certain importance. 

But it may be confidently assumed that the things brought up will veryfrequently be zoological novelties; or, better still, zoologicalantiquities, which, in the tranquil and little-changed depths of theocean, have escaped the causes of destruction at work in the shallows, and represent the predominant population of a past age. 

It has been seen that Audouin and Milne Edwards foresaw the generalinfluence of the study of distribution in depth upon the interpretationof geological phenomena. Forbes connected the two orders of inquiry stillmore closely; and in the thoughtful essay "On the connection between thedistribution of the existing Fauna and Flora of the British Isles, andthe geological changes which have affected their area, especially duringthe epoch of the Northern drift, " to which reference has already beenmade, he put forth a most pregnant suggestion. 

In certain parts of the sea bottom in the immediate vicinity of theBritish Islands, as in the Clyde district, among the Hebrides, in theMoray Firth, and in the German Ocean, there are depressed areas, forming akind of submarine valleys, the centres of which are from 80 to 100fathoms, or more, deep. These depressions are inhabited by assemblages ofmarine animals, which differ from those found over the adjacent andshallower region, and resemble those which are met with much farthernorth, on the Norwegian coast. Forbes called these Scandinaviandetachments "Northern outliers. "

How did these isolated patches of a northern population get into thesedeep places? To explain the mystery, Forbes called to mind the fact that, in the epoch which immediately preceded the present, the climate was muchcolder (whence the name of "glacial epoch" applied to it); and that theshells which are found fossil, or sub-fossil, in deposits of that age areprecisely such as are now to be met with only in the Scandinavian, orstill more Arctic, regions. Undoubtedly, during the glacial epoch, thegeneral population of our seas had, universally, the northern aspectwhich is now presented only by the "northern outliers"; just as thevegetation of the land, down to the sea-level, had the northern characterwhich is, at present, exhibited only by the plants which live on the topsof our mountains. But, as the glacial epoch passed away, and the presentclimatal conditions were developed, the northern plants were able tomaintain themselves only on the bleak heights, on which southern formscould not compete with them. And, in like manner, Forbes suggested that, after the glacial epoch, the northern animals then inhabiting the seabecame restricted to the deeps in which they could hold their own againstinvaders from the south, better fitted than they to flourish in thewarmer waters of the shallows. Thus depth in the sea corresponded in itseffect upon distribution to height on the land. 

The same idea is applied to the explanation of a similar anomaly in theFauna of the Aegean:--

"In the deepest of the regions of depth of the Aegean, the representationof a Northern Fauna is maintained, partly by identical and partly byrepresentative forms.... The presence of the latter is essentially due tothe law (of representation of parallels of latitude by zones of depth), whilst that of the former species depended on their transmission fromtheir parent seas during a former epoch, and subsequent isolation. Thatepoch was doubtless the newer Pliocene or Glacial Era, when the _Myatruncata_ and other northern forms now extinct in the Mediterranean, andfound fossil in the Sicilian tertiaries, ranged into that sea. Thechanges which there destroyed the _shallow water_ glacial forms, did notaffect those living in the depths, and which still survive. "[6]

[Footnote 6: _Memoirs of the Geological Survey of Great Britain_, Vol. I. P. 390. ]

The conception that the inhabitants of local depressions of the seabottom might be a remnant of the ancient population of the area, whichhad held their own in these deep fastnesses against an invading Fauna, asBritons and Gaels have held out in Wales and in Scotland againstencroaching Teutons, thus broached by Forbes, received a widerapplication than Forbes had dreamed of when the sounding machine firstbrought up specimens of the mud of the deep sea. As I have pointed outelsewhere, [7] it at once became obvious that the calcareous sticky mud ofthe Atlantic was made up, in the main, of shells of _Globigerina_ andother _Foraminifera_, identical with those of which the true chalk iscomposed, and the identity extended even to the presence of thosesingular bodies, the Coccoliths and Coccospheres, the true nature ofwhich is not yet made out. Here then were organisms, as old as thecretaceous epoch, still alive, and doing their work of rock-making at thebottom of existing seas. What if _Globigerina_ and the Coccoliths shouldnot be the only survivors of a world passed away, which are hiddenbeneath three miles of salt water? The letter which Dr. Wyville Thomsonwrote to Dr. Carpenter in May, 1868, out of which all these expeditionshave grown, shows that this query had become a practical problem in Dr. Thomson's mind at that time; and the desirableness of solving the problemis put in the foreground of his reasons for urging the Government toundertake the work of exploration:--

[Footnote 7: See above, "On a Piece of Chalk, " p. 13. ]

"Two years ago, M. Sars, Swedish Government Inspector of Fisheries, hadan opportunity, in his official capacity, of dredging off the LoffotenIslands at a depth of 300 fathoms. I visited Norway shortly after hisreturn, and had an opportunity of studying with his father, ProfessorSars, some of his results. Animal forms were _abundant_; many of themwere new to science; and among them was one of surpassing interest, thesmall crinoid, of which you have a specimen, and which we at oncerecognised as a degraded type of the _Apiocrinidoe_, an order hithertoregarded as extinct, which attained its maximum in the Pear Encrinites ofthe Jurassic period, and whose latest representative hitherto known wasthe _Bourguettocrinus_ of the chalk. Some years previously, Mr. Absjornsen, dredging in 200 fathoms in the Hardangerfjord, procuredseveral examples of a Starfish (_Brisinga_), which seems to find itsnearest ally in the fossil genus _Protaster_. These observations place itbeyond a doubt that animal life is abundant in the ocean at depthsvarying from 200 to 300 fathoms, that the forms at these great depthsdiffer greatly from those met with in ordinary dredgings, and that, atall events in some cases, these animals are closely allied to, and wouldseem to be directly descended from, the Fauna of the early tertiaries. 

"I think the latter result might almost have been anticipated; and, probably, further investigation will largely add to this class of data, and will give us an opportunity of testing our determinations of thezoological position of some fossil types by an examination of the softparts of their recent representatives. The main cause of the destruction, the migration, and the extreme modification of animal types, appear to bechange of climate, chiefly depending upon oscillations of the earth'scrust. These oscillations do not appear to have ranged, in the Northernportion of the Northern Hemisphere, much beyond 1, 000 feet since thecommencement of the Tertiary Epoch. The temperature of deep waters seemsto be constant for all latitudes at 39°; so that an immense area of theNorth Atlantic must have had its conditions unaffected by tertiary orpost-tertiary oscillations. "[8]

[Footnote 8: The Depths of the Sea, pp. 51-52. ]

As we shall see, the assumption that the temperature of the deep sea iseverywhere 39° F. (4° Cent. ) is an error, which Dr. Wyville Thomsonadopted from eminent physical writers; but the general justice of thereasoning is not affected by this circumstance, and Dr. Thomson'sexpectation has been, to some extent, already verified. 

Thus besides _Globigerina_, there are eighteen species of deep-sea_Foraminifera_ identical with species found in the chalk. Imbedded in thechalky mud of the deep sea, in many localities, are innumerable cup-shaped sponges, provided with six-rayed silicious spicula, so disposedthat the wall of the cup is formed of a lacework of flinty thread. Notless abundant, in some parts of the chalk formation, are the fossilsknown as _Ventriculites_, well described by Dr. Thomson as "elegant vasesor cups, with branching root-like bases, or groups of regularly orirregularly spreading tubes delicately fretted on the surface with animpressed network like the finest lace"; and he adds, "When we comparesuch recent forms as _Aphrocallistes, Iphiteon, Holtenia_, and_Askonema_, with certain series of the chalk _Ventriculites_, therecannot be the slightest doubt that they belong to the same family--insome cases to very nearly allied genera. "[9]

[Footnote 9: _The Depths of the Sea_, p. 484. ]

Professor Duncan finds "several corals from the coast of Portugal morenearly allied to chalk forms than to any others. "

The Stalked Crinoids or Feather Stars, so abundant in ancient times, arenow exclusively confined to the deep sea, and the late explorations haveyielded forms of old affinity, the existence of which has hitherto beenunsuspected. The general character of the group of star fishes imbeddedin the white chalk is almost the same as in the modern Fauna of the deepAtlantic. The sea urchins of the deep sea, while none of them arespecifically identical with any chalk form, belong to the same generalgroups, and some closely approach extinct cretaceous genera. 

Taking these facts in conjunction with the positive evidence of theexistence, during the Cretaceous epoch, of a deep ocean where now liesthe dry land of central and southern Europe, northern Africa, and westernand southern Asia; and of the gradual diminution of this ocean during theolder tertiary epoch, until it is represented at the present day by suchteacupfuls as the Caspian, the Black Sea, and the Mediterranean; thesupposition of Dr. Thomson and Dr. Carpenter that what is now the deepAtlantic, was the deep Atlantic (though merged in a vast easterlyextension) in the Cretaceous epoch, and that the _Globigerina_ mud hasbeen accumulating there from that time to this, seems to me to have agreat degree of probability. And I agree with Dr. Wyville Thomson againstSir Charles Lyell (it takes two of us to have any chance against hisauthority) in demurring to the assertion that "to talk of chalk havingbeen uninterruptedly formed in the Atlantic is as inadmissible in ageographical as in a geological sense. "

If the word "chalk" is to be used as a stratigraphical term andrestricted to _Globigerina_ mud deposited during the Cretaceous epoch, ofcourse it is improper to call the precisely similar mud of more recentdate, chalk. If, on the other hand, it is to be used as a mineralogicalterm, I do not see how the modern and the ancient chalks are to beseparated--and, looking at the matter geographically, I see no reason todoubt that a boring rod driven from the surface of the mud which formsthe floor of the mid-Atlantic would pass through one continuous mass of_Globigerina_ mud, first of modern, then of tertiary, and then ofmesozoic date; the "chalks" of different depths and ages beingdistinguished merely by the different forms of other organisms associatedwith the _Globigerinoe_. 

On the other hand, I think it must be admitted that a belief in thecontinuity of the modern with the ancient chalk has nothing to do withthe proposition that we can, in any sense whatever, be said to be stillliving in the Cretaceous epoch. When the _Challenger's_ trawl brings upan _Ichthyosaurus_, along with a few living specimens of _Belemnites_ and_Turrilites_, it may be admitted that she has come upon a cretaceous"outlier. " A geological period is characterized not only by the presenceof those creatures which lived in it, but by the absence of those whichhave only come into existence later; and, however large a proportion oftrue cretaceous forms may be discovered in the deep sea, the modern typesassociated with them must be abolished before the Fauna, as a whole, could, with any propriety, be termed Cretaceous. 

I have now indicated some of the chief lines of Biological inquiry, inwhich the _Challenger_ has special opportunities for doing good service, and in following which she will be carrying out the work alreadycommenced by the _Lightning_ and _Porcupine_ in their cruises of 1868 andsubsequent years. 

But biology, in the long run, rests upon physics, and the first conditionfor arriving at a sound theory of distribution in the deep sea, is theprecise ascertainment of the conditions of life; or, in other words, afull knowledge of all those phenomena which are embraced under the headof the Physical Geography of the Ocean. 

Excellent work has already been done in this direction, chiefly under thesuperintendence of Dr. Carpenter, by the _Lightning_ and the_Porcupine_, [10] and some data of fundamental importance to the physicalgeography of the sea have been fixed beyond a doubt. 

[Footnote 10: _Proceedings of the Royal Society_, 1870 and 1872]

Thus, though it is true that sea-water steadily contracts as it coolsdown to its freezing point, instead of expanding before it reaches itsfreezing point as fresh water does, the truth has been steadily ignoredby even the highest authorities in physical geography, and the erroneousconclusions deduced from their erroneous premises have been widelyaccepted as if they were ascertained facts. Of course, if sea-water, likefresh water, were heaviest at a temperature of 39° F. And got lighter asit approached 32° F. , the water of the bottom of the deep sea could notbe colder than 39°. But one of the first results of the carefulascertainment of the temperature at different depths, by means ofthermometers specially contrived for the avoidance of the errors producedby pressure, was the proof that, below 1000 fathoms in the Atlantic, downto the greatest depths yet sounded, the water has a temperature alwayslower than 38° Fahr. , whatever be the temperature of the water at thesurface. And that this low temperature of the deepest water is probablythe universal rule for the depths of the open ocean is shown, amongothers, by Captain Chimmo's recent observations in the Indian ocean, between Ceylon and Sumatra, where, the surface water ranging from 85°-81°Fahr. , the temperature at the bottom, at a depth of 2270 to 2656 fathoms, was only from 34° to 32° Fahr. 

As the mean temperature of the superficial layer of the crust of theearth may be taken at about 50° Fahr. , it follows that the bottom layerof the deep sea in temperate and hot latitudes, is, on the average, muchcolder than either of the bodies with which it is in contact; for thetemperature of the earth is constant, while that of the air rarely fallsso low as that of the bottom water in the latitudes in question; and evenwhen it does, has time to affect only a comparatively thin stratum of thesurface water before the return of warm weather. 

How does this apparently anomalous state of things come about? If wesuppose the globe to be covered with a universal ocean, it can hardly bedoubted that the cold of the regions towards the poles must tend to causethe superficial water of those regions to contract and becomespecifically heavier. Under these circumstances, it would have noalternative but to descend and spread over the sea bottom, while itsplace would be taken by warmer water drawn from the adjacent regions. Thus, deep, cold, polar-equatorial currents, and superficial, warmer, equatorial-polar currents, would be set up; and as the former would havea less velocity of rotation from west to east than the regions towardswhich they travel, they would not be due southerly or northerly currents, but south-westerly in the northern hemisphere, and north-westerly in thesouthern; while, by a parity of reasoning, the equatorial-polar warmcurrents would be north-easterly in the northern hemisphere, and south-easterly in the southern. Hence, as a north-easterly current has the samedirection as a south-westerly wind, the direction of the northernequatorial-polar current in the extra-tropical part of its course wouldpretty nearly coincide with that of the anti-trade winds. The freezing ofthe surface of the polar sea would not interfere with the movement thusset up. For, however bad a conductor of heat ice may be, the unfrozensea-water immediately in contact with the undersurface of the ice mustneeds be colder than that further off; and hence will constantly tend todescend through the subjacent warmer water. 

In this way, it would seem inevitable that the surface waters of thenorthern and southern frigid zones must, sooner or later, find their wayto the bottom of the rest of the ocean; and there accumulate to athickness dependent on the rate at which they absorb heat from the crustof the earth below, and from the surface water above. 

If this hypothesis be correct, it follows that, if any part of the oceanin warm latitudes is shut off from the influence of the cold polarunderflow, the temperature of its deeps should be less cold than thetemperature of corresponding depths in the open sea. Now, in theMediterranean, Nature offers a remarkable experimental proof of just thekind needed. It is a landlocked sea which runs nearly east and west, between the twenty-ninth and forty-fifth parallels of north latitude. Roughly speaking, the average temperature of the air over it is 75° Fahr. In July and 48° in January. 

This great expanse of water is divided by the peninsula of Italy(including Sicily), continuous with which is a submarine elevationcarrying less than 1, 200 feet of water, which extends from Sicily to CapeBon in Africa, into two great pools--an eastern and a western. Theeastern pool rapidly deepens to more than 12, 000 feet, and sends off tothe north its comparatively shallow branches, the Adriatic and the AegeanSeas. The western pool is less deep, though it reaches some 10, 000 feet. And, just as the western end of the eastern pool communicates by ashallow passage, not a sixth of its greatest depth, with the westernpool, so the western pool is separated from the Atlantic by a ridge whichruns between Capes Trafalgar and Spartel, on which there is hardly 1, 000feet of water. All the water of the Mediterranean which lies deeper thanabout 150 fathoms, therefore, is shut off from that of the Atlantic, andthere is no communication between the cold layer of the Atlantic (below1, 000 fathoms) and the Mediterranean. Under these circumstances, what isthe temperature of the Mediterranean? Everywhere below 600 feet it isabout 55° Fahr. ; and consequently, at its greatest depths, it is some 20°warmer than the corresponding depths of the Atlantic. 

It seems extremely difficult to account for this difference in any otherway, than by adopting the views so strongly and ably advocated by Dr. Carpenter, that, in the existing distribution of land and water, such acirculation of the water of the ocean does actually occur, astheoretically must occur, in the universal ocean, with which we started. 

It is quite another question, however, whether this theoreticcirculation, true cause as it may be, is competent to give rise to suchmovements of sea-water, in mass, as those currents, which have commonlybeen regarded as northern extensions of the Gulf-stream. I shall notventure to touch upon this complicated problem; but I may take occasionto remark that the cause of a much simpler phenomenon--the stream ofAtlantic water which sets through the Straits of Gibraltar, eastward, atthe rate of two or three miles an hour or more, does not seem to be soclearly made out as is desirable. 

The facts appear to be that the water of the Mediterranean is veryslightly denser than that of the Atlantic (1. 0278 to 1. 0265), and thatthe deep water of the Mediterranean is slightly denser than that of thesurface; while the deep water of the Atlantic is, if anything, lighterthan that of the surface. Moreover, while a rapid superficial current issetting in (always, save in exceptionally violent easterly winds) throughthe Straits of Gibraltar, from the Atlantic to the Mediterranean, a deepundercurrent (together with variable side currents) is setting outthrough the Straits, from the Mediterranean to the Atlantic. 

Dr. Carpenter adopts, without hesitation, the view that the cause of thisindraught of Atlantic water is to be sought in the much more rapidevaporation which takes place from the surface of the Mediterranean thanfrom that of the Atlantic; and thus, by lowering the level of the former, gives rise to an indraught from the latter. 

But is there any sound foundation for the three assumptions involvedhere? Firstly, that the evaporation from the Mediterranean, as a whole, is much greater than that from the Atlantic under correspondingparallels; secondly, that the rainfall over the Mediterranean makes upfor evaporation less than it does over the Atlantic; and thirdly, supposing these two questions answered affirmatively: Are not thesesources of loss in the Mediterranean fully covered by the prodigiousquantity of fresh water which is poured into it by great rivers andsubmarine springs? Consider that the water of the Ebro, the Rhine, thePo, the Danube, the Don, the Dnieper, and the Nile, all flow directly orindirectly into the Mediterranean; that the volume of fresh water whichthey pour into it is so enormous that fresh water may sometimes be baledup from the surface of the sea off the Delta of the Nile, while the landis not yet in sight; that the water of the Black Sea is half fresh, andthat a current of three or four miles an hour constantly streams from itMediterraneanwards through the Bosphorus;--consider, in addition, that nofewer than ten submarine springs of fresh water are known to burst up inthe Mediterranean, some of them so large that Admiral Smyth calls them"subterranean rivers of amazing volume and force"; and it would seem, onthe face of the matter, that the sun must have enough to do to keep thelevel of the Mediterranean down; and that, possibly, we may have to seekfor the cause of the small superiority in saline contents of theMediterranean water in some condition other than solar evaporation. 

Again, if the Gibraltar indraught is the effect of evaporation, why doesit go on in winter as well as in summer?

All these are questions more easily asked than answered; but they must beanswered before we can accept the Gibraltar stream as an example of acurrent produced by indraught with any comfort. 

The Mediterranean is not included in the _Challenger's_ route, but shewill visit one of the most promising and little explored ofhydrographical regions--the North Pacific, between Polynesia and theAsiatic and American shores; and doubtless the store of observations uponthe currents of this region, which she will accumulate, when comparedwith what we know of the North Atlantic, will throw a powerful light uponthe present obscurity of the Gulf-stream problem. 

III

ON SOME OF THE RESULTS OF THE EXPEDITION OF H. M. S. _CHALLLENGER_

[1875]

In May, 1873, I drew attention[1] to the important problems connectedwith the physics and natural history of the sea, to the solution of whichthere was every reason to hope the cruise of H. M. S. _Challenger_ wouldfurnish important contributions. The expectation then expressed has notbeen disappointed. Reports to the Admiralty, papers communicated to theRoyal Society, and large collections which have already been sent home, have shown that the _Challenger's_ staff have made admirable use of theirgreat opportunities; and that, on the return of the expedition in 1874, their performance will be fully up to the level of their promise. Indeed, I am disposed to go so far as to say, that if nothing more came of the_Challengers_ expedition than has hitherto been yielded by herexploration of the nature of the sea bottom at great depths, a fullscientific equivalent of the trouble and expense of her equipment wouldhave been obtained. 

[Footnote 1: See the preceding Essay. ]

In order to justify this assertion, and yet, at the same time, not toclaim more for Professor Wyville Thomson and his colleagues than is theirdue, I must give a brief history of the observations which have precededtheir exploration of this recondite field of research, and endeavour tomake clear what was the state of knowledge in December, 1872, and whatnew facts have been added by the scientific staff of the _Challenger_. Sofar as I have been able to discover, the first successful attempt tobring up from great depths more of the sea bottom than would adhere to asounding-lead, was made by Sir John Ross, in the voyage to the Arcticregions which he undertook in 1818. In the Appendix to the narrative ofthat voyage, there will be found an account of a very ingenious apparatuscalled "clams"--a sort of double scoop--of his own contrivance, which SirJohn Ross had made by the ship's armourer; and by which, being inBaffin's Bay, in 72° 30' N. And 77° 15' W. , he succeeded in bringing upfrom 1, 050 fathoms (or 6, 300 feet), "several pounds" of a "fine greenmud, " which formed the bottom of the sea in this region. Captain (now SirEdward) Sabine, who accompanied Sir John Ross on this cruise, says ofthis mud that it was "soft and greenish, and that the lead sunk severalfeet into it. " A similar "fine green mud" was found to compose the seabottom in Davis Straits by Goodsir in 1845. Nothing is certainly known ofthe exact nature of the mud thus obtained, but we shall see that the mudof the bottom of the Antarctic seas is described in curiously similarterms by Dr. Hooker, and there is no doubt as to the composition of thisdeposit. 

In 1850, Captain Penny collected in Assistance Bay, in Kingston Bay, andin Melville Bay, which lie between 73° 45' and 74° 40' N. , specimens ofthe residuum left by melted surface ice, and of the sea bottom in theselocalities. Dr. Dickie, of Aberdeen, sent these materials to Ehrenberg, who made out[2] that the residuum of the melted ice consisted for themost part of the silicious cases of diatomaceous plants, and of thesilicious spicula of sponges; while, mixed with these, were a certainnumber of the equally silicious skeletons of those low animal organisms, which were termed _Polycistineoe_ by Ehrenberg, but are now known as_Radiolaria_. 

[Footnote 2: _Ueber neue Anschauungen des kleinsten nördlichenPolarlebens_. --Monatsberichte d. K. Akad. Berlin, 1853. ]

In 1856, a very remarkable addition to our knowledge of the nature of thesea bottom in high northern latitudes was made by Professor Bailey ofWest Point. Lieutenant Brooke, of the United States Navy, who wasemployed in surveying the Sea of Kamschatka, had succeeded in obtainingspecimens of the sea bottom from greater depths than any hithertoreached, namely from 2, 700 fathoms (16, 200 feet) in 56° 46' N. , and 168°18' E. ; and from 1, 700 fathoms (10, 200 feet) in 60° 15' N. And 170° 53'E. On examining these microscopically, Professor Bailey found, asEhrenberg had done in the case of mud obtained on the opposite side ofthe Arctic region, that the fine mud was made up of shells of_Diatomacoe_, of spicula of sponges, and of _Radiolaria_, with a smalladmixture of mineral matters, but without a trace of any calcareousorganisms. 

Still more complete information has been obtained concerning the natureof the sea bottom in the cold zone around the south pole. Between theyears 1839 and 1843, Sir James Clark Ross executed his famous Antarcticexpedition, in the course of which he penetrated, at two widely distantpoints of the Antarctic zone, into the high latitudes of the shores ofVictoria Land and of Graham's Land, and reached the parallel of 80° S. Sir James Ross was himself a naturalist of no mean acquirements, and Dr. Hooker, [3] the present President of the Royal Society, accompanied him asnaturalist to the expedition, so that the observations upon the fauna andflora of the Antarctic regions made during this cruise were sure to havea peculiar value and importance, even had not the attention of thevoyagers been particularly directed to the importance of noting theoccurrence of the minutest forms of animal and vegetable life in theocean. 

[Footnote 3: Now Sir Joseph Hooker. 1894. ]

Among the scientific instructions for the voyage drawn up by a committeeof the Royal Society, however, there is a remarkable letter from VonHumboldt to Lord Minto, then First Lord of the Admiralty, in which, amongother things, he dwells upon the significance of the researches into themicroscopic composition of rocks, and the discovery of the great sharewhich microscopic organisms take in the formation of the crust of theearth at the present day, made by Ehrenberg in the years 1836-39. Ehrenberg, in fact, had shown that the extensive beds of "rotten-stone"or "Tripoli" which occur in various parts of the world, and notably atBilin in Bohemia, consisted of accumulations of the silicious cases andskeletons of _Diatomaceoe_, sponges, and _Radiolaria_; he had proved thatsimilar deposits were being formed by _Diatomaceoe_, in the pools of theThiergarten in Berlin and elsewhere, and had pointed out that, if it werecommercially worth while, rotten-stone might be manufactured by a processof diatom-culture. Observations conducted at Cuxhaven in 1839, hadrevealed the existence, at the surface of the waters of the Baltic, ofliving Diatoms and _Radiolaria_ of the same species as those which, in afossil state, constitute extensive rocks of tertiary age at Caltanisetta, Zante, and Oran, on the shores of the Mediterranean. 

Moreover, in the fresh-water rotten-stone beds of Bilin, Ehrenberg hadtraced out the metamorphosis, effected apparently by the action ofpercolating water, of the primitively loose and friable deposit oforganized particles, in which the silex exists in the hydrated or solublecondition. The silex, in fact, undergoes solution and slow redeposition, until, in ultimate result, the excessively fine-grained sand, eachparticle of which is a skeleton, becomes converted into a dense opalinestone, with only here and there an indication of an organism. 

From the consideration of these facts, Ehrenberg, as early as the year1839, had arrived at the conclusion that rocks, altogether similar tothose which constitute a large part of the crust of the earth, must beforming, at the present day, at the bottom of the sea; and he threw outthe suggestion that even where no trace of organic structure is to befound in the older rocks, it may have been lost by metamorphosis. [4]

[Footnote 4: _Ueber die noch jetzt zahlreich lebende Thierarten derKreidebildung und den Organismus der Polythalamien. Abhandlungen der Kön. Akad. Der Wissenchaften. _ 1839. _Berlin_. 1841. I am afraid that thisremarkable paper has been somewhat overlooked in the recent discussionsof the relation of ancient rocks to modern deposits. ]

The results of the Antarctic exploration, as stated by Dr. Hooker in the"Botany of the Antarctic Voyage, " and in a paper which he read beforethe British Association in 1847, are of the greatest importance inconnection with these views, and they are so clearly stated in the formerwork, which is somewhat inaccessible, that I make no apology for quotingthem at length--

"The waters and the ice of the South Polar Ocean were alike found toabound with microscopic vegetables belonging to the order _Diatomaceoe_. Though much too small to be discernible by the naked eye, they occurredin such countless myriads as to stain the berg and the pack ice whereverthey were washed by the swell of the sea; and, when enclosed in thecongealing surface of the water, they imparted to the brash and pancakeice a pale ochreous colour. In the open ocean, northward of the frozenzone, this order, though no doubt almost universally present, generallyeludes the search of the naturalist; except when its species arecongregated amongst that mucous scum which is sometimes seen floating onthe waves, and of whose real nature we are ignorant; or when the colouredcontents of the marine animals who feed on these Algae are examined. Tothe south, however, of the belt of ice which encircles the globe, betweenthe parallels of 50° and 70° S. , and in the waters comprised between thatbelt and the highest latitude ever attained by man, this vegetation isvery conspicuous, from the contrast between its colour and the white snowand ice in which it is imbedded. Insomuch, that in the eightieth degree, all the surface ice carried along by the currents, the sides of everyberg and the base of the great Victoria Barrier itself, within reach ofthe swell, were tinged brown, as if the polar waters were charged withoxide of iron. 

"As the majority of these plants consist of very simple vegetable cells, enclosed in indestructible silex (as other Algae are in carbonate oflime), it is obvious that the death and decomposition of such multitudesmust form sedimentary deposits, proportionate in their extent to thelength and exposure of the coast against which they are washed, inthickness to the power of such agents as the winds, currents, and sea, which sweep them more energetically to certain positions, and in purity, to the depth of the water and nature of the bottom. Hence we detectedtheir remains along every icebound shore, in the depths of the adjacentocean, between 80 and 400 fathoms. Off Victoria Barrier (a perpendicularwall of ice between one and two hundred feet above the level of the sea)the bottom of the ocean was covered with a stratum of pure white or greenmud, composed principally of the silicious shells of the _Diatomaceoe_. These, on being put into water, rendered it cloudy like milk, and tookmany hours to subside. In the very deep water off Victoria and Graham'sLand, this mud was particularly pure and fine; but towards the shallowshores there existed a greater or less admixture of disintegrated rockand sand; so that the organic compounds of the bottom frequently bore buta small proportion to the inorganic. " ... 

"The universal existence of such an invisible vegetation as that of theAntarctic Ocean, is a truly wonderful fact, and the more from its notbeing accompanied by plants of a high order. During the years we spentthere, I had been accustomed to regard the phenomena of life as differingtotally from what obtains throughout all other latitudes, for everythingliving appeared to be of animal origin. The ocean swarmed with_Mollusca_, and particularly entomostracous _Crustacea_, small whales, and porpoises; the sea abounded with penguins and seals, and the air withbirds; the animal kingdom was ever present, the larger creatures preyingon the smaller, and these again on smaller still; all seemed carnivorous. The herbivorous were not recognised, because feeding on a microscopicherbage, of whose true nature I had formed an erroneous impression. Itis, therefore, with no little satisfaction that I now class the_Diatomaceoe_ with plants, probably maintaining in the South Polar Oceanthat balance between the vegetable and the animal kingdoms which prevailsover the surface of our globe. Nor is the sustenance and nutrition of theanimal kingdom the only function these minute productions may perform;they may also be the purifiers of the vitiated atmosphere, and thusexecute in the Antarctic latitudes the office of our trees and grass turfin the temperate regions, and the broad leaves of the palm, &c. , in thetropics. " ... 

With respect to the distribution of the _Diatomaceoe_, Dr. Hookerremarks:--

"There is probably no latitude between that of Spitzbergen and VictoriaLand, where some of the species of either country do not exist: Iceland, Britain, the Mediterranean Sea, North and South America, and the SouthSea Islands, all possess Antarctic _Diatomaceoe_. The silicious coats ofspecies only known living in the waters of the South Polar Ocean, have, during past ages, contributed to the formation of rocks; and thus theyoutlive several successive creations of organized beings. The phonolitestones of the Rhine, and the Tripoli stone, contain species identicalwith what are now contributing to form a sedimentary deposit (andperhaps, at some future period, a bed of rock) extending in onecontinuous stratum for 400 measured miles. I allude to the shores of theVictoria Barrier, along whose coast the soundings examined wereinvariably charged with diatomaceous remains, constituting a bank whichstretches 200 miles north from the base of Victoria Barrier, while theaverage depth of water above it is 300 fathoms, or 1, 800 feet. Again, some of the Antarctic species have been detected floating in theatmosphere which overhangs the wide ocean between Africa and America. Theknowledge of this marvellous fact we owe to Mr. Darwin, who, when he wasat sea off the Cape de Verd Islands, collected an impalpable powder whichfell on Captain Fitzroy's ship. He transmitted this dust to Ehrenberg, who ascertained it to consist of the silicious coats, chiefly of American_Diatomaceoe_, which were being wafted through the upper region of theair, when some meteorological phenomena checked them in their course anddeposited them on the ship and surface of the ocean. 

"The existence of the remains of many species of this order (and amongstthem some Antarctic ones) in the volcanic ashes, pumice, and scoriae ofactive and extinct volcanoes (those of the Mediterranean Sea andAscension Island, for instance) is a fact bearing immediately upon thepresent subject. Mount Erebus, a volcano 12, 400 feet high, of the firstclass in dimensions and energetic action, rises at once from the ocean inthe seventy-eighth degree of south latitude, and abreast of the_Diatomaceoe_ bank, which reposes in part on its base. Hence it may notappear preposterous to conclude that, as Vesuvius receives the waters ofthe Mediterranean, with its fish, to eject them by its crater, so thesubterranean and subaqueous forces which maintain Mount Erebus inactivity may occasionally receive organic matter from the bank, anddisgorge it, together with those volcanic products, ashes and pumice. 

"Along the shores of Graham's Land and the South Shetland Islands, wehave a parallel combination of igneous and aqueous action, accompaniedwith an equally copious supply of _Diatomaceoe_. In the Gulf of Erebusand Terror, fifteen degrees north of Victoria Land, and placed on theopposite side of the globe, the soundings were of a similar nature withthose of the Victoria Land and Barrier, and the sea and ice as full of_Diatomaceoe_. This was not only proved by the deep sea lead, but by theexamination of bergs which, once stranded, had floated off and becomereversed, exposing an accumulation of white friable mud frozen to theirbases, which abounded with these vegetable remains. "

The _Challenger_ has explored the Antarctic seas in a region intermediatebetween those examined by Sir James Ross's expedition; and theobservations made by Dr. Wyville Thomson and his colleagues in everyrespect confirm those of Dr. Hooker:--

"On the 11th of February, lat. 60° 52' S. , long. 80° 20' E. , and March 3, lat. 53° 55' S. , long. 108° 35' E. , the sounding instrument came upfilled with a very fine cream-coloured paste, which scarcely effervescedwith acid, and dried into a very light, impalpable, white powder. This, when examined under the microscope, was found to consist almost entirelyof the frustules of Diatoms, some of them wonderfully perfect in all thedetails of their ornament, and many of them broken up. The species ofDiatoms entering into this deposit have not yet been worked up, but theyappear to be referable chiefly to the genera _Fragillaria, Coscinodiscus, Choetoceros, Asteromphalus_, and _Dictyocha_, with fragments of theseparated rods of a singular silicious organism, with which we wereunacquainted, and which made up a large proportion of the finer matter ofthis deposit. Mixed with the Diatoms there were a few small_Globigerinoe_, some of the tests and spicules of Radiolarians, and somesand particles; but these foreign bodies were in too small proportion toaffect the formation as consisting practically of Diatoms alone. On the4th of February, in lat. 52°, 29' S. , long. , 71° 36" E. , a little to thenorth of the Heard Islands, the tow-net, dragging a few fathoms below thesurface, came up nearly filled with a pale yellow gelatinous mass. Thiswas found to consist entirely of Diatoms of the same species as thosefound at the bottom. By far the most abundant was the little bundle ofsilicious rods, fastened together loosely at one end, separating from oneanother at the other end, and the whole bundle loosely twisted into aspindle. The rods are hollow, and contain the characteristic endochromeof the _Diatomaceoe_. Like the _Globigerina_ ooze, then, which itsucceeds to the southward in a band apparently of no great width, thematerials of this silicious deposit are derived entirely from the surfaceand intermediate depths. It is somewhat singular that Diatoms did notappear to be in such large numbers on the surface over the Diatom ooze asthey were a little further north. This may perhaps be accounted for byour not having struck their belt of depth with the tow-net; or it ispossible that when we found it on the 11th of February the bottom depositwas really shifted a little to the south by the warm current, theexcessively fine flocculent _débris_ of the Diatoms taking a certain timeto sink. The belt of Diatom ooze is certainly a little further to thesouthward in long. 83° E. , in the path of the reflux of the Agulhascurrent, than in long. 108° E. 

"All along the edge of the ice-pack--everywhere, in fact, to the south ofthe two stations--on the 11th of February on our southward voyage, and onthe 3rd of March on our return, we brought up fine sand and grayish mud, with small pebbles of quartz and felspar, and small fragments of mica-slate, chlorite-slate, clay-slate, gneiss, and granite. This deposit, Ihave no doubt, was derived from the surface like the others, but in thiscase by the melting of icebergs and the precipitation of foreign mattercontained in the ice. 

"We never saw any trace of gravel or sand, or any material necessarilyderived from land, on an iceberg. Several showed vertical or irregularfissures filled with discoloured ice or snow; but, when looked atclosely, the discoloration proved usually to be very slight, and theeffect at a distance was usually due to the foreign material filling thefissure reflecting light less perfectly than the general surface of theberg. I conceive that the upper surface of one of these great tabularsouthern icebergs, including by far the greater part of its bulk, andculminating in the portion exposed above the surface of the sea, wasformed by the piling up of successive layers of snow during the period, amounting perhaps to several centuries, during which the ice-cap wasslowly forcing itself over the low land and out to sea over a long extentof gentle slope, until it reached a depth considerably above 200 fathoms, when the lower specific weight of the ice caused an upward strain whichat length overcame the cohesion of the mass, and portions were rent offand floated away. If this be the true history of the formation of theseicebergs, the absence of all land _débris_ in the portion exposed abovethe surface of the sea is readily understood. If any such exist, it mustbe confined to the lower part of the berg, to that part which has at onetime or other moved on the floor of the ice-cap. 

"The icebergs, when they are first dispersed, float in from 200 to 250fathoms. When, therefore, they have been drifted to latitudes of 65° or64° S. , the bottom of the berg just reaches the layer at which thetemperature of the water is distinctly rising, and it is rapidly melted, and the mud and pebbles with which it is more or less charged areprecipitated. That this precipitation takes place all over the area wherethe icebergs are breaking up, constantly, and to a considerable extent, is evident from the fact of the soundings being entirely composed of suchdeposits; for the Diatoms, _Globigerinoe_, and radiolarians are presenton the surface in large numbers; and unless the deposit from the ice wereabundant it would soon be covered and masked by a layer of the exuvia ofsurface organisms. "

The observations which have been detailed leave no doubt that theAntarctic sea bottom, from a little to the south of the fiftiethparallel, as far as 80° S. , is being covered by a fine deposit ofsilicious mud, more or less mixed, in some parts, with the ice-borne_débris_ of polar lands and with the ejections of volcanoes. Thesilicious particles which constitute this mud, are derived, in part, fromthe diatomaceous plants and radiolarian animals which throng the surface, and, in part, from the spicula of sponges which live at the bottom. Theevidence respecting the corresponding Arctic area is less complete, butit is sufficient to justify the conclusion that an essentially similarsilicious cap is being formed around the northern pole. 

There is no doubt that the constituent particles of this mud mayagglomerate into a dense rock, such as that formed at Oran on the shoresof the Mediterranean, which is made up of similar materials. Moreover, inthe case of freshwater deposits of this kind it is certain that theaction of percolating water may convert the originally soft and friable, fine-grained sandstone into a dense, semi-transparent opaline stone, thesilicious organized skeletons being dissolved, and the silex re-depositedin an amorphous state. Whether such a metamorphosis as this occurs insubmarine deposits, as well as in those formed in fresh water, does notappear; but there seems no reason to doubt that it may. And hence it maynot be hazardous to conclude that very ordinary metamorphic agencies mayconvert these polar caps into a form of quartzite. 

In the great intermediate zone, occupying some 110° of latitude, whichseparates the circumpolar Arctic and Antarctic areas of siliciousdeposit, the Diatoms and _Radiolaria_ of the surface water and thesponges of the bottom do not die out, and, so far as some forms areconcerned, do not even appear to diminish in total number; though, on arough estimate, it would appear that the proportion of _Radiolaria_ toDiatoms is much greater than in the colder seas. Nevertheless thecomposition of the deep-sea mud of this intermediate zone is entirelydifferent from that of the circumpolar regions. 

The first exact information respecting the nature of this mud at depthsgreater than 1, 000 fathoms was given by Ehrenberg, in the account whichhe published in the "Monatsberichte" of the Berlin Academy for the year1853, of the soundings obtained by Lieut. Berryman, of the United StatesNavy, in the North Atlantic, between Newfoundland and the Azores. 

Observations which confirm those of Ehrenberg in all essential respectshave been made by Professor Bailey, myself, Dr. Wallich, Dr. Carpenter, and Professor Wyville Thomson, in their earlier cruises; and thecontinuation of the _Globigerina_ ooze over the South Pacific has beenproved by the recent work of the _Challenger_, by which it is also shown, for the first time, that, in passing from the equator to high southernlatitudes, the number and variety of the _Foraminifera_ diminishes, andeven the _Globigerinoe_ become dwarfed. And this result, it will beobserved, is in entire accordance with the fact already mentioned that, in the sea of Kamschatka, the deep-sea mud was found by Bailey to containno calcareous organisms. 

Thus, in the whole of the "intermediate zone, " the silicious depositwhich is being formed there, as elsewhere, by the accumulation of sponge-spicula, _Radiolaria_, and Diatoms, is obscured and overpowered by theimmensely greater amount of calcareous sediment, which arises from theaggregation of the skeletons of dead _Foraminifera_. The similarity ofthe deposit, thus composed of a large percentage of carbonate of lime, and a small percentage of silex, to chalk, regarded merely as a kind ofrock, which was first pointed out by Ehrenberg, [5] is now admitted on allhands; nor can it be reasonably doubted, that ordinary metamorphicagencies are competent to convert the "modern chalk" into hard limestoneor even into crystalline marble. 

[Footnote 5: The following passages in Ehrenberg's memoir on _TheOrganisms in the Chalk which are still living_ (1839), are conclusive:--

"7. The dawning period of the existing living organic creation, if such aperiod is distinguishable (which is doubtful), can only be supposed tohave existed on the other side of, and below, the chalk formation; andthus, either the chalk, with its widespread and thick beds, must enterinto the series of newer formations; or some of the accepted four greatgeological periods, the quaternary, tertiary, and secondary formations, contain organisms which still live. It is more probable, in theproportion of 3 to 1, that the transition or primary period is notdifferent, but that it is only more difficult to examine and understand, by reason of the gradual and prolonged chemical decomposition andmetamorphosis of many of its organic constituents. "

"10. By the mass-forming _Infasoria_ and _Polythalamia_, secondary arenot distinguishable from tertiary formations; and, from what has beensaid, it is possible that, at this very day, rock masses are forming inthe sea, and being raised by volcanic agencies, the constitution ofwhich, on the whole, is altogether similar to that of the chalk. Thechalk remains distinguishable by its organic remains as a formation, butnot as a kind of rock. "]

Ehrenberg appears to have taken it for granted that the _Globigerinoe_and other _Foraminifera_ which are found in the deep-sea mud, live at thegreat depths in which their remains are found; and he supports thisopinion by producing evidence that the soft parts of these organisms arepreserved, and may be demonstrated by removing the calcareous matter withdilute acids. In 1857, the evidence for and against this conclusionappeared to me to be insufficient to warrant a positive conclusion oneway or the other, and I expressed myself in my report to the Admiralty onCaptain Dayman's soundings in the following terms:--

"When we consider the immense area over which this deposit is spread, thedepth at which its formation is going on, and its similarity to chalk, and still more to such rocks as the marls of Caltanisetta, the question, whence are all these organisms derived? becomes one of high scientificinterest. 

"Three answers have suggested themselves:--

"In accordance with the prevalent view of the limitation of life tocomparatively small depths, it is imagined either: 1, that theseorganisms have drifted into their present position from shallower waters;or 2, that they habitually live at the surface of the ocean, and onlyfall down into their present position. 

"1. I conceive that the first supposition is negatived by the extremelymarked zoological peculiarity of the deep-sea fauna. 

"Had the _Globigerinoe_ been drifted into their present position fromshallow water, we should find a very large proportion of thecharacteristic inhabitants of shallow waters mixed with them, and thiswould the more certainly be the case, as the large _Globigerinoe_, soabundant in the deep-sea soundings, are, in proportion to their size, more solid and massive than almost any other _Foraminifera_. But the factis that the proportion of other _Foraminifera_ is exceedingly small, norhave I found as yet, in the deep-sea deposits, any such matters asfragments of molluscous shells, of _Echini_, &c. , which abound in shallowwaters, and are quite as likely to be drifted as the heavy_Globigerinoe_. Again, the relative proportions of young and fully formed_Globigerinoe_ seem inconsistent with the notion that they have travelledfar. And it seems difficult to imagine why, had the deposit beenaccumulated in this way, _Coscinodisci_ should so almost entirelyrepresent the _Diatomaceoe_. 

"2. The second hypothesis is far more feasible, and is strongly supportedby the fact that many _Polycistineoe [Radiolaria]_ and _Coscinodisci_ arewell known to live at the surface of the ocean. Mr. Macdonald, Assistant-Surgeon of H. M. S. _Herald_, now in the South-Western Pacific, has latelysent home some very valuable observations on living forms of this kind, met with in the stomachs of oceanic mollusks, and therefore certainlyinhabitants of the superficial layer of the ocean. But it is a singularcircumstance that only one of the forms figured by Mr. Macdonald is atall like a _Globigerina_, and there are some peculiarities about eventhis which make me greatly doubt its affinity with that genus. The form, indeed, is not unlike that of a _Globigerina_, but it is provided withlong radiating processes, of which I have never seen any trace in_Globigerina_. Did they exist, they might explain what otherwise is agreat objection to this view, viz. , how is it conceivable that the heavy_Globigerina_ should maintain itself at the surface of the water?

"If the organic bodies in the deep-sea soundings have neither beendrifted, nor have fallen from above, there remains but one alternative--they must have lived and died where they are. 

"Important objections, however, at once suggest themselves to this view. How can animal life be conceived to exist under such conditions of light, temperature, pressure, and aeration as must obtain at these vast depths?

"To this one can only reply that we know for a certainty that even veryhighly-organized animals do continue to live at a depth of 300 and 400fathoms, inasmuch as they have been dredged up thence; and that thedifference in the amount of light and heat at 400 and at 2, 000 fathoms isprobably, so to speak, very far less than the difference in complexity oforganisation between these animals and the humbler _Protozoa_ and_Protophyta_ of the deep-sea soundings. 

"I confess, though as yet far from regarding it proved that the_Globigerinoe_ live at these depths, the balance of probabilities seemsto me to incline in that direction. And there is one circumstance whichweighs strongly in my mind. It may be taken as a law that any genus ofanimals which is found far back in time is capable of living under agreat variety of circumstances as regards light, temperature, andpressure. Now, the genus _Globigerina_ is abundantly represented in thecretaceous epoch, and perhaps earlier. 

"I abstain, however, at present from drawing any positive conclusions, preferring rather to await the result of more extended observations. "[6]

[Footnote 6: Appendix to Report on Deep-sea Soundings in the AtlanticOcean, by Lieut. -Commander Joseph Dayman. 1857. ]

Dr. Wallich, Professor Wyville Thomson, and Dr. Carpenter concluded thatthe _Globigerinoe_ live at the bottom. Dr. Wallich writes in 1862--"Bysinking very fine gauze nets to considerable depths, I have repeatedlysatisfied myself that _Globigerina_ does not occur in the superficialstrata of the ocean. "[7] Moreover, having obtained certain living star-fish from a depth of 1, 260 fathoms, and found their stomachs full of"fresh-looking _Globigerinoe_" and their _débris_--he adduces this factin support of his belief that the _Globigerinoe_ live at the bottom. 

[Footnote 7: The _North Atlantic Sea-bed_, p. 137. ]

On the other hand, Müller, Haeckel, Major Owen, Mr. Gwyn Jeffries, andother observers, found that _Globigerinoe_, with the allied genera_Orbulina_ and _Pulvinulina_, sometimes occur abundantly at the surfaceof the sea, the shells of these pelagic forms being not unfrequentlyprovided with the long spines noticed by Macdonald; and in 1865 and 1866, Major Owen more especially insisted on the importance of this fact. Therecent work of the _Challenger_ fully confirms Major Owen's statement. Inthe paper recently published in the proceedings of the Royal Society, [8]from which a quotation has already been made, Professor Wyville Thomsonsays:--

"I had formed and expressed a very strong opinion on the matter. Itseemed to me that the evidence was conclusive that the _Foraminifera_which formed the _Globigerina_ ooze lived on the bottom, and that theoccurrence of individuals on the surface was accidental and exceptional;but after going into the thing carefully, and considering the mass ofevidence which has been accumulated by Mr. Murray, I now admit that I wasin error; and I agree with him that it may be taken as proved that allthe materials of such deposits, with the exception, of course, of theremains of animals which we now know to live at the bottom at all depths, which occur in the deposit as foreign bodies, are derived from thesurface. 

[Footnote 8: "Preliminary Notes on the Nature of the Sea-bottom procuredby the soundings of H. M. S. _Challenger_ during her cruise in the SouthernSeas, in the early part of the year 1874. "--_Proceedings of the RoyalSociety_, Nov. 26, 1874. ]

"Mr. Murray has combined with a careful examination of the soundings aconstant use of the tow-net, usually at the surface, but also at depthsof from ten to one hundred fathoms; and he finds the closest relation toexist between the surface fauna of any particular locality and thedeposit which is taking place at the bottom. In all seas, from theequator to the polar ice, the tow-net contains _Globigerinoe_. They aremore abundant and of a larger size in warmer seas; several varieties, attaining a large size and presenting marked varietal characters, arefound in the intertropical area of the Atlantic. In the latitude ofKerguelen they are less numerous and smaller, while further south theyare still more dwarfed, and only one variety, the typical _Globigerinabulloides_, is represented. The living _Globigerinoe_ from the tow-netare singularly different in appearance from the dead shells we find atthe bottom. The shell is clear and transparent, and each of the poreswhich penetrate it is surrounded by a raised crest, the crest roundadjacent pores coalescing into a roughly hexagonal network, so that thepores appear to lie at the bottom of a hexagonal pit. At each angle ofthis hexagon the crest gives off a delicate flexible calcareous spine, which is sometimes four or five times the diameter of the shell inlength. The spines radiate symmetrically from the direction of the centreof each chamber of the shell, and the sheaves of long transparent needlescrossing one another in different directions have a very beautifuleffect. The smaller inner chambers of the shell are entirely filled withan orange-yellow granular sarcode; and the large terminal chamber usuallycontains only a small irregular mass, or two or three small masses runtogether, of the same yellow sarcode stuck against one side, theremainder of the chamber being empty. No definite arrangement and noapproach to structure was observed in the sarcode, and nodifferentiation, with the exception of round bright-yellow oil-globules, very much like those found in some of the radiolarians, which arescattered, apparently irregularly, in the sarcode. We never have beenable to detect, in any of the large number of _Globigerinoe_ which wehave examined, the least trace of pseudopodia, or any extension, in anyform, of the sarcode beyond the shell. 

 * * * * *

"In specimens taken with the tow-net the spines are very usually absent;but that is probably on account of their extreme tenuity; they are brokenoff by the slightest touch. In fresh examples from the surface, the dotsindicating the origin of the lost spines may almost always be made outwith a high power. There are never spines on the _Globigerinoe_ from thebottom, even in the shallowest water. "

There can now be no doubt, therefore, that _Globigerinoe_ live at the topof the sea; but the question may still be raised whether they do not alsolive at the bottom. In favour of this view, it has been urged that theshells of the _Globigerinoe_ of the surface never possess such thickwalls as those which are fouled at the bottom, but I confess that I doubtthe accuracy of this statement. Again, the occurrence of minute_Globigerinoe_ in all stages of development, at the greatest depths, isbrought forward as evidence that they live _in situ_. But considering theextent to which the surface organisms are devoured, withoutdiscrimination of young and old, by _Salpoe_ and the like, it is notwonderful that shells of all ages should be among the rejectamenta. Norcan the presence of the soft parts of the body in the shells which formthe _Globigerina_ ooze, and the fact, if it be one, that animals livingat the bottom use them as food, be considered as conclusive evidence thatthe _Globigerinoe_ live at the bottom. Such as die at the surface, andeven many of those which are swallowed by other animals, may retain muchof their protoplasmic matter when they reach the depths at which thetemperature sinks to 34° or 32° Fahrenheit, where decomposition mustbecome exceedingly slow. 

Another consideration appears to me to be in favour of the view that the_Globigerinoe_ and their allies are essentially surface animals. This isthe fact brought out by the _Challenger's_ work, that they have asouthern limit of distribution, which can hardly depend upon anything butthe temperature of the surface water. And it is to be remarked that thissouthern limit occurs at a lower latitude in the Antarctic seas than itdoes in the North Atlantic. According to Dr. Wallich ("The North AtlanticSea Bed, " p. 157) _Globigerina_ is the prevailing form in the depositsbetween the Faroe Islands and Iceland, and between Iceland and EastGreenland--or, in other words, in a region of the sea-bottom which liesaltogether north of the parallel of 60° N. ; while in the southern seas, the _Globigerinoe_ become dwarfed and almost disappear between 50° and55° S. On the other hand, in the sea of Kamschatka, the _Globigerinoe_have vanished in 56° N. , so that the persistence of the _Globigerina_ooze in high latitudes, in the North Atlantic, would seem to depend onthe northward curve of the isothermals peculiar to this region; and it isdifficult to understand how the formation of _Globigerina_ ooze can beaffected by this climatal peculiarity unless it be effected by surfaceanimals. 

Whatever may be the mode of life of the _Foraminifera_, to which thecalcareous element of the deep-sea "chalk" owes its existence, the factthat it is the chief and most widely spread material of the sea-bottom inthe intermediate zone, throughout both the Atlantic and Pacific Oceans, and the Indian Ocean, at depths from a few hundred to over two thousandfathoms, is established. But it is not the only extensive deposit whichis now taking place. In 1853, Count Pourtalès, an officer of the UnitedStates Coast Survey, which has done so much for scientific hydrography, observed, that the mud forming the sea-bottom at depths of one hundredand fifty fathoms, in 31° 32' N. , 79° 35' W. , off the Coast of Florida, was "a mixture, in about equal proportions, of _Globigerinoe_ and blacksand, probably greensand, as it makes a green mark when crushed onpaper. " Professor Bailey, examining these grains microscopically, foundthat they were casts of the interior cavities of _Foraminifera_, consisting of a mineral known as _Glauconite_, which is a silicate ofiron and alumina. In these casts the minutest cavities and finest tubesin the Foraminifer were sornetilnes reproduced in solid counterparts ofthe glassy mineral, while the calcareous original had been entirelydissolved away. 

Contemporaneously with these observations, the indefatigable Ehrenberghad discovered that the "greensands" of the geologist were largely madeup of casts of a similar character, and proved the existence of_Foraminifera_ at a very ancient geological epoch, by discovering suchcasts in a greensand of Lower Silurian age, which occurs near St. Petersburg. 

Subsequently, Messrs. Parker and Jones discovered similar casts inprocess of formation, the original shell not having disappeared, inspecimens of the sea-bottom of the Australian seas, brought home by thelate Professor Jukes. And the _Challenger_ has observed a deposit of asimilar character in the course of the Agulhas current, near the Cape ofGood Hope, and in some other localities not yet defined. 

It would appear that this infiltration of _Foraminifera_ shells with_Glauconite_ does not take place at great depths, but rather in what maybe termed a sublittoral region, ranging from a hundred to three hundredfathoms. It cannot be ascribed to any local cause, for it takes place, not only over large areas in the Gulf of Mexico and the Coast of Florida, but in the South Atlantic and in the Pacific. But what are the conditionswhich determine its occurrence, and whence the silex, the iron, and thealumina (with perhaps potash and some other ingredients in smallquantity) of which the _Glauconite_ is composed, proceed, is a point onwhich no light has yet been thrown. For the present we must be contentwith the fact that, in certain areas of the "intermediate zone, "greensand is replacing and representing the primitively calcareo-silicious ooze. 

The investigation of the deposits which are now being formed in the basinof the Mediterranean, by the late Professor Edward Forbes, by ProfessorWilliamson and more recently by Dr. Carpenter, and a comparison of theresults thus obtained with what is known of the surface fauna, havebrought to light the remarkable fact, that while the surface and theshallows abound with _Foraminifera_ and other calcareous shelledorganisms, the indications of life become scanty at depths beyond 500 or600 fathoms, while almost all traces of it disappear at greater depths, and at 1, 000 to 2, 000 fathoms the bottom is covered with a fine clay. 

Dr. Carpenter has discussed the significance of this remarkable fact, andhe is disposed to attribute the absence of life at great depths, partlyto the absence of any circulation of the water of the Mediterranean atsuch depths, and partly to the exhaustion of the oxygen of the water bythe organic matter contained in the fine clay, which he conceives to beformed by the finest particles of the mud brought down by the riverswhich flow into the Mediterranean. 

However this may be, the explanation thus offered of the presence of thefine mud, and of the absence of organisms which ordinarily live at thebottom, does not account for the absence of the skeletons of theorganisms which undoubtedly abound at the surface of the Mediterranean;and it would seem to have no application to the remarkable factdiscovered by the _Challenger_, that in the open Atlantic and PacificOceans, in the midst of the great intermediate zone, and thousands ofmiles away from the embouchure of any river, the sea-bottom, at depthsapproaching to and beyond 3, 000 fathoms, no longer consists of_Globigerina_ ooze, but of an excessively fine red clay. 

Professor Thomson gives the following account of this capitaldiscovery:--

"According to our present experience, the deposit of _Globigerina_ oozeis limited to water of a certain depth, the extreme limit of the purecharacteristic formation being placed at a depth of somewhere about 2, 250fathoms. Crossing from these shallower regions occupied by the ooze intodeeper soundings, we find, universally, that the calcareous formationgradually passes into, and is finally replaced by, an extremely fine pureclay, which occupies, speaking generally, all depths below 2, 500 fathoms, and consists almost entirely of a silicate of the red oxide of iron andalumina. The transition is very slow, and extends over several hundredfathoms of increasing depth; the shells gradually lose their sharpness ofoutline, and assume a kind of 'rotten' look and a brownish colour, andbecome more and more mixed with a fine amorphous red-brown powder, whichincreases steadily in proportion until the lime has almost entirelydisappeared. This brown matter is in the finest possible state ofsubdivision, so fine that when, after sifting it to separate anyorganisms it might contain, we put it into jars to settle, it remainedfor days in suspension, giving the water very much the appearance andcolour of chocolate. 

"In indicating the nature of the bottom on the charts, we came, fromexperience and without any theoretical considerations, to use three termsfor soundings in deep water. Two of these, Gl. Oz. And r. Cl. , were verydefinite, and indicated strongly-marked formations, with apparently butfew characters in common; but we frequently got soundings which we couldnot exactly call '_Globigerina_ ooze' or 'red clay, ' and before we werefully aware of the nature of these, we were in the habit of indicatingthem as 'grey ooze' (gr. Oz. ) We now recognise the 'grey ooze' as anintermediate stage between the _Globigerina_ ooze and the red clay; wefind that on one side, as it were, of an ideal line, the red claycontains more and more of the material of the calcareous ooze, while onthe other, the ooze is mixed with an increasing proportion of 'red clay. '

"Although we have met with the same phenomenon so frequently, that wewere at length able to predict the nature of the bottom from the depth ofthe soundings with absolute certainty for the Atlantic and the SouthernSea, we had, perhaps, the best opportunity of observing it in our firstsection across the Atlantic, between Teneriffe and St. Thomas. The firstfour stations on this section, at depths from 1, 525 to 2, 220 fathoms, show _Globigerina_ ooze. From the last of these, which is about 300 milesfrom Teneriffe, the depth gradually increases to 2, 740 fathoms at 500, and 2, 950 fathoms at 750 miles from Teneriffe. The bottom in these twosoundings might have been called 'grey ooze, ' for although its nature hasaltered entirely from the _Globigerina_ ooze, the red clay into which itis rapidly passing still contains a considerable admixture of carbonateof lime. 

"The depth goes on increasing to a distance of 1, 150 miles fromTeneriffe, when it reaches 3, 150 fathoms; there the clay is pure andsmooth, and contains scarcely a trace of lime. From this great depth thebottom gradually rises, and, with decreasing depth, the grey colour andthe calcareous composition of the ooze return. Three soundings in 2, 050, 1, 900, and 1, 950 fathoms on the 'Dolphin Rise' gave highly characteristicexamples of the _Globigerina_ formation. Passing from the middle plateauof the Atlantic into the western trough, with depths a little over 3, 000fathoms, the red clay returned in all its purity; and our last sounding, in 1, 420 fathoms, before reaching Sombrero, restored the _Globigerina_ooze with its peculiar associated fauna. 

"This section shows also the wide extension and the vast geologicalimportance of the red clay formation. The total distance from Teneriffeto Sombrero is about 2, 700 miles. Proceeding from east to west, we have--

About 80 miles of volcanic mud and sand, " 350 " _Globigerina_ ooze, " 1, 050 " red clay, " 330 " _Globigerina_ ooze, " 850 " red clay, " 40 " _Globigerina_ ooze;

giving a total of 1, 900 miles of red clay to 720 miles of _Globigerina_ooze. 

"The nature and origin of this vast deposit of clay is a question of thevery greatest interest; and although I think there can be no doubt thatit is in the main solved, yet some matters of detail are still involvedin difficulty. My first impression was that it might be the most minutelydivided material, the ultimate sediment produced by the disintegration ofthe land, by rivers and by the action of the sea on exposed coasts, andheld in suspension and distributed by ocean currents, and only makingitself manifest in places unoccupied by the _Globigerina_ ooze. Severalcircumstances seemed, however, to negative this mode of origin. Theformation seemed too uniform: wherever we met with it, it had the samecharacter, and it only varied in composition in containing less or morecarbonate of lime. 

"Again, the were gradually becoming more and more convinced that all theimportant elements of the _Globigerina_ ooze lived on the surface, and itseemed evident that, so long as the condition on the surface remained thesame, no alteration of contour at the bottom could possibly prevent itsaccumulation; and the surface conditions in the Mid-Atlantic were veryuniform, a moderate current of a very equal temperature passingcontinuously over elevations and depressions, and everywhere yielding tothe tow-net the ooze-forming _Foraminifera_ in the same proportion. TheMid-Atlantic swarms with pelagic _Mollusca_, and, in moderate depths, theshells of these are constantly mixed with the _Globigerina_ ooze, sometimes in number sufficient to make up a considerable portion of itsbulk. It is clear that these shells must fall in equal numbers upon thered clay, but scarcely a trace of one of them is ever brought up by thedredge on the red clay area. It might be possible to explain the absenceof shell-secreting animals living on the bottom, on the supposition thatthe nature of the deposit was injurious to them; but then the idea of acurrent sufficiently strong to sweep them away is negatived by theextreme fineness of the sediment which is being laid down; the absence ofsurface shells appears to be intelligible only on the supposition thatthey are in some way removed. 

"We conclude, therefore, that the 'red clay' is not an additionalsubstance introduced from without, and occupying certain depressedregions on account of some law regulating its deposition, but that it isproduced by the removal, by some means or other, over these areas, of thecarbonate of lime, which forms probably about 98 per cent. Of thematerial of the _Globigerina_ ooze. We can trace, indeed, everysuccessive stage in the removal of the carbonate of lime in descendingthe slope of the ridge or plateau where the _Globigerina_ ooze isforming, to the region of the clay. We find, first, that the shells ofpteropods and other surface _Mollusca_ which are constantly falling onthe bottom, are absent, or, if a few remain, they are brittle and yellow, and evidently decaying rapidly. These shells of _Mollusca_ decompose moreeasily and disappear sooner than the smaller, and apparently moredelicate, shells of rhizopods. The smaller _Foraminifera_ now give way, and are found in lessening proportion to the larger; the coccoliths firstlose their thin outer border and then disappear; and the clubs of therhabdoliths get worn out of shape, and are last seen, under a high power, as infinitely minute cylinders scattered over the field. The larger_Foraminifera_ are attacked, and instead of being vividly white anddelicately sculptured, they become brown and worn, and finally they breakup, each according to its fashion; the chamber-walls of _Globigerina_fall into wedge-shaped pieces, which quickly disappear, and a thick roughcrust breaks away from the surface of _Orbulina_, leaving a thin innersphere, at first beautifully transparent, but soon becoming opaque andcrumbling away. 

"In the meantime the proportion of the amorphous 'red clay' to thecalcareous elements of all kinds increases, until the latter disappear, with the exception of a few scattered shells of the larger_Foraminifera_, which are still found even in the most characteristicsamples of the 'red clay. '

"There seems to be no room left for doubt that the red clay isessentially the insoluble residue, the _ash_, as it were, of thecalcareous organisms which form the _Globigerina_ ooze, after thecalcareous matter has been by some means removed. An ordinary mixture ofcalcareous _Foraminifera_ with the shells of pteropods, forming a fairsample of _Globigerina_ ooze from near St. Thomas, was carefully washed, and subjected by Mr. Buchanan to the action of weak acid; and he foundthat there remained after the carbonate of lime had been removed, about 1per cent. Of a reddish mud, consisting of silica, alumina, and the redoxide of iron. This experiment has been frequently repeated withdifferent samples of _Globigerina_ ooze, and always with the result thata small proportion of a red sediment remains, which possesses all thecharacters of the red clay. "

 * * * * *

"It seems evident from the observations here recorded, that _clay_, whichwe have hitherto looked upon as essentially the product of thedisintegration of older rocks, may be, under certain circumstances, anorganic formation like chalk; that, as a matter of fact, an area on thesurface of the globe, which we have shown to be of vast extent, althoughwe are still far from having ascertained its limits, is being covered bysuch a deposit at the present day. 

"It is impossible to avoid associating such a formation with the fine, smooth, homogeneous clays and schists, poor in fossils, but showing worm-tubes and tracks, and bunches of doubtful branching things, such asOldhamia, silicious sponges, and thin-shelled peculiar shrimps. Suchformations, more or less metamorphosed, are very familiar, especially tothe student of palaeozoic geology, and they often attain a vast thickness. One is inclined, from the great resemblance between them in compositionand in the general character of the included fauna, to suspect that thesemay be organic formations, like the modern red clay of the Atlantic andSouthern Sea, accumulations of the insoluble ashes of shelled creatures. 

"The dredging in the red clay on the 13th of March was usually rich. Thebag contained examples, those with calcareous shells rather stunted, ofmost of the characteristic deep-water groups of the Southern Sea, including _Umbellularia, Euplectella, Pterocrinus, Brisinga, Ophioglypha, Pourtalesia_, and one or two _Mollusca_. This is, however, very rarelythe case. Generally the red clay is barren, or contains only a very smallnumber of forms. "

It must be admitted that it is very difficult, at present, to frame anysatisfactory explanation of the mode of origin of this singular depositof red clay. 

I cannot say that the theory put forward tentatively, and with muchreservation by Professor Thomson, that the calcareous matter is dissolvedout by the relatively fresh water of the deep currents from the Antarcticregions, appears satisfactory to me. Nor do I see my way to theacceptance of the suggestion of Dr. Carpenter, that the red clay is theresult of the decomposition of previously-formed greensand. At presentthere is no evidence that greensand casts are ever formed at greatdepths; nor has it been proved that _Glauconite_ is decomposable by theagency of water and carbonic acid. 

I think it probable that we shall have to wait some time for a sufficientexplanation of the origin of the abyssal red clay, no less than for thatof the sublittoral greensand in the intermediate zone. But the importanceof the establishment of the fact that these various deposits are beingformed in the ocean, at the present day, remains the same; whether its_rationale_ be understood or not. 

For, suppose the globe to be evenly covered with sea, to a depth say of athousand fathoms--then, whatever might be the mineral matter composingthe sea-bottom, little or no deposit would be formed upon it, theabrading and denuding action of water, at such a depth, being exceedinglyslight. 

Next, imagine sponges, _Radiolaria, Foraminifera_, and diatomaceousplants, such as those which now exist in the deep-sea, to be introduced:they would be distributed according to the same laws as at present, thesponges (and possibly some of the _Foraminifera_), covering the bottom, while other _Foraminifera_, with the _Radiolaria_ and _Diatomacea_, wouldincrease and multiply in the surface waters. In accordance with theexisting state of things, the _Radiolaria_ and Diatoms would have auniversal distribution, the latter gathering most thickly in the polarregions, while the _Foraminifera_ would be largely, if not exclusively, confined to the intermediate zone; and, as a consequence of thisdistribution, a bed of "chalk" would begin to form in the intermediatezone, while caps of silicious rock would accumulate on the circumpolarregions. 

Suppose, further, that a part of the intermediate area were raised towithin two or three hundred fathoms of the surface--for anything that weknow to the contrary, the change of level might determine thesubstitution of greensand for the "chalk"; while, on the other hand, ifpart of the same area were depressed to three thousand fathoms, thatchange might determine the substitution of a different silicate ofalumina and iron--namely, clay--for the "chalk" that would otherwise beformed. 

If the _Challenger_ hypothesis, that the red clay is the residue left bydissolved _Foraminiferous_ skeletons, is correct, then all these depositsalike would be directly, or indirectly, the product of living organisms. But just as a silicious deposit may be metamorphosed into opal orquartzite, and chalk into marble, so known metamorphic agencies maymetamorphose clay into schist, clay-slate, slate, gneiss, or evengranite. And thus, by the agency of the lowest and simplest of organisms, our imaginary globe might be covered with strata, of all the chief kindsof rock of which the known crust of the earth is composed, of indefinitethickness and extent. 

The bearing of the conclusions which are now either established, orhighly probable, respecting the origin of silicious, calcareous, andclayey rocks, and their metamorphic derivatives, upon the archaeology ofthe earth, the elucidation of which is the ultimate object of thegeologist, is of no small importance. 

A hundred years ago the singular insight of Linnaeus enabled him to saythat "fossils are not the children but the parents of rocks, "[9] and thewhole effect of the discoveries made since his time has been to compile alarger and larger commentary upon this text. It is, at present, aperfectly tenable hypothesis that all siliceous and calcareous rocks areeither directly, or indirectly, derived from material which has, at onetime or other, formed part of the organized framework of livingorganisms. Whether the same generalization may be extended to aluminousrocks, depends upon the conclusion to be drawn from the facts respectingthe red clay areas brought to light by the _Challenger_. If we accept theview taken by Wyville Thomson and his colleagues--that the red clay isthe residuum left after the calcareous matter of the _Globigerinoe_ oozehas been dissolved away--then clay is as much a product of life aslimestone, and all known derivatives of clay may have formed part ofanimal bodies. 

[Footnote 9: "Petrificata montium calcariorum non filii sed parentessunt, cum omnis calx oriatur ab animalibus. "--_Systema Naturae_, Ed. Xii. , t. Iii. , p. 154. It must be recollected that Linnaeus included silex, aswell as limestone, under the name of "calx, " and that he would probablyhave arranged Diatoms among animals, as part of "chaos. " Ehrenberg quotesanother even more pithy passage, which I have not been able to find inany edition of the _Systema_ accessible to me: "Sic lapides abanimalibus, nec vice versa. Sic runes saxei non primaevi, sed temporisfiliae. "]

So long as the _Globigerinoe_;, actually collected at the surface, havenot been demonstrated to contain the elements of clay, the _Challenger_hypothesis, as I may term it, must be accepted with reserve andprovisionally, but, at present, I cannot but think that it is moreprobable than any other suggestion which has been made. 

Accepting it provisionally, we arrive at the remarkable result that allthe chief known constituents of the crust of the earth may have formedpart of living bodies; that they may be the "ash" of protoplasm; that the"_rupes saxei_" are not only _"temporis, "_ but "_vitae filiae_"; and, consequently, that the time during which life has been active on theglobe may be indefinitely greater than the period, the commencement ofwhich is marked by the oldest known rocks, whether fossiliferous orunfossiliferous. 

And thus we are led to see where the solution of a great problem andapparent paradox of geology may lie. Satisfactory evidence now existsthat some animals in the existing world have been derived by a process ofgradual modification from pre-existing forms. It is undeniable, forexample, that the evidence in favour of the derivation of the horse fromthe later tertiary _Hipparion_, and that of the _Hipparion_ from_Anchitherium_, is as complete and cogent as such evidence can reasonablybe expected to be; and the further investigations into the history of thetertiary mammalia are pushed, the greater is the accumulation of evidencehaving the same tendency. So far from palaeontology lending no support tothe doctrine of evolution--as one sees constantly asserted--thatdoctrine, if it had no other support, would have been irresistibly forcedupon us by the palaeontological discoveries of the last twenty years. 

If, however, the diverse forms of life which now exist have been producedby the modification of previously-existing less divergent forms, therecent and extinct species, taken as a whole, must fall into series whichmust converge as we go back in time. Hence, if the period represented bythe rocks is greater than, or co-extensive with, that during which lifehas existed, we ought, somewhere among the ancient formations, to arriveat the point to which all these series converge, or from which, in otherwords, they have diverged--the primitive undifferentiated protoplasmicliving things, whence the two great series of plants and animals havetaken their departure. 

But, as a matter of fact, the amount of convergence of series, inrelation to the time occupied by the deposition of geological formations, is extraordinarily small. Of all animals the higher _Vertebrata_ are themost complex; and among these the carnivores and hoofed animals(_Ungulata_) are highly differentiated. Nevertheless, although thedifferent lines of modification of the _Carnivora_ and those of the_Ungulata_, respectively, approach one another, and, although each groupis represented by less differentiated forms in the older tertiary rocksthan at the present day, the oldest tertiary rocks do not bring us nearthe primitive form of either. If, in the same way, the convergence of thevaried forms of reptiles is measured against the time during which theirremains are preserved--which is represented by the whole of the tertiaryand mesozoic formations--the amount of that convergence is far smallerthan that of the lines of mammals between the present time and thebeginning of the tertiary epoch. And it is a broad fact that, the lowerwe go in the scale of organization, the fewer signs are there ofconvergence towards the primitive form from whence all must havediverged, if evolution be a fact. Nevertheless, that it is a fact in somecases, is proved, and I, for one, have not the courage to suppose thatthe mode in which some species have taken their origin is different fromthat in which the rest have originated. 

What, then, has become of all the marine animals which, on the hypothesisof evolution, must have existed in myriads in those seas, wherein themany thousand feet of Cambrian and Laurentian rocks now devoid, or almostdevoid, of any trace of life were deposited?

Sir Charles Lyell long ago suggested that the azoic character of theseancient formations might be due to the fact that they had undergoneextensive metamorphosis; and readers of the "Principles of Geology" willbe familiar with the ingenious manner in which he contrasts the theory ofthe Gnome, who is acquainted only with the interior of the earth, withthose of ordinary philosophers, who know only its exterior. 

The metamorphism contemplated by the great modern champion of rationalgeology is, mainly, that brought about by the exposure of rocks tosubterranean heat; and where no such heat could be shown to haveoperated, his opponents assumed that no metamorphosis could have takenplace. But the formation of greensand, and still more that of the "redclay" (if the _Challenger_ hypothesis be correct) affords an insight intoa new kind of metamorphosis--not igneous, but aqueous--by which theprimitive nature of a deposit may be masked as completely as it can be bythe agency of heat. And, as Wyville Thomson suggests, in the passage Ihave quoted above (p. 17), it further enables us to assign a new causefor the occurrence, so puzzling hitherto, of thousands of feet ofunfossiliferous fine-grained schists and slates, in the midst offormations deposited in seas which certainly abounded in life. If thegreat deposit of "red clay" now forming in the eastern valley of theAtlantic were metamorphosed into slate and then upheaved, it wouldconstitute an "azoic" rock of enormous extent. And yet that rock is nowforming in the midst of a sea which swarms with living beings, the greatmajority of which are provided with calcareous or silicious shells andskeletons; and, therefore, are such as, up to this time, we should havetermed eminently preservable. 

Thus the discoveries made by the _Challenger_ expedition, like all recentadvances in our knowledge of the phenomena of biology, or of the changesnow being effected in the structure of the surface of the earth, are inaccordance with and lend strong support to, that doctrine ofUniformitarianism, which, fifty years ago, was held only by a smallminority of English geologists--Lyell, Scrope, and De la Beche--but now, thanks to the long-continued labours of the first two, and mainly tothose of Sir Charles Lyell, has gradually passed from the position of aheresy to that of catholic doctrine. 

Applied within the limits of the time registered by the known fraction ofthe crust of the earth, I believe that uniformitarianism is unassailable. The evidence that, in the enormous lapse of time between the depositionof the lowest Laurentian strata and the present day, the forces whichhave modified the surface of the crust of the earth were different inkind, or greater in the intensity of their action, than those which arenow occupied in the same work, has yet to be produced. Such evidence aswe possess all tends in the contrary direction, and is in favour of thesame slow and gradual changes occurring then as now. 

But this conclusion in nowise conflicts with the deductions of thephysicist from his no less clear and certain data. It may be certain thatthis globe has cooled down from a condition in which life could not haveexisted; it may be certain that, in so cooling, its contracting crustmust have undergone sudden convulsions, which were to our earthquakes asan earthquake is to the vibration caused by the periodical eruption of aGeyser; but in that case, the earth must, like other respectable parents, have sowed her wild oats, and got through her turbulent youth, before we, her children, have any knowledge of her. 

So far as the evidence afforded by the superficial crust of the earthgoes, the modern geologist can, _ex animo_, repeat the saying of Hutton, "We find no vestige of a beginning--no prospect of an end. " However, hewill add, with Hutton, "But in thus tracing back the natural operationswhich have succeeded each other, and mark to us the course of time past, we come to a period in which we cannot see any further. " And if he seekto peer into the darkness of this period, he will welcome the lightproffered by physics and mathematics. 

IV

YEAST

[1871]

It has been known, from time immemorial, that the sweet liquids which maybe obtained by expressing the juices of the fruits and stems of variousplants, or by steeping malted barley in hot water, or by mixing honeywith water--are liable to undergo a series of very singular changes, iffreely exposed to the air and left to themselves, in warm weather. However clear and pellucid the liquid may have been when first prepared, however carefully it may have been freed, by straining and filtration, from even the finest visible impurities, it will not remain clear. Aftera time it will become cloudy and turbid; little bubbles will be seenrising to the surface, and their abundance will increase until the liquidhisses as if it were simmering on the fire. By degrees, some of the solidparticles which produce the turbidity of the liquid collect at itssurface into a scum, which is blown up by the emerging air-bubbles into athick, foamy froth. Another moiety sinks to the bottom, and accumulatesas a muddy sediment, or "lees. "

When this action has continued, with more or less violence, for a certaintime, it gradually moderates. The evolution of bubbles slackens, andfinally comes to an end; scum and lees alike settle at the bottom, andthe fluid is once more clear and transparent. But it has acquiredproperties of which no trace existed in the original liquid. Instead ofbeing a mere sweet fluid, mainly composed of sugar and water, the sugarhas more or less completely disappeared; and it has acquired thatpeculiar smell and taste which we call "spirituous. " Instead of beingdevoid of any obvious effect upon the animal economy, it has becomepossessed of a very wonderful influence on the nervous system; so that insmall doses it exhilarates, while in larger it stupefies, and may evendestroy life. 

Moreover, if the original fluid is put into a still, and heatedmoderately, the first and last product of its distillation is simplewater; while, when the altered fluid is subjected to the same process, the matter which is first condensed in the receiver is found to be aclear, volatile substance, which is lighter than water, has a pungenttaste and smell, possesses the intoxicating powers of the fluid in aneminent degree, and takes fire the moment it is brought in contact with aflame. The Alchemists called this volatile liquid, which they obtainedfrom wine, "spirits of wine, " just as they called hydrochloric acid"spirits of salt, " and as we, to this day, call refined turpentine"spirits of turpentine. " As the "spiritus, " or breath, of a man wasthought to be the most refined and subtle part of him, the intelligentessence of man was also conceived as a sort of breath, or spirit; and, byanalogy, the most refined essence of anything was called its "spirit. "And thus it has come about that we use the same word for the soul of manand for a glass of gin. 

At the present day, however, we even more commonly use another name forthis peculiar liquid--namely, "alcohol, " and its origin is not lesssingular. The Dutch physician, Van Helmont, lived in the latter part ofthe sixteenth and the beginning of the seventeenth century--in thetransition period between alchemy and chemistry--and was rather morealchemist than chemist. Appended to his "Opera Omnia, " published in 1707, there is a very needful "Clavis ad obscuriorum sensum referendum, " inwhich the following passage occurs. --

"ALCOHOL. --Chymicis est liquor aut pulvis summé subtilisatus, vocabuloOrientalibus quoque, cum primis Habessinis, familiari, quibus _cohol_speciatim pulverem impalpabilem ex antimonio pro oculis tingendis denotat... Hodie autem, ob analogiam, quivis pulvis tenerior ut pulvis oculorumcancri summé subtilisatus _alcohol_ audit, haud aliter ac spiritusrectificatissimi _alcolisati_ dicuntur. "

Similarly, Robert Boyle speaks of a fine powder as "alcohol"; and, solate as the middle of the last century, the English lexicographer, NathanBailey, defines "alcohol" as "the pure substance of anything separatedfrom the more gross, a very fine and impalpable powder, or a very pure, well-rectified spirit. " But, by the time of the publication ofLavoisier's "Traité Elémentaire de Chimie, " in 1789, the term "alcohol, ""alkohol, " or "alkool" (for it is spelt in all three ways), which VanHelmont had applied primarily to a fine powder, and only secondarily tospirits of wine, had lost its primary meaning altogether; and, from theend of the last century until now, it has, I believe, been usedexclusively as the denotation of spirits of wine, and bodies chemicallyallied to that substance. 

The process which gives rise to alcohol in a saccharine fluid is knowntones as "fermentation"; a term based upon the apparent boiling up or"effervescence" of the fermenting liquid, and of Latin origin. 

Our Teutonic cousins call the same process "gähren, " "gäsen, " "göschen, "and "gischen"; but, oddly enough, we do not seem to have retained theirverb or their substantive denoting the action itself, though we do usenames identical with, or plainly derived from, theirs for the scum andlees. These are called, in Low German, "gäscht" and "gischt"; in Anglo-Saxon, "gest, " "gist, " and "yst, " whence our "yeast. " Again, in LowGerman and in Anglo-Saxon there is another name for yeast, having theform "barm, " or "beorm"; and, in the Midland Counties, "barm" is the nameby which yeast is still best known. In High German, there is a third namefor yeast, "hefe, " which is not represented in English, so far as I know. 

All these words are said by philologers to be derived from rootsexpressive of the intestine motion of a fermenting substance. Thus "hefe"is derived from "heben, " to raise; "barm" from "beren" or "bären, " tobear up; "yeast, " "yst, " and "gist, " have all to do with seething andfoam, with "yeasty" waves, and "gusty" breezes. 

The same reference to the swelling up of the fermenting substance is seenin the Gallo-Latin terms "levure" and "leaven. "

It is highly creditable to the ingenuity of our ancestors that thepeculiar property of fermented liquids, in virtue of which they "makeglad the heart of man, " seems to have been known in the remotest periodsof which we have any record. All savages take to alcoholic fluids as ifthey were to the manner born. Our Vedic forefathers intoxicatedthemselves with the juice of the "soma"; Noah, by a not unnaturalreaction against a superfluity of water, appears to have taken theearliest practicable opportunity of qualifying that which he was obligedto drink; and the ghosts of the ancient Egyptians were solaced bypictures of banquets in which the wine-cup passes round, graven on thewalls of their tombs. A knowledge of the process of fermentation, therefore, was in all probability possessed by the prehistoricpopulations of the globe; and it must have become a matter of greatinterest even to primaeval wine-bibbers to study the methods by whichfermented liquids could be surely manufactured. No doubt it was soondiscovered that the most certain, as well as the most expeditious, way ofmaking a sweet juice ferment was to add to it a little of the scum, orlees, of another fermenting juice. And it can hardly be questioned thatthis singular excitation of fermentation in one fluid, by a sort ofinfection, or inoculation, of a little ferment taken from some otherfluid, together with the strange swelling, foaming, and hissing of thefermented substance, must have always attracted attention from the morethoughtful. Nevertheless, the commencement of the scientific analysis ofthe phenomena dates from a period not earlier than the first half of theseventeenth century. 

At this time, Van Helmont made a first step, by pointing out that thepeculiar hissing and bubbling of a fermented liquid is due, not to theevolution of common air (which he, as the inventor of the term "gas, "calls "gas ventosum"), but to that of a peculiar kind of air such as isoccasionally met with in caves, mines, and wells, and which he calls "gassylvestre. "

But a century elapsed before the nature of this "gas sylvestre, " or, asit was afterwards called, "fixed air, " was clearly determined, and it wasfound to be identical with that deadly "choke-damp" by which the lives ofthose who descend into old wells, or mines, or brewers' vats, aresometimes suddenly ended; and with the poisonous aëriform fluid which isproduced by the combustion of charcoal, and now goes by the name ofcarbonic acid gas. 

During the same time it gradually became evident that the presence ofsugar was essential to the production of alcohol and the evolution ofcarbonic acid gas, which are the two great and conspicuous products offermentation. And finally, in 1787, the Italian chemist, Fabroni, madethe capital discovery that the yeast ferment, the presence of which isnecessary to fermentation, is what he termed a "vegeto-animal" substance;that is, a body which gives of ammoniacal salts when it is burned, andis, in other ways, similar to the gluten of plants and the albumen andcasein of animals. 

These discoveries prepared the way for the illustrious Frenchman, Lavoisier, who first approached the problem of fermentation with acomplete conception of the nature of the work to be done. The words inwhich he expresses this conception, in the treatise on elementarychemistry to which reference has already been made, mark the year 1789 asthe commencement of a revolution of not less moment in the world ofscience than that which simultaneously burst over the political world, and soon engulfed Lavoisier himself in one of its mad eddies. 

"We may lay it down as an incontestable axiom that, in all the operationsof art and nature, nothing is created; an equal quantity of matter existsboth before, and after the experiment: the quality and quantity of theelements remain precisely the same, and nothing takes place beyondchanges and modifications in the combinations of these elements. Uponthis principle the whole art of performing chemical experiments depends;we must always suppose an exact equality between the elements of the bodyexamined and those of the products of its analysis. 

"Hence, since from must of grapes we procure alcohol and carbonic acid, Ihave an undoubted right to suppose that must consists of carbonic acidand alcohol. From these premisses we have two modes of ascertaining whatpasses during vinous fermentation: either by determining the nature of, and the elements which compose, the fermentable substances; or byaccurately examining the products resulting from fermentation; and it isevident that the knowledge of either of these must lead to accurateconclusions concerning the nature and composition of the other. Fromthese considerations it became necessary accurately to determine theconstituent elements of the fermentable substances; and for this purposeI did not make use of the compound juices of fruits, the rigorousanalysis of which is perhaps impossible, but made choice of sugar, whichis easily analysed, and the nature of which I have already explained. This substance is a true vegetable oxyd, with two bases, composed ofhydrogen and carbon, brought to the state of an oxyd by means of acertain proportion of oxygen; and these three elements are combined insuch a way that a very slight force is sufficient to destroy theequilibrium of their connection. "

After giving the details of his analysis of sugar and of the products offermentation, Lavoisier continues:--

"The effect of the vinous fermentation upon sugar is thus reduced to themere separation of its elements into two portions; one part is oxygenatedat the expense of the other, so as to form carbonic acid; while the otherpart, being disoxygenated in favour of the latter, is converted into thecombustible substance called alkohol; therefore, if it were possible tore-unite alkohol and carbonic acid together, we ought to form sugar. "[1]

[Footnote 1: _Elements of Chemistry_. By M. Lavoisier. Translated byRobert Kerr. Second Edition, 1793 (pp. 186-196). ]

Thus Lavoisier thought he had demonstrated that the carbonic acid and thealcohol which are produced by the process of fermentation, are equal inweight to the sugar which disappears; but the application of the morerefined methods of modern chemistry to the investigation of the productsof fermentation by Pasteur, in 1860, proved that this is not exactlytrue, and that there is a deficit of from 5 to 7 per cent of the sugarwhich is not covered by the alcohol and carbonic acid evolved. Thegreater part of this deficit is accounted for by the discovery of twosubstances, glycerine and succinic acid, of the existence of whichLavoisier was unaware, in the fermented liquid. But about 1-1/2 per cent. Still remains to be made good. According to Pasteur, it has beenappropriated by the yeast, but the fact that such appropriation takesplace cannot be said to be actually proved. 

However this may be, there can be no doubt that the constituent elementsof fully 98 per cent. Of the sugar which has vanished during fermentationhave simply undergone rearrangement; like the soldiers of a brigade, whoat the word of command divide themselves into the independent regimentsto which they belong. The brigade is sugar, the regiments are carbonicacid, succinic acid, alcohol, and glycerine. 

From the time of Fabroni, onwards, it has been admitted that the agent bywhich this surprising rearrangement of the particles of the sugar iseffected is the yeast. But the first thoroughly conclusive evidence ofthe necessity of yeast for the fermentation of sugar was furnished byAppert, whose method of preserving perishable articles of food excited somuch attention in France at the beginning of this century. Gay-Lussac, inhis "Mémoire sur la Fermentation, "[2] alludes to Appert's method ofpreserving beer-wort unfermented for an indefinite time, by simplyboiling the wort and closing the vessel in which the boiling fluid iscontained, in such a way as thoroughly to exclude air; and he shows that, if a little yeast be introduced into such wort, after it has cooled, thewort at once begins to ferment, even though every precaution be taken toexclude air. And this statement has since received full confirmation fromPasteur. 

[Footnote 2: _Annales de Chimie_, 1810. ]

On the other hand, Schwann, Schroeder and Dutch, and Pasteur, have amplyproved that air may be allowed to have free access to beer-wort, withoutexciting fermentation, if only efficient precautions are taken to preventthe entry of particles of yeast along with the air. 

Thus, the truth that the fermentation of a simple solution of sugar inwater depends upon the presence of yeast, rests upon an unassailablefoundation; and the inquiry into the exact nature of the substance whichpossesses such a wonderful chemical influence becomes profoundlyinteresting. 

The first step towards the solution of this problem was made twocenturies ago by the patient and painstaking Dutch naturalist, Leeuwenhoek, who in the year 1680 wrote thus:--

"Saepissime examinavi fermnentum cerevisiae, semperque hoc ex globulis permateriam pellucidam fluitantibus, quarm cerevisiam esse censui, constareobservavi: vidi etiam evidentissime, unumquemque hujus fermenti globulumdenuo ex sex distinctis globulis constare, accurate eidem quantitate etformae, cui globulis sanguinis nostri, respondentibus. 

"Verum talis mihi de horum origine et formatione conceptus formabam;globulis nempe ex quibus farina Tritici, Hordei, Avenae, Fagotritici, seconstat aquae calore dissolvi et aquae commisceri; hac, vero aqua, quamcerevisiam vocare licet, refrigescente, multos ex minimis particulis incerevisia coadunari, et hoc pacto efficere particulam sive globulum, quaesexta pars est globuli faecis, et iterum sex ex hisce globulisconjungi. "[3]

[Footnote 3: Leeuwenhoek, _Arcana Naturae Detecta. _ Ed. Nov. , 1721. ]

Thus Leeuwenhoek discovered that yeast consists of globules floating in afluid; but he thought that they were merely the starchy particles of thegrain from which the wort was made, rearranged. He discovered the factthat yeast had a definite structure, but not the meaning of the fact. Acentury and a half elapsed, and the investigation of yeast wasrecommenced almost simultaneously by Cagniard de la Tour in France, andby Schwann and Kützing in Germany. The French observer was the first topublish his results; and the subject received at his hands and at thoseof his colleague, the botanist Turpin, full and satisfactoryinvestigation. 

The main conclusions at which they arrived are these. The globular, oroval, corpuscles which float so thickly in the yeast as to make it muddy, though the largest are not more than one two-thousandth of an inch indiameter, and the smallest may measure less than one seven-thousandth ofan inch, are living organisms. They multiply with great rapidity bygiving off minute buds, which soon attain the size of their parent, andthen either become detached or remain united, forming the compoundglobules of which Leeuwenhoek speaks, though the constancy of theirarrangement in sixes existed only in the worthy Dutchman's imagination. 

It was very soon made out that these yeast organisms, to which Turpingave the name of _Torula cerevisioe_, were more nearly allied to thelower Fungi than to anything else. Indeed Turpin, and subsequentlyBerkeley and Hoffmann, believed that they had traced the development ofthe _Torula_ into the well-known and very common mould--the _Penicilliumglaucum_. Other observers have not succeeded in verifying thesestatements; and my own observations lead me to believe, that while theconnection between _Torula_ and the moulds is a very close one, it is ofa different nature from that which has been supposed. I have never beenable to trace the development of _Torula_ into a true mould; but it isquite easy to prove that species of true mould, such as _Penicillium_, when sown in an appropriate nidus, such as a solution of tartrate ofammonia and yeast-ash, in water, with or without sugar, give rise to_Toruloe_, similar in all respects to _T. Cerevisioe_, except that theyare, on the average, smaller. Moreover, Bail has observed the developmentof a _Torula_ larger than _T. Cerevisioe_, from a _Mucor_, a mould alliedto _Penicillium_. 

It follows, therefore, that the _Toruloe_, or organisms of yeast, areveritable plants; and conclusive experiments have proved that the powerwhich causes the rearrangement of the molecules of the sugar isintimately connected with the life and growth of the plant. In fact, whatever arrests the vital activity of the plant also prevents it fromexciting fermentation. 

Such being the facts with regard to the nature of yeast, and the changeswhich it effects in sugar, how are they to be accounted for? Beforemodern chemistry had come into existence, Stahl, stumbling, with thestride of genius, upon the conception which lies at the bottom of allmodern views of the process, put forward the notion that the ferment, being in a state of internal motion, communicated that motion to thesugar, and thus caused its resolution into new substances. And Lavoisier, as we have seen, adopts substantially the same view. But Fabroni, full ofthe then novel conception of acids and bases and double decompositions, propounded the hypothesis that sugar is an oxide with two bases, and theferment a carbonate with two bases; that the carbon of the ferment uniteswith the oxygen of the sugar, and gives rise to carbonic acid; while thesugar, uniting with the nitrogen of the ferment, produces a new substanceanalogous to opium. This is decomposed by distillation, and gives rise toalcohol. Next, in 1803, Thénard propounded a hypothesis which partakessomewhat of the nature of both Stahl's and Fabroni's views. "I do notbelieve with Lavoisier, " he says, "that all the carbonic acid formedproceeds from the sugar. How, in that case, could we conceive the actionof the ferment on it? I think that the first portions of the acid are dueto a combination of the carbon of the ferment with the oxygen of thesugar, and that it is by carrying off a portion of oxygen from the lastthat the ferment causes the fermentation to commence--the equilibriumbetween the principles of the sugar being disturbed, they combine afreshto form carbonic acid and alcohol. "

The three views here before us may be familiarly exemplified by supposingthe sugar to be a card-house. According to Stahl, the ferment is somebodywho knocks the table, and shakes the card-house down; according toFabroni, the ferment takes out some cards, but puts others in theirplaces; according to Thénard, the ferment simply takes a card out of thebottom story, the result of which is that all the others fall. 

As chemistry advanced, facts came to light which put a new face uponStahl's hypothesis, and gave it a safer foundation than it previouslypossessed. The general nature of these phenomena may be thus stated:--Abody, A, without giving to, or taking from, another body B, any materialparticles, causes B to decompose into other substances, C, D, E, the sumof the weights of which is equal to the weight of B, which decomposes. Thus, bitter almonds contain two substances, amygdalin and synaptase, which can be extracted, in a separate state, from the bitter almonds. Theamygdalin thus obtained, if dissolved in water, undergoes no change; butif a little synaptase be added to the solution, the amygdalin splits upinto bitter almond oil, prussic acid, and a kind of sugar. 

A short time after Cagniard de la Tour discovered the yeast plant, Liebig, struck with the similarity between this and other such processesand the fermentation of sugar, put forward the hypothesis that yeastcontains a substance which acts upon sugar, as synaptase acts uponamygdalin. And as the synaptase is certainly neither organized nor alive, but a mere chemical substance, Liebig treated Cagniard de la Tour'sdiscovery with no small contempt, and, from that time to the present, hassteadily repudiated the notion that the decomposition of the sugar is, inany sense, the result of the vital activity of the _Torula_. But, thoughthe notion that the _Torula_ is a creature which eats sugar and excretescarbonic acid and alcohol, which is not unjustly ridiculed in the mostsurprising paper that ever made its appearance in a grave scientificjournal, [4] may be untenable, the fact that the _Toruloe_ are alive, andthat yeast does not excite fermentation unless it contains living_Toruloe_, stands fast. Moreover, of late years, the essentialparticipation of living organisms in fermentation other than thealcoholic, has been clearly made out by Pasteur and other chemists. 

[Footnote 4: "Das enträthselte Geheimniss der geistigen Gährung(Vorlänfige briefliche Mittheilung)" is the title of an anonymouscontribution to Wöhler and Liebig's _Annalen der Pharmacie_ for 1839, inwhich a somewhat Rabelaisian imaginary description of the organisation ofthe "yeast animals" and of the manner in which their functions areperformed, is given with a circumstantiality worthy of the author of_Gulliver's Travels_. As a specimen of the writer's humour, his accountof what happens when fermentation comes to an end may suffice. "Sobaldnämlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sichgegenseitig selbst auf, was durch eine eigene Manipulation geschieht;alles wird verdant bis auf die Eier, welche unverändert durch denDarmkanal hineingehen; man hat zuletzt wieder gährungsfähige Hefe, nämlich den Saamen der Thiere, der übrig bleibt. "] However, it may beasked, is there any necessary opposition between the so-called "vital"and the strictly physico-chemical views of fermentation? It is quitepossible that the living _Torula_ may excite fermentation in sugar, because it constantly produces, as an essential part of its vitalmanifestations, some substance which acts upon the sugar, just as thesynaptase acts upon the amygdalin. Or it may be, that, without theformation of any such special substance, the physical condition of theliving tissue of the yeast plant is sufficient to effect that smalldisturbance of the equilibrium of the particles of the sugar, whichLavoisier thought sufficient to effect its decomposition. 

Platinum in a very fine state of division--known as platinum black, or_noir de platine_--has the very singular property of causing alcohol tochange into acetic acid with great rapidity. The vinegar plant, which isclosely allied to the yeast plant, has a similar effect upon dilutealcohol, causing it to absorb the oxygen of the air, and become convertedinto vinegar; and Liebig's eminent opponent, Pasteur, who has done somuch for the theory and the practice of vinegar-making, himself suggeststhat in this case--

"La cause du phénomène physique qui accompagne la vie de la plante résidedans un état physique propre, analogue à celui du noir de platine. Maisil est essentiel de remarquer que cet état physique de la plante estétroitement lié avec la vie de cette plante. "[5]

[Footnote 5: _Etudes sur les Mycodermes_, Comptes-Rendus, liv. , 1862. ]

Now, if the vinegar plant gives rise to the oxidation of alcohol, onaccount of its merely physical constitution, it is at any rate possiblethat the physical constitution of the yeast plant may exert a decomposinginfluence on sugar. 

But, without presuming to discuss a question which leads us into the veryarcana of chemistry, the present state of speculation upon the _modusoperandi_ of the yeast plant in producing fermentation is represented, onthe one hand, by the Stahlian doctrine, supported by Liebig, according towhich the atoms of the sugar are shaken into new combinations eitherdirectly by the _Toruloe_, or indirectly, by some substance formed bythem; and, on the other hand, by the Thénardian doctrine, supported byPasteur, according to which the yeast plant assimilates part of thesugar, and, in so doing, disturbs the rest, and determines its resolutioninto the products of fermentation. Perhaps the two views are not so muchopposed as they seem at first sight to be. 

But the interest which attaches to the influence of the yeast plants uponthe medium in which they live and grow does not arise solely from itsbearing upon the theory of fermentation. So long ago as 1838, Turpincompared the _Toruloe_ to the ultimate elements of the tissues of animalsand plants--"Les organes élémentaires de leurs tissus, comparables auxpetits végétaux des levures ordinaires, sont aussi les décompositeurs dessubstances qui les environnent. "

Almost at the same time, and, probably, equally guided by his study ofyeast, Schwann was engaged in those remarkable investigations into theform and development of the ultimate structural elements of the tissuesof animals, which led him to recognise their fundamental identity withthe ultimate structural elements of vegetable organisms. 

The yeast plant is a mere sac, or "cell, " containing a semi-fluid matter, and Schwann's microscopic analysis resolved all living organisms, in thelong run, into an aggregation of such sacs or cells, variously modified;and tended to show, that all, whatever their ultimate complication, begintheir existence in the condition of such simple cells. 

In his famous "Mikroskopische Untersuchungen" Schwann speaks of _Torula_as a "cell"; and, in a remarkable note to the passage in which he refersto the yeast plant, Schwann says:--

"I have been unable to avoid mentioning fermentation, because it is themost fully and exactly known operation of cells, and represents, in thesimplest fashion, the process which is repeated by every cell of theliving body. "

In other words, Schwann conceives that every cell of the living bodyexerts an influence on the matter which surrounds and permeates it, analogous to that which a _Torula_ exerts on the saccharine solution bywhich it is bathed. A wonderfully suggestive thought, opening up views ofthe nature of the chemical processes of the living body, which havehardly yet received all the development of which they are capable. 

Kant defined the special peculiarity of the living body to be that theparts exist for the sake of the whole and the whole for the sake of theparts. But when Turpin and Schwann resolved the living body into anaggregation of quasi-independent cells, each, like a _Torula_, leadingits own life and having its own laws of growth and development, theaggregation being dominated and kept working towards a definite end onlyby a certain harmony among these units, or by the superaddition of acontrolling apparatus, such as a nervous system, this conception ceasedto be tenable. The cell lives for its own sake, as well as for the sakeof the whole organism; and the cells which float in the blood, live atits expense, and profoundly modify it, are almost as much independentorganisms as the _Toruloe_ which float in beer-wort. 

Schwann burdened his enunciation of the "cell theory" with two falsesuppositions; the one, that the structures he called "nucleus"[6] and"cell-wall" are essential to a cell; the other, that cells are usuallyformed independently of other cells; but, in 1839, it was a vast andclear gain to arrive at the conception, that the vital functions of allthe higher animals and plants are the resultant of the forces inherent inthe innumerable minute cells of which they are composed, and that each ofthem is, itself, an equivalent of one of the lowest and simplest ofindependent living beings--the _Torula_. 

[Footnote 6: Later investigations have thrown an entirely new light uponthe structure and the functional importance of the nucleus; and haveproved that Schwann did not over-estimate its importance. 1894. ]

From purely morphological investigations, Turpin and Schwann, as we haveseen, arrived at the notion of the fundamental unity of structure ofliving beings. And, before long, the researches of chemists gradually ledup to the conception of the fundamental unity of their composition. 

So far back as 1803, Thénard pointed out, in most distinct terms, theimportant fact that yeast contains a nitrogenous "animal" substance; andthat such a substance is contained in all ferments. Before him, Fabroniand Fourcroy speak of the "vegeto-animal" matter of yeast. In 1844 Mulderendeavoured to demonstrate that a peculiar substance, which he called"protein, " was essentially characteristic of living matter. 

In 1846, Payen writes:--

"Enfin, une loi sans exception me semble apparaître dans les faitsnombreux que j'ai observés et conduire à envisager sous un nouveau jourla vie végétale; si je ne m'abuse, tout ce que dans les tissus végétauxla vue directe où amplifiée nous permet de discerner sous la forme decellules et de vaisseaux, ne représente autre chose que les enveloppesprotectrices, les réservoirs et les conduits, à l'aide desquels les corpsanimés qui les secrètent et les façonnent, se logent, puisent etcharrient leurs aliments, déposent et isolent les matières excrétées. "

And again:--

"Afin de compléter aujourd'hui l'énoncé du fait général, je rappelleraique les corps, doué des fonctions accomplies dans les tissus des plantes, sont formés des éléments qui constituent, en proportion peu variable, lesorganismes animaux; qu'ainsi l'on est conduit à reconnaître une immenseunité de composition élémentaire dans tous les corps vivants de lanature. "[7]

[Footnote 7: Mém. Sur les Développements des Végétaux, &c. --_Mém. Présentées_. Ix. 1846. ]

In the year (1846) in which these remarkable passages were published, theeminent German botanist, Von Mohl invented the word "protoplasm, " as aname for one portion of those nitrogenous contents of the cells of livingplants, the close chemical resemblance of which to the essentialconstituents of living animals is so strongly indicated by Payen. Andthrough the twenty-five years that have passed, since the matter of lifewas first called protoplasm, a host of investigators, among whom Cohn, Max Schulze, and Kühne must be named as leaders, have accumulatedevidence, morphological, physiological, and chemical, in favour of that"immense unité de composition élémentaire dans tous les corps vivants dela nature, " into which Payen had, so early, a clear insight. 

As far back as 1850, Cohn wrote, apparently without any knowledge of whatPayen had said before him:--

"The protoplasm of the botanist, and the contractile substance andsarcode of the zoologist, must be, if not identical, yet in a high degreeanalogous substances. Hence, from this point of view, the differencebetween animals and plants consists in this; that, in the latter, thecontractile substance, as a primordial utricle, is enclosed within aninert cellulose membrane, which permits it only to exhibit an internalmotion, expressed by the phenomena of rotation and circulation, while, inthe former, it is not so enclosed. The protoplasm in the form of theprimordial utricle is, as it were, the animal element in the plant, butwhich is imprisoned, and only becomes free in the animal; or, to stripoff the metaphor which obscures simple thought, the energy of organicvitality which is manifested in movement is especially exhibited by anitrogenous contractile substance, which in plants is limited andfettered by an inert membrane, in animals not so. "[8]

[Footnote 8: Cohn, "Ueber Protococcus pluvialis, " in the _Nova Acta_ for1850. ]

In 1868, thinking that an untechnical statement of the views currentamong the leaders of biological science might be interesting to thegeneral public, I gave a lecture embodying them in Edinburgh. Those whohave not made the mistake of attempting to approach biology, either bythe high _à priori_ road of mere philosophical speculation, or by themere low _à posteriori_ lane offered by the tube of a microscope, buthave taken the trouble to become acquainted with well-ascertained factsand with their history, will not need to be told that in what I had tosay "as regards protoplasm" in my lecture "On the Physical Basis of Life"(Vol. I. Of these Essays, p. 130), there was nothing new; and, as I hope, nothing that the present state of knowledge does not justify us inbelieving to be true. Under these circumstances, my surprise may beimagined, when I found, that the mere statement of facts and of views, long familiar to me as part of the common scientific property ofContinental workers, raised a sort of storm in this country, not only byexciting the wrath of unscientific persons whose pet prejudices theyseemed to touch, but by giving rise to quite superfluous explosions onthe part of some who should have been better informed. 

Dr. Stirling, for example, made my essay the subject of a specialcritical lecture, [9] which I have read with much interest, though, Iconfess, the meaning of much of it remains as dark to me as does the"Secret of Hegel" after Dr. Stirling's elaborate revelation of it. Dr. Stirling's method of dealing with the subject is peculiar. "Protoplasm"is a question of history, so far as it is a name; of fact, so far as itis a thing. Dr. Stirling, has not taken the trouble to refer to theoriginal authorities for his history, which is consequently a travesty;and still less has he concerned himself with looking at the facts, butcontents himself with taking them also at second-hand. A most amusingexample of this fashion of dealing with scientific statements isfurnished by Dr. Stirling's remarks upon my account of the protoplasm ofthe nettle hair. That account was drawn up from careful and often-repeated observation of the facts. Dr. Stirling thinks he is offering avalid criticism, when he says that my valued friend Professor Strickergives a somewhat different statement about protoplasm. But why in theworld did not this distinguished Hegelian look at a nettle hair forhimself, before venturing to speak about the matter at all? Why troublehimself about what either Stricker or I say, when any tyro can see thefacts for himself, if he is provided with those not rare articles, anettle and a microscope? But I suppose this would have been"_Aufklärung_"--a recurrence to the base common-sense philosophy of theeighteenth century, which liked to see before it believed, and tounderstand before it criticised Dr. Stirling winds up his paper with thefollowing paragraph:--

[Footnote 9: Subsequently published under the title of "As regardsProtoplasm. "]

"In short, the whole position of Mr. Huxley, (1) that all organismsconsist alike of the same life-matter, (2) which life-matter is, for itspart, due only to chemistry, must be pronounced untenable--nor lessuntenable (3) the materialism he would found on it. "

The paragraph contains three distinct assertions concerning my views, andjust the same number of utter misrepresentations of them. That which Ihave numbered (1) turns on the ambiguity of the word "same, " for adiscussion of which I would refer Dr. Stirling to a great hero of"_Aufklärung_" Archbishop Whately; statement number (2) is, in myjudgment, absurd, and certainly I have never said anything resembling it;while, as to number (3), one great object of my essay was to show thatwhat is called "materialism" has no sound philosophical basis!

As we have seen, the study of yeast has led investigators face to facewith problems of immense interest in pure chemistry, and in animal andvegetable morphology. Its physiology is not less rich in subjects forinquiry. Take, for example, the singular fact that yeast will increaseindefinitely when grown in the dark, in water containing only tartrate ofammonia a small percentage of mineral salts and sugar. Out of thesematerials the _Toruloe_ will manufacture nitrogenous protoplasm, cellulose, and fatty matters, in any quantity, although they are whollydeprived of those rays of the sun, the influence of which is essential tothe growth of ordinary plants. There has been a great deal of speculationlately, as to how the living organisms buried beneath two or threethousand fathoms of water, and therefore in all probability almostdeprived of light, live. If any of them possess the same powers as yeast(and the same capacity for living without light is exhibited by someother fungi) there would seem to be no difficulty about the matter. 

Of the pathological bearings of the study of yeast, and other suchorganisms, I have spoken elsewhere. It is certain that, in some animals, devastating epidemics are caused by fungi of low order--similar to thoseof which _Torula_ is a sort of offshoot. It is certain that such diseasesare propagated by contagion and infection, in just the same way asordinary contagious and infectious diseases are propagated. Of course, itdoes not follow from this, that all contagious and infectious diseasesare caused by organisms of as definite and independent a character as the_Torula_; but, I think, it does follow that it is prudent and wise tosatisfy one's self in each particular case, that the "germ theory" cannotand will not explain the facts, before having recourse to hypotheseswhich have no equal support from analogy. 

V

ON THE FORMATION OF COAL

[1870]

The lumps of coal in a coal-scuttle very often have a roughly cubicalform. If one of them be picked out and examined with a little care, itwill be found that its six sides are not exactly alike. Two oppositesides are comparatively smooth and shining, while the other four are muchrougher, and are marked by lines which run parallel with the smoothsides. The coal readily splits along these lines, and the split surfacesthus formed are parallel with the smooth faces. In other words, there isa sort of rough and incomplete stratification in the lump of coal, as ifit were a book, the leaves of which had stuck together very closely. 

Sometimes the faces along which the coal splits are not smooth, butexhibit a thin layer of dull, charred-looking substance, which is knownas "mineral charcoal. "

Occasionally one of the faces of a lump of coal will present impressions, which are obviously those of the stem, or leaves, of a plant; but thoughhard mineral masses of pyrites, and even fine mud, may occur here andthere, neither sand nor pebbles are met with. 

When the coal burns, the chief ultimate products of its combustion arecarbonic acid, water, and ammoniacal products, which escape up thechimney; and a greater or less amount of residual earthy salts, whichtake the form of ash. These products are, to a great extent, such aswould result from the burning of so much wood. 

These properties of coal may be made out without any very refinedappliances, but the microscope reveals something more. Black and opaqueas ordinary coal is, slices of it become transparent if they are cementedin Canada balsam, and rubbed down very thin, in the ordinary way ofmaking thin sections of non-transparent bodies. But as the thin slices, made in this way, are very apt to crack and break into fragments, it isbetter to employ marine glue as the cementing material. By the use ofthis substance, slices of considerable size and of extreme thinness andtransparency may be obtained. [1]

[Footnote 1: My assistant in the Museum of Practical Geology, Mr. Newton, invented this excellent method of obtaining thin slices of coal. ]

Now let us suppose two such slices to be prepared from our lump of coal--one parallel with the bedding, the other perpendicular to it; and let uscall the one the horizontal, and the other the vertical, section. Thehorizontal section will present more or less rounded yellow patches andstreaks, scattered irregularly through the dark brown, or blackish, ground substance; while the vertical section will exhibit mere elongatedbars and granules of the same yellow materials, disposed in lines whichcorrespond, roughly, with the general direction of the bedding of thecoal. 

This is the microscopic structure of an ordinary piece of coal. But if agreat series of coals, from different localities and seams, or even fromdifferent parts of the same seam, be examined, this structure will befound to vary in two directions. In the anthracitic, or stone-coals, which burn like coke, the yellow matter diminishes, and the groundsubstance becomes more predominant, blacker, and more opaque, until itbecomes impossible to grind a section thin enough to be translucent;while, on the other hand, in such as the "Better-Bed" coal of theneighbourhood of Bradford, which burns with much flame, the coal is of afar lighter, colour and transparent sections are very easily obtained. Inthe browner parts of this coal, sharp eyes will readily detect multitudesof curious little coin-shaped bodies, of a yellowish brown colour, embedded in the dark brown ground substance. On the average, these littlebrown bodies may have a diameter of about one-twentieth of an inch. Theylie with their flat surfaces nearly parallel with the two smooth faces ofthe block in which they are contained; and, on one side of each, theremay be discerned a figure, consisting of three straight linear marks, which radiate from the centre of the disk, but do not quite reach itscircumference. In the horizontal section these disks are often convertedinto more or less complete rings; while in the vertical sections theyappear like thick hoops, the sides of which have been pressed together. The disks are, therefore, flattened bags; and favourable sections showthat the three-rayed marking is the expression of three clefts, whichpenetrate one wall of the bag. 

The sides of the bags are sometimes closely approximated; but, when thebags are less flattened, their cavities are, usually, filled withnumerous, irregularly rounded, hollow bodies, having the same kind ofwall as the large ones, but not more than one seven-hundredth of an inchin diameter. 

In favourable specimens, again, almost the whole ground substance appearsto be made up of similar bodies--more or less carbonized or blackened--and, in these, there can be no doubt that, with the exception of patchesof mineral charcoal, here and there, the whole mass of the coal is madeup of an accumulation of the larger and of the smaller sacs. 

But, in one and the same slice, every transition can be observed fromthis structure to that which has been described as characteristic ofordinary coal. The latter appears to rise out of the former, by thebreaking-up and increasing carbonization of the larger and the smallersacs. And, in the anthracitic coals, this process appears to have gone tosuch a length, as to destroy the original structure altogether, and toreplace it by a completely carbonized substance. 

Thus coal may be said, speaking broadly, to be composed of twoconstituents: firstly, mineral charcoal; and, secondly, coal proper. Thenature of the mineral charcoal has long since been determined. Itsstructure shows it to consist of the remains of the stems and leaves ofplants, reduced a little more than their carbon. Again, some of the coalis made up of the crushed and flattened bark, or outer coat, of the stemsof plants, the inner wood of which has completely decayed away. But whatI may term the "saccular matter" of the coal, which, either in itsprimary or in its degraded form constitutes by far the greater part ofall the bituminous coals I have examined, is certainly not mineralcharcoal; nor is its structure that of any stem or leaf. Hence its realnature is at first by no means apparent, and has been the subject of muchdiscussion. 

The first person who threw any light upon the problem, as far as I havebeen able to discover, was the well-known geologist, Professor Morris. Itis now thirty-four years since he carefully described and figured thecoin-shaped bodies, or larger sacs, as I have called them, in a noteappended to the famous paper "On the Coalbrookdale Coal-Field, " publishedat that time, by the present President of the Geological Society, Mr. Prestwich. With much sagacity, Professor Morris divined the real natureof these bodies, and boldly affirmed them to be the spore-cases of aplant allied to the living club-mosses. 

But discovery sometimes makes a long halt; and it is only a few yearssince Mr. Carruthers determined the plant (or rather one of the plants)which produces these spore-cases, by finding the discoidal sacs stilladherent to the leaves of the fossilized cone which produced them. Hegave the name of _Flemingites gracilis_ to the plant of which the conesform a part. The branches and stem of this plant are not yet certainlyknown, but there is no sort of doubt that it was closely allied to the_Lepidodendron_, the remains of which abound in the coal formation. The_Lepidodendra_ were shrubs and trees which put one more in mind of an_Araucaria_ than of any other familiar plant; and the ends of thefruiting branches were terminated by cones, or catkins, somewhat like thebodies so named in a fir, or a willow. These conical fruits, however, didnot produce seeds; but the leaves of which they were composed bore upontheir surfaces sacs full of spores or sporangia, such as those one seeson the under surface of a bracken leaf. Now, it is these sporangia of theLepidodendroid plant _Flemingites_ which were identified by Mr. Carruthers with the free sporangia described by Professor Morris, whichare the same as the large sacs of which I have spoken. And, more thanthis, there is no doubt that the small sacs are the spores, which wereoriginally contained in the sporangia. 

The living club-mosses are, for the most part, insignificant and creepingherbs, which, superficially, very closely resemble true mosses, and noneof them reach more than two or three feet in height. But, in theiressential structure, they very closely resemble the earliestLepidodendroid trees of the coal: their stems and leaves are similar; soare their cones; and no less like are the sporangia and spores; whileeven in their size, the spores of the _Lepidodendron_ and those of theexisting _Lycopodium_, or club-moss, very closely approach one another. 

Thus, the singular conclusion is forced upon us, that the greater and thesmaller sacs of the "Better-Bed" and other coals, in which the primitivestructure is well preserved, are simply the sporangia and spores ofcertain plants, many of which were closely allied to the existing club-mosses. And if, as I believe, it can be demonstrated that ordinary coalis nothing but "saccular" coal which has undergone a certain amount ofthat alteration which, if continued, would convert it into anthracite;then, the conclusion is obvious, that the great mass of the coal we burnis the result of the accumulation of the spores and spore-cases ofplants, other parts of which have furnished the carbonized stems and themineral charcoal, or have left their impressions on the surfaces of thelayer. 

Of the multitudinous speculations which, at various times, have beenentertained respecting the origin and mode of formation of coal, severalappear to be negatived, and put out of court, by the structural facts thesignificance of which I have endeavoured to explain. These facts, forexample, do not permit us to suppose that coal is an accumulation ofpeaty matter, as some have held. 

Again, the late Professor Quekett was one of the first observers who gavea correct description of what I have termed the "saccular" structure ofcoal; and, rightly perceiving that this structure was something quitedifferent from that of any known plant, he imagined that it proceededfrom some extinct vegetable organism which was peculiarly abundantamongst the coal-forming plants. But this explanation is at once shown tobe untenable when the smaller and the larger sacs are proved to be sporesor sporangia. 

Some, once more, have imagined that coal was of submarine origin; andthough the notion is amply and easily refuted by other considerations, itmay be worth while to remark, that it is impossible to comprehend how amass of light and resinous spores should have reached the bottom of thesea, or should have stopped in that position if they had got there. 

At the same time, it is proper to remark that I do not presume to suggestthat all coal must needs have the same structure; or that there may notbe coals in which the proportions of wood and spores, or spore-cases, arevery different from those which I have examined. All I repeat is, thatnone of the coals which have come under my notice have enabled me toobserve such a difference. But, according to Principal Dawson, who has sosedulously examined the fossil remains of plants in North America, it isotherwise with the vast accumulations of coal in that country. 

"The true coal, " says Dr. Dawson, "consists principally of the flattenedbark of Sigillarioid and other trees, intermixed with leaves of Ferns and_Cordaites_, and other herbaceous _débris_, and with fragments of decayedwood, constituting 'mineral charcoal, ' all these materials havingmanifestly alike grown and accumulated where we find them. "[2]

[Footnote 2: _Acadian Geology_, 2nd edition, p. 135. ]

When I had the pleasure of seeing Principal Dawson in London last summer, I showed him my sections of coal, and begged him to re-examine some ofthe American coals on his return to Canada, with an eye to the presenceof spores and sporangia, such as I was able to show him in our Englishand Scotch coals. He has been good enough to do so; and in a letter datedSeptember 26th, 1870, he informs me that--

"Indications of spore-cases are rare, except in certain coarse shalycoals and portions of coals, and in the roofs of the seams. The mostmarked case I have yet met with is the shaly coal referred to ascontaining _Sporangites_ in my paper on the conditions of accumulation ofcoal ("Journal of the Geological Society, " vol. Xxii. Pp. 115, 139, and165). The purer coals certainly consist principally of cubical tissueswith some true woody matter, and the spore-cases, &c. , are chiefly in thecoarse and shaly layers. This is my old doctrine in my two papers in the"Journal of the Geological Society, " and I see nothing to modify it. Yourobservations, however, make it probable that the frequent _clear spots_in the cannels are spore-cases. "

Dr. Dawson's results are the more remarkable, as the numerous specimensof British coal, from various localities, which I have examined, tell onetale as to the predominance of the spore and sporangium element in theircomposition; and as it is exactly in the finest and purest coals, such asthe "Better-Bed" coal of Lowmoor, that the spores and sporangia obviouslyconstitute almost the entire mass of the deposit. 

Coal, such as that which has been described, is always found in sheets, or "seams, " varying from a fraction of an inch to many feet in thickness, enclosed in the substance of the earth at very various depths, betweenbeds of rock of different kinds. As a rule, every seam of coal rests upona thicker, or thinner, bed of clay, which is known as "under-clay. " Thesealternations of beds of coal, clay, and rock may be repeated many times, and are known as the "coal-measures"; and in some regions, as in SouthWales and in Nova Scotia, the coal-measures attain a thickness of twelveor fourteen thousand feet, and enclose eighty or a hundred seams of coal, each with its under-clay, and separated from those above and below bybeds of sandstone and shale. 

The position of the beds which constitute the coal-measures is infinitelydiverse. Sometimes they are tilted up vertically, sometimes they arehorizontal, sometimes curved into great basins; sometimes they come tothe surface, sometimes they are covered up by thousands of feet of rock. But, whatever their present position, there is abundant and conclusiveevidence that every under-clay was once a surface soil. Not only docarbonized root-fibres frequently abound in these under-clays; but thestools of trees, the trunks of which are broken off and confounded withthe bed of coal, have been repeatedly found passing into radiating roots, still embedded in the under-clay. On many parts of the coast of England, what are commonly known as "submarine forests" are to be seen at lowwater. They consist, for the most part, of short stools of oak, beech, and fir-trees, still fixed by their long roots in the bed of blue clay inwhich they originally grew. If one of these submarine forest beds shouldbe gradually depressed and covered up by new deposits, it would presentjust the same characters as an under-clay of the coal, if the_Sigillaria_ and _Lepidodendron_ of the ancient world were substitutedfor the oak, or the beech, of our own times. 

In a tropical forest, at the present day, the trunks of fallen trees, andthe stools of such trees as may have been broken by the violence ofstorms, remain entire for but a short time. Contrary to what might beexpected, the dense wood of the tree decays, and suffers from the ravagesof insects, more swiftly than the bark. And the traveller, setting hisfoot on a prostrate trunk, finds that it is a mere shell, which breaksunder his weight, and lands his foot amidst the insects, or the reptiles, which have sought food or refuge within. 

The trees of the coal forests present parallel conditions. When thefallen trunks which have entered into the composition of the bed of coalare identifiable, they are mere double shells of bark, flattened togetherin consequence of the destruction of the woody core; and Sir CharlesLyell and Principal Dawson discovered, in the hollow stools of coal treesof Nova Scotia, the remains of snails, millipedes, and salamander-likecreatures, embedded in a deposit of a different character from that whichsurrounded the exterior of the trees. Thus, in endeavouring to comprehendthe formation of a seam of coal, we must try to picture to ourselves athick forest, formed for the most part of trees like gigantic club-mosses, mares'-tails, and tree-ferns, with here and there some that hadmore resemblance to our existing yews and fir-trees. We must supposethat, as the seasons rolled by, the plants grew and developed theirspores and seeds; that they shed these in enormous quantities, whichaccumulated on the ground beneath; and that, every now and then, theyadded a dead frond or leaf; or, at longer intervals, a rotten branch, ora dead trunk, to the mass. 

A certain proportion of the spores and seeds no doubt fulfilled theirobvious function, and, carried by the wind to unoccupied regions, extended the limits of the forest; many might be washed away by rain intostreams, and be lost; but a large portion must have remained, toaccumulate like beech-mast, or acorns, beneath the trees of a modernforest. 

But, in this case it may be asked, why does not our English coal consistof stems and leaves to a much greater extent than it does? What is thereason of the predominance of the spores and spore-cases in it?

A ready answer to this question is afforded by the study of a livingfull-grown club-moss. Shake it upon a piece of paper, and it emits acloud of fine dust, which falls over the paper, and is the well-knownLycopodium powder. Now this powder used to be, and I believe still is, employed for two objects which seem, at first sight, to have noparticular connection with one another. It is, or was, employed in makinglightning, and in making pills. The coats of the spores contain so muchresinous matter, that a pinch of Lycopodium powder, thrown through theflame of a candle, burns with an instantaneous flash, which has long doneduty for lightning on the stage. And the same character makes it acapital coating for pills; for the resinous powder prevents the drug frombeing wetted by the saliva, and thus bars the nauseous flavour from thesensitive papilla; of the tongue. 

But this resinous matter, which lies in the walls of the spores andsporangia, is a substance not easily altered by air and water, and hencetends to preserve these bodies, just as the bituminized cereclothpreserves an Egyptian mummy; while, on the other hand, the merely woodystem and leaves tend to rot, as fast as the wood of the mummy's coffinhas rotted. Thus the mixed heap of spores, leaves, and stems in the coal-forest would be persistently searched by the long-continued action of airand rain; the leaves and stems would gradually be reduced to little buttheir carbon, or, in other words, to the condition of mineral charcoal inwhich we find them; while the spores and sporangia remained as acomparatively unaltered and compact residuum. 

There is, indeed, tolerably clear evidence that the coal must, under somecircumstances, have been converted into a substance hard enough to berolled into pebbles, while it yet lay at the surface of the earth; for insome seams of coal, the courses of rivulets, which must have been livingwater, while the stratum in which their remains are found was still atthe surface, have been observed to contain rolled pebbles of the verycoal through which the stream has cut its way. 

The structural facts are such as to leave no alternative but to adopt theview of the origin of such coal as I have described, which has just beenstated; but, happily, the process is not without analogy at the presentday. I possess a specimen of what is called "white coal" from Australia. It is an inflammable material, burning with a bright flame and havingmuch the consistence and appearance of oat-cake, which, I am informedcovers a considerable area. It consists, almost entirely, of a compactedmass of spores and spore-cases. But the fine particles of blown sandwhich are scattered through it, show that it must have accumulated, subaërially, upon the surface of a soil covered by a forest ofcryptogamous plants, probably tree-ferns. 

As regards this important point of the subaërial region of coal, I amglad to find myself in entire accordance with Principal Dawson, who baseshis conclusions upon other, but no less forcible, considerations. In apassage, which is the continuation of that already cited, he writes:--

"(3) The microscopical structure and chemical composition of the beds ofcannel coal and earthy bitumen, and of the more highly bituminous andcarbonaceous shale, show them to have been of the nature of the finevegetable mud which accumulates in the ponds and shallow lakes of modernswamps. When such tine vegetable sediment is mixed, as is often the case, with clay, it becomes similar to the bituminous limestone and calcareo-bituminous shales of the coal-measures. (4) A few of the under-clays, which support beds of coal, are of the nature of the vegetable mud abovereferred to; but the greater part are argillo-arenaceous in composition, with little vegetable matter, and bleached by the drainage from them ofwater containing the products of vegetable decay. They are, in short, loamy or clay soils, and must have been sufficiently above water to admitof drainage. The absence of sulphurets, and the occurrence of carbonateof iron in connection with them, prove that, when they existed as soils, rain-water, and not sea-water, percolated them. (5) The coal and thefossil forests present many evidences of subaërial conditions. Most ofthe erect and prostrate trees had become hollow shells of bark beforethey were finally embedded, and their wood had broken into cubical piecesof mineral charcoal. Land-snails and galley-worms (_Xylobius_) crept intothem, and they became dens, or traps, for reptiles. Large quantities ofmineral charcoal occur on the surface of all the large beds of coal. Noneof these appearances could have been produced by subaqueous action. (6)Though the roots of the _Sigillaria_ bear more resemblance to therhizomes of certain aquatic plants; yet, structurally, they areabsolutely identical with the roots of Cycads, which the stems alsoresemble. Further, the _Sigillarioe_ grew on the same soils whichsupported Conifers, _Lepidodendra_, _Cordaites_, and Ferns-plants whichcould not have grown in water. Again, with the exception perhaps of some_Pinnularioe_, and _Asterophyllites_, there is a remarkable absence fromthe coal measures of any form of properly aquatic vegetation. (7) Theoccurrence of marine, or brackish-water animals, in the roofs of coal-beds, or even in the coal itself, affords no evidence of subaqueousaccumulation, since the same thing occurs in the case of modern submarineforests. For these and other reasons, some of which are more fully statedin the papers already referred to, while I admit that the areas of coalaccumulation were frequently submerged, I must maintain that the truecoal is a subaërial accumulation by vegetable growth on soils, wet andswampy it is true, but not submerged. "

I am almost disposed to doubt whether it is necessary to make theconcession of "wet and swampy"; otherwise, there is nothing that I knowof to be said against this excellent conspectus of the reasons forbelieving in the subaërial origin of coal. 

But the coal accumulated upon the area covered by one of the greatforests of the carboniferous epoch would in course of time, have beenwasted away by the small, but constant, wear and tear of rain and streamshad the land which supported it remained at the same level, or beengradually raised to a greater elevation. And, no doubt, as much coal asnow exists has been destroyed, after its formation, in this way. What arenow known as coal districts owe their importance to the fact that theywere areas of slow depression, during a greater or less portion of thecarboniferous epoch; and that, in virtue of this circumstance, MotherEarth was enabled to cover up her vegetable treasures, and preserve themfrom destruction. 

Wherever a coal-field now exists, there must formerly have been freeaccess for a great river, or for a shallow sea, bearing sediment in theshape of sand and mud. When the coal-forest area became slowly depressed, the waters must have spread over it, and have deposited their burden uponthe surface of the bed of coal, in the form of layers, which are nowconverted into shale, or sandstone. Then followed a period of rest, inwhich the superincumbent shallow waters became completely filled up, andfinally replaced, by fine mud, which settled down into a new under-clay, and furnished the soil for a fresh forest growth. This flourished, andheaped up its spores and wood into coal, until the stage of slowdepression recommenced. And, in some localities, as I have mentioned, theprocess was repeated until the first of the alternating beds had sunk tonear three miles below its original level at the surface of the earth. 

In reflecting on the statement, thus briefly made, of the main factsconnected with the origin of the coal formed during the carboniferousepoch, two or three considerations suggest themselves. 

In the first place, the great phantom of geological time rises before thestudent of this, as of all other, fragments of the history of our earth--springing irrepressibly out of the facts, like the Djin from the jarwhich the fishermen so incautiously opened; and like the Djin again, being vaporous, shifting, and indefinable, but unmistakably gigantic. However modest the bases of one's calculation may be, the minimum of timeassignable to the coal period remains something stupendous. 

Principal Dawson is the last person likely to be guilty of exaggerationin this matter, and it will be well to consider what he has to say aboutit:--

"The rate of accumulation of coal was very slow. The climate of theperiod, in the northern temperate zone, was of such a character that thetrue conifers show rings of growth, not larger, nor much less distinct, than those of many of their modern congeners. The _Sigillarioe_ and_Calamites_ were not, as often supposed, composed wholly, or evenprincipally, of lax and soft tissues, or necessarily short-lived. Theformer had, it is true, a very thick inner bark; but their dense woodyaxis, their thick and nearly imperishable outer bark, and their scantyand rigid foliage, would indicate no very rapid growth or decay. In thecase of the _Sigillarioe_, the variations in the leaf-scars in differentparts of the trunk, the intercalation of new ridges at the surfacerepresenting that of new woody wedges in the axis, the transverse marksleft by the stages of upward growth, all indicate that several years musthave been required for the growth of stems of moderate size. The enormousroots of these trees, and the condition of the coal-swamps, must haveexempted them from the danger of being overthrown by violence. Theyprobably fell in successive generations from natural decay; and makingevery allowance for other materials, we may safely assert that every footof thickness of pure bituminous coal implies the quiet growth and fall ofat least fifty generations of _Sigillarioe_, and therefore an undisturbedcondition of forest growth enduring through many centuries. Further, there is evidence that an immense amount of loose parenchymatous tissue, and even of wood, perished by decay, and we do not know to what extenteven the most durable tissues may have disappeared in this way; so that, in many coal-seams, we may have only a very small part of the vegetablematter produced. "

Undoubtedly the force of these reflections is not diminished when thebituminous coal, as in Britain, consists of accumulated spores and spore-cases, rather than of stems. But, suppose we adopt Principal Dawson'sassumption, that one foot of coal represents fifty generations of coalplants; and, further, make the moderate supposition that each generationof coal plants took ten years to come to maturity--then, each foot-thickness of coal represents five hundred years. The superimposed beds ofcoal in one coal-field may amount to a thickness of fifty or sixty feet, and therefore the coal alone, in that field, represents 500 x 50 = 25, 000years. But the actual coal is but an insignificant portion of the totaldeposit, which, as has been seen, may amount to between two and threemiles of vertical thickness. Suppose it be 12, 000 feet--which is 240times the thickness of the actual coal--is there any reason why we shouldbelieve it may not have taken 240 times as long to form? I know of none. But, in this case, the time which the coal-field represents would be25, 000 x 240 = 6, 000, 000 years. As affording a definite chronology, ofcourse such calculations as these are of no value; but they have much usein fixing one's attention upon a possible minimum. A man may be puzzledif he is asked how long Rome took a-building; but he is proverbially safeif he affirms it not to have been built in a day; and our geologicalcalculations are all, at present, pretty much on that footing. 

A second consideration which the study of the coal brings prominentlybefore the mind of any one who is familiar with palaeontology is, that thecoal Flora, viewed in relation to the enormous period of time which itlasted, and to the still vaster period which has elapsed since itflourished, underwent little change while it endured, and in its peculiarcharacters, differs strangely little from that which at present exist. 

The same species of plants are to be met with throughout the wholethickness of a coal-field, and the youngest are not sensibly differentfrom the oldest. But more than this. Notwithstanding that thecarboniferous period is separated from us by more than the whole timerepresented by the secondary and tertiary formations, the great types ofvegetation were as distinct then as now. The structure of the modernclub-moss furnishes a complete explanation of the fossil remains of the_Lepidodendra_, and the fronds of some of the ancient ferns are hard todistinguish from existing ones. At the same time, it must be remembered, that there is nowhere in the world, at present, any _forest_ which bearsmore than a rough analogy with a coal-forest. The types may remain, butthe details of their form, their relative proportions, their associates, are all altered. And the tree-fern forest of Tasmania, or New Zealand, gives one only a faint and remote image of the vegetation of the ancientworld. 

Once more, an invariably-recurring lesson of geological history, atwhatever point its study is taken up: the lesson of the almost infiniteslowness of the modification of living forms. The lines of the pedigreesof living things break off almost before they begin to converge. 

Finally, yet another curious consideration. Let us suppose that one ofthe stupid, salamander-like Labyrinthodonts, which pottered, with muchbelly and little leg, like Falstaff in his old age, among the coal-forests, could have had thinking power enough in his small brain toreflect upon the showers of spores which kept on falling through yearsand centuries, while perhaps not one in ten million fulfilled itsapparent purpose, and reproduced the organism which gave it birth: surelyhe might have been excused for moralizing upon the thoughtless and wantonextravagance which Nature displayed in her operations. 

But we have the advantage over our shovel-headed predecessor--or possiblyancestor--and can perceive that a certain vein of thrift runs throughthis apparent prodigality. Nature is never in a hurry, and seems to havehad always before her eyes the adage, "Keep a thing long enough, and youwill find a use for it. " She has kept her beds of coal many millions ofyears without being able to find much use for them; she has sent themdown beneath the sea, and the sea-beasts could make nothing of them; shehas raised them up into dry land, and laid the black veins bare, andstill, for ages and ages, there was no living thing on the face of theearth that could see any sort of value in them; and it was only the otherday, so to speak, that she turned a new creature out of her workshop, whoby degrees acquired sufficient wits to make a fire, and then to discoverthat the black rock would burn. 

I suppose that nineteen hundred years ago, when Julius Caesar was goodenough to deal with Britain as we have dealt with New Zealand, theprimaeval Briton, blue with cold and woad, may have known that the strangeblack stone, of which he found lumps here and there in his wanderings, would burn, and so help to warm his body and cook his food. Saxon, Dane, and Norman swarmed into the land. The English people grew into a powerfulnation, and Nature still waited for a full return of the capital she hadinvested in the ancient club-mosses. The eighteenth century arrived, andwith it James Watt. The brain of that man was the spore out of which wasdeveloped the modern steam-engine, and all the prodigious trees andbranches of modern industry which have grown out of this. But coal is asmuch an essential condition of this growth and development as carbonicacid is for that of a club-moss. Wanting coal, we could not have smeltedthe iron needed to make our engines, nor have worked our engines when wehad got them. But take away the engines, and the great towns of Yorkshireand Lancashire vanish like a dream. Manufactures give place toagriculture and pasture, and not ten men can live where now ten thousandare amply supported. 

Thus, all this abundant wealth of money and of vivid life is Nature'sinterest upon her investment in club-mosses, and the like, so long ago. But what becomes of the coal which is burnt in yielding this interest?Heat comes out of it, light comes out of it; and if we could gathertogether all that goes up the chimney, and all that remains in the grateof a thoroughly-burnt coal-fire, we should find ourselves in possessionof a quantity of carbonic acid, water, ammonia, and mineral matters, exactly equal in weight to the coal. But these are the very matters withwhich Nature supplied the club-mosses which made the coal She is paidback principal and interest at the same time; and she straightway investsthe carbonic acid, the water, and the ammonia in new forms of life, feeding with them the plants that now live. Thrifty Nature! Surely noprodigal, but most notable of housekeepers!

VI

ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS

[1876]

In the whole history of science there is nothing more remarkable than therapidity of the growth of biological knowledge within the last half-century, and the extent of the modification which has thereby beeneffected in some of the fundamental conceptions of the naturalist. 

In the second edition of the "Règne Animal, " published in 1828, Cuvierdevotes a special section to the "Division of Organised Beings intoAnimals and Vegetables, " in which the question is treated with thatcomprehensiveness of knowledge and clear critical judgment whichcharacterise his writings, and justify us in regarding them asrepresentative expressions of the most extensive, if not the profoundest, knowledge of his time. He tells us that living beings have beensubdivided from the earliest times into _animated beings_, which possesssense and motion, and _inanimated beings_, which are devoid of thesefunctions and simply vegetate. 

Although the roots of plants direct themselves towards moisture, andtheir leaves towards air and light, --although the parts of some plantsexhibit oscillating movements without any perceptible cause, and theleaves of others retract when touched, --yet none of these movementsjustify the ascription to plants of perception or of will. From themobility of animals, Cuvier, with his characteristic partiality forteleological reasoning, deduces the necessity of the existence in them ofan alimentary cavity, or reservoir of food, whence their nutrition may bedrawn by the vessels, which are a sort of internal roots; and, in thepresence of this alimentary cavity, he naturally sees the primary and themost important distinction between animals and plants. 

Following out his teleological argument, Cuvier remarks that theorganisation of this cavity and its appurtenances must needs varyaccording to the nature of the aliment, and the operations which it hasto undergo, before it can be converted into substances fitted forabsorption; while the atmosphere and the earth supply plants with juicesready prepared, and which can be absorbed immediately. As the animal bodyrequired to be independent of heat and of the atmosphere, there were nomeans by which the motion of its fluids could be produced by internalcauses. Hence arose the second great distinctive character of animals, orthe circulatory system, which is less important than the digestive, sinceit was unnecessary, and therefore is absent, in the more simple animals. 

Animals further needed muscles for locomotion and nerves for sensibility. Hence, says Cuvier, it was necessary that the chemical composition of theanimal body should be more complicated than that of the plant; and it isso, inasmuch as an additional substance, nitrogen, enters into it as anessential element; while, in plants, nitrogen is only accidentally joinedwith he three other fundamental constituents of organic beings--carbon, hydrogen, and oxygen. Indeed, he afterwards affirms that nitrogen ispeculiar to animals; and herein he places the third distinction betweenthe animal and the plant. The soil and the atmosphere supply plants withwater, composed of hydrogen and oxygen; air, consisting of nitrogen andoxygen; and carbonic acid, containing carbon and oxygen. They retain thehydrogen and the carbon, exhale the superfluous oxygen, and absorb littleor no nitrogen. The essential character of vegetable life is theexhalation of oxygen, which is effected through the agency of light. Animals, on the contrary, derive their nourishment either directly orindirectly from plants. They get rid of the superfluous hydrogen andcarbon, and accumulate nitrogen. The relations of plants and animals tothe atmosphere are therefore inverse. The plant withdraws water andcarbonic acid from the atmosphere, the animal contributes both to it. Respiration--that is, the absorption of oxygen and the exhalation ofcarbonic acid--is the specially animal function of animals, andconstitutes their fourth distinctive character. 

Thus wrote Cuvier in 1828. But, in the fourth and fifth decades of thiscentury, the greatest and most rapid revolution which biological sciencehas ever undergone was effected by the application of the modernmicroscope to the investigation of organic structure; by the introductionof exact and easily manageable methods of conducting the chemicalanalysis of organic compounds; and finally, by the employment ofinstruments of precision for the measurement of the physical forces whichare at work in the living economy. 

That the semi-fluid contents (which we now term protoplasm) of the cellsof certain plants, such as the _Charoe_ are in constant and regularmotion, was made out by Bonaventura Corti a century ago; but the fact, important as it was, fell into oblivion, and had to be rediscovered byTreviranus in 1807. Robert Brown noted the more complex motions of theprotoplasm in the cells of _Tradescantia_ in 1831; and now such movementsof the living substance of plants are well known to be some of the mostwidely-prevalent phenomena of vegetable life. 

Agardh, and other of the botanists of Cuvier's generation, who occupiedthemselves with the lower plants, had observed that, under particularcircumstances, the contents of the cells of certain water-weeds were setfree, and moved about with considerable velocity, and with all theappearances of spontaneity, as locomotive bodies, which, from theirsimilarity to animals of simple organisation, were called "zoospores. "Even as late as 1845, however, a botanist of Schleiden's eminence dealtvery sceptically with these statements; and his scepticism was the morejustified, since Ehrenberg, in his elaborate and comprehensive work onthe _Infusoria_, had declared the greater number of what are nowrecognised as locomotive plants to be animals. 

At the present day, innumerable plants and free plant cells are known topass the whole or part of their lives in an actively locomotivecondition, in no wise distinguishable from that of one of the simpleranimals; and, while in this condition, their movements are, to allappearance, as spontaneous--as much the product of volition--as those ofsuch animals. 

Hence the teleological argument for Cuvier's first diagnostic character--the presence in animals of an alimentary cavity, or internal pocket, inwhich they can carry about their nutriment--has broken down, so far, atleast, as his mode of stating it goes. And, with the advance ofmicroscopic anatomy, the universality of the fact itself among animalshas ceased to be predicable. Many animals of even complex structure, which live parasitically within others, are wholly devoid of analimentary cavity. Their food is provided for them, not only readycooked, but ready digested, and the alimentary canal, become superfluous, has disappeared. Again, the males of most Rotifers have no digestiveapparatus; as a German naturalist has remarked, they devote themselvesentirely to the "Minnedienst, " and are to be reckoned among the fewrealisations of the Byronic ideal of a lover. Finally, amidst the lowestforms of animal life, the speck of gelatinous protoplasm, whichconstitutes the whole body, has no permanent digestive cavity or mouth, but takes in its food anywhere; and digests, so to speak, all over itsbody. But although Cuvier's leading diagnosis of the animal from theplant will not stand a strict test, it remains one of the most constantof the distinctive characters of animals. And, if we substitute for thepossession of an alimentary cavity, the power of taking solid nutrimentinto the body and there digesting it, the definition so changed willcover all animals except certain parasites, and the few and exceptionalcases of non-parasitic animals which do not feed at all. On the otherhand, the definition thus amended will exclude all ordinary vegetableorganisms. 

Cuvier himself practically gives up his second distinctive mark when headmits that it is wanting in the simpler animals. 

The third distinction is based on a completely erroneous conception ofthe chemical differences and resemblances between the constituents ofanimal and vegetable organisms, for which Cuvier is not responsible, asit was current among contemporary chemists. It is now established thatnitrogen is as essential a constituent of vegetable as of animal livingmatter; and that the latter is, chemically speaking, just as complicatedas the former. Starchy substances, cellulose and sugar, once supposed tobe exclusively confined to plants, are now known to be regular and normalproducts of animals. Amylaceous and saccharine substances are largelymanufactured, even by the highest animals; cellulose is widespread as aconstituent of the skeletons of the lower animals; and it is probablethat amyloid substances are universally present in the animal organism, though not in the precise form of starch. 

Moreover, although it remains true that there is an inverse relationbetween the green plant in sunshine and the animal, in so far as, underthese circumstances, the green plant decomposes carbonic acid and exhalesoxygen, while the animal absorbs oxygen and exhales carbonic acid; yet, the exact researches of the modern chemical investigators of thephysiological processes of plants have clearly demonstrated the fallacyof attempting to draw any general distinction between animals andvegetables on this ground. In fact, the difference vanishes with thesunshine, even in the case of the green plant; which, in the dark, absorbs oxygen and gives out carbonic acid like any animal. [1] On theother hand, those plants, such as the fungi, which contain no chlorophylland are not green, are always, so far as respiration is concerned, in theexact position of animals. They absorb oxygen and give out carbonic acid. 

[Footnote 1: There is every reason to believe that living plants, likeliving animals, always respire, and, in respiring, absorb oxygen and giveoff carbonic acid; but, that in green plants exposed to daylight or tothe electric light, the quantity of oxygen evolved in consequence of thedecomposition of carbonic acid by a special apparatus which green plantspossess exceeds that absorbed in the concurrent respiratory process. ]

Thus, by the progress of knowledge, Cuvier's fourth distinction betweenthe animal and the plant has been as completely invalidated as the thirdand second; and even the first can be retained only in a modified formand subject to exceptions. 

But has the advance of biology simply tended to break down olddistinctions, without establishing new ones?

With a qualification, to be considered presently, the answer to thisquestion is undoubtedly in the affirmative. The famous researches ofSchwann and Schleiden in 1837 and the following years, founded the modernscience of histology, or that branch of anatomy which deals with theultimate visible structure of organisms, as revealed by the microscope;and, from that day to this, the rapid improvement of methods ofinvestigation, and the energy of a host of accurate observers, have givengreater and greater breadth and firmness to Schwann's greatgeneralisation, that a fundamental unity of structure obtains in animalsand plants; and that, however diverse may be the fabrics, or _tissues_, of which their bodies are composed, all these varied structures resultfrom the metamorphosis of morphological units (termed _cells_, in a moregeneral sense than that in which the word "cells" was at first employed), which are not only similar in animals and in plants respectively, butpresent a close resemblance, when those of animals and those of plantsare compared together. 

The contractility which is the fundamental condition of locomotion, hasnot only been discovered to exist far more widely among plants than wasformerly imagined; but, in plants, the act of contraction has been foundto be accompanied, as Dr. Burdon Sanderson's interesting investigationshave shown, by a disturbance of the electrical state of the contractilesubstance, comparable to that which was found by Du Bois Reymond to be aconcomitant of the activity of ordinary muscle in animals. 

Again, I know of no test by which the reaction of the leaves of theSundew and of other plants to stimuli, so fully and carefully studied byMr. Darwin, can be distinguished from those acts of contraction followingupon stimuli, which are called "reflex" in animals. 

On each lobe of the bilobed leaf of Venus's fly-trap (_Dionoeamuscipula_) are three delicate filaments which stand out at right anglefrom the surface of the leaf. Touch one of them with the end of a finehuman hair and the lobes of the leaf instantly close together[2] invirtue of an act of contraction of part of their substance, just as thebody of a snail contracts into its shell when one of its "horns" isirritated. 

[Footnote 2: Darwin, _Insectivorous Plants_, p. 289. ]

The reflex action of the snail is the result of the presence of a nervoussystem in the animal. A molecular change takes place in the nerve of thetentacle, is propagated to the muscles by which the body is retracted, and causing them to contract, the act of retraction is brought about. Ofcourse the similarity of the acts does not necessarily involve theconclusion that the mechanism by which they are effected is the same; butit suggests a suspicion of their identity which needs careful testing. 

The results of recent inquiries into the structure of the nervous systemof animals converge towards the conclusion that the nerve fibres, whichwe have hitherto regarded as ultimate elements of nervous tissue, are notsuch, but are simply the visible aggregations of vastly more attenuatedfilaments, the diameter of which dwindles down to the limits of ourpresent microscopic vision, greatly as these have been extended by modernimprovements of the microscope; and that a nerve is, in its essence, nothing but a linear tract of specially modified protoplasm between twopoints of an organism--one of which is able to affect the other by meansof the communication so established. Hence, it is conceivable that eventhe simplest living being may possess a nervous system. And the questionwhether plants are provided with a nervous system or not, thus acquires anew aspect, and presents the histologist and physiologist with a problemof extreme difficulty, which must be attacked from a new point of viewand by the aid of methods which have yet to be invented. 

Thus it must be admitted that plants may be contractile and locomotive;that, while locomotive, their movements may have as much appearance ofspontaneity as those of the lowest animals; and that many exhibitactions, comparable to those which are brought about by the agency of anervous system in animals. And it must be allowed to be possible thatfurther research may reveal the existence of something comparable to anervous system in plants. So that I know not where we can hope to findany absolute distinction between animals and plants, unless we return totheir mode of nutrition, and inquire whether certain differences of amore occult character than those imagined to exist by Cuvier, and whichcertainly hold good for the vast majority of animals and plants, are ofuniversal application. 

A bean may be supplied with water in which salts of ammonia and certainother mineral salts are dissolved in due proportion; with atmospheric aircontaining its ordinary minute dose of carbonic acid; and with nothingelse but sunlight and heat. Under these circumstances, unnatural as theyare, with proper management, the bean will thrust forth its radicle andits plumule; the former will grow down into roots, the latter grow upinto the stem and leaves of a vigorous bean-plant; and this plant will, in due time, flower and produce its crop of beans, just as if it weregrown in the garden or in the field. 

The weight of the nitrogenous protein compounds, of the oily, starchy, saccharine and woody substances contained in the full-grown plant and itsseeds, will be vastly greater than the weight of the same substancescontained in the bean from which it sprang. But nothing has been suppliedto the bean save water, carbonic acid, ammonia, potash, lime, iron, andthe like, in combination with phosphoric, sulphuric, and other acids. Neither protein, nor fat, nor starch, nor sugar, nor any substance in theslightest degree resembling them, has formed part of the food of thebean. But the weights of the carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, and other elementary bodies contained in the bean-plant, and in the seeds which it produces, are exactly equivalent to theweights of the same elements which have disappeared from the materialssupplied to the bean during its growth. Whence it follows that the beanhas taken in only the raw materials of its fabric, and has manufacturedthem into bean-stuffs. 

The bean has been able to perform this great chemical feat by the help ofits green colouring matter, or chlorophyll; for it is only the greenparts of the plant which, under the influence of sunlight, have themarvellous power of decomposing carbonic acid, setting free the oxygenand laying hold of the carbon which it contains. In fact, the beanobtains two of the absolutely indispensable elements of its substancefrom two distinct sources; the watery solution, in which its roots areplunged, contains nitrogen but no carbon; the air, to which the leavesare exposed, contains carbon, but its nitrogen is in the state of a freegas, in which condition the bean can make no use of it;[3] and thechlorophyll[4] is the apparatus by which the carbon is extracted from theatmospheric carbonic acid--the leaves being the chief laboratories inwhich this operation is effected. 

[Footnote 3: I purposely assume that the air with which the bean issupplied in the case stated contains no ammoniacal salts. ]

[Footnote 4: The recent researches of Pringsheim have raised a host ofquestions as to the exact share taken by chlorophyll in the chemicaloperations which are effected by the green parts of plants. It may bethat the chlorophyll is only a constant concomitant of the actualdeoxidising apparatus. ]

The great majority of conspicuous plants are, as everybody knows, green;and this arises from the abundance of their chlorophyll. The few whichcontain no chlorophyll and are colourless, are unable to extract thecarbon which they require from atmospheric carbonic acid, and lead aparasitic existence upon other plants; but it by no means follows, oftenas the statement has been repeated, that the manufacturing power ofplants depends on their chlorophyll, and its interaction with the rays ofthe sun. On the contrary, it is easily demonstrated, as Pasteur firstproved, that the lowest fungi, devoid of chlorophyll, or of anysubstitute for it, as they are, nevertheless possess the characteristicmanufacturing powers of plants in a very high degree. Only it isnecessary that they should be supplied with a different kind of rawmaterial; as they cannot extract carbon from carbonic acid, they must befurnished with something else that contains carbon. Tartaric acid is sucha substance; and if a single spore of the commonest and most troublesomeof moulds--_Penicillium_--be sown in a saucerful of water, in whichtartrate of ammonia, with a small percentage of phosphates and sulphatesis contained, and kept warm, whether in the dark or exposed to light, itwill, in a short time, give rise to a thick crust of mould, whichcontains many million times the weight of the original spore, in proteincompounds and cellulose. Thus we have a very wide basis of fact for thegeneralisation that plants are essentially characterised by theirmanufacturing capacity--by their power of working up mere mineral mattersinto complex organic compounds. 

Contrariwise, there is a no less wide foundation for the generalisationthat animals, as Cuvier puts it, depend directly or indirectly uponplants for the materials of their bodies; that is, either they areherbivorous, or they eat other animals which are herbivorous. 

But for what constituents of their bodies are animals thus dependent uponplants? Certainly not for their horny matter; nor for chondrin, theproximate chemical element of cartilage; nor for gelatine; nor forsyntonin, the constituent of muscle; nor for their nervous or biliarysubstances; nor for their amyloid matters; nor, necessarily, for theirfats. 

It can be experimentally demonstrated that animals can make these forthemselves. But that which they cannot make, but must, in all knowncases, obtain directly or indirectly from plants, is the peculiarnitrogenous matter, protein. Thus the plant is the ideal _prolétaire_ ofthe living world, the worker who produces; the animal, the idealaristocrat, who mostly occupies himself in consuming, after the manner ofthat noble representative of the line of Zähdarm, whose epitaph iswritten in "Sartor Resartus. "

Here is our last hope of finding a sharp line of demarcation betweenplants and animals; for, as I have already hinted, there is a borderterritory between the two kingdoms, a sort of no-man's-land, theinhabitants of which certainly cannot be discriminated and brought totheir proper allegiance in any other way. 

Some months ago, Professor Tyndall asked me to examine a drop of infusionof hay, placed under an excellent and powerful microscope, and to tellhim what I thought some organisms visible in it were. I looked andobserved, in the first place, multitudes of _Bacteria_ moving about withtheir ordinary intermittent spasmodic wriggles. As to the vegetablenature of these there is now no doubt. Not only does the closeresemblance of the _Bacteria_ to unquestionable plants, such as the_Oscillatorioe_ and the lower forms of _Fungi_, justify this conclusion, but the manufacturing test settles the question at once. It is onlyneedful to add a minute drop of fluid containing _Bacteria_, to water inwhich tartrate, phosphate, and sulphate of ammonia are dissolved; and, ina very short space of time, the clear fluid becomes milky by reason oftheir prodigious multiplication, which, of course, implies themanufacture of living Bacterium-stuff out of these merely saline matters. 

But other active organisms, very much larger than the _Bacteria_, attaining in fact the comparatively gigantic dimensions of 1/3000 of aninch or more, incessantly crossed the field of view. Each of these had abody shaped like a pear, the small end being slightly incurved andproduced into a long curved filament, or _cilium_, of extreme tenuity. Behind this, from the concave side of the incurvation, proceeded anotherlong cilium, so delicate as to be discernible only by the use of thehighest powers and careful management of the light. In the centre of thepear-shaped body a clear round space could occasionally be discerned, butnot always; and careful watching showed that this clear vacuity appearedgradually, and then shut up and disappeared suddenly, at regularintervals. Such a structure is of common occurrence among the lowestplants and animals, and is known as a _contractile vacuole_. 

The little creature thus described sometimes propelled itself with greatactivity, with a curious rolling motion, by the lashing of the frontcilium, while the second cilium trailed behind; sometimes it anchoreditself by the hinder cilium and was spun round by the working of theother, its motions resembling those of an anchor buoy in a heavy sea. Sometimes, when two were in full career towards one another, each wouldappear dexterously to get out of the other's way; sometimes a crowd wouldassemble and jostle one another, with as much semblance of individualeffort as a spectator on the Grands Mulets might observe with a telescopeamong the specks representing men in the valley of Chamounix. 

The spectacle, though always surprising, was not new to me. So my replyto the question put to me was, that these organisms were what biologistscall _Monads_, and though they might be animals, it was also possiblethat they might, like the _Bacteria_, be plants. My friend received myverdict with an expression which showed a sad want of respect forauthority. He would as soon believe that a sheep was a plant. Naturallypiqued by this want of faith, I have thought a good deal over the matter;and, as I still rest in the lame conclusion I originally expressed, andmust even now confess that I cannot certainly say whether this creatureis an animal or a plant, I think it may be well to state the grounds ofmy hesitation at length. But, in the first place, in order that I mayconveniently distinguish this "Monad" from the multitude of other thingswhich go by the same designation, I must give it a name of its own. Ithink (though, for reasons which need not be stated at present, I am notquite sure) that it is identical with the species _Monas lens_ as definedby the eminent French microscopist Dujardin, though his magnifying powerwas probably insufficient to enable him to see that it is curiously likea much larger form of monad which he has named _Heteromita_. I shall, therefore, call it not _Monas_, but _Heteromita lens_. 

I have been unable to devote to my _Heteromita_ the prolonged studyneedful to work out its whole history, which would involve weeks, or itmay be months, of unremitting attention. But I the less regret thiscircumstance, as some remarkable observations recently published byMessrs. Dallinger and Drysdale[5] on certain Monads, relate, in part, toa form so similar to my _Heteromita lens_, that the history of the onemay be used to illustrate that of the other. These most patient andpainstaking observers, who employed the highest attainable powers of themicroscope and, relieving one another, kept watch day and night over thesame individual monads, have been enabled to trace out the whole historyof their _Heteromita_; which they found in infusions of the heads offishes of the Cod tribe. 

[Footnote 5: "Researches in the Life-history of a Cercomonad: a Lesson inBiogenesis"; and "Further Researches in the Life-history of the Monads, "--_Monthly Microscopical Journal_, 1873. ]

Of the four monads described and figured by these investigators, one, asI have said, very closely resembles _Heteromita lens_ in everyparticular, except that it has a separately distinguishable centralparticle or "nucleus, " which is not certainly to be made out in_Heteromita lens_; and that nothing is said by Messrs. Dallinger andDrysdale of the existence of a contractile vacuole in this monad, thoughthey describe it in another. 

Their _Heteromita_, however, multiplied rapidly by fission. Sometimes atransverse constriction appeared; the hinder half developed a new cilium, and the hinder cilium gradually split from its base to its free end, until it was divided into two; a process which, considering the fact thatthis fine filament cannot be much more than 1/100000 of an inch indiameter, is wonderful enough. The constriction of the body extendedinwards until the two portions were united by a narrow isthmus; finally, they separated and each swam away by itself, a complete _Heteromita_, provided with its two cilia. Sometimes the constriction took alongitudinal direction, with the same ultimate result. In each case theprocess occupied not more than six or seven minutes. At this rate, asingle _Heteromita_ would give rise to a thousand like itself in thecourse of an hour, to about a million in two hours, and to a numbergreater than the generally assumed number of human beings now living inthe world in three hours; or, if we give each _Heteromita_ an hour'senjoyment of individual existence, the same result will be obtained inabout a day. The apparent suddenness of the appearance of multitudes ofsuch organisms as these in any nutritive fluid to which one obtainsaccess is thus easily explained. 

During these processes of multiplication by fission, the _Heteromita_remains active; but sometimes another mode of fission occurs. The bodybecomes rounded and quiescent, or nearly so; and, while in this restingstate, divides into two portions, each of which is rapidly converted intoan active _Heteromita_. 

A still more remarkable phenomenon is that kind of multiplication whichis preceded by the union of two monads, by a process which is termed_conjugation_. Two active _Heteromitoe_ become applied to one another, and then slowly and gradually coalesce into one body. The two nuclei runinto one; and the mass resulting from the conjugation of the two_Heteromitoe_, thus fused together, has a triangular form. The two pairsof cilia are to be seen, for some time, at two of the angles, whichanswer to the small ends of the conjoined monads; but they ultimatelyvanish, and the twin organism, in which all visible traces oforganisation have disappeared, falls into a state of rest. Sudden wave-like movements of its substance next occur; and, in a short time, theapices of the triangular mass burst, and give exit to a dense yellowish, glairy fluid, filled with minute granules. This process, which, it willbe observed, involves the actual confluence and mixture of the substanceof two distinct organisms, is effected in the space of about two hours. 

The authors whom I quote say that they "cannot express" the excessiveminuteness of the granules in question, and they estimate their diameterat less than 1/200000 of an inch. Under the highest powers of themicroscope, at present applicable, such specks are hardly discernible. Nevertheless, particles of this size are massive when compared tophysical molecules; whence there is no reason to doubt that each, smallas it is, may have a molecular structure sufficiently complex to giverise to the phenomena of life. And, as a matter of fact, by patientwatching of the place at which these infinitesimal living particles weredischarged, our observers assured themselves of their growth anddevelopment into new monads. In about four hours from their being setfree, they had attained a sixth of the length of the parent, with thecharacteristic cilia, though at first they were quite motionless; and, infour hours more, they had attained the dimensions and exhibited all theactivity of the adult. These inconceivably minute particles are thereforethe germs of the _Heteromita_; and from the dimensions of these germs itis easily shown that the body formed by conjugation may, at a lowestimate, have given exit to thirty thousand of them; a result of amatrimonial process whereby the contracting parties, without a metaphor, "become one flesh, " enough to make a Malthusian despair of the future ofthe Universe. 

I am not aware that the investigators from whom I have borrowed thishistory have endeavoured to ascertain whether their monads take solidnutriment or not; so that though they help us very much to fill up theblanks in the history of my _Heteromita_, their observations throw nolight on the problem we are trying to solve--Is it an animal or is it aplant?

Undoubtedly it is possible to bring forward very strong arguments infavour of regarding _Heteromita_ as a plant. 

For example, there is a Fungus, an obscure and almost microscopic mould, termed _Peronospora infestans_. Like many other Fungi, the _Peronosporoe_are parasitic upon other plants; and this particular _Peronospora_happens to have attained much notoriety and political importance, in away not without a parallel in the career of notorious politicians, namely, by reason of the frightful mischief it has done to mankind. Forit is this _Fungus_ which is the cause of the potato disease; and, therefore, _Peronospora infestans_ (doubtless of exclusively Saxonorigin, though not accurately known to be so) brought about the Irishfamine. The plants afflicted with the malady are found to be infested bya mould, consisting of fine tubular filaments, termed _hyphoe_, whichburrow through the substance of the potato plant, and appropriate tothemselves the substance of their host; while, at the same time, directlyor indirectly, they set up chemical changes by which even its woodyframework becomes blackened, sodden, and withered. 

In structure, however, the _Peronospora_ is as much a mould as the common_Penicillium_; and just as the _Penicillium_ multiplies by the breakingup of its hyphoe into separate rounded bodies, the spores; so, in the_Peronospora_, certain of the hyphoe grow out into the air through theinterstices of the superficial cells of the potato plant, and developspores. Each of these hyphoe usually gives off several branches. The endsof the branches dilate and become closed sacs, which eventually drop offas spores. The spores falling on some part of the same potato plant, orcarried by the wind to another, may at once germinate, throwing outtubular prolongations which become hyphoe, and burrow into the substanceof the plant attacked. But, more commonly, the contents of the sporedivide into six or eight separate portions. The coat of the spore givesway, and each portion then emerges as an independent organism, which hasthe shape of a bean, rather narrower at one end than the other, convex onone side, and depressed or concave on the opposite. From the depression, two long and delicate cilia proceed, one shorter than the other, anddirected forwards. Close to the origin of these cilia, in the substanceof the body, is a regularly pulsating, contractile vacuole. The shortercilium vibrates actively, and effects the locomotion of the organism, while the other trails behind; the whole body rolling on its axis withits pointed end forwards. 

The eminent botanist, De Bary, who was not thinking of our problem, tellsus, in describing the movements of these "Zoospores, " that, as they swimabout, "Foreign bodies are carefully avoided, and the whole movement hasa deceptive likeness to the voluntary changes of place which are observedin microscopic animals. "

After swarming about in this way in the moisture on the surface of a leafor stem (which, film though it may be, is an ocean to such a fish) forhalf an hour, more or less, the movement of the zoospore becomes slower, and is limited to a slow turning upon its axis, without change of place. It then becomes quite quiet, the cilia disappear, it assumes a sphericalform, and surrounds itself with a distinct, though delicate, membranouscoat. A protuberance then grows out from one side of the sphere, andrapidly increasing in length, assumes the character of a hypha. Thelatter penetrates into the substance of the potato plant, either byentering a stomate, or by boring through the wall of an epidermic cell, and ramifies, as a mycelium, in the substance of the plant, destroyingthe tissues with which it comes in contact. As these processes ofmultiplication take place very rapidly, millions of spores are soon setfree from a single infested plant; and, from their minuteness, they arereadily transported by the gentlest breeze. Since, again, the zoosporesset free from each spore, in virtue of their powers of locomotion, swiftly disperse themselves over the surface, it is no wonder that theinfection, once started, soon spreads from field to field, and extendsits ravages over a whole country. 

However, it does not enter into my present plan to treat of the potatodisease, instructively as its history bears upon that of other epidemics;and I have selected the case of the _Peroganspora_ simply because itaffords an example of an organism, which, in one stage of its existence, is truly a "Monad, " indistinguishable by any important character from our_Heteromita_, and extraordinarily like it in some respects. And yet this"Monad" can be traced, step by step, through the series of metamorphoseswhich I have described, until it assumes the features of an organism, which is as much a plant as is an oak or an elm. 

Moreover, it would be possible to pursue the analogy farther. Undercertain circumstances, a process of conjugation takes place in the_Peronospora_. Two separate portions of its protoplasm become fusedtogether, surround themselves with a thick coat and give rise to a sortof vegetable egg called an _oospore_. After a period of rest, thecontents of the oospore break up into a number of zoospores like thosealready described, each of which, after a period of activity, germinatesin the ordinary way. This process obviously corresponds with theconjugation and subsequent setting free of germs in the _Heteromita_. 

But it may be said that the _Peronospora_ is, after all, a questionablesort of plant; that it seems to be wanting in the manufacturing power, selected as the main distinctive character of vegetable life; or, at anyrate, that there is no proof that it does not get its protein matterready made from the potato plant. 

Let us, therefore, take a case which is not open to these objections. 

There are some small plants known to botanists as members of the genus_Colcochaete_, which, without being truly parasitic, grow upon certainwater-weeds, as lichens grow upon trees. The little plant has the form ofan elegant green star, the branching arms of which are divided intocells. Its greenness is due to its chlorophyll, and it undoubtedly hasthe manufacturing power in full degree, decomposing carbonic acid andsetting oxygen free, under the influence of sunlight. But theprotoplasmic contents of some of the cells of which the plant is made upoccasionally divide, by a method similar to that which effects thedivision of the contents of the _Peronospora_ spore; and the severedportions are then set free as active monad-like zoospores. Each is ovaland is provided at one extremity with two long active cilia. Propelled bythese, it swims about for a longer or shorter time, but at length comesto a state of rest and gradually grows into a _Coleochaete_. Moreover, asin the _Peronospora_, conjugation may take place and result in anoospore; the contents of which divide and are set free as monadiformgerms. 

If the whole history of the zoospores of _Peronospora_ and of_Coleochaete_ were unknown, they would undoubtedly be classed among"Monads" with the same right as _Heteromita_; why then may not_Heteromita_ be a plant, even though the cycle of forms through which itpasses shows no terms quite so complex as those which occur in_Peronospora_ and _Coleochaete_? And, in fact, there are some greenorganisms, in every respect characteristically plants, such as_Chlamydomonas_, and the common _Volvox_, or so-called "Globeanimalcule, " which run through a cycle of forms of just the same simplecharacter as those of _Heteromita_. 

The name of _Chlamydomonas_ is applied to certain microscopic greenbodies, each of which consists of a protoplasmic central substanceinvested by a structureless sac. The latter contains cellulose, as inordinary plants; and the chlorophyll which gives the green colour enablesthe _Chlamydomonas_ to decompose carbonic acid and fix carbon as they do. Two long cilia protrude through the cell-wall, and effect the rapidlocomotion of this "monad, " which, in all respects except its mobility, is characteristically a plant. Under ordinary circumstances, the_Chlamydomonas_ multiplies by simple fission, each splitting into two orinto four parts, which separate and become independent organisms. Sometimes, however, the _Chlamydomonas_ divides into eight parts, each ofwhich is provided with four instead of two cilia. These "zoospores"conjugate in pairs, and give rise to quiescent bodies, which multiply bydivision, find eventually pass into the active state. 

Thus, so far as outward form and the general character of the cycle ofmodifications, through which the organism passes in the course of itslife, are concerned, the resemblance between _Chlamydomonas_ and_Heteromita_ is of the closest description. And on the face of the matterthere is no ground for refusing to admit that _Heteromita_ may be relatedto _Chlamydomonas_, as the colourless fungus is to the green alga. _Volvox_ may be compared to a hollow sphere, the wall of which is made upof coherent Chlamydomonads; and which progresses with a rotating motioneffected by the paddling of the multitudinous pairs of cilia whichproject from its surface. Each _Volvox_-monad, moreover, possesses a redpigment spot, like the simplest form of eye known among animals. Themethods of fissive multiplication and of conjugation observed in themonads of this locomotive globe are essentially similar to those observedin _Chlamydomonas_; and, though a hard battle has been fought over it, _Volvox_ is now finally surrendered to the Botanists. 

Thus there is really no reason why _Heteromita_ may not be a plant; andthis conclusion would be very satisfactory, if it were not equally easyto show that there is really no reason why it should not be an animal. For there are numerous organisms presenting the closest resemblance to_Heteromita_, and, like it, grouped under the general name of "Monads, "which, nevertheless, can be observed to take in solid nutriment, andwhich, therefore, have a virtual, if not an actual, mouth and digestivecavity, and thus come under Cuvier's definition of an animal. Numerousforms of such animals have been described by Ehrenberg, Dujardin, H. James Clark, and other writers on the _Infusoria_. Indeed, in anotherinfusion of hay in which my _Heteromita lens_ occurred, there wereinnumerable such infusorial animalcules belonging to the well-knownspecies _Colpoda cucullus_. [6]

[Footnote 6: Excellently described by Stein, almost all of whosestatements I have verified. ]

Full-sized specimens of this animalcule attain a length of between 1/300or 1/400 of an inch, so that it may have ten times the length and athousand times the mass of a _Heteromita_. In shape, it is not altogetherunlike _Heteromita_. The small end, however, is not produced into onelong cilium, but the general surface of the body is covered with smallactively vibrating ciliary organs, which are only longest at the smallend. At the point which answers to that from which the two cilia arise in_Heteromita_, there is a conical depression, the mouth; and, in youngspecimens, a tapering filament, which reminds one of the posterior ciliumof _Heteromita_, projects from this region. 

The body consists of a soft granular protoplasmic substance, the middleof which is occupied by a large oval mass called the "nucleus"; while, atits hinder end, is a "contractile vacuole, " conspicuous by its regularrhythmic appearances and disappearances. Obviously, although the_Colpoda_ is not a monad, it differs from one only in subordinatedetails. Moreover, under certain conditions, it becomes quiescent, incloses itself in a delicate case or _cyst_, and then divides into two, four, or more portions, which are eventually set free and swim about asactive _Colpodoe_. 

But this creature is an unmistakable animal, and full-sized _Colpodoe_may be fed as easily as one feeds chickens. It is only needful to diffusevery finely ground carmine through the water in which they live, and, ina very short time, the bodies of the _Colpodoe_ are stuffed with thedeeply-coloured granules of the pigment. 

And if this were not sufficient evidence of the animality of _Colpoda_, there comes the fact that it is even more similar to another well-knownanimalcule, _Paramoecium_, than it is to a monad. But _Paramoecium_ is sohuge a creature compared with those hitherto discussed--it reaches 1/120of an inch or more in length--that there is no difficulty in making outits organisation in detail; and in proving that it is not only an animal, but that it is an animal which possesses a somewhat complicatedorganisation. For example, the surface layer of its body is different instructure from the deeper parts. There are two contractile vacuoles, fromeach of which radiates a system of vessel-like canals; and not only isthere a conical depression continuous with a tube, which serve as mouthand gullet, but the food ingested takes a definite course, and refuse isrejected from a definite region. Nothing is easier than to feed theseanimals, and to watch the particles of indigo or carmine accumulate atthe lower end of the gullet. From this they gradually project, surroundedby a ball of water, which at length passes with a jerk, oddly simulatinga gulp, into the pulpy central substance of the body, there to circulateup one side and down the other, until its contents are digested andassimilated. Nevertheless, this complex animal multiplies by division, asthe monad does, and, like the monad, undergoes conjugation. It stands inthe same relation to _Heteromita_ on the animal side, as _Coleochaete_does on the plant side. Start from either, and such an insensible seriesof gradations leads to the monad that it is impossible to say at anystage of the progress where the line between the animal and the plantmust be drawn. 

There is reason to think that certain organisms which pass through amonad stage of existence, such as the _Myxomycetes_, are, at one time oftheir lives, dependent upon external sources for their protein matter, orare animals; and, at another period, manufacture it, or are plants. Andseeing that the whole progress of modern investigation is in favour ofthe doctrine of continuity, it is a fair and probable speculation--thoughonly a speculation--that, as there are some plants which can manufactureprotein out of such apparently intractable mineral matters as carbonicacid, water, nitrate of ammonia, metallic and earthy salts; while othersneed to be supplied with their carbon and nitrogen in the somewhat lessraw form of tartrate of ammonia and allied compounds; so there may be yetothers, as is possibly the case with the true parasitic plants, which canonly manage to put together materials still better prepared--still morenearly approximated to protein--until we arrive at such organisms as the_Psorospermioe_ and the _Panhistophyton_, which are as much animal asvegetable in structure, but are animal in their dependence on otherorganisms for their food. 

The singular circumstance observed by Meyer, that the _Torula_ of yeast, though an indubitable plant, still flourishes most vigorously whensupplied with the complex nitrogenous substance, pepsin; the probabilitythat the _Peronospora_ is nourished directly by the protoplasm of thepotato-plant; and the wonderful facts which have recently been brought tolight respecting insectivorous plants, all favour this view; and tend tothe conclusion that the difference between animal and plant is one ofdegree rather than of kind, and that the problem whether, in a givencase, an organism is an animal or a plant, may be essentially insoluble. 

VII

A LOBSTER; OR, THE STUDY OF ZOOLOGY

[1861]

Natural history is the name familiarly applied to the study of theproperties of such natural bodies as minerals, plants, and animals; thesciences which embody the knowledge man has acquired upon these subjectsare commonly termed Natural Sciences, in contradistinction to other so-called "physical" sciences; and those who devote themselves especially tothe pursuit of such sciences have been and are commonly termed"Naturalists. "

Linnaeus was a naturalist in this wide sense, and his "Systema Naturae" wasa work upon natural history, in the broadest acceptation of the term; init, that great methodising spirit embodied all that was known in his timeof the distinctive characters of minerals, animals, and plants. But theenormous stimulus which Linnaeus gave to the investigation of nature soonrendered it impossible that any one man should write another "SystemaNaturae, " and extremely difficult for any one to become even a naturalistsuch as Linnaeus was. 

Great as have been the advances made by all the three branches ofscience, of old included under the title of natural history, there can beno doubt that zoology and botany have grown in an enormously greaterratio than mineralogy; and hence, as I suppose, the name of "naturalhistory" has gradually become more and more definitely attached to theseprominent divisions of the subject, and by "naturalist" people have meantmore and more distinctly to imply a student of the structure and functionof living beings. 

However this may be, it is certain that the advance of knowledge hasgradually widened the distance between mineralogy and its old associates, while it has drawn zoology and botany closer together; so that of lateyears it has been found convenient (and indeed necessary) to associatethe sciences which deal with vitality and all its phenomena under thecommon head of "biology"; and the biologists have come to repudiate anyblood-relationship with their foster-brothers, the mineralogists. 

Certain broad laws have a general application throughout both the animaland the vegetable worlds, but the ground common to these kingdoms ofnature is not of very wide extent, and the multiplicity of details is sogreat, that the student of living beings finds himself obliged to devotehis attention exclusively either to the one or the other. If he elects tostudy plants, under any aspect, we know at once what to call him. He is abotanist, and his science is botany. But if the investigation of animallife be his choice, the name generally applied to him will vary accordingto the kind of animals he studies, or the particular phenomena of animallife to which he confines his attention. If the study of man is hisobject, he is called an anatomist, or a physiologist, or an ethnologist;but if he dissects animals, or examines into the mode in which theirfunctions are performed, he is a comparative anatomist or comparativephysiologist. If he turns his attention to fossil animals, he is apalaeontologist. If his mind is more particularly directed to the specificdescription, discrimination, classification, and distribution of animals, he is termed a zoologist. 

For the purpose of the present discourse, however, I shall recognise noneof these titles save the last, which I shall employ as the equivalent ofbotanist, and I shall use the term zoology is denoting the whole doctrineof animal life, in contradistinction to botany, which signifies the wholedoctrine of vegetable life. 

Employed in this sense, zoology, like botany, is divisible into threegreat but subordinate sciences, morphology, physiology, and distribution, each of which may, to a very great extent, be studied independently ofthe other. 

Zoological morphology is the doctrine of animal form or structure. Anatomy is one of its branches; development is another; whileclassification is the expression of the relations which different animalsbear to one another, in respect of their anatomy and their development. 

Zoological distribution is the study of animals in relation to theterrestrial conditions which obtain now, or have obtained at any previousepoch of the earth's history. 

Zoological physiology, lastly, is the doctrine of the functions oractions of animals. It regards animal bodies as machines impelled bycertain forces, and performing an amount of work which can be expressedin terms of the ordinary forces of nature. The final object of physiologyis to deduce the facts of morphology, on the one hand, and those ofdistribution on the other, from the laws of the molecular forces ofmatter. 

Such is the scope of zoology. But if I were to content myself with theenunciation of these dry definitions, I should ill exemplify that methodof teaching this branch of physical science, which it is my chiefbusiness to-night to recommend. Let us turn away then from abstractdefinitions. Let us take some concrete living thing, some animal, thecommoner the better, and let us see how the application of common senseand common logic to the obvious facts it presents, inevitably leads usinto all these branches of zoological science. 

I have before me a lobster. When I examine it, what appears to be themost striking character it presents? Why, I observe that this part whichwe call the tail of the lobster, is made up of six distinct hard ringsand a seventh terminal piece. If I separate one of the middle rings, saythe third, I find it carries upon its under surface a pair of limbs orappendages, each of which consists of a stalk and two terminal pieces. Sothat I can represent a transverse section of the ring and its appendagesupon the diagram board in this way. 

If I now take the fourth ring, I find it has the same structure, and sohave the fifth and the second; so that, in each of these divisions of thetail, I find parts which correspond with one another, a ring and twoappendages; and in each appendage a stalk and two end pieces. Thesecorresponding parts are called, in the technical language of anatomy, "homologous parts. " The ring of the third division is the "homologue" ofthe ring of the fifth, the appendage of the former is the homologue ofthe appendage of the latter. And, as each division exhibits correspondingparts in corresponding places, we say that all the divisions areconstructed upon the same plan. But now let us consider the sixthdivision. It is similar to, and yet different from, the others. The ringis essentially the same as in the other divisions; but the appendageslook at first as if they were very different; and yet when we regard themclosely, what do we find? A stalk and two terminal divisions, exactly asin the others, but the stalk is very short and very thick, the terminaldivisions are very broad and flat, and one of them is divided into twopieces. 

I may say, therefore, that the sixth segment is like the others in plan, but that it is modified in its details. 

The first segment is like the others, so far as its ring is concerned, and though its appendages differ from any of those yet examined in thesimplicity of their structure, parts corresponding with the stem and oneof the divisions of the appendages of the other segments can be readilydiscerned in them. 

Thus it appears that the lobster's tail is composed of a series ofsegments which are fundamentally similar, though each presents peculiarmodifications of the plan common to all. But when I turn to the forepartof the body I see, at first, nothing but a great shield-like shell, called technically the "carapace, " ending in front in a sharp spine, oneither side of which are the curious compound eyes, set upon the ends ofstout movable stalks. Behind these, on the under side of the body, aretwo pairs of long feelers, or antennae, followed by six pairs of jawsfolded against one another over the mouth, and five pairs of legs, theforemost of these being the great pinchers, or claws, of the lobster. 

It looks, at first, a little hopeless to attempt to find in this complexmass a series of rings, each with its pair of appendages, such as I haveshown you in the abdomen, and yet it is not difficult to demonstratetheir existence. Strip off the legs, and you will find that each pair isattached to a very definite segment of the under wall of the body; butthese segments, instead of being the lower parts of free rings, as in thetail, are such parts of rings which are all solidly united and boundtogether; and the like is true of the jaws, the feelers, and the eye-stalks, every pair of which is borne upon its own special segment. Thusthe conclusion is gradually forced upon us, that the body of the lobsteris composed of as many rings as there are pairs of appendages, namely, twenty in all, but that the six hindmost rings remain free and movable, while the fourteen front rings become firmly soldered together, theirbacks forming one continuous shield--the carapace. 

Unity of plan, diversity in execution, is the lesson taught by the studyof the rings of the body, and the same instruction is given still moreemphatically by the appendages. If I examine the outermost jaw I find itconsists of three distinct portions, an inner, a middle, and an outer, mounted upon a common stem; and if I compare this jaw with the legsbehind it, or the jaws in front of it, I find it quite easy to see, that, in the legs, it is the part of the appendage which corresponds with theinner division, which becomes modified into what we know familiarly asthe "leg, " while the middle division disappears, and the outer divisionis hidden under the carapace. Nor is it more difficult to discern that, in the appendages of the tail, the middle division appears again and theouter vanishes; while, on the other hand, in the foremost jaw, the so-called mandible, the inner division only is left; and, in the same way, the parts of the feelers and of the eye-stalks can be identified withthose of the legs and jaws. 

But whither does all this tend? To the very remarkable conclusion that aunity of plan, of the same kind as that discoverable in the tail orabdomen of the lobster, pervades the whole organisation of its skeleton, so that I can return to the diagram representing any one of the rings ofthe tail, which I drew upon the board, and by adding a third division toeach appendage, I can use it as a sort of scheme or plan of any ring ofthe body. I can give names to all the parts of that figure, and then if Itake any segment of the body of the lobster, I can point out to youexactly, what modification the general plan has undergone in thatparticular segment; what part has remained movable, and what has becomefixed to another; what has been excessively developed and metamorphosedand what has been suppressed. 

But I imagine I hear the question, How is all this to be tested? No doubtit is a pretty and ingenious way of looking at the structure of anyanimal; but is it anything more? Does Nature acknowledge, in any deeperway, this unity of plan we seem to trace?

The objection suggested by these questions is a very valid and importantone, and morphology was in an unsound state so long as it rested upon themere perception of the analogies which obtain between fully formed parts. The unchecked ingenuity of speculative anatomists proved itself fullycompetent to spin any number of contradictory hypotheses out of the samefacts, and endless morphological dreams threatened to supplant scientifictheory. 

Happily, however, there is a criterion of morphological truth, and a suretest of all homologies. Our lobster has not always been what we see it;it was once an egg, a semifluid mass of yolk, not so big as a pin's head, contained in a transparent membrane, and exhibiting not the least traceof any one of those organs, the multiplicity and complexity of which, inthe adult, are so surprising. After a time, a delicate patch of cellularmembrane appeared upon one face of this yolk, and that patch was thefoundation of the whole creature, the clay out of which it would bemoulded. Gradually investing the yolk, it became subdivided by transverseconstrictions into segments, the forerunners of the rings of the body. Upon the ventral surface of each of the rings thus sketched out, a pairof bud-like prominences made their appearance--the rudiments of theappendages of the ring. At first, all the appendages were alike, but, asthey grew, most of them became distinguished into a stem and two terminaldivisions, to which, in the middle part of the body, was added a thirdouter division; and it was only at a later period, that by themodification, or absorption, of certain of these primitive constituents, the limbs acquired their perfect form. 

Thus the study of development proves that the doctrine of unity of planis not merely a fancy, that it is not merely one way of looking at thematter, but that it is the expression of deep-seated natural facts. Thelegs and jaws of the lobster may not merely be regarded as modificationsof a common type, --in fact and in nature they are so, --the leg and thejaw of the young animal being, at first, indistinguishable. 

These are wonderful truths, the more so because the zoologist finds themto be of universal application. The investigation of a polype, of asnail, of a fish, of a horse, or of a man, would have led us, though by aless easy path, perhaps, to exactly the same point. Unity of planeverywhere lies hidden under the mask of diversity of structure--thecomplex is everywhere evolved out of the simple. Every animal has atfirst the form of an egg, and every animal and every organic part, inreaching its adult state, passes through conditions common to otheranimals and other adult parts; and this leads me to another point. I havehitherto spoken as if the lobster were alone in the world, but, as I needhardly remind you, there are myriads of other animal organisms. Of these, some, such as men, horses, birds, fishes, snails, slugs, oysters, corals, and sponges, are not in the least like the lobster. But other animals, though they may differ a good deal from the lobster, are yet either verylike it, or are like something that is like it. The cray fish, the rocklobster, and the prawn, and the shrimp, for example, however different, are yet so like lobsters, that a child would group them as of the lobsterkind, in contradistinction to snails and slugs; and these last againwould form a kind by themselves, in contradistinction to cows, horses, and sheep, the cattle kind. 

But this spontaneous grouping into "kinds" is the first essay of thehuman mind at classification, or the calling by a common name of thosethings that are alike, and the arranging them in such a manner as best tosuggest the sum of their likenesses and unlikenesses to other things. 

Those kinds which include no other subdivisions than the sexes, orvarious breeds, are called, in technical language, species. The Englishlobster is a species, our cray fish is another, our prawn is another. Inother countries, however, there are lobsters, cray fish, and prawns, verylike ours, and yet presenting sufficient differences to deservedistinction. Naturalists, therefore, express this resemblance and thisdiversity by grouping them as distinct species of the same "genus. " Butthe lobster and the cray fish, though belonging to distinct genera, havemany features in common, and hence are grouped together in an assemblagewhich is called a family. More distant resemblances connect the lobsterwith the prawn and the crab, which are expressed by putting all theseinto the same order. Again, more remote, but still very definite, resemblances unite the lobster with the woodlouse, the king crab, thewater flea, and the barnacle, and separate them from all other animals;whence they collectively constitute the larger group, or class, _Crustacea_. But the _Crustacea_ exhibit many peculiar features in commonwith insects, spiders, and centipedes, so that these are grouped into thestill larger assemblage or "province" _Articulata_; and, finally, therelations which these have to worms and other lower animals, areexpressed by combining the whole vast aggregate into the sub-kingdom of_Annulosa_. 

If I had worked my way from a sponge instead of a lobster, I should havefound it associated, by like ties, with a great number of other animalsinto the sub-kingdom _Protozoa_; if I had selected a fresh-water polypeor a coral, the members of what naturalists term the sub-kingdom_Coelenterata_, would have grouped themselves around my type; had a snailbeen chosen, the inhabitants of all univalve and bivalve, land and water, shells, the lamp shells, the squids, and the sea-mat would have graduallylinked themselves on to it as members of the same sub-kingdom of_Mollusca_; and finally, starting from man, I should have been compelledto admit first, the ape, the rat, the horse, the dog, into the sameclass; and then the bird, the crocodile, the turtle, the frog, and thefish, into the same sub-kingdom of _Vertebrata_. 

And if I had followed out all these various lines of classificationfully, I should discover in the end that there was no animal, eitherrecent or fossil, which did not at once fall into one or other of thesesub-kingdoms. In other words, every animal is organised upon one or otherof the five, or more, plans, the existence of which renders ourclassification possible. And so definitely and precisely marked is thestructure of each animal, that, in the present state of our knowledge, there is not the least evidence to prove that a form, in the slightestdegree transitional between any of the two groups _Vertebrata, Annulosa, Mollusca_, and _Coelenterata_, either exists, or has existed, during thatperiod of the earth's history which is recorded by the geologist. [1]Nevertheless, you must not for a moment suppose, because no suchtransitional forms are known, that the members of the sub-kingdoms aredisconnected from, or independent of, one another. On the contrary, intheir earliest condition they are all similar, and the primordial germsof a man, a dog, a bird, a fish, a beetle, a snail, and a polype are, inno essential structural respects, distinguishable. 

[Footnote 1: The different grouping necessitated by later knowledge doesnot affect the principle of the argument. --1894. ]

In this broad sense, it may with truth be said, that all living animals, and all those dead faunae which geology reveals, are bound together by anall-pervading unity of organisation, of the same character, though notequal in degree, to that which enables us to discern one and the sameplan amidst the twenty different segments of a lobster's body. Truly ithas been said, that to a clear eye the smallest fact is a window throughwhich the Infinite may be seen. 

Turning from these purely morphological considerations, let us nowexamine into the manner in which the attentive study of the lobsterimpels us into other lines of research. 

Lobsters are found in all the European seas; but on the opposite shoresof the Atlantic and in the seas of the southern hemisphere they do notexist. They are, however, represented in these regions by very closelyallied, but distinct forms--the _Homarus Americanus_ and the _HomarusCapensis:_ so that we may say that the European has one species of_Homuarus_; the American, another; the African, another; and thus theremarkable facts of geographical distribution begin to dawn upon us. 

Again, if we examine the contents of the earth's crust, we shall find inthe latter of those deposits, which have served as the great buryinggrounds of past ages, numberless lobster-like animals, but none sosimilar to our living lobster as to make zoologists sure that theybelonged even to the same genus. If we go still further back in time, wediscover, in the oldest rocks of all, the remains of animals, constructedon the same general plan as the lobster, and belonging to the same greatgroup of _Crustacea_; but for the most part totally different from thelobster, and indeed from any other living form of crustacean; and thus wegain a notion of that successive change of the animal population of theglobe, in past ages, which is the most striking fact revealed by geology. 

Consider, now, where our inquiries have led us. We studied our typemorphologically, when we determined its anatomy and its development, andwhen comparing it, in these respects, with other animals, we made out itsplace in a system of classification. If we were to examine every animalin a similar manner, we should establish a complete body of zoologicalmorphology. 

Again, we investigated the distribution of our type in space and in time, and, if the like had been done with every animal, the sciences ofgeographical and geological distribution would have attained their limit. 

But you will observe one remarkable circumstance, that, up to this point, the question of the life of these organisms has not come underconsideration. Morphology and distribution might be studied almost aswell, if animals and plants were a peculiar kind of crystals, andpossessed none of those functions which distinguish living beings soremarkably. But the facts of morphology and distribution have to beaccounted for, and the science, the aim of which it is to account forthem, is Physiology. 

Let us return to our lobster once more. If we watched the creature in itsnative element, we should see it climbing actively the submerged rocks, among which it delights to live, by means of its strong legs; or swimmingby powerful strokes of its great tail, the appendages of the sixth jointof which are spread out into a broad fan-like Propeller: seize it, and itwill show you that its great claws are no mean weapons of offence;suspend a piece of carrion among its haunts, and it will greedily devourit, tearing and crushing the flesh by means of its multitudinous jaws. 

Suppose that we had known nothing of the lobster but as an inert mass, anorganic crystal, if I may use the phrase, and that we could suddenly seeit exerting all these powers, what wonderful new ideas and new questionswould arise in our minds! The great new question would be, "How does allthis take place?" the chief new idea would be, the idea of adaptation topurpose, --the notion, that the constituents of animal bodies are not mereunconnected parts, but organs working together to an end. Let us considerthe tail of the lobster again from this point of view. Morphology hastaught us that it is a series of segments composed of homologous parts, which undergo various modifications--beneath and through which a commonplan of formation is discernible. But if I look at the same partphysiologically, I see that it is a most beautifully constructed organ oflocomotion, by means of which the animal can swiftly propel itself eitherbackwards or forwards. 

But how is this remarkable propulsive machine made to perform itsfunctions? If I were suddenly to kill one of these animals and to takeout all the soft parts, I should find the shell to be perfectly inert, tohave no more power of moving itself than is possessed by the machinery ofa mill when disconnected from its steam-engine or water-wheel. But if Iwere to open it, and take out the viscera only, leaving the white flesh, I should perceive that the lobster could bend and extend its tail as wellas before. If I were to cut off the tail, I should cease to find anyspontaneous motion in it; but on pinching any portion of the flesh, Ishould observe that it underwent a very curious change--each fibrebecoming shorter and thicker. By this act of contraction, as it istermed, the parts to which the ends of the fibre are attached are, ofcourse, approximated; and according to the relations of their points ofattachment to the centres of motions of the different rings, the bendingor the extension of the tail results. Close observation of the newly-opened lobster would soon show that all its movements are due to the samecause--the shortening and thickening of these fleshy fibres, which aretechnically called muscles. 

Here, then, is a capital fact. The movements of the lobster are due tomuscular contractility. But why does a muscle contract at one time andnot at another? Why does one whole group of muscles contract when thelobster wishes to extend his tail, and another group when he desires tobend it? What is it originates, directs, and controls the motive power?

Experiment, the great instrument for the ascertainment of truth inphysical science, answers this question for us. In the head of thelobster there lies a small mass of that peculiar tissue which is known asnervous substance. Cords of similar matter connect his brain of thelobster, directly or indirectly, with the muscles. Now, if thesecommunicating cords are cut, the brain remaining entire, the power ofexerting what we call voluntary motion in the parts below the section isdestroyed; and, on the other hand, if, the cords remaining entire, thebrain mass be destroyed, the same voluntary mobility is equally lost. Whence the inevitable conclusion is, that the power of originating thesemotions resides in the brain and is propagated along the nervous cords. 

In the higher animals the phenomena which attend this transmission havebeen investigated, and the exertion of the peculiar energy which residesin the nerves has been found to be accompanied by a disturbance of theelectrical state of their molecules. 

If we could exactly estimate the signification of this disturbance; if wecould obtain the value of a given exertion of nerve force by determiningthe quantity of electricity, or of heat, of which it is the equivalent;if we could ascertain upon what arrangement, or other condition of themolecules of matter, the manifestation of the nervous and muscularenergies depends (and doubtless science will some day or other ascertainthese points), physiologists would have attained their ultimate goal inthis direction; they would have determined the relation of the motiveforce of animals to the other forms of force found in nature; and if thesame process had been successfully performed for all the operations whichare carried on in, and by, the animal frame, physiology would be perfect, and the facts of morphology and distribution would be deducible from thelaws which physiologists had established, combined with those determiningthe condition of the surrounding universe. 

There is not a fragment of the organism of this humble animal whose studywould not lead us into regions of thought as large as those which I havebriefly opened up to you; but what I have been saying, I trust, has notonly enabled you to form a conception of the scope and purport ofzoology, but has given you an imperfect example of the manner in which, in my opinion, that science, or indeed any physical science, may be besttaught. The great matter is, to make teaching real and practical, byfixing the attention of the student on particular facts; but at the sametime it should be rendered broad and comprehensive, by constant referenceto the generalisations of which all particular facts are illustrations. The lobster has served as a type of the whole animal kingdom, and itsanatomy and physiology have illustrated for us some of the greatesttruths of biology. The student who has once seen for himself the factswhich I have described, has had their relations explained to him, and hasclearly comprehended them, has, so far, a knowledge of zoology, which isreal and genuine, however limited it may be, and which is worth more thanall the mere reading knowledge of the science he could ever acquire. Hiszoological information is, so far, knowledge and not mere hearsay. 

And if it were nay business to fit you for the certificate in zoologicalscience granted by this department, I should pursue a course preciselysimilar in principle to that which I have taken to-night. I should selecta fresh-water sponge, a fresh-water polype or a _Cyanoea_, a fresh-watermussel, a lobster, a fowl, as types of the five primary divisions of theanimal kingdom. I should explain their structure very fully, and show howeach illustrated the great principles of zoology. Having gone verycarefully and fully over this ground, I should feel that you had a safefoundation, and I should then take you in the same way, but lessminutely, over similarly selected illustrative types of the classes; andthen I should direct your attention to the special forms enumerated underthe head of types, in this syllabus, and to the other facts therementioned. 

That would, speaking generally, be my plan. But I have undertaken toexplain to you the best mode of acquiring and communicating a knowledgeof zoology, and you may therefore fairly ask me for a more detailed andprecise account of the manner in which I should propose to furnish youwith the information I refer to. 

My own impression is, that the best model for all kinds of training inphysical science is that afforded by the method of teaching anatomy, inuse in the medical schools. This method consists of three elements--lectures, demonstrations, and examinations. 

The object of lectures is, in the first place, to awaken the attentionand excite the enthusiasm of the student; and this, I am sure, may beeffected to a far greater extent by the oral discourse and by thepersonal influence of a respected teacher than in any other way. Secondly, lectures have the double use of guiding the student to thesalient points of a subject, and at the same time forcing him to attendto the whole of it, and not merely to that part which takes his fancy. And lastly, lectures afford the student the opportunity of seekingexplanations of those difficulties which will, and indeed ought to, arisein the course of his studies. 

What books shall I read? is a question constantly put by the student tothe teacher. My reply usually is, "None: write your notes out carefullyand fully; strive to understand them thoroughly; come to me for theexplanation of anything you cannot understand; and I would rather you didnot distract your mind by reading. " A properly composed course oflectures ought to contain fully as much matter as a student canassimilate in the time occupied by its delivery; and the teacher shouldalways recollect that his business is to feed, and not to cram theintellect. Indeed, I believe that a student who gains from a course oflectures the simple habit of concentrating his attention upon adefinitely limited series of facts, until they are thoroughly mastered, has made a step of immeasurable importance. 

But, however good lectures may be, and however extensive the course ofreading by which they are followed up, they are but accessories to thegreat instrument of scientific teaching--demonstration. If I insistunweariedly, nay fanatically, upon the importance of physical science asan educational agent, it is because the study of any branch of science, if properly conducted, appears to me to fill up a void left by all othermeans of education. I have the greatest respect and love for literature;nothing would grieve me more than to see literary training other than avery prominent branch of education: indeed, I wish that real literarydiscipline were far more attended to than it is; but I cannot shut myeyes to the fact, that there is a vast difference between men who havehad a purely literary, and those who have had a sound scientific, training. 

Seeking for the cause of this difference, I imagine I can find it in thefact that, in the world of letters, learning and knowledge are one, andbooks are the source of both; whereas in science, as in life, learningand knowledge are distinct, and the study of things, and not of books, isthe source of the latter. 

All that literature has to bestow may be obtained by reading and bypractical exercise in writing and in speaking; but I do not exaggeratewhen I say, that none of the best gifts of science are to be won by thesemeans. On the contrary, the great benefit which a scientific educationbestows, whether is training or as knowledge, is dependent upon theextent to which the mind of the student is brought into immediate contactwith facts--upon the degree to which he learns the habit of appealingdirectly to Nature, and of acquiring through his senses concrete imagesof those properties of things, which are, and always will be, butapproximatively expressed in human language. Our way of looking atNature, and of speaking about her, varies from year to year; but a factonce seen, a relation of cause and effect, once demonstrativelyapprehended, are possessions which neither change nor pass away, but, onthe contrary, form fixed centres, about which other truths aggregate bynatural affinity. 

Therefore, the great business of the scientific teacher is, to imprintthe fundamental, irrefragable facts of his science, not only by wordsupon the mind, but by sensible impressions upon the eye, and ear, andtouch of the student, in so complete a manner, that every term used, orlaw enunciated, should afterwards call up vivid images of the particularstructural, or other, facts which furnished the demonstration of the law, or the illustration of the term. 

Now this important operation can only be achieved by constantdemonstration, which may take place to a certain imperfect extent duringa lecture, but which ought also to be carried on independently, and whichshould be addressed to each individual student, the teacher endeavouring, not so much to show a thing to the learner, as to make him see it forhimself. 

I am well aware that there are great practical difficulties in the way ofeffectual zoological demonstrations. The dissection of animals is notaltogether pleasant, and requires much time; nor is it easy to secure anadequate supply of the needful specimens. The botanist has here a greatadvantage; his specimens are easily obtained, are clean and wholesome, and can be dissected in a private house as well as anywhere else; andhence, I believe, the fact, that botany is so much more readily andbetter taught than its sister science. But, be it difficult or be iteasy, if zoological science is to be properly studied, demonstration, and, consequently, dissection, must be had. Without it, no man can have areally sound knowledge of animal organisation. 

A good deal may be done, however, without actual dissection on thestudent's part, by demonstration upon specimens and preparations; and inall probability it would not be very difficult, were the demandsufficient, to organise collections of such objects, sufficient for allthe purposes of elementary teaching, at a comparatively cheap rate. Evenwithout these, much might be effected, if the zoological collections, which are open to the public, were arranged according to what has beentermed the "typical principle"; that is to say, if the specimens exposedto public view were so selected that the public could learn somethingfrom them, instead of being, as at present, merely confused by theirmultiplicity. For example, the grand ornithological gallery at theBritish Museum contains between two and three thousand species of birds, and sometimes five or six specimens of a species. They are very pretty tolook at, and some of the cases are, indeed, splendid; but I willundertake to say, that no man but a professed ornithologist has evergathered much information from the collection. Certainly, no one of thetens of thousands of the general public who have walked through thatgallery ever knew more about the essential peculiarities of birds when heleft the gallery than when he entered it. But if, somewhere in that vasthall, there were a few preparations, exemplifying the leading structuralpeculiarities and the mode of development of a common fowl; if the typesof the genera, the leading modifications in the skeleton, in the plumageat various ages, in the mode of nidification, and the like, among birds, were displayed; and if the other specimens were put away in a place wherethe men of science, to whom they are alone useful, could have free accessto them, I can conceive that this collection might become a greatinstrument of scientific education. 

The last implement of the teacher to which I have adverted isexamination--a means of education now so thoroughly understood that Ineed hardly enlarge upon it. I hold that both written and oralexaminations are indispensable, and, by requiring the description ofspecimens, they may be made to supplement demonstration. 

Such is the fullest reply the time at my disposal will allow me to giveto the question--how may a knowledge of zoology be best acquired andcommunicated?

But there is a previous question which may be moved, and which, in fact, I know many are inclined to move. It is the question, why should teachersbe encouraged to acquire a knowledge of this, or any other branch ofphysical science? What is the use, it is said, of attempting to makephysical science a branch of primary education? Is it not probable thatteachers, in pursuing such studies, will be led astray from theacquirement of more important but less attractive knowledge? And, even ifthey can learn something of science without prejudice to theirusefulness, what is the good of their attempting to instil that knowledgeinto boys whose real business is the acquisition of reading, writing, andarithmetic?

These questions are, and will be, very commonly asked, for they arisefrom that profound ignorance of the value and true position of physicalscience, which infests the minds of the most highly educated andintelligent classes of the community. But if I did not feel well assuredthat they are capable of being easily and satisfactorily answered; thatthey have been answered over and over again; and that the time will comewhen men of liberal education will blush to raise such questions--Ishould be ashamed of my position here to-night. Without doubt, it is yourgreat and very important function to carry out elementary education;without question, anything that should interfere with the faithfulfulfilment of that duty on your part would be a great evil; and if Ithought that your acquirement of the elements of physical science, andyour communication of those elements to your pupils, involved any sort ofinterference with your proper duties, I should be the first person toprotest against your being encouraged to do anything of the kind. 

But is it true that the acquisition of such a knowledge of science as isproposed, and the communication of that knowledge, are calculated toweaken your usefulness? Or may I not rather ask, is it possible for youto discharge your functions properly without these aids?

What is the purpose of primary intellectual education? I apprehend thatits first object is to train the young in the use of those toolswherewith men extract knowledge from the ever-shifting succession ofphenomena which pass before their eyes; and that its second object is toinform them of the fundamental laws which have been found by experienceto govern the course of things, so that they may not be turned out intothe world naked, defenceless, and a prey to the events they mightcontrol. 

A boy is taught to read his own and other languages, in order that he mayhave access to infinitely wider stores of knowledge than could ever beopened to him by oral intercourse with his fellow men; he learns towrite, that his means of communication with the rest of mankind may beindefinitely enlarged, and that he may record and store up the knowledgehe acquires. He is taught elementary mathematics, that he may understandall those relations of number and form, upon which the transactions ofmen, associated in complicated societies, are built, and that he may havesome practice in deductive reasoning. 

All these operations of reading, writing, and ciphering, are intellectualtools, whose use should, before all things, be learned, and learnedthoroughly; so that the youth may be enabled to make his life that whichit ought to be, a continual progress in learning and in wisdom. 

But, in addition, primary education endeavours to fit a boy out with acertain equipment of positive knowledge. He is taught the great laws ofmorality; the religion of his sect; so much history and geography as willtell him where the great countries of the world are, what they are, andhow they have become what they are. 

Without doubt all these are most fitting and excellent things to teach aboy; I should be very sorry to omit any of them from any scheme ofprimary intellectual education. The system is excellent, so far as itgoes. 

But if I regard it closely, a curious reflection arises. I suppose that, fifteen hundred years ago, the child of any well-to-do Roman citizen wastaught just these same things; reading and writing in his own, and, perhaps, the Greek tongue; the elements of mathematics; and the religion, morality, history, and geography current in his time. Furthermore, I donot think I err in affirming, that, if such a Christian Roman boy, whohad finished his education, could be transplanted into one of our publicschools, and pass through its course of instruction, he would not meetwith a single unfamiliar line of thought; amidst all the new facts hewould have to learn, not one would suggest a different mode of regardingthe universe from that current in his own time. 

And yet surely there is some great difference between the civilisation ofthe fourth century and that of the nineteenth, and still more between theintellectual habits and tone of thought of that day and this?

And what has made this difference? I answer fearlessly--The prodigiousdevelopment of physical science within the last two centuries. 

Modern civilisation rests upon physical science; take away her gifts toour own country, and our position among the leading nations of the worldis gone to-morrow; for it is physical science only that makesintelligence and moral energy stronger than brute force. 

The whole of modern thought is steeped in science; it has made its wayinto the works of our best poets, and even the mere man of letters, whoaffects to ignore and despise science, is unconsciously impregnated withher spirit, and indebted for his best products to her methods. I believethat the greatest intellectual revolution mankind has yet seen is nowslowly taking place by her agency. She is teaching the world that theultimate court of appeal is observation and experiment, and notauthority; she is teaching it to estimate the value of evidence; she iscreating a firm and living faith in the existence of immutable moral andphysical laws, perfect obedience to which is the highest possible aim ofan intelligent being. 

But of all this your old stereotyped system of education takes no note. Physical science, its methods, its problems, and its difficulties, willmeet the poorest boy at every turn, and yet we educate him in such amanner that he shall enter the world as ignorant of the existence of themethods and facts of science as the day he was born. The modern world isfull of artillery; and we turn out our children to do battle in it, equipped with the shield and sword of an ancient gladiator. 

Posterity will cry shame on us if we do not remedy this deplorable stateof things. Nay, if we live twenty years longer, our own consciences willcry shame on us. 

It is my firm conviction that the only way to remedy it is to make theelements of physical science an integral part of primary education. Ihave endeavoured to show you how that may be done for that branch ofscience which it is my business to pursue; and I can but add, that Ishould look upon the day when every schoolmaster throughout this land wasa centre of genuine, however rudimentary, scientific knowledge, as anepoch in the history of the country. 

But let me entreat you to remember my last words. Addressing myself toyou, as teachers, I would say, mere book learning in physical science isa sham and a delusion--what you teach, unless you wish to be impostors, that you must first know; and real knowledge in science means personalacquaintance with the facts, be they few or many. [2]

[Footnote 2: It has been suggested to me that these words may be taken toimply a discouragement on my part of any sort of scientific instructionwhich does not give an acquaintance with the facts at first hand. Butthis is not my meaning. The ideal of scientific teaching is, no doubt, asystem by which the scholar sees every fact for himself, and the teachersupplies only the explanations. Circumstances, however, do not oftenallow of the attainment of that ideal, and we must put up with the nextbest system--one in which the scholar takes a good deal on trust from ateacher, who, knowing the facts by his own knowledge, can describe themwith so much vividness as to enable his audience to form competent ideasconcerning them. The system which I repudiate is that which allowsteachers who have not come into direct contact with the leading facts ofa science to pass their second-hand information on. The scientific virus, like vaccine lymph, if passed through too long a succession of organisms, will lose all its effect in protecting the young against the intellectualepidemics to which they are exposed. 

[The remarks on p. 222 applied to the Natural History Collection of theBritish Museum in 1861. The visitor to the Natural History Museum in 1894need go no further than the Great Hall to see the realisation of my hopesby the present Director. ]]

VIII

BIOGENESIS AND ABIOGENESIS

(THE PRESIDENTIAL ADDRESS TO THE BRITISH ASSOCIATION FOR THE ADVANCEMENTOF SCIENCE FOR 1870)

It has long been the custom for the newly installed President of theBritish Association for the Advancement of Science to take advantage ofthe elevation of the position in which the suffrages of his colleagueshad, for the time, placed him, and, casting his eyes around the horizonof the scientific world, to report to them what could be seen from hiswatch-tower; in what directions the multitudinous divisions of the noblearmy of the improvers of natural knowledge were marching; what importantstrongholds of the great enemy of us all, ignorance, had been recentlycaptured; and, also, with due impartiality, to mark where the advancedposts of science had been driven in, or a long-continued siege had madeno progress. 

I propose to endeavour to follow this ancient precedent, in a mannersuited to the limitations of my knowledge and of my capacity. I shall notpresume to attempt a panoramic survey of the world of science, nor evento give a sketch of what is doing in the one great province of biology, with some portions of which my ordinary occupations render me familiar. But I shall endeavour to put before you the history of the rise andprogress of a single biological doctrine; and I shall try to give somenotion of the fruits, both intellectual and practical, which we owe, directly or indirectly, to the working out, by seven generations ofpatient and laborious investigators, of the thought which arose, morethan two centuries ago, in the mind of a sagacious and observant Italiannaturalist. 

It is a matter of everyday experience that it is difficult to preventmany articles of food from becoming covered with mould; that fruit, soundenough to all appearance, often contains grubs at the core; that meat, left to itself in the air, is apt to putrefy and swarm with maggots. Evenordinary water, if allowed to stand in an open vessel, sooner or laterbecomes turbid and full of living matter. 

The philosophers of antiquity, interrogated as to the cause of thesephenomena, were provided with a ready and a plausible answer. It did notenter their minds even to doubt that these low forms of life weregenerated in the matters in which they made their appearance. Lucretius, who had drunk deeper of the scientific spirit than any poet of ancient ormodern times except Goethe, intends to speak as a philosopher, ratherthan as a poet, when he writes that "with good reason the earth hasgotten the name of mother, since all things are produced out of theearth. And many living creatures, even now, spring out of the earth, taking form by the rains and the heat of the sun. "[1] The axiom ofancient science, "that the corruption of one thing is the birth ofanother, " had its popular embodiment in the notion that a seed diesbefore the young plant springs from it; a belief so widespread and sofixed, that Saint Paul appeals to it in one of the most splendidoutbursts of his fervid eloquence:--

"Thou fool, that which thou sowest is not quickened, except it die. "[2]

[Footnote 1: It is thus that Mr. Munro renders

"Linquitur, ut merito maternum nomen adeptaTerra sit, e terra quoniam sunt cuncta creata. Multaque nunc etiam exsistant animalia terrisImbribus et calido solis concreta vapore. "

_De Rerum Natura_, lib. V. 793-796. 

But would not the meaning of the last line be better rendered "Developedin rain-water and in the warm vapours raised by the sun"?]

[Footnote 2: 1 Corinthians xv. 36. ]

The proposition that life may, and does, proceed from that which has nolife, then, was held alike by the philosophers, the poets, and thepeople, of the most enlightened nations, eighteen hundred years ago; andit remained the accepted doctrine of learned and unlearned Europe, through the Middle Ages, down even to the seventeenth century. 

It is commonly counted among the many merits of our great countryman, Harvey, that he was the first to declare the opposition of fact tovenerable authority in this, as in other matters; but I can discover nojustification for this widespread notion. After careful search throughthe "Exercitationes de Generatione, " the most that appears clear to meis, that Harvey believed all animals and plants to spring from what heterms a "_primordium vegetale_, " a phrase which may nowadays be rendered"a vegetative germ"; and this, he says, is _"oviforme_, " or "egg-like";not, he is careful to add, that it necessarily has the shape of an egg, but because it has the constitution and nature of one. That this"_primordium oviforme_" must needs, in all cases, proceed from a livingparent is nowhere expressly maintained by Harvey, though such an opinionmay be thought to be implied in one or two passages; while, on the otherhand, he does, more than once, use language which is consistent only witha full belief in spontaneous or equivocal generation. [3] In fact, themain concern of Harvey's wonderful little treatise is not withgeneration, in the physiological sense, at all, but with development; andhis great object is the establishment of the doctrine of epigenesis. 

[Footnote 3: See the following passage in Exercitatio I. :--"Item _spontenascentia_ dicuntur; non quod ex _putredine_ oriunda sint, sed quod casu, naturae sponte, et aequivocâ (ut aiunt) generatione, a parentibus suidissimilibus proveniant. " Again, in _De Uteri Membranis:_--"In cunctorumviventium generatione (sicut diximus) hoc solenne est, ut ortum ducunt a_primordio_ aliquo, quod tum materiam tum elficiendi potestatem in sehabet: sitque, adeo id, ex quo et a quo quicquid nascitur, ortum suumducat. Tale primordium in animalibus (_sive ab aliis generantibusproveniant, sive sponte, aut ex putredine nascentur_) est humor intunicâ, aliquâaut putami ne conclusus. " Compare also what Redi has to sayrespecting Harvey's opinions, _Esperienze_, p. 11. ]

The first distinct enunciation of the hypothesis that all living matterhas sprung from pre-existing living matter, came from a contemporary, though a junior, of Harvey, a native of that country, fertile in mengreat in all departments of human activity, which was to intellectualEurope, in the sixteenth and seventeenth centuries, what Germany is inthe nineteenth. It was in Italy, and from Italian teachers, that Harveyreceived the most important part of his scientific education. And it wasa student trained in the same schools, Francesco Redi--a man of thewidest knowledge and most versatile abilities, distinguished alike asscholar, poet, physician, and naturalist--who, just two hundred and twoyears ago, published his "Esperienze intorno alla Generazione degl'Insetti, " and gave to the world the idea, the growth of which it is mypurpose to trace. Redi's book went through five editions in twenty years;and the extreme simplicity of his experiments, and the clearness of hisarguments, gained for his views, and for their consequences, almostuniversal acceptance. 

Redi did not trouble himself much with speculative considerations, butattacked particular cases of what was supposed to be "spontaneousgeneration" experimentally. Here are dead animals, or pieces of meat, says he; I expose them to the air in hot weather, and in a few days theyswarm with maggots. You tell me that these are generated in the deadflesh; but if I put similar bodies, while quite fresh, into a jar, andtie some fine gauze over the top of the jar, not a maggot makes itsappearance, while the dead substances, nevertheless, putrefy just in thesame way as before. It is obvious, therefore, that the maggots are notgenerated by the corruption of the meat; and that the cause of theirformation must be a something which is kept away by gauze. But gauze willnot keep away aëriform bodies, or fluids. This something must, therefore, exist in the form of solid particles too big to get through the gauze. Nor is one long left in doubt what these solid particles are; for theblowflies, attracted by the odour of the meat, swarm round the vessel, and, urged by a powerful but in this case misleading instinct, lay eggsout of which maggots are immediately hatched, upon the gauze. Theconclusion, therefore, is unavoidable; the maggots are not generated bythe meat, but the eggs which give rise to them are brought through theair by the flies. 

These experiments seem almost childishly simple, and one wonders how itwas that no one ever thought of them before. Simple as they are, however, they are worthy of the most careful study, for every piece ofexperimental work since done, in regard to this subject, has been shapedupon the model furnished by the Italian philosopher. As the results ofhis experiments were the same, however varied the nature of the materialshe used, it is not wonderful that there arose in Redi's mind apresumption, that, in all such cases of the seeming production of lifefrom dead matter, the real explanation was the introduction of livinggerms from without into that dead matter. [4] And thus the hypothesis thatliving matter always arises by the agency of pre-existing living matter, took definite shape; and had, henceforward, a right to be considered anda claim to be refuted, in each particular case, before the production ofliving matter in any other way could be admitted by careful reasoners. Itwill be necessary for me to refer to this hypothesis so frequently, that, to save circumlocution, I shall call it the hypothesis of _Biogenesis_;and I shall term the contrary doctrine--that living matter may beproduced by not living matter--the hypothesis of _Abiogenesis_. 

[Footnote 4: "Pure contentandomi sempre in questa ed in ciascuna altrocosa, da ciascuno più savio, là dove io difettuosamente parlassi, essercorretto; non tacero, che per molte osservazioni molti volti da me fatte, mi sento inclinato a credere che la terra, da quelle prime piante, e daquei primi animali in poi, che ella nei primi giorni del mondo produsseper comandemento del sovrano ed omnipotente Fattore, non abbia mai piùprodotto da se medesima nè erba nè albero, nè animale alcuno perfetto oimperfetto che ei se fosse; e che tutto quello, che ne' tempi trapassatiè nato e che ora nascere in lei, o da lei veggiamo, venga tutto dallasemenza reale e vera delle piante, e degli animali stessi, i quali colmezzo del proprio seme la loro spezie conservano. E se bene tutto giornoscorghiamo da' cadaveri degli animali, e da tutte quante le maniere dell'erbe, e de' fiori, e dei frutti imputriditi, e corrotti nascere vermiinfiniti--

'Nonne vides quaecunque mora, fluidoque caloreCorpora tabescunt in parva animalia verti'--

Io mi sento, dico, inclinato, a credere che tutti quei vermi si generinodal seme paterno; e che le carni, e l' erbe, e l' altre cose tutteputrefatte, o putrefattibili non facciano altra parte, nè abbiano altroufizio nella generazione degl' insetti, se non d'apprestare un luogo o unnido proporzionato, in cui dagli animali nel tempo della figliatura sienoportati, e partoriti i vermi, o l' uova o l' altre semenze dei vermi, iquali tosto che nati sono, trovano in esso nido un sufficiente alimentoabilissimo per nutricarsi: e se in quello non son portate dalle madriqueste suddette semenze, niente mai, e replicatamente niente, vi s'ingegneri e nasca. "--REDI, _Esperienze_, pp. 14-16. ]

In the seventeenth century, as I have said, the latter was the dominantview, sanctioned alike by antiquity and by authority; and it isinteresting to observe that Redi did not escape the customary tax upon adiscoverer of having to defend himself against the charge of impugningthe authority of the Scriptures;[5] for his adversaries declared that thegeneration of bees from the carcase of a dead lion is affirmed, in theBook of Judges, to have been the origin of the famous riddle with whichSamson perplexed the Philistines:--

Out of the eater came forth meat, And out of the strong came forth sweetness. 

[Footnote 5: "Molti, e molti altri ancora vi potrei annoverare, se nonfossi chiamato a rispondere alle rampogne di alcuni, che bruscamente mirammentano ciò, che si legge nel capitolo quattordicesimo del sacrosantoLibro de' giudici ... "--REDI, _loc. Cit. _ p. 45. ]

Against all odds, however, Redi, strong with the strength of demonstrablefact, did splendid battle for Biogenesis; but it is remarkable that heheld the doctrine in a sense which, if he lead lived in these times, would have infallibly caused him to be classed among the defenders of"spontaneous generation. " "Omne vivum ex vivo, " "no life withoutantecedent life, " aphoristically sums up Redi's doctrine; but he went nofurther. It is most remarkable evidence of the philosophic caution andimpartiality of his mind, that although he had speculatively anticipatedthe manner in which grubs really are deposited in fruits and in the gallsof plants, he deliberately admits that the evidence is insufficient tobear him out; and he therefore prefers the supposition that they aregenerated by a modification of the living substance of the plantsthemselves. Indeed, he regards these vegetable growths as organs, bymeans of which the plant gives rise to an animal, and looks upon thisproduction of specific animals as the final cause of the galls and of, atany rate, some fruits. And he proposes to explain the occurrence ofparasites within the animal body in the same way. [6]

[Footnote 6: The passage (_Esperienze_, p. 129) is worth quoting infull:--

"Se dovessi palesarvi il mio sentimento crederei che i frutti, i legumi, gli alberi e le foglie, in due maniere inverminassero. Una, perchèvenendo i bachi per dí fuora, e cercando l' alimento, col rodere ciaprono la strada, ed arrivano alla più interna midolla de' frutti e de'legni. L'altra maniera si è, che io per me stimerei, che non fosse granfatto disdicevole il credere, che quell' anima o quella virtù, la qualegenera i fiori ed i frutti nelle piante viventi, sia quella stessa chegeneri ancora i bachi di esse piante. E chi sà, forse, che molti fruttidegli alberi non sieno prodotti, non per un fine primario e principale, ma bensi per un uffizio secondario e servile, destinato alla generazionedi que' vermi, servendo a loro in vece di matrice, in cui dimorino unprefisso e determinato tempo; il quale arrivato escan fuora a godere ilsole. 

"Io m' immagino, che questo mio pensiero non vi parrà totalmento unparadosso; mentro farete riflessione a quelle tanto sorte di galle, digallozzole, di coccole, di ricci, di calici, di cornetti ed i lappole, che son produtte dalle quercel, dalle farnie, da' cerri, da' sugheri, da'leeci e da altri simili alberi de ghianda; imperciocchè in quellogallozzole, e particolarmente nelle più grosse, che si chiamano coronati, ne' ricci capelluti, che ciuffoli da' nostri contadini son detti; neiricci legnosi del cerro, ne' ricci stellati della quercia, nelle galluzzedella foglia del leccio si vede evidentissimamente, che la prima eprincipale intenzione della natura è formare dentro di quelle un animalevolante; vedendosi nel centro della gallozzola un uovo, che col cresceree col maturarsi di essa gallozzola va crescendo e maturando anch' egli, ecresce altresi a suo tempo quel verme, che nell' uovo si racchiude; ilqual verme, quando la gallozzola è finita di maturare e che è venuto iltermine destinato al suo nascimento, diventa, di verme che era, unamosca.... Io vi confesso ingenuamente, che prima d'aver fatte queste mieesperienze intorno alla generazione degl' insetti mi dava a credere, oper dir meglio sospettava, che forse la gallozzola nascesse, perchèarrivando la mosca nel tempo della primavera, e facendo una piccolissimafessura ne' rami più teneri della quercia, in quella fessura nascondesseuno de suoi semi, il quale fosse cagione che sbocciasse fuora lagallozzola; e che mai non si vedessero galle o gallozzole o ricci ocornetti o calici o coccole, se non in que' rami, ne' quali le moscheavessero depositate le loro semenze; e mi dava ad intendere, che legallozzole fossero una malattia cagionata nelle querce dalle punturedelle mosche, in quella giusa stessa che dalle punture d'altri animalettisimiglievoli veggiamo crescere de' tumori ne' corpi degli animali. "]

It is of great importance to apprehend Redi's position rightly; for thelines of thought he laid down for us are those upon which naturalistshave been working ever since. Clearly, he held _Biogenesis_ as against_Abiogenesis;_ and I shall immediately proceed, in the first place, toinquire how far subsequent investigation has borne him out in so doing. 

But Redi also thought that there were two modes of Biogenesis. By the onemethod, which is that of common and ordinary occurrence, the livingparent gives rise to offspring which passes through the same cycle ofchanges as itself--like gives rise to like; and this has been termed_Homogenesis_. By the other mode, the living parent was supposed to giverise to offspring which passed through a totally different series ofstates from those exhibited by the parent, and did not return into thecycle of the parent; this is what ought to be called _Heterogenesis_, theoffspring being altogether, and permanently, unlike the parent. The termHeterogenesis, however, has unfortunately been used in a different sense, and M. Milne-Edwards has therefore substituted for it _Xenogenesis_, which means the generation of something foreign. After discussing Redi'shypothesis of universal Biogenesis, then, I shall go on to ask how farthe growth of science justifies his other hypothesis of Xenogenesis. 

The progress of the hypothesis of Biogenesis was triumphant and uncheckedfor nearly a century. The application of the microscope to anatomy in thehands of Grew, Leeuwenhoek, Swammerdam, Lyonnet, Vallisnieri, Réaurnur, and other illustrious investigators of nature of that day, displayed sucha complexity of organisation in the lowest and minutest forms, andeverywhere revealed such a prodigality of provision for theirmultiplication by germs of one sort or another, that the hypothesis ofAbiogenesis began to appear not only untrue, but absurd; and, in themiddle of the eighteenth century, when Needham and Buffon took up thequestion, it was almost universally discredited. [7]

[Footnote 7: Needham, writing in 1750, says:--

"Les naturalistes modernes s'accordent unaninement à établir, comme unevérité certaine, que toute plante vient do sa sémence spécifique, toutanimal d'un oeuf ou de quelque chose d'analogue préexistant dans laplante, ou dans l'animal de même espèce qui l'a produit. "--_NouvellesObservations_, p. 169. 

"Les naturalistes out généralemente cru que les animaux microscopiquesétaient engendrés par des oeufs transportés dans l'air, ou déposés dansdes eaux dormantes par des insectes volans. "--_Ibid. _ p. 176. ]

But the skill of the microscope makers of the eighteenth century soonreached its limit. A microscope magnifying 400 diameters was a _chefd'oeuvre_ of the opticians of that day; and, at the same time, by nomeans trustworthy. But a magnifying power of 400 diameters, even whendefinition reaches the exquisite perfection of our modern achromaticlenses, hardly suffices for the mere discernment of the smallest forms oflife. A speck, only 1/25th of an inch in diameter, has, at ten inchesfrom the eye, the same apparent size as an object 1/10000th of an inch indiameter, when magnified 400 times; but forms of living matter abound, the diameter of which is not more than 1/40000th of an inch. A filteredinfusion of hay, allowed to stand for two days, will swarm with livingthings among which, any which reaches the diameter of a human red blood-corpuscle, or about 1/3200th of an inch, is a giant. It is only bybearing these facts in mind, that we can deal fairly with the remarkablestatements and speculations put forward by Buffon and Needham in themiddle of the eighteenth century. 

When a portion of any animal or vegetable body is infused in water, itgradually softens and disintegrates; and, as it does so, the water isfound to swarm with minute active creatures, the so-called InfusorialAnimalcules, none of which can be seen, except by the aid of themicroscope; while a large proportion belong to the category of smallestthings of which I have spoken, and which must have looked like mere dotsand lines under the ordinary microscopes of the eighteenth century. 

Led by various theoretical considerations which I cannot now discuss, butwhich looked promising enough in the lights of their time, Buffon andNeedham doubted the applicability of Redi's hypothesis to the infusorialanimalcules, and Needham very properly endeavoured to put the question toan experimental test. He said to himself, If these infusorial animalculescome from germs, their germs must exist either in the substance infused, or in the water with which the infusion is made, or in the superjacentair. Now the vitality of all germs is destroyed by heat. Therefore, if Iboil the infusion, cork it up carefully, cementing the cork over withmastic, and then heat the whole vessel by heaping hot ashes over it, Imust needs kill whatever germs are present. Consequently, if Redi'shypothesis hold good, when the infusion is taken away and allowed tocool, no animalcules ought to be developed in it; whereas, if theanimalcules are not dependent on pre-existing germs, but are generatedfrom the infused substance, they ought, by and by, to make theirappearance. Needham found that, under the circumstances in which he madehis experiments, animalcules always did arise in the infusions, when asufficient time had elapsed to allow for their development. 

In much of his work Needham was associated with Buffon, and the resultsof their experiments fitted in admirably with the great Frenchnaturalist's hypothesis of "organic molecules, " according to which, lifeis the indefeasible property of certain indestructible molecules ofmatter, which exist in all living things, and have inherent activities bywhich they are distinguished from not living matter. Each individualliving organism is formed by their temporary combination. They stand toit in the relation of the particles of water to a cascade, or awhirlpool; or to a mould, into which the water is poured. The form of theorganism is thus determined by the reaction between external conditionsand the inherent activities of the organic molecules of which it iscomposed; and, as the stoppage of a whirlpool destroys nothing but aform, and leaves the molecules of the water, with all their inherentactivities intact, so what we call the death and putrefaction of ananimal, or of a plant, is merely the breaking up of the form, or mannerof association, of its constituent organic molecules, which are then setfree as infusorial animalcules. 

It will be perceived that this doctrine is by no means identical with_Abiogenesis_, with which it is often confounded. On this hypothesis, apiece of beef, or a handful of hay, is dead only in a limited sense. Thebeef is dead ox, and the hay is dead grass; but the "organic molecules"of the beef or the hay are not dead, but are ready to manifest theirvitality as soon as the bovine or herbaceous shrouds in which they areimprisoned are rent by the macerating action of water. The hypothesistherefore must be classified under Xenogenesis, rather than underAbiogenesis. Such as it was, I think it will appear, to those who will bejust enough to remember that it was propounded before the birth of modernchemistry, and of the modern optical arts, to be a most ingenious andsuggestive speculation. 

But the great tragedy of Science--the slaying of a beautiful hypothesisby an ugly fact--which is so constantly being enacted under the eyes ofphilosophers, was played, almost immediately, for the benefit of Buffonand Needham. 

Once more, an Italian, the Abbé Spallanzani, a worthy successor andrepresentative of Redi in his acuteness, his ingenuity, and his learning, subjected the experiments and the conclusions of Needham to a searchingcriticism. It might be true that Needham's experiments yielded resultssuch as he had described, but did they bear out his arguments? Was it notpossible, in the first place, he had not completely excluded the air byhis corks and mastic? And was it not possible, in the second place, thathe had not sufficiently heated his infusions and the superjacent air?Spallanzani joined issue with the English naturalist on both these pleas, and he showed that if, in the first place, the glass vessels in which theinfusions were contained were hermetically sealed by fusing their necks, and if, in the second place, they were exposed to the temperature ofboiling water for three-quarters of an hour, [8] no animalcules ever madetheir appearance within them. It must be admitted that the experimentsand arguments of Spallanzani furnish a complete and a crushing reply tothose of Needham. But we all too often forget that it is one thing torefute a proposition, and another to prove the truth of a doctrine which, implicitly or explicitly, contradicts that proposition; and the advanceof science soon showed that though Needham might be quite wrong, it didnot follow that Spallanzani was quite right. 

[Footnote 8: See Spallanzani, _Opere_, vi. Pp. 42 and 51. ]

Modern Chemistry, the birth of the latter half of the eighteenth century, grew apace, and soon found herself face to face with the great problemswhich biology had vainly tried to attack without her help. The discoveryof oxygen led to the laying of the foundations of a scientific theory ofrespiration, and to an examination of the marvellous interactions oforganic substances with oxygen. The presence of free oxygen appeared tobe one of the conditions of the existence of life, and of those singularchanges in organic matters which are known as fermentation andputrefaction. The question of the generation of the infusory animalculesthus passed into a new phase. For what might not have happened to theorganic matter of the infusions, or to the oxygen of the air, inSpallanzani's experiments? What security was there that the developmentof life which ought to have taken place had not been checked or preventedby these changes?

The battle had to be fought again. It was needful to repeat theexperiments under conditions which would make sure that neither theoxygen of the air, nor the composition of the organic matter, was alteredin such a manner as to interfere with the existence of life. 

Schulze and Schwann took up the question from this point of view in 1836and 1837. The passage of air through red-hot glass tubes, or throughstrong sulphuric acid, does not alter the proportion of its oxygen, whileit must needs arrest, or destroy, any organic matter which may becontained in the air. These experimenters, therefore, contrivedarrangements by which the only air which should come into contact with aboiled infusion should be such as had either passed through red-hot tubesor through strong sulphuric acid. The result which they obtained was thatan infusion so treated developed no living things, while, if the sameinfusion was afterwards exposed to the air, such things appeared rapidlyand abundantly. The accuracy of these experiments has been alternatelydenied and affirmed. Supposing then, to be accepted, however, all thatthey really proved was that the treatment to which the air was subjecteddestroyed _something_ that was essential to the development of life inthe infusion. This "something" might be gaseous, fluid, or solid; that itconsisted of germs remained only an hypothesis of greater or lessprobability. 

Contemporaneously with these investigations a remarkable discovery wasmade by Cagniard de la Tour. He found that common yeast is composed of avast accumulation of minute plants. The fermentation of must, or of wort, in the fabrication of wine and of beer, is always accompanied by therapid growth and multiplication of these _Toruloe_. Thus, fermentation, in so far as it was accompanied by the development of microscopicalorganisms in enormous numbers, became assimilated to the decomposition ofan infusion of ordinary animal or vegetable matter; and it was an obvioussuggestion that the organisms were, in some way or other, the causes bothof fermentation and of putrefaction. The chemists, with Berzelius andLiebig at their head, at first laughed this idea to scorn; but in 1843, aman then very young, who has since performed the unexampled feat ofattaining to high eminence alike in Mathematics, Physics, and Physiology--I speak of the illustrious Helmholtz--reduced the matter to the test ofexperiment by a method alike elegant and conclusive. Helmholtz separateda putrefying or a fermenting liquid from one which was simply putrescibleor fermentable by a membrane which allowed the fluids to pass through andbecome intermixed, but stopped the passage of solids. The result was, that while the putrescible or the fermentable liquids became impregnatedwith the results of the putrescence or fermentation which was going on onthe other side of the membrane, they neither putrefied (in the ordinaryway) nor fermented; nor were any of the organisms which abounded in thefermenting or putrefying liquid generated in them. Therefore the cause ofthe development of these organisms must lie in something which cannotpass through membranes; and as Helmholtz's investigations were longantecedent to Graham's researches upon colloids, his natural conclusionwas that the agent thus intercepted must be a solid material. In point offact, Helmholtz's experiments narrowed the issue to this: that whichexcites fermentation and putrefaction, and at the same time gives rise toliving forms in a fermentable or putrescible fluid, is not a gas and isnot a diffusible fluid; therefore it is either a colloid, or it is matterdivided into very minute solid particles. 

The researches of Schroeder and Dusch in 1854, and of Schroeder alone, in1859, cleared up this point by experiments which are simply refinementsupon those of Redi. A lump of cotton-wool is, physically speaking, a pileof many thicknesses of a very fine gauze, the fineness of the meshes ofwhich depends upon the closeness of the compression of the wool. Now, Schroeder and Dusch found, that, in the case of all the putrefiablematerials which they used (except milk and yolk of egg), an infusionboiled, and then allowed to come into contact with no air but such as hadbeen filtered through cotton-wool, neither putrefied, nor fermented, nordeveloped living forms. It is hard to imagine what the fine sieve formedby the cotton-wool could have stopped except minute solid particles. Still the evidence was incomplete until it had been positively shown, first, that ordinary air does contain such particles; and, secondly, thatfiltration through cotton-wool arrests these particles and allows onlyphysically pure air to pass. This demonstration has been furnished withinthe last year by the remarkable experiments of Professor Tyndall. It hasbeen a common objection of Abiogenists that, if the doctrine of Biogenyis true, the air must be thick with germs; and they regard this as theheight of absurdity. But nature occasionally is exceedingly unreasonable, and Professor Tyndall has proved that this particular absurdity maynevertheless be a reality. He has demonstrated that ordinary air is nobetter than a sort of stirabout of excessively minute solid particles;that these particles are almost wholly destructible by heat; and thatthey are strained off, and the air rendered optically pure, by its beingpassed through cotton-wool. 

It remains yet in the order of logic, though not of history, to show thatamong these solid destructible particles, there really do exist germscapable of giving rise to the development of living forms in suitablemenstrua. This piece of work was done by M. Pasteur in those beautifulresearches which will ever render his name famous; and which, in spite ofall attacks upon them, appear to me now, as they did seven years ago, [9]to be models of accurate experimentation and logical reasoning. Hestrained air through cotton-wool, and found, as Schroeder and Dusch haddone, that it contained nothing competent to give rise to the developmentof life in fluids highly fitted for that purpose. But the importantfurther links in the chain of evidence added by Pasteur are three. In thefirst place he subjected to microscopic examination the cotton-wool whichhad served as strainer, and found that sundry bodies clearly recognisableas germs, were among the solid particles strained off. Secondly, heproved that these germs were competent to give rise to living forms bysimply sowing them in a solution fitted for their development. And, thirdly, he showed that the incapacity of air strained through cotton-wool to give rise to life, was not due to any occult change effected inthe constituents of the air by the wool, by proving that the cotton-woolmight be dispensed with altogether, and perfectly free access leftbetween the exterior air and that in the experimental flask. If the neckof the flask is drawn out into a tube and bent downwards; and if, afterthe contained fluid has been carefully boiled, the tube is heatedsufficiently to destroy any germs which may be present in the air whichenters as the fluid cools, the apparatus may be left to itself for anytime and no life will appear in the fluid. The reason is plain. Althoughthere is free communication between the atmosphere laden with germs andthe germless air in the flask, contact between the two takes place onlyin the tube; and as the germs cannot fall upwards, and there are nocurrents, they never reach the interior of the flask. But if the tube bebroken short off where it proceeds from the flask, and free access bethus given to germs falling vertically out of the air, the fluid, whichhas remained clear and desert for months, becomes, in a few days, turbidand full of life. 

[Footnote 9: _Lectures to Working Men on the Causes of the Phenomena ofOrganic Nature_, 1863. (See Vol. II. Of these Essays. )]

These experiments have been repeated over and over again by independentobservers with entire success; and there is one very simple mode ofseeing the facts for one's self, which I may as well describe. 

Prepare a solution (much used by M. Pasteur, and often called "Pasteur'ssolution") composed of water with tartrate of ammonia, sugar, and yeast-ash dissolved therein. [10] Divide it into three portions in as manyflasks; boil all three for a quarter of an hour; and, while the steam ispassing out, stop the neck of one with a large plug of cotton-wool, sothat this also may be thoroughly steamed. Now set the flasks aside tocool, and, when their contents are cold, add to one of the open ones adrop of filtered infusion of hay which has stood for twenty-four hours, and is consequently hill of the active and excessively minute organismsknown as _Bacteria_. In a couple of days of ordinary warm weather thecontents of this flask will be milky from the enormous multiplication of_Bacteria_. The other flask, open and exposed to the air, will, sooner orlater, become milky with _Bacteria_, and patches of mould may appear init; while the liquid in the flask, the neck of which is plugged withcotton-wool, will remain clear for an indefinite time. I have sought invain for any explanation of these facts, except the obvious one, that theair contains germs competent to give rise to _Bacteria_, such as thosewith which the first solution has been knowingly and purposelyinoculated, and to the mould-_Fungi_. And I have not yet been able tomeet with any advocate of Abiogenesis who seriously maintains that theatoms of sugar, tartrate of ammonia, yeast-ash, and water, under noinfluence but that of free access of air and the ordinary temperature, re-arrange themselves and give rise to the protoplasm of _Bacterium_. Butthe alternative is to admit that these _Bacteria_ arise from germs in theair; and if they are thus propagated, the burden of proof that other likeforms are generated in a different manner, must rest with the assertor ofthat proposition. 

[Footnote 10: Infusion of hay treated in the same way yields similarresults; but as it contains organic matter, the argument which followscannot be based upon it. ]

To sum up the effect of this long chain of evidence:--

It is demonstrable that a fluid eminently fit for the development of thelowest forms of life, but which contains neither germs, nor any proteincompound, gives rise to living things in great abundance if it is exposedto ordinary air; while no such development takes place, if the air withwhich it is in contact is mechanically freed from the solid particleswhich ordinarily float in it, and which may be made visible byappropriate means. 

It is demonstrable that the great majority of these particles aredestructible by heat, and that some of them are germs, or livingparticles, capable of giving rise to the same forms of life as thosewhich appear when the fluid is exposed to unpurified air. 

It is demonstrable that inoculation of the experimental fluid with a dropof liquid known to contain living particles gives rise to the samephenomena as exposure to unpurified air. 

And it is further certain that these living particles are so minute thatthe assumption of their suspension in ordinary air presents not theslightest difficulty. On the contrary, considering their lightness andthe wide diffusion of the organisms which produce them, it is impossibleto conceive that they should not be suspended in the atmosphere inmyriads. 

Thus the evidence, direct and indirect, in favour of _Biogenesis_ for allknown forms of life must, I think, be admitted to be of great weight. 

On the other side, the sole assertions worthy of attention are thathermetically sealed fluids, which have been exposed to great and long-continued heat, have sometimes exhibited living forms of low organisationwhen they have been opened. 

The first reply that suggests itself is the probability that there mustbe some error about these experiments, because they are performed on anenormous scale every day with quite contrary results. Meat, fruits, vegetables, the very materials of the most fermentable and putrescibleinfusions, are preserved to the extent, I suppose I may say, of thousandsof tons every year, by a method which is a mere application ofSpallanzani's experiment. The matters to be preserved are well boiled ina tin case provided with a small hole, and this hole is soldered up whenall the air in the case has been replaced by steam. By this method theymay be kept for years without putrefying, fermenting, or getting mouldy. Now this is not because oxygen is excluded, inasmuch as it is now provedthat free oxygen is not necessary for either fermentation orputrefaction. It is not because the tins are exhausted of air, for_Vibriones_ and _Bacteria_ live, as Pasteur has shown, without air orfree oxygen. It is not because the boiled meats or vegetables are notputrescible or fermentable, as those who have had the misfortune to be ina ship supplied with unskilfully closed tins well know. What is it, therefore, but the exclusion of germs? I think that Abiogenists are boundto answer this question before they ask us to consider new experiments ofprecisely the same order. 

And in the next place, if the results of the experiments I refer to arereally trustworthy, it by no means follows that Abiogenesis has takenplace. The resistance of living matter to heat is known to vary withinconsiderable limits, and to depend, to some extent, upon the chemical andphysical qualities of the surrounding medium. But if, in the presentstate of science, the alternative is offered us, --either germs can standa greater heat than has been supposed, or the molecules of dead matter, for no valid or intelligible reason that is assigned, are able to re-arrange themselves into living bodies, exactly such as can bedemonstrated to be frequently produced in another way, --I cannotunderstand how choice can be, even for a moment, doubtful. 

But though I cannot express this conviction of mine too strongly, I mustcarefully guard myself against the supposition that I intend to suggestthat no such thing as Abiogenesis ever has taken place in the past, orever will take place in the future. With organic chemistry, molecularphysics, and physiology yet in their infancy, and every day makingprodigious strides, I think it would be the height of presumption for anyman to say that the conditions under which matter assumes the propertieswe call "vital" may not, some day, be artificially brought together. AllI feel justified in affirming is, that I see no reason for believing thatthe feat has been performed yet. 

And looking back through the prodigious vista of the past, I find norecord of the commencement of life, and therefore I am devoid of anymeans of forming a definite conclusion as to the conditions of itsappearance. Belief, in the scientific sense of the word, is a seriousmatter, and needs strong foundations. To say, therefore, in the admittedabsence of evidence, that I have any belief as to the mode in which theexisting forms of life have originated, would be using words in a wrongsense. But expectation is permissible where belief is not; and if it weregiven me to look beyond the abyss of geologically recorded time to thestill more remote period when the earth was passing through physical andchemical conditions, which it can no more see again than a man can recallhis infancy, I should expect to be a witness of the evolution of livingprotoplasm from not living matter. I should expect to see it appear underforms of great simplicity, endowed, like existing fungi, with the powerof determining the formation of new protoplasm from such matters asammonium carbonates, oxalates and tartrates, alkaline and earthyphosphates, and water, without the aid of light. That is the expectationto which analogical reasoning leads me; but I beg you once more torecollect that I have no right to call my opinion anything but an act ofphilosophical faith. 

So much for the history of the progress of Redi's great doctrine ofBiogenesis, which appears to me, with the limitations I have expressed, to be victorious along the whole line at the present day. 

As regards the second problem offered to us by Redi, whether Xenogenesisobtains, side by side with Homogenesis, --whether, that is, there existnot only the ordinary living things, giving rise to offspring which runthrough the same cycle as themselves, but also others, producingoffspring which are of a totally different character from themselves, --the researches of two centuries have led to a different result. That thegrubs found in galls are no product of the plants on which the gallsgrow, but are the result of the introduction of the eggs of insects intothe substance of these plants, was made out by Vallisnieri, Réaumur, andothers, before the end of the first half of the eighteenth century. Thetapeworms, bladderworms, and flukes continued to be a stronghold of theadvocates of Xenogenesis for a much longer period. Indeed, it is onlywithin the last thirty years that the splendid patience of Von Siebold, Van Beneden, Leuckart, Küchenmeister, and other helminthologists, hassucceeded in tracing every such parasite, often through the strangestwanderings and metamorphoses, to an egg derived from a parent, actuallyor potentially like itself; and the tendency of inquiries elsewhere hasall been in the same direction. A plant may throw off bulbs, but these, sooner or later, give rise to seeds or spores, which develop into theoriginal form. A polype may give rise to Medusae, or a pluteus to anEchinoderm, but the Medusa and the Echinoderm give rise to eggs whichproduce polypes or glutei, and they are therefore only stages in thecycle of life of the species. 

But if we turn to pathology, it offers us some remarkable approximationsto true Xenogenesis. 

As I have already mentioned, it has been known since the time ofVallisnieri and of Réaumur, that galls in plants, and tumours in cattle, are caused by insects, which lay their eggs in those parts of the animalor vegetable frame of which these morbid structures are outgrowths. Again, it is a matter of familiar experience to everybody that merepressure on the skin will give rise to a corn. Now the gall, the tumour, and the corn are parts of the living body, which have become, to acertain degree, independent and distinct organisms. Under the influenceof certain external conditions, elements of the body, which should havedeveloped in due subordination to its general plan, set up for themselvesand apply the nourishment which they receive to their own purposes. 

From such innocent productions as corns and warts, there are allgradations to the serious tumours which, by their mere size and themechanical obstruction they cause, destroy the organism out of which theyare developed; while, finally, in those terrible structures known ascancers, the abnormal growth has acquired powers of reproduction andmultiplication, and is only morphologically distinguishable from theparasitic worm, the life of which is neither more nor less closely boundup with that of the infested organism. 

If there were a kind of diseased structure, the histological elements ofwhich were capable of maintaining a separate and independent existenceout of the body, it seems to me that the shadowy boundary between morbidgrowth and Xenogenesis would be effaced. And I am inclined to think thatthe progress of discovery has almost brought us to this point already. Ihave been favoured by Mr. Simon with an early copy of the last publishedof the valuable "Reports on the Public Health, " which, in his capacity oftheir medical officer, he annually presents to the Lords of the PrivyCouncil. The appendix to this report contains an introductory essay "Onthe Intimate Pathology of Contagion, " by Dr. Burdon-Sanderson, which isone of the clearest, most comprehensive, and well-reasoned discussions ofa great question which has come under my notice for a long time. I referyou to it for details and for the authorities for the statements I amabout to make. 

You are familiar with what happens in vaccination. A minute cut is madein the skin, and an infinitesimal quantity of vaccine matter is insertedinto the wound. Within a certain time a vesicle appears in the place ofthe wound, and the fluid which distends this vesicle is vaccine matter, in quantity a hundred or a thousandfold that which was originallyinserted. Now what has taken place in the course of this operation? Hasthe vaccine matter, by its irritative property, produced a mere blister, the fluid of which has the same irritative property? Or does the vaccinematter contain living particles, which have grown and multiplied wherethey have been planted? The observations of M. Chauveau, extended andconfirmed by Dr. Sanderson himself, appear to leave no doubt upon thishead. Experiments, similar in principle to those of Helmholtz onfermentation and putrefaction, have proved that the active element in thevaccine lymph is non-diffusible, and consists of minute particles notexceeding 1/20000th of an inch in diameter, which are made visible in thelymph by the microscope. Similar experiments have proved that two of themost destructive of epizootic diseases, sheep-pox and glanders, are alsodependent for their existence and their propagation upon extremely smallliving solid particles, to which the title of _microzymes_ is applied. Ananimal suffering under either of these terrible diseases is a source ofinfection and contagion to others, for precisely the same reason as a tubof fermenting beer is capable of propagating its fermentation by"infection, " or "contagion, " to fresh wort. In both cases it is the solidliving particles which are efficient; the liquid in which they float, andat the expense of which they live, being altogether passive. 

Now arises the question, are these microzymes the results of_Homogenesis_, or of _Xenogenesis?_ are they capable, like the_Toruloe_ of yeast, of arising only by the development of pre-existinggerms? or may they be, like the constituents of a nut-gall, the resultsof a modification and individualisation of the tissues of the body inwhich they are found, resulting from the operation of certain conditions?Are they parasites in the zoological sense, or are they merely whatVirchow has called "heterologous growths"? It is obvious that thisquestion has the most profound importance, whether we look at it from apractical or from a theoretical point of view. A parasite may be stampedout by destroying its germs, but a pathological product can only beannihilated by removing the conditions which give rise to it. 

It appears to me that this great problem will have to be solved for eachzymotic disease separately, for analogy cuts two ways. I have dwelt uponthe analogy of pathological modification, which is in favour of thexenogenetic origin of microzymes; but I must now speak of the equallystrong analogies in favour of the origin of such pestiferous particles bythe ordinary process of the generation of like from like. 

It is, at present, a well-established fact that certain diseases, both ofplants and of animals, which have all the characters of contagious andinfectious epidemics, are caused by minute organisms. The smut of wheatis a well-known instance of such a disease, and it cannot be doubted thatthe grape-disease and the potato-disease fall under the same category. Among animals, insects are wonderfully liable to the ravages ofcontagious and infectious diseases caused by microscopic _Fungi_. 

In autumn, it is not uncommon to see flies motionless upon a window-pane, with a sort of magic circle, in white, drawn round them. On microscopicexamination, the magic circle is found to consist of innumerable spores, which have been thrown off in all directions by a minute fungus called_Empusa muscoe_, the spore-forming filaments of which stand out like apile of velvet from the body of the fly. These spore-forming filamentsare connected with others which fill the interior of the fly's body likeso much fine wool, having eaten away and destroyed the creature'sviscera. This is the full-grown condition of the _Empusa_. If traced backto its earliest stages, in flies which are still active, and to allappearance healthy, it is found to exist in the form of minute corpuscleswhich float in the blood of the fly. These multiply and lengthen intofilaments, at the expense of the fly's substance; and when they have atlast killed the patient, they grow out of its body and give off spores. Healthy flies shut up with diseased ones catch this mortal disease, andperish like the others. A most competent observer, M. Cohn, who studiedthe development of the _Empusa_ very carefully, was utterly unable todiscover in what manner the smallest germs of the _Empusa_ got into thefly. The spores could not be made to give rise to such germs bycultivation; nor were such germs discoverable in the air, or in the foodof the fly. It looked exceedingly like a case of Abiogenesis, or, at anyrate, of Xenogenesis; and it is only quite recently that the real courseof events has been made out. It has been ascertained, that when one ofthe spores falls upon the body of a fly, it begins to germinate, andsends out a process which bores its way through the fly's skin; this, having reached the interior cavities of its body, gives off the minutefloating corpuscles which are the earliest stage of the _Empusa_. Thedisease is "contagious, " because a healthy fly coming in contact with adiseased one, from which the spore-bearing filaments protrude, is prettysure to carry off a spore or two. It is "infectious" because the sporesbecome scattered about all sorts of matter in the neighbourhood of theslain flies. 

The silkworm has long been known to be subject to a very fatal andinfectious disease called the _Muscardine_. Audouin transmitted it byinoculation. This disease is entirely due to the development of a fungus, _Botrytis Bassiana_, in the body of the caterpillar; and itscontagiousness and infectiousness are accounted for in the same way asthose of the fly-disease. But, of late years, a still more seriousepizootic has appeared among the silkworms; and I may mention a few factswhich will give you some conception of the gravity of the injury which ithas inflicted on France alone. 

The production of silk has been for centuries an important branch ofindustry in Southern France, and in the year 1853 it had attained such amagnitude that the annual produce of the French sericulture was estimatedto amount to a tenth of that of the whole world, and represented a money-value of 117, 000, 000 francs, or nearly five millions sterling. What maybe the sum which would represent the money-value of all the industriesconnected with the working up of the raw silk thus produced, is more thanI can pretend to estimate. Suffice it to say, that the city of Lyons isbuilt upon French silk as much as Manchester was upon American cottonbefore the civil war. 

Silkworms are liable to many diseases; and, even before 1853, a peculiarepizootic, frequently accompanied by the appearance of dark spots uponthe skin (whence the name of "Pébrine" which it has received), had beennoted for its mortality. But in the years following 1853 this maladybroke out with such extreme violence, that, in 1858, the silk-crop wasreduced to a third of the amount which it had reached in 1853; and, uptill within the last year or two, it has never attained half the yield of1853. This means not only that the great number of people engaged in silkgrowing are some thirty millions sterling poorer than they might havebeen; it means not only that high prices have had to be paid for importedsilkworm eggs, and that, after investing his money in them, in paying formulberry-leaves and for attendance, the cultivator has constantly seenhis silkworms perish and himself plunged in ruin; but it means that thelooms of Lyons have lacked employment, and that, for years, enforcedidleness and misery have been the portion of a vast population which, informer days, was industrious and well-to-do. 

In 1858 the gravity of the situation caused the French Academy ofSciences to appoint Commissioners, of whom a distinguished naturalist, M. De Quatrefages, was one, to inquire into the nature of this disease, and, if possible, to devise some means of staying the plague. In reading theReport[11] made by M. De Quatrefages in 1859, it is exceedinglyinteresting to observe that his elaborate study of the Pébrine forced theconviction upon his mind that, in its mode of occurrence and propagation, the disease of the silkworm is, in every respect, comparable to thecholera among mankind. But it differs from the cholera, and so far is amore formidable malady, in being hereditary, and in being, under somecircumstances, contagious as well as infectious. 

[Footnote 11: _Études sur les Maladies actuelles des Vers à Soie_, p. 53. ]

The Italian naturalist, Filippi, discovered in the blood of the silkwormsaffected by this strange disorder a multitude of cylindrical corpuscles, each about 1/6000th of an inch long. These have been carefully studied byLebert, and named by him _Panhistophyton_; for the reason that insubjects in which the disease is strongly developed, the corpuscles swarmin every tissue and organ of the body, and even pass into the undevelopedeggs of the female moth. But are these corpuscles causes, or mereconcomitants, of the disease? Some naturalists took one view and someanother; and it was not until the French Government, alarmed by thecontinued ravages of the malady, and the inefficiency of the remedieswhich had been suggested, despatched M. Pasteur to study it, that thequestion received its final settlement; at a great sacrifice, not only ofthe time and peace of mind of that eminent philosopher, but, I regret tohave to add, of his health. 

But the sacrifice has not been in vain. It is now certain that thisdevastating, cholera-like, Pébrine, is the effect of the growth andmultiplication of the _Panhistophyton_ in the silkworm. It is contagiousand infectious, because the corpuscles of the _Panhistophyton_ pass awayfrom the bodies of the diseased caterpillars, directly or indirectly, tothe alimentary canal of healthy silkworms in their neighbourhood; it ishereditary because the corpuscles enter into the eggs while they arebeing formed, and consequently are carried within them when they arelaid; and for this reason, also, it presents the very singularpeculiarity of being inherited only on the mother's side. There is not asingle one of all the apparently capricious and unaccountable phenomenapresented by the Pébrine, but has received its explanation from the factthat the disease is the result of the presence of the microscopicorganism, _Panhistophyton_. 

Such being the facts with respect to the Pébrine, what are theindications as to the method of preventing it? It is obvious that thisdepends upon the way in which the _Panhistophyton_ is generated. If itmay be generated by Abiogenesis, or by Xenogenesis, within the silkwormor its moth, the extirpation of the disease must depend upon theprevention of the occurrence of the conditions under which thisgeneration takes place. But if, on the other hand, the _Panhistophyton_is an independent organism, which is no more generated by the silkwormthan the mistletoe is generated by the apple-tree or the oak on which itgrows, though it may need the silkworm for its development in the sameway as the mistletoe needs the tree, then the indications are totallydifferent. The sole thing to be done is to get rid of and keep away thegerms of the _Panhistophyton_. As might be imagined, from the course ofhis previous investigations, M. Pasteur was led to believe that thelatter was the right theory; and, guided by that theory, he has devised amethod of extirpating the disease, which has proved to be completelysuccessful wherever it has been properly carried out. 

There can be no reason, then, for doubting that, among insects, contagious and infectious diseases, of great malignity, are caused byminute organisms which are produced from pre-existing germs, or byhomogenesis; and there is no reason, that I know of, for believing thatwhat happens in insects may not take place in the highest animals. Indeed, there is already strong evidence that some diseases of anextremely malignant and fatal character to which man is subject, are asmuch the work of minute organisms as is the Pébrine. I refer for thisevidence to the very striking facts adduced by Professor Lister in hisvarious well-known publications on the antiseptic method of treatment. Itappears to me impossible to rise from the perusal of those publicationswithout a strong conviction that the lamentable mortality which sofrequently dogs the footsteps of the most skilful operator, and thosedeadly consequences of wounds and injuries which seem to haunt the verywalls of great hospitals, and are, even now, destroying more men than dieof bullet or bayonet, are due to the importation of minute organisms intowounds, and their increase and multiplication; and that the surgeon whosaves most lives will be he who best works out the practical consequencesof the hypothesis of Redi. 

I commenced this Address by asking you to follow me in an attempt totrace the path which has been followed by a scientific idea, in its longand slow progress from the position of a probable hypothesis to that ofan established law of nature. Our survey has not taken us into veryattractive regions; it has lain, chiefly, in a land flowing with theabominable, and peopled with mere grubs and mouldiness. And it may beimagined with what smiles and shrugs, practical and seriouscontemporaries of Redi and of Spallanzani may have commented on the wasteof their high abilities in toiling at the solution of problems which, though curious enough in themselves, could be of no conceivable utilityto mankind. 

Nevertheless, you will have observed that before we had travelled veryfar upon our road, there appeared, on the right hand and on the left, fields laden with a harvest of golden grain, immediately convertible intothose things which the most solidly practical men will admit to havevalue--viz. , money and life. 

The direct loss to France caused by the Pébrine in seventeen years cannotbe estimated at less than fifty millions sterling; and if we add to thiswhat Redi's idea, in Pasteur's hands, has done for the wine-grower andfor the vinegar-maker, and try to capitalise its value, we shall findthat it will go a long way towards repairing the money losses caused bythe frightful and calamitous war of this autumn. And as to the equivalentof Redi's thought in life, how can we over-estimate the value of thatknowledge of the nature of epidemic and epizootic diseases, andconsequently of the means of checking, or eradicating them, the dawn ofwhich has assuredly commenced?

Looking back no further than ten years, it is possible to select three(1863, 1864, and 1869) in which the total number of deaths from scarlet-fever alone amounted to ninety thousand. That is the return of killed, the maimed and disabled being left out of sight. Why, it is to be hopedthat the list of killed in the present bloodiest of all wars will notamount to more than this! But the facts which I have placed before youmust leave the least sanguine without a doubt that the nature and thecauses of this scourge will, one day, be as well understood as those ofthe Pébrine are now; and that the long-suffered massacre of our innocentswill come to an end. 

And thus mankind will have one more admonition that "the people perishfor lack of knowledge"; and that the alleviation of the miseries, and thepromotion of the welfare, of men must be sought, by those who will notlose their pains, in that diligent, patient, loving study of all themultitudinous aspects of Nature, the results of which constitute exactknowledge, or Science. It is the justification and the glory of thisgreat meeting that it is gathered together for no other object than theadvancement of the moiety of science which deals with those phenomena ofnature which we call physical. May its endeavours be crowned with a fullmeasure of success!

IX

GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE

[1862]

Merchants occasionally go through a wholesome, though troublesome and notalways satisfactory, process which they term "taking stock. " After allthe excitement of speculation, the pleasure of gain, and the pain ofloss, the trader makes up his mind to face facts and to learn the exactquantity and quality of his solid and reliable possessions. 

The man of science does well sometimes to imitate this procedure; and, forgetting for the time the importance of his own small winnings, to re-examine the common stock in trade, so that he may make sure how far thestock of bullion in the cellar--on the faith of whose existence so muchpaper has been circulating--is really the solid gold of truth. 

The Anniversary Meeting of the Geological Society seems to be an occasionwell suited for an undertaking of this kind--for an inquiry, in fact, into the nature and value of the present results of palaeontologicalinvestigation; and the more so, as all those who have paid closeattention to the late multitudinous discussions in which palaeontology isimplicated, must have felt the urgent necessity of some such scrutiny. 

First in order, as the most definite and unquestionable of all theresults of palaeontology, must be mentioned the immense extension andimpulse given to botany, zoology, and comparative anatomy, by theinvestigation of fossil remains. Indeed, the mass of biological facts hasbeen so greatly increased, and the range of biological speculation hasbeen so vastly widened, by the researches of the geologist andpalaeontologist, that it is to be feared there are naturalists inexistence who look upon geology as Brindley regarded rivers. "Rivers, "said the great engineer, "were made to feed canals;" and geology, someseem to think, was solely created to advance comparative anatomy. 

Were such a thought justifiable, it could hardly expect to be receivedwith favour by this assembly. But it is not justifiable. Your favouritescience has her own great aims independent of all others; and if, notwithstanding her steady devotion to her own progress, she can scattersuch rich alms among her sisters, it should be remembered that hercharity is of the sort that does not impoverish, but "blesseth him thatgives and him that takes. "

Regard the matter as we will, however, the facts remain. Nearly 40, 000species of animals and plants have been added to the Systema Naturae bypalaeontological research. This is a living population equivalent to thatof a new continent in mere number; equivalent to that of a newhemisphere, if we take into account the small population of insects asyet found fossil, and the large proportion and peculiar organisation ofmany of the Vertebrata. 

But, beyond this, it is perhaps not too much to say that, except for thenecessity of interpreting palaeontological facts, the laws of distributionwould have received less careful study; while few comparative anatomists(and those not of the first order) would have been induced by mere loveof detail, as such, to study the minutiae of osteology, were it not thatin such minutiae lie the only keys to the most interesting riddles offeredby the extinct animal world. 

These assuredly are great and solid gains. Surely it is matter for nosmall congratulation that in half a century (for palaeontology, though itdawned earlier, came into full day only with Cuvier) a subordinate branchof biology should have doubled the value and the interest of the wholegroup of sciences to which it belongs. 

But this is not all. Allied with geology, palaeontology has establishedtwo laws of inestimable importance: the first, that one and the same areaof the earth's surface has been successively occupied by very differentkinds of living beings; the second, that the order of successionestablished in one locality holds good, approximately, in all. 

The first of these laws is universal and irreversible; the second is aninduction from a vast number of observations, though it may possibly, andeven probably, have to admit of exceptions. As a consequence of thesecond law, it follows that a peculiar relation frequently subsistsbetween series of strata containing organic remains, in differentlocalities. The series resemble one another not only in virtue of ageneral resemblance of the organic remains in the two, but also in virtueof a resemblance in the order and character of the serial succession ineach. There is a resemblance of arrangement; so that the separate termsof each series, as well as the whole series, exhibit a correspondence. 

Succession implies time; the lower members of an undisturbed series ofsedimentary rocks are certainly older than the upper; and when the notionof age was once introduced as the equivalent of succession, it was nowonder that correspondence in succession came to be looked upon as acorrespondence in age, or "contemporaneity. " And, indeed, so long asrelative age only is spoken of, correspondence in succession _is_correspondence in age; it is _relative_ contemporaneity. 

But it would have been very much better for geology if so loose andambiguous a word as "contemporaneous" had been excluded from herterminology, and if, in its stead, some term expressing similarity ofserial relation, and excluding the notion of time altogether, had beenemployed to denote correspondence in position in two or more series ofstrata. 

In anatomy, where such correspondence of position has constantly to bespoken of, it is denoted by the word "homology" and its derivatives; andfor Geology (which after all is only the anatomy and physiology of theearth) it might be well to invent some single word, such as "homotaxis"(similarity of order), in order to express an essentially similar idea. This, however, has not been done, and most probably the inquiry will atonce be made--To what end burden science with a new and strange term inplace of one old, familiar, and part of our common language?

The reply to this question will become obvious as the inquiry into theresults of palaeontology is pushed further. 

Those whose business it is to acquaint themselves specially with theworks of palaeontologists, in fact, will be fully aware that very few, ifany, would rest satisfied with such a statement of the conclusions oftheir branch of biology as that which has just been given. 

Our standard repertories of palaeontology profess to teach us far higherthings--to disclose the entire succession of living forms upon thesurface of the globe; to tell us of a wholly different distribution ofclimatic conditions in ancient times; to reveal the character of thefirst of all living existences; and to trace out the law of progress fromthem to us. 

It may not be unprofitable to bestow on these professions a somewhat morecritical examination than they have hitherto received, in order toascertain how far they rest on an irrefragable basis; or whether, afterall, it might not be well for palaeontologists to learn a little morecarefully that scientific "ars artium, " the art of saying "I don't know. "And to this end let us define somewhat more exactly the extent of thesepretensions of palaeontology. 

Every one is aware that Professor Bronn's "Untersuchungen" and ProfessorPictet's "Traité de Paléontologie" are works of standard authority, familiarly consulted by every working palaeontologist. It is desirable tospeak of these excellent books, and of their distinguished authors, withthe utmost respect, and in a tone as far as possible removed from carpingcriticism; indeed, if they are specially cited in this place, it ismerely in justification of the assertion that the following propositions, which may be found implicitly, or explicitly, in the works in question, are regarded by the mass of palaeontologists and geologists, not only onthe Continent but in this country, as expressing some of the best-established results of palaeontology. Thus:--

Animals and plants began their existence together, not long after thecommencement of the deposition of the sedimentary rocks; and thensucceeded one another, in such a manner, that totally distinct faunae andflorae occupied the whole surface of the earth, one after the other, andduring distinct epochs of time. 

A geological formation is the sum of all the strata deposited over thewhole surface of the earth during one of these epochs: a geological faunaor flora is the sum of all the species of animals or plants whichoccupied the whole surface of the globe, during one of these epochs. 

The population of the earth's surface was at first very similar in allparts, and only from the middle of the Tertiary epoch onwards, began toshow a distinct distribution in zones. 

The constitution of the original population, as well as the numericalproportions of its members, indicates a warmer and, on the whole, somewhat tropical climate, which remained tolerably equable throughoutthe year. The subsequent distribution of living beings in zones is theresult of a gradual lowering of the general temperature, which firstbegan to be felt at the poles. 

It is not now proposed to inquire whether these doctrines are true orfalse; but to direct your attention to a much simpler though veryessential preliminary question--What is their logical basis? what are thefundamental assumptions upon which they all logically depend? and what isthe evidence on which those fundamental propositions demand our assent?

These assumptions are two: the first, that the commencement of thegeological record is coëval with the commencement of life on the globe;the second, that geological contemporaneity is the same thing aschronological synchrony. Without the first of these assumptions therewould of course be no ground for any statement respecting thecommencement of life; without the second, all the other statements cited, every one of which implies a knowledge of the state of different parts ofthe earth at one and the same time, will be no less devoid ofdemonstration. 

The first assumption obviously rests entirely on negative evidence. Thisis, of course, the only evidence that ever can be available to prove thecommencement of any series of phenomena; but, at the same time, it mustbe recollected that the value of negative evidence depends entirely onthe amount of positive corroboration it receives. If A. B. Wishes to provean _alibi_, it is of no use for him to get a thousand witnesses simply toswear that they did not see him in such and such a place, unless thewitnesses are prepared to prove that they must have seen him had he beenthere. But the evidence that animal life commenced with the Lingula-flags, _e. G. _, would seem to be exactly of this unsatisfactoryuncorroborated sort. The Cambrian witnesses simply swear they "haven'tseen anybody their way"; upon which the counsel for the other sideimmediately puts in ten or twelve thousand feet of Devonian sandstones tomake oath they never saw a fish or a mollusk, though all the world knowsthere were plenty in their time. 

But then it is urged that, though the Devonian rocks in one part of theworld exhibit no fossils, in another they do, while the lower Cambrianrocks nowhere exhibit fossils, and hence no living being could haveexisted in their epoch. 

To this there are two replies: the first that the observational basis ofthe assertion that the lowest rocks are nowhere fossiliferous is anamazingly small one, seeing how very small an area, in comparison to thatof the whole world, has yet been fully searched; the second, that theargument is good for nothing unless the unfossiliferous rocks in questionwere not only _contemporaneous_ in the geological sense, but_synchronous_ in the chronological sense. To use the _alibi_ illustrationagain. If a man wishes to prove he was in neither of two places, A and B, on a given day, his witnesses for each place must be prepared to answerfor the whole day. If they can only prove that he was not at A in themorning, and not at B in the afternoon, the evidence of his absence fromboth is nil, because he might have been at B in the morning and at A inthe afternoon. 

Thus everything depends upon the validity of the second assumption. Andwe must proceed to inquire what is the real meaning of the word"contemporaneous" as employed by geologists. To this end a concreteexample may be taken. 

The Lias of England and the Lias of Germany, the Cretaceous rocks ofBritain and the Cretaceous rocks of Southern India, are termed bygeologists "contemporaneous" formations; but whenever any thoughtfulgeologist is asked whether he means to say that they were depositedsynchronously, he says, "No, --only within the same great epoch. " And if, in pursuing the inquiry, he is asked what may be the approximate value intime of a "great epoch"--whether it means a hundred years, or a thousand, or a million, or ten million years--his reply is, "I cannot tell. "

If the further question be put, whether physical geology is in possessionof any method by which the actual synchrony (or the reverse) of any twodistant deposits can be ascertained, no such method can be heard of; itbeing admitted by all the best authorities that neither similarity ofmineral composition, nor of physical character, nor even directcontinuity of stratum, are _absolute_ proofs of the synchronism of evenapproximated sedimentary strata: while, for distant deposits, there seemsto be no kind of physical evidence attainable of a nature competent todecide whether such deposits were formed simultaneously, or whether theypossess any given difference of antiquity. To return to an examplealready given: All competent authorities will probably assent to theproposition that physical geology does not enable us in any way to replyto this question--Were the British Cretaceous rocks deposited at the sametime as those of India, or are they a million of years younger or amillion of years older?

Is palaeontology able to succeed where physical geology fails? Standardwriters on palaeontology, as has been seen, assume that she can. They takeit for granted, that deposits containing similar organic remains aresynchronous--at any rate in a broad sense; and yet, those who will studythe eleventh and twelfth chapters of Sir Henry De La Beche's remarkable"Researches in Theoretical Geology, " published now nearly thirty yearsago, and will carry out the arguments there most luminously stated, totheir logical consequences, may very easily convince themselves that evenabsolute identity of organic contents is no proof of the synchrony ofdeposits, while absolute diversity is no proof of difference of date. SirHenry De La Beche goes even further, and adduces conclusive evidence toshow that the different parts of one and the same stratum, having asimilar composition throughout, containing the same organic remains, andhaving similar beds above and below it, may yet differ to any conceivableextent in age. 

Edward Forbes was in the habit of asserting that the similarity of theorganic contents of distant formations was _prima facie_ evidence, not oftheir similarity, but of their difference of age; and holding as he didthe doctrine of single specific centres, the conclusion was as legitimateas any other; for the two districts must have been occupied by migrationfrom one of the two, or from an intermediate spot, and the chancesagainst exact coincidence of migration and of imbedding are infinite. 

In point of fact, however, whether the hypothesis of single or ofmultiple specific centres be adopted, similarity of organic contentscannot possibly afford any proof of the synchrony of the deposits whichcontain them; on the contrary, it is demonstrably compatible with thelapse of the most prodigious intervals of time, and with theinterposition of vast changes in the organic and inorganic worlds, between the epochs in which such deposits were formed. 

On what amount of similarity of their faunae is the doctrine of thecontemporaneity of the European and of the North American Siluriansbased? In the last edition of Sir Charles Lyell's "Elementary Geology" itis stated, on the authority of a former President of this Society, thelate Daniel Sharpe, that between 30 and 40 per cent. Of the species ofSilurian Mollusca are common to both sides of the Atlantic. By way of dueallowance for further discovery, let us double the lesser number andsuppose that 60 per cent. Of the species are common to the North Americanand the British Silurians. Sixty per cent. Of species in common is, then, proof of contemporaneity. 

Now suppose that, a million or two of years hence, when Britain has madeanother dip beneath the sea and has come up again, some geologist appliesthis doctrine, in comparing the strata laid bare by the upheaval of thebottom, say, of St. George's Channel with what may then remain of theSuffolk Crag. Reasoning in the same way, he will at once decide theSuffolk Crag and the St. George's Channel beds to be contemporaneous;although we happen to know that a vast period (even in the geologicalsense) of time, and physical changes of almost unprecedented extent, separate the two. But if it be a demonstrable fact that stratacontaining more than 60 or 70 per cent. Of species of Mollusca in common, and comparatively close together, may yet be separated by an amount ofgeological time sufficient to allow of some of the greatest physicalchanges the world has seen, what becomes of that sort of contemporaneitythe sole evidence of which is a similarity of facies, or the identity ofhalf a dozen species, or of a good many genera?

And yet there is no better evidence for the contemporaneity assumed byall who adopt the hypothesis of universal faunae and florae, of auniversally uniform climate, and of a sensible cooling of the globeduring geological time. 

There seems, then, no escape from the admission that neither physicalgeology, nor palaeontology, possesses any method by which the absolutesynchronism of two strata can be demonstrated. All that geology can proveis local order of succession. It is mathematically certain that, in anygiven vertical linear section of an undisturbed series of sedimentarydeposits, the bed which lies lowest is the oldest. In many other verticallinear sections of the same series, of course, corresponding beds willoccur in a similar order; but, however great may be the probability, noman can say with absolute certainty that the beds in the two sectionswere synchronously deposited. For areas of moderate extent, it isdoubtless true that no practical evil is likely to result from assumingthe corresponding beds to be synchronous or strictly contemporaneous; andthere are multitudes of accessory circumstances which may fully justifythe assumption of such synchrony. But the moment the geologist has todeal with large areas, or with completely separated deposits, themischief of confounding that "homotaxis" or "similarity of arrangement, "which _can_ be demonstrated, with "synchrony" or "identity of date, " forwhich there is not a shadow of proof, under the one common term of"contemporaneity" becomes incalculable, and proves the constant source ofgratuitous speculations. 

For anything that geology or palaeontology are able to show to thecontrary, a Devonian fauna and flora in the British Islands may have beencontemporaneous with Silurian life in North America, and with aCarboniferous fauna and flora in Africa. Geographical provinces and zonesmay have been as distinctly marked in the Palaeozoic epoch as at present, and those seemingly sudden appearances of new genera and species, whichwe ascribe to new creation, may be simple results of migration. 

It may be so; it may be otherwise. In the present condition of ourknowledge and of our methods, one verdict--"not proven, and notprovable"--must be recorded against all the grand hypotheses of thepalaeontologist respecting the general succession of life on the globe. The order and nature of terrestrial life, as a whole, are open questions. Geology at present provides us with most valuable topographical records, but she has not the means of working them into a universal history. Issuch a universal history, then, to be regarded as unattainable? Are allthe grandest and most interesting problems which offer themselves to thegeological student, essentially insoluble? Is he in the position of ascientific Tantalus--doomed always to thirst for a knowledge which hecannot obtain? The reverse is to be hoped; nay, it may not be impossibleto indicate the source whence help will come. 

In commencing these remarks, mention was made of the great obligationsunder which the naturalist lies to the geologist and palaeontologist. Assuredly the time will come when these obligations will be repaidtenfold, and when the maze of the world's past history, through which thepure geologist and the pure palaeontologist find no guidance, will besecurely threaded by the clue furnished by the naturalist. 

All who are competent to express an opinion on the subject are, atpresent, agreed that the manifold varieties of animal and vegetable formhave not either come into existence by chance, nor result from capriciousexertions of creative power; but that they have taken place in a definiteorder, the statement of which order is what men of science term a naturallaw. Whether such a law is to be regarded as an expression of the mode ofoperation of natural forces, or whether it is simply a statement of themanner in which a supernatural power has thought fit to act, is asecondary question, so long as the existence of the law and thepossibility of its discovery by the human intellect are granted. But hemust be a half-hearted philosopher who, believing in that possibility, and having watched the gigantic strides of the biological sciences duringthe last twenty years, doubts that science will sooner or later make thisfurther step, so as to become possessed of the law of evolution oforganic forms--of the unvarying order of that great chain of causes andeffects of which all organic forms, ancient and modern, are the links. And then, if ever, we shall be able to begin to discuss, with profit, thequestions respecting the commencement of life, and the nature of thesuccessive populations of the globe, which so many seem to think arealready answered. 

The preceding arguments make no particular claim to novelty; indeed theyhave been floating more or less distinctly before the minds of geologistsfor the last thirty years; and if, at the present time, it has seemeddesirable to give them more definite and systematic expression, it isbecause palaeontology is every day assuming a greater importance, and nowrequires to rest on a basis the firmness of which is thoroughly wellassured. Among its fundamental conceptions, there must be no confusionbetween what is certain and what is more or less probable. [1] But, pending the construction of a surer foundation than palaeontology nowpossesses, it may be instructive, assuming for the nonce the generalcorrectness of the ordinary hypothesis of geological contemporaneity, toconsider whether the deductions which are ordinarily drawn from the wholebody of palaeontological facts are justifiable. 

[Footnote 1: "Le plus grand service qu'on puisse rendre à la science estd'y faire place nette avant d'y rien construire. "--CUVIER. ]

The evidence on which such conclusions are based is of two kinds, negative and positive. The value of negative evidence, in connection withthis inquiry, has been so fully and clearly discussed in an address fromthe chair of this Society, [2] which none of us have forgotten, thatnothing need at present be said about it; the more, as the considerationswhich have been laid before you have certainly not tended to increaseyour estimation of such evidence. It will be preferable to turn to thepositive facts of palaeontology, and to inquire what they tell us. 

[Footnote 2: Anniversary Address for 1851, _Quart. Journ. Geol. Soc. _vol. Vii. ]

We are all accustomed to speak of the number and the extent of thechanges in the living population of the globe during geological time assomething enormous: and indeed they are so, if we regard only thenegative differences which separate the older rocks from the more modern, and if we look upon specific and generic changes as great changes, whichfrom one point of view, they truly are. But leaving the negativedifferences out of consideration, and looking only at the positive datafurnished by the fossil world from a broader point of view--from that ofthe comparative anatomist who has made the study of the greatermodifications of animal form his chief business--a surprise of anotherkind dawns upon the mind; and under _this_ aspect the smallness of thetotal change becomes as astonishing as was its greatness under the other. 

There are two hundred known orders of plants; of these not one iscertainly known to exist exclusively in the fossil state. The whole lapseof geological time has as yet yielded not a single new ordinal type ofvegetable structure. [3]

[Footnote 3: See Hooker's _Introductory Essay to the Flora of Tasmania_, p. Xxiii. ]

The positive change in passing from the recent to the ancient animalworld is greater, but still singularly small. No fossil animal is sodistinct from those now living as to require to be arranged even in aseparate class from those which contain existing forms. It is only whenwe come to the orders, which may be roughly estimated at about a hundredand thirty, that we meet with fossil animals so distinct from those nowliving as to require orders for themselves; and these do not amount, onthe most liberal estimate, to more than about 10 per cent. Of the whole. 

There is no certainly known extinct order of Protozoa; there is but oneamong the Coelenterata--that of the rugose corals; there is none amongthe Mollusca; there are three, the Cystidea, Blastoidea, andEdrioasterida, among the Echinoderms; and two, the Trilobita andEurypterida, among the Crustacea; making altogether five for the greatsub-kingdom of Annulosa. Among Vertebrates there is no ordinally distinctfossil fish: there is only one extinct order of Amphibia--theLabyrinthodonts; but there are at least four distinct orders of Reptilia, viz. The Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria, andperhaps another or two. There is no known extinct order of Birds, and nocertainly known extinct order of Mammals, the ordinal distinctness of the"Toxodontia" being doubtful. 

The objection that broad statements of this kind, after all, rest largelyon negative evidence is obvious, but it has less force than may at firstbe supposed; for, as might be expected from the circumstances of thecase, we possess more abundant positive evidence regarding Fishes andmarine Mollusks than respecting any other forms of animal life; and yetthese offer us, through the whole range of geological time, no speciesordinally distinct from those now living; while the far less numerousclass of Echinoderms presents three, and the Crustacea two, such orders, though none of these come down later than the Palaeozoic age. Lastly, theReptilia present the extraordinary and exceptional phenomenon of as manyextinct as existing orders, if not more; the four mentioned maintainingtheir existence from the Lias to the Chalk inclusive. 

Some years ago one of your Secretaries pointed out another kind ofpositive palaeontological evidence tending towards the same conclusion--afforded by the existence of what he termed "persistent types" ofvegetable and of animal life. [4] He stated, on the authority of Dr. Hooker, that there are Carboniferous plants which appear to begenerically identical with some now living; that the cone of the Oolitic_Araucaria_ is hardly distinguishable from that of an existing species;that a true _Pinus_ appears in the Purbecks and a _Juglans_ in the Chalk;while, from the Bagshot Sands, a _Banksia_, the wood of which is notdistinguishable from that of species now living in Australia, had beenobtained. 

[Footnote 4: See the abstract of a Lecture "On the Persistent Types ofAnimal Life, " in the _Notices of the Meetings of the Royal Institution ofGreat Britain_. --June 3, 1859, vol. Iii. P. 151. ]

Turning to the animal kingdom, he affirmed the tabulate corals of theSilurian rocks to be wonderfully like those which now exist; while eventhe families of the Aporosa were all represented in the older Mesozoicrocks. 

Among the Mollusca similar facts were adduced. Let it be borne in mindthat _Avicula, Mytilus, Chiton, Natica, Patella, Trochus, Discina, Orbicula, Lingula, Rhynchonclla_, and _Nautilus_, all of which areexisting _genera_, are given without a doubt as Silurian in the lastedition of "Siluria"; while the highest forms of the highest Cephalopodsare represented in the Lias by a genus _Belemnoteuthis_, which presentsthe closest relation to the existing _Loligo_. 

The two highest groups of the Annulosa, the Insecta and the Arachnida, are represented in the Coal, either by existing genera, or by formsdiffering from existing genera in quite minor peculiarities. 

Turning to the Vertebrata, the only palaeozoic Elasmobranch Fish of whichwe have any complete knowledge is the Devonian and Carboniferous_Pleuracanthus_, which differs no more from existing Sharks than these dofrom one another. 

Again, vast as is the number of undoubtedly Ganoid fossil Fishes, andgreat as is their range in time, a large mass of evidence has recentlybeen adduced to show that almost all those respecting which we possesssufficient information, are referable to the same sub-ordinal groups asthe existing _Lepidosteus, Polypterus_, and Sturgeon; and that a singularrelation obtains between the older and the younger Fishes; the former, the Devonian Ganoids, being almost all members of the same sub-order as_Polypterus_, while the Mesozoic Ganoids are almost all similarly alliedto _Lepidosteus_. [5]

[Footnote 5: "Memoirs of the Geological Survey of the United Kingdom. --Decade x. Preliminary Essay upon the Systematic Arrangement of the Fishesof the Devonian Epoch. "]

Again, what can be more remarkable than the singular constancy ofstructure preserved throughout a vast period of time by the family of thePycnodonts and by that of the true Coelacanths; the former persisting, with but insignificant modifications, from the Carboniferous to theTertiary rocks, inclusive; the latter existing, with still less change, from the Carboniferous rocks to the Chalk, inclusive?

Among Reptiles, the highest living group, that of the Crocodilia, isrepresented, at the early part of the Mesozoic epoch, by speciesidentical in the essential characters of their organisation with thosenow living, and differing from the latter only in such matters as theform of the articular facets of the vertebral centra, in the extent towhich the nasal passages are separated from the cavity of the mouth bybone, and in the proportions of the limbs. 

And even as regards the Mammalia, the scanty remains of Triassic andOolitic species afford no foundation for the supposition that theorganisation of the oldest forms differed nearly so much from some ofthose which now live as these differ from one another. 

It is needless to multiply these instances; enough has been said tojustify the statement that, in view of the immense diversity of knownanimal and vegetable forms, and the enormous lapse of time indicated bythe accumulation of fossiliferous strata, the only circumstance to bewondered at is, not that the changes of life, as exhibited by positiveevidence, have been so great but that they have been so small. 

Be they great or small, however, it is desirable to attempt to estimatethem. Let us, therefore, take each great division of the animal world insuccession, and, whenever an order or a family can be shown to have had aprolonged existence, let us endeavour to ascertain how far the latermembers of the group differ from the earlier ones. If these latermembers, in all or in many cases, exhibit a certain amount ofmodification, the fact is, so far, evidence in favour of a general law ofchange; and, in a rough way, the rapidity of that change will be measuredby the demonstrable amount of modification. On the other hand, it must berecollected that the absence of any modification, while it may leave thedoctrine of the existence of a law of change without positive support, cannot possibly disprove all forms of that doctrine, though it may afforda sufficient refutation of many of them. 

The PROTOZOA. --The Protozoa are represented throughout the whole range ofgeological series, from the Lower Silurian formation to the present day. The most ancient forms recently made known by Ehrenberg are exceedinglylike those which now exist: no one has ever pretended that the differencebetween any ancient and any modern Foraminifera is of more than genericvalue, nor are the oldest Foraminifera either simpler, more embryonic, orless differentiated, than the existing forms. 

The COELENTERATA. --The Tabulate Corals have existed from the Silurianepoch to the present day, but I am not aware that the ancient_Heliolites_ possesses a single mark of a more embryonic or lessdifferentiated character, or less high organisation, than the existing_Heliopora_. As for the Aporose Corals, in what respect is the Silurian_Paloeocyclus_ less highly organised or more embryonic than the modern_Fungia_, or the Liassic Aporosa than the existing members of the samefamilies?

The _Mollusca_--In what sense is the living _Waldheimia_ less embryonic, or more specialised, than the palaeozoic _Spirifer_; or the existing_Rhynchonelloe, Cranioe, Discinoe, Linguloe_, than the Silurian speciesof the same genera? In what sense can _Loligo_ or _Spirula_ be said to bemore specialised, or less embryonic, than _Belemnites_; or the modernspecies of Lamellibranch and Gasteropod genera, than the Silurian speciesof the same genera?

The ANNULOSA. --The Carboniferous Insecta and Arachnida are neither lessspecialised, nor more embryonic, than these that now live, nor are theLiassic Cirripedia and Macrura; while several of the Brachyura, whichappear in the Chalk, belong to existing genera; and none exhibit eitheran intermediate, or an embryonic, character. 

The VERTEBRATA. --Among fishes I have referred to the Coelacanthini(comprising the genera _Coelacanthus, Holophagus, Undina_, and_Macropoma_) as affording an example of a persistent type; and it is mostremarkable to note the smallness of the differences between any of thesefishes (affecting at most the proportions of the body and fins, and thecharacter and sculpture of the scales), notwithstanding their enormousrange in time. In all the essentials of its very peculiar structure, the_Macropoma_ of the Chalk is identical with the _Coelacanthus_ of theCoal. Look at the genus _Lepidotus_, again, persisting without amodification of importance from the Liassic to the Eocene formationsinclusively. 

Or among the Teleostei--in what respect is the _Beryx_ of the Chalk moreembryonic, or less differentiated, than _Beryx lineatus_ of King George'sSound?

Or to turn to the higher Vertebrata--in what sense are the LiassicChelonia inferior to those which now exist? How are the CretaceousIchthyosauria, Plesiosauria, or Pterosauria less embryonic, or moredifferentiated, species than those of the Lias?

Or lastly, in what circumstance is the _Phascolotherium_ more embryonic, or of a more generalised type, than the modern Opossum; or a _Lophiodon_, or a _Paloeotherium_, than a modern _Tapirus_ or _Hyrax_?

These examples might be almost indefinitely multiplied, but surely theyare sufficient to prove that the only safe and unquestionable testimonywe can procure--positive evidence--fails to demonstrate any sort ofprogressive modification towards a less embryonic, or less generalised, type in a great many groups of animals of long-continued geologicalexistence. In these groups there is abundant evidence of variation--noneof what is ordinarily understood as progression; and, if the knowngeological record is to be regarded as even any considerable fragment ofthe whole, it is inconceivable that any theory of a necessarilyprogressive development can stand, for the numerous orders and familiescited afford no trace of such a process. 

But it is a most remarkable fact, that, while the groups which have beenmentioned, and many besides, exhibit no sign of progressive modification, there are others, co-existing with them, under the same conditions, inwhich more or less distinct indications of such a process seems to betraceable. Among such indications I may remind you of the predominance ofHolostome Gasteropoda in the older rocks as compared with that ofSiphonostone Gasteropoda in the later. A case less open to the objectionof negative evidence, however, is that afforded by the TetrabranchiateCephalopoda, the forms of the shells and of the septal sutures exhibitinga certain increase of complexity in the newer genera. Here, however, oneis met at once with the occurrence of _Orthoceras_ and _Baculites_ at thetwo ends of the series, and of the fact that one of the simplest genera, _Nautilus_, is that which now exists. 

The Crinoidea, in the abundance of stalked forms in the ancientformations as compared with their present rarity, seem to present us witha fair case of modification from a more embryonic towards a lessembryonic condition. But then, on careful consideration of the facts, theobjection arises that the stalk, calyx, and arms of the palaeozoic Crinoidare exceedingly different from the corresponding organs of a larval_Comatula_; and it might with perfect justice be argued that_Actinocrinus_ and _Eucalyptocrinus_, for example, depart to the full aswidely, in one direction, from the stalked embryo of _Comatula_, as_Comatula_ itself does in the other. 

The Echinidea, again, are frequently quoted as exhibiting a gradualpassage from a more generalised to a more specialised type, seeing thatthe elongated, or oval, Spatangoids appear after the spheroidalEchinoids. But here it might be argued, on the other hand, that thespheroidal Echinoids, in reality, depart further from the general planand from the embryonic form than the elongated Spatangoids do; and thatthe peculiar dental apparatus and the pedicellariae of the former aremarks of at least as great differentiation as the petaloid ambulacra andsemitae of the latter. 

Once more, the prevalence of Macrurous before Brachyurous Podophthalmiais, apparently, a fair piece of evidence in favour of progressivemodification in the same order of Crustacea; and yet the case will notstand much sifting, seeing that the Macrurous Podophthalmia depart as farin one direction from the common type of Podophthalmia, or from anyembryonic condition of the Brachyura, as the Brachyura do in the other;and that the middle terms between Macrura and Brachyura--the Anomura--arelittle better represented in the older Mesozoic rocks than the Brachyuraare. 

None of the cases of progressive modification which are cited from amongthe Invertebrata appear to me to have a foundation less open to criticismthan these; and if this be so, no careful reasoner would, I think, beinclined to lay very great stress upon them. Among the Vertebrata, however, there are a few examples which appear to be far less open toobjection. 

It is, in fact, true of several groups of Vertebrata which have livedthrough a considerable range of time, that the endoskeleton (moreparticularly the spinal column) of the older genera presents a lessossified, and, so far, less differentiated, condition than that of theyounger genera. Thus the Devonian Ganoids, though almost all members ofthe same sub-order as _Polypterus_, and presenting numerous importantresemblances to the existing genus, which possesses biconclave vertebrae, are, for the most part, wholly devoid of ossified vertebral centra. TheMesozoic Lepidosteidae, again, have, at most, biconcave vertebrae, whilethe existing _Lepidosteus_ has Salamandroid, opisthocoelous, vertebrae. So, none of the Palaeozoic Sharks have shown themselves to be possessed ofossified vertebrae, while the majority of modern Sharks possess suchvertebrae. Again, the more ancient Crocodilia and Lacertilia have vertebraewith the articular facets of their centra flattened or biconcave, whilethe modern members of the same group have them procoelous. But the mostremarkable examples of progressive modification of the vertebral column, in correspondence with geological age, are those afforded by thePycnodonts among fish, and the Labyrinthodonts among Amphibia. 

The late able ichthyologist Heckel pointed out the fact, that, while thePycnodonts never possess true vertebral centra, they differ in the degreeof expansion and extension of the ends of the bony arches of the vertebraeupon the sheath of the notochord; the Carboniferous forms exhibitinghardly any such expansion, while the Mesozoic genera present a greaterand greater development, until, in the Tertiary forms, the expanded endsbecome suturally united so as to form a sort of false vertebra. Hermannvon Meyer, again, to whose luminous researches we are indebted for ourpresent large knowledge of the organisation of the older Labyrinthodonts, has proved that the Carboniferous _Archegosaurus_ had very imperfectlydeveloped vertebral centra, while the Triassic _Mastodonsaurus_ had thesame parts completely ossified. [6]

[Footnote 6: As this Address is passing through the press (March 7, 1862), evidence lies before me of the existence of a new Labyrinthodont(_Pholidogaster_), from the Edinburgh coal-field with well-ossifiedvertebral centra. ]

The regularity and evenness of the dentition of the _Anoplotherium_, ascontrasted with that of existing Artiodactyles, and the assumed nearerapproach of the dentition of certain ancient Carnivores to the typicalarrangement, have also been cited as exemplifications of a law ofprogressive development, but I know of no other cases based on positiveevidence which are worthy of particular notice. 

What then does an impartial survey of the positively ascertained truthsof palaeontology testify in relation to the common doctrines ofprogressive modification, which suppose that modification to have takenplace by a necessary progress from more to less embryonic forms, or frommore to less generalised types, within the limits of the periodrepresented by the fossiliferous rocks?

It negatives those doctrines; for it either shows us no evidence of anysuch modification, or demonstrates it to have been very slight; and as tothe nature of that modification, it yields no evidence whatsoever thatthe earlier members of any long-continued group were more generalised instructure than the later ones. To a certain extent, indeed, it may besaid that imperfect ossification of the vertebral column is an embryoniccharacter; but, on the other hand, it would be extremely incorrect tosuppose that the vertebral columns of the older Vertebrata are in anysense embryonic in their whole structure. 

Obviously, if the earliest fossiliferous rocks now known are coëval withthe commencement of life, and if their contents give us any justconception of the nature and the extent of the earliest fauna and flora, the insignificant amount of modification which can be demonstrated tohave taken place in any one group of animals, or plants, is quiteincompatible with the hypothesis that all living forms are the results ofa necessary process of progressive development, entirely comprised withinthe time represented by the fossiliferous rocks. 

Contrariwise, any admissible hypothesis of progressive modification mustbe compatible with persistence without progression, through indefiniteperiods. And should such an hypothesis eventually be proved to be true, in the only way in which it can be demonstrated, viz. By observation andexperiment upon the existing forms of life, the conclusion willinevitably present itself, that the Palaeozoic Mesozoic, and Cainozoicfaunae and florae, taken together, bear somewhat the same proportion to thewhole series of living beings which have occupied this globe, as theexisting fauna and flora do to them. 

Such are the results of palaeontology as they appear, and have for someyears appeared, to the mind of an inquirer who regards that study simplyas one of the applications of the great biological sciences, and whodesires to see it placed upon the same sound basis as other branches ofphysical inquiry. If the arguments which have been brought forward arevalid, probably no one, in view of the present state of opinion, will beinclined to think the time wasted which has been spent upon theirelaboration. 

X

GEOLOGICAL REFORM

[1869]

"A great reform in geological speculation seems now to have becomenecessary. "

"It is quite certain that a great mistake has been made--that Britishpopular geology at the present time is in direct opposition to theprinciples of Natural Philosophy. "[1]

[Footnote 1: On Geological Time. By Sir W. Thomson, LL. D. _Transactionsof the Geological Society of Glasgow_, vol. Iii. ]

In reviewing the course of geological thought during the past year, forthe purpose of discovering those matters to which I might most fitlydirect your attention in the Address which it now becomes my duty todeliver from the Presidential Chair, the two somewhat alarming sentenceswhich I have just read, and which occur in an able and interesting essayby an eminent natural philosopher, rose into such prominence before mymind that they eclipsed everything else. 

It surely is a matter of paramount importance for the British geologists(some of them very popular geologists too) here in solemn annual sessionassembled, to inquire whether the severe judgment thus passed upon themby so high an authority as Sir William Thomson is one to which they mustplead guilty _sans phrase_, or whether they are prepared to say "notguilty, " and appeal for a reversal of the sentence to that higher courtof educated scientific opinion to which we are all amenable. 

As your attorney-general for the time being, I thought I could not dobetter than get up the case with a view of advising you. It is true thatthe charges brought forward by the other side involve the considerationof matters quite foreign to the pursuits with which I am ordinarilyoccupied; but, in that respect, I am only in the position which is, ninetimes out of ten, occupied by counsel, who nevertheless contrive to gaintheir causes, mainly by force of mother-wit and common-sense, aided bysome training in other intellectual exercises. 

Nerved by such precedents, I proceed to put my pleading before you. 

And the first question with which I propose to deal is, What is it towhich Sir W. Thomson refers when he speaks of "geological speculation"and "British popular geology"?

I find three, more or less contradictory, systems of geological thought, each of which might fairly enough claim these appellations, standing sideby side in Britain. I shall call one of them CATASTROPHISM, anotherUNIFORMITARIANISM, the third EVOLUTIONISM; and I shall try briefly tosketch the characters of each, that you may say whether theclassification is, or is not, exhaustive. 

By CATASTROPHISM, I mean any form of geological speculation which, inorder to account for the phenomena of geology, supposes the operation offorces different in their nature, or immeasurably different in power, from those which we at present see in action in the universe. 

The Mosaic cosmogony is, in this sense, catastrophic, because it assumesthe operation of extra-natural power. The doctrine of violent upheavals, _débâcles_, and cataclysms in general, is catastrophic, so far as itassumes that these were brought about by causes which have now noparallel. There was a time when catastrophism might, pre-eminently, haveclaimed the title of "British popular geology"; and assuredly it has yetmany adherents, and reckons among its supporters some of the mosthonoured members of this Society. 

By UNIFORMITARIANISM, I mean especially, the teaching of Hutton and ofLyell. 

That great though incomplete work, "The Theory of the Earth, " seems to meto be one of the most remarkable contributions to geology which isrecorded in the annals of the science. So far as the not-living world isconcerned, uniformitarianism lies there, not only in germ, but in blossomand fruit. 

If one asks how it is that Hutton was led to entertain views so far inadvance of those prevalent in his time, in some respects; while, inothers, they seem almost curiously limited, the answer appears to me tobe plain. 

Hutton was in advance of the geological speculation of his time, because, in the first place, he had amassed a vast store of knowledge of the factsof geology, gathered by personal observation in travels of considerableextent; and because, in the second place, he was thoroughly trained inthe physical and chemical science of his day, and thus possessed, as muchas any one in his time could possess it, the knowledge which is requisitefor the just interpretation of geological phenomena, and the habit ofthought which fits a man for scientific inquiry. 

It is to this thorough scientific training that I ascribe Hutton's steadyand persistent refusal to look to other causes than those now inoperation, for the explanation of geological phenomena. 

Thus he writes:--"I do not pretend, as he [M. De Luc] does in his theory, to describe the beginning of things. I take things such as I find them atpresent; and from these I reason with regard to that which must havebeen. "[2]

[Footnote 2: _The Theory of the Earth_, vol. I. P. 173, note. ]

And again:--"A theory of the earth, which has for object truth, can haveno retrospect to that which had preceded the present order of the world;for this order alone is what we have to reason upon; and to reasonwithout data is nothing but delusion. A theory, therefore, which islimited to the actual constitution of this earth cannot be allowed toproceed one step beyond the present order of things. "[3]

[Footnote 3: _Ibid. _, vol. I. P. 281. ]

And so clear is he, that no causes beside such as are now in operationare needed to account for the character and disposition of the componentsof the crust of the earth, that he says, broadly and boldly:--" ... Thereis no part of the earth which has not had the same origin, so far as thisconsists in that earth being collected at the bottom of the sea, andafterwards produced, as land, along with masses of melted substances, bythe operation of mineral causes. "[4]

[Footnote 4: _Ibid. _. P. 371. ]

But other influences were at work upon Hutton beside those of a mindlogical by nature, and scientific by sound training; and the peculiarturn which his speculations took seems to me to be unintelligible, unlessthese be taken into account. The arguments of the French astronomers andmathematicians, which, at the end of the last century, were held todemonstrate the existence of a compensating arrangement among thecelestial bodies, whereby all perturbations eventually reduced themselvesto oscillations on each side of a mean position, and the stability of thesolar system was secured, had evidently taken strong hold of Hutton'smind. 

In those oddly constructed periods which seem to have prejudiced manypersons against reading his works, but which are full of that peculiar, if unattractive, eloquence which flows from mastery of the subject, Hutton says:--

"We have now got to the end of our reasoning; we have no data further toconclude immediately from that which actually is. But we have got enough;we have the satisfaction to find, that in Nature there is wisdom, system, and consistency. For having, in the natural history of this earth, seen asuccession of worlds, we may from this conclude that there is a system inNature; in like manner as, from seeing revolutions of the planets, it isconcluded, that there is a system by which they are intended to continuethose revolutions. But if the succession of worlds is established in thesystem of nature, it is in vain to look for anything higher in the originof the earth. The result, therefore, of this physical inquiry is, that wefind no vestige of a beginning, --no prospect of an end. "[5]

[Footnote 5: _Ibid. _, vol. I. P. 200. ]

Yet another influence worked strongly upon Hutton. Like most philosophersof his age, he coquetted with those final causes which have been namedbarren virgins, but which might be more fitly termed the _hetairoe_ ofphilosophy, so constantly have they led men astray. The final cause ofthe existence of the world is, for Hutton, the production of life andintelligence. 

"We have now considered the globe of this earth as a machine, constructedupon chemical as well as mechanical principles, by which its differentparts are all adapted, in form, in quality, and in quantity, to a certainend; an end attained with certainty or success; and an end from which wemay perceive wisdom, in contemplating the means employed. 

"But is this world to be considered thus merely as a machine, to last nolonger than its parts retain their present position, their proper formsand qualities? Or may it not be also considered as an organised body?such as has a constitution in which the necessary decay of the machine isnaturally repaired, in the exertion of those productive powers by whichit had been formed. 

"This is the view in which we are now to examine the globe; to see ifthere be, in the constitution of this world, a reproductive operation, bywhich a ruined constitution may be again repaired, and a duration orstability thus procured to the machine, considered as a world sustainingplants and animals. "[6]

[Footnote 6: _Ibid. _, vol. I. Pp. 16, 17. ]

Kirwan, and the other Philistines of the day, accused Hutton of declaringthat his theory implied that the world never had a beginning, and neverdiffered in condition from its present state. Nothing could be moregrossly unjust, as he expressly guards himself against any suchconclusion in the following terms:--

"But in thus tracing back the natural operations which have succeededeach other, and mark to us the course of time past, we come to a periodin which we cannot see any farther. This, however, is not the beginningof the operations which proceed in time and according to the wise economyof this world; nor is it the establishing of that which, in the course oftime, had no beginning; it is only the limit of our retrospective view ofthose operations which have come to pass in time, and have been conductedby supreme intelligence. "[7]

[Footnote 7: _Ibid. _, vol. I. P. 223. ]

I have spoken of Uniformitarianism as the doctrine of Hutton and ofLyell. If I have quoted the older writer rather than the newer, it isbecause his works are little known, and his claims on our veneration toofrequently forgotten, not because I desire to dim the fame of his eminentsuccessor. Few of the present generation of geologists have readPlayfair's "Illustrations, " fewer still the original "Theory of theEarth"; the more is the pity; but which of us has not thumbed every pageof the "Principles of Geology"? I think that he who writes fairly thehistory of his own progress in geological thought, will not be able toseparate his debt to Hutton from his obligations to Lyell; and thehistory of the progress of individual geologists is the history ofgeology. 

No one can doubt that the influence of uniformitarian views has beenenormous, and, in the main, most beneficial and favourable to theprogress of sound geology. 

Nor can it be questioned that Uniformitarianism has even a stronger titlethan Catastrophism to call itself the geological speculation of Britain, or, if you will, British popular geology. For it is eminently a Britishdoctrine, and has even now made comparatively little progress on thecontinent of Europe. Nevertheless, it seems to me to be open to seriouscriticism upon one of its aspects. 

I have shown how unjust was the insinuation that Hutton denied abeginning to the world. But it would not be unjust to say that hepersistently in practice, shut his eyes to the existence of that priorand different state of things which, in theory, he admitted; and, in thisaversion to look beyond the veil of stratified rocks, Lyell follows him. 

Hutton and Lyell alike agree in their indisposition to carry theirspeculations a step beyond the period recorded in the most ancient stratanow open to observation in the crust of the earth. This is, for Hutton, "the point in which we cannot see any farther"; while Lyell tells us, --

"The astronomer may find good reasons for ascribing the earth's form tothe original fluidity of the mass, in times long antecedent to the firstintroduction of living beings into the planet; but the geologist must becontent to regard the earliest monuments which it is his task tointerpret, as belonging to a period when the crust had already acquiredgreat solidity and thickness, probably as great as it now possesses, andwhen volcanic rocks, not essentially differing from those now produced, were formed from time to time, the intensity of volcanic heat beingneither greater nor less than it is now. "[8]

[Footnote 8: _Principles of Geology_, vol. Ii. P. 211. ]

And again, "As geologists, we learn that it is not only the presentcondition of the globe which has been suited to the accommodation ofmyriads of living creatures, but that many former states also have beenadapted to the organisation and habits of prior races of beings. Thedisposition of the seas, continents and islands, and the climates, havevaried; the species likewise have been changed; and yet they have allbeen so modelled, on types analogous to those of existing plants andanimals, as to indicate, throughout, a perfect harmony of design andunity of purpose. To assume that the evidence of the beginning, or end, of so vast a scheme lies within the reach of our philosophical inquiries, or even of our speculations, appears to be inconsistent with a justestimate of the relations which subsist between the finite powers of manand the attributes of an infinite and eternal Being. "[9]

[Footnote 9: _Ibid. _, vol. Ii. P. 613. ]

The limitations implied in these passages appear to me to constitute theweakness and the logical defect of Uniformitarianism. No one will imputeblame to Hutton that, in face of the imperfect condition, in his day, ofthose physical sciences which furnish the keys to the riddles of geology, he should have thought it practical wisdom to limit his theory to anattempt to account for "the present order of things"; but I am at a lossto comprehend why, for all time, the geologist must be content to regardthe oldest fossiliferous rocks as the _ultima Thule_ of his science; orwhat there is inconsistent with the relations between the finite and theinfinite mind, in the assumption, that we may discern somewhat of thebeginning, or of the end, of this speck in space we call our earth. Thefinite mind is certainly competent to trace out the development of thefowl within the egg; and I know not on what ground it should find moredifficulty in unravelling the complexities Of the development of theearth. In fact, as Kant has well remarked, [10] the cosmical process isreally simpler than the biological. 

[Footnote 10: "Man darf es sich also nicht befremden lassen, wenn ichmich unterstehe zu sagen, dass eher die Bildung aller Himmelskörper, dieUrsache ihrer Bewegungen, kurz der Ursprung der gantzen gegenwärtigenVerfassung des Weltbaues werden können eingesehen werden, ehe dieErzeugung eines einzigen Krautes oder einer Raupe aus mechanischenGründen, deutlich und vollständig kund werden wird. "--KANT'S _SämmtlicheWerke_, Bd. I. P. 220. ]

This attempt to limit, at a particular point, the progress of inductiveand deductive reasoning from the things which are, to those which were--this faithlessness to its own logic, seems to me to have costUniformitarianism the place, as the permanent form of geologicalspeculation, which it might otherwise have held. 

It remains that I should put before you what I understand to be the thirdphase of geological speculation--namely, EVOLUTIONISM. 

I shall not make what I have to say on this head clear, unless I diverge, or seem to diverge, for a while, from the direct path of my discourse, sofar as to explain what I take to be the scope of geology itself. Iconceive geology to be the history of the earth, in precisely the samesense as biology is the history of living beings; and I trust you willnot think that I am overpowered by the influence of a dominant pursuit ifI say that I trace a close analogy between these two histories. 

If I study a living being, under what heads does the knowledge I obtainfall? I can learn its structure, or what we call its ANATOMY; and itsDEVELOPMENT, or the series of changes which it passes through to acquireits complete structure. Then I find that the living being has certainpowers resulting from its own activities, and the interaction of thesewith the activities of other things--the knowledge of which isPHYSIOLOGY. Beyond this the living being has a position in space andtime, which is its DISTRIBUTION. All these form the body of ascertainablefacts which constitute the _status quo_ of the living creature. But thesefacts have their causes; and the ascertainment of these causes is thedoctrine of AETIOLOGY. 

If we consider what is knowable about the earth, we shall find that suchearth-knowledge--if I may so translate the word geology--falls into thesame categories. 

What is termed stratigraphical geology is neither more nor less than theanatomy of the earth; and the history of the succession of the formationsis the history of a succession of such anatomies, or corresponds withdevelopment, as distinct from generation. 

The internal heat of the earth, the elevation and depression of itscrust, its belchings forth of vapours, ashes, and lava, are itsactivities, in as strict a sense as are warmth and the movements andproducts of respiration the activities of an animal. The phenomena of theseasons, of the trade winds, of the Gulf-stream, are as much the resultsof the reaction between these inner activities and outward forces, as arethe budding of the leaves in spring and their falling in autumn theeffects of the interaction between the organisation of a plant and thesolar light and heat. And, as the study of the activities of the livingbeing is called its physiology, so are these phenomena the subject-matterof an analogous telluric physiology, to which we sometimes give the nameof meteorology, sometimes that of physical geography, sometimes that ofgeology. Again, the earth has a place in space and in time, and relationsto other bodies in both these respects, which constitute itsdistribution. This subject is usually left to the astronomer; but aknowledge of its broad outlines seems to me to be an essentialconstituent of the stock of geological ideas. 

All that can be ascertained concerning the structure, succession ofconditions, actions, and position in space of the earth, is the matter offact of its natural history. But, as in biology, there remains the matterof reasoning from these facts to their causes, which is just as muchscience as the other, and indeed more; and this constitutes geologicalaetiology. 

Having regard to this general scheme of geological knowledge and thought, it is obvious that geological speculation may be, so to speak, anatomicaland developmental speculation, so far as it relates to points ofstratigraphical arrangement which are out of reach of direct observation;or, it may be physiological speculation so far as it relates toundetermined problems relative to the activities of the earth; or, it maybe distributional speculation, if it deals with modifications of theearth's place in space; or, finally, it will be aetiological speculationif it attempts to deduce the history of the world, as a whole, from theknown properties of the matter of the earth, in the conditions in whichthe earth has been placed. 

For the purposes of the present discourse I may take this last to be whatis meant by "geological speculation. "

Now Uniformitarianism, as we have seen, tends to ignore geologicalspeculation in this sense altogether. 

The one point the catastrophists and the uniformitarians agreed upon, when this Society was founded, was to ignore it. And you will find, ifyou look back into our records, that our revered fathers in geologyplumed themselves a good deal upon the practical sense and wisdom of thisproceeding. As a temporary measure, I do not presume to challenge itswisdom; but in all organised bodies temporary changes are apt to producepermanent effects; and as time has slipped by, altering all theconditions which may have made such mortification of the scientific fleshdesirable, I think the effect of the stream of cold water which hassteadily flowed over geological speculation within these walls has beenof doubtful beneficence. 

The sort of geological speculation to which I am now referring(geological aetiology, in short) was created, as a science, by that famousphilosopher Immanuel Kant, when, in 1775, he wrote his "General NaturalHistory and Theory of the Celestial Bodies; or an Attempt to account forthe Constitutional and the Mechanical Origin of the Universe uponNewtonian principles. "[11]

[Footnote 11: Grant (_History of Physical Astronomy_, p. 574) makes butthe briefest reference to Kant. ]

In this very remarkable but seemingly little-known treatise, [12] Kantexpounds a complete cosmogony, in the shape of a theory of the causeswhich have led to the development of the universe from diffused atoms ofmatter endowed with simple attractive and repulsive forces. 

[Footnote 12: "Allgemeine Naturgeschichte und Theorie des Himmels; oderVersuch von der Verfassung und dem mechanischen Ursprunge des ganzenWeltgebäudes nach Newton'schen Grundsatzen abgehandelt. "--KANT'S_Sämmtliche Werke_, Bd. I. P. 207. ]

"Give me matter, " says Kant, "and I will build the world;" and heproceeds to deduce from the simple data from which he starts, a doctrinein all essential respects similar to the well-known "Nebular Hypothesis"of Laplace. [13] He accounts for the relation of the masses and thedensities of the planets to their distances from the sun, for theeccentricities of their orbits, for their rotations, for theirsatellites, for the general agreement in the direction of rotation amongthe celestial bodies, for Saturn's ring, and for the zodiacal light. Hefinds in each system of worlds, indications that the attractive force ofthe central mass will eventually destroy its organisation, byconcentrating upon itself the matter of the whole system; but, as theresult of this concentration, he argues for the development of an amountof heat which will dissipate the mass once more into a molecular chaossuch as that in which it began. 

[Footnote 13: _Système du Monde_, tome ii. Chap. 6. ]

Kant pictures to himself the universe as once an infinite expansion offormless and diffused matter. At one point of this he supposes a singlecentre of attraction set up; and, by strict deductions from admitteddynamical principles, shows how this must result in the development of aprodigious central body, surrounded by systems of solar and planetaryworlds in all stages of development. In vivid language he depicts thegreat world-maelstrom, widening the margins of its prodigious eddy in theslow progress of millions of ages, gradually reclaiming more and more ofthe molecular waste, and converting chaos into cosmos. But what is gainedat the margin is lost in the centre; the attractions of the centralsystems bring their constituents together, which then, by the heatevolved, are converted once more into molecular chaos. Thus the worldsthat are, lie between the ruins of the worlds that have been, and thechaotic materials of the worlds that shall be; and in spite of all wasteand destruction, Cosmos is extending his borders at the expense of Chaos. 

Kant's further application of his views to the earth itself is to befound in his "Treatise on Physical Geography"[14] (a term under which thethen unknown science of geology was included), a subject which he hadstudied with very great care and on which he lectured for many years. Thefourth section of the first part of this Treatise is called "History ofthe great Changes which the Earth has formerly undergone and is stillundergoing, " and is, in fact, a brief and pregnant essay upon theprinciples of geology. Kant gives an account first "of the gradualchanges which are now taking place" under the heads of such as are causedby earthquakes, such as are brought about by rain and rivers, such as areeffected by the sea, such as are produced by winds and frost; and, finally, such as result from the operations of man. 

[Footnote 14: Kant's _Sämmtliche Werke_, Bd. Viii. P. 145. ]

The second part is devoted to the "Memorials of the Changes which theEarth has undergone in remote Antiquity. " These are enumerated as:--A. Proofs that the sea formerly covered the whole earth. B. Proofs that thesea has often been changed into dry land and then again into sea. C. Adiscussion of the various theories of the earth put forward byScheuchzer, Moro, Bonnet, Woodward, White, Leibnitz, Linnaeus, and Buffon. 

The third part contains an "Attempt to give a sound explanation of theancient history of the earth. "

I suppose that it would be very easy to pick holes in the details ofKant's speculations, whether cosmological, or specially telluric, intheir application. But for all that, he seems to me to have been thefirst person to frame a complete system of geological speculation byfounding the doctrine of evolution. 

With as much truth as Hutton, Kant could say, "I take things just as Ifind them at present, and, from these, I reason with regard to that whichmust have been. " Like Hutton, he is never tired of pointing out that "inNature there is wisdom, system, and consistency. " And, as in these greatprinciples, so in believing that the cosmos has a reproductive operation"by which a ruined constitution may be repaired, " he forestalls Hutton;while, on the other hand, Kant is true to science. He knows no bounds togeological speculation but those of the intellect. He reasons back to abeginning of the present state of things; he admits the possibility of anend. 

I have said that the three schools of geological speculation which I havetermed Catastrophism, Uniformitarianism, and Evolutionism, are commonlysupposed to be antagonistic to one another; and I presume it will havebecome obvious that in my belief, the last is destined to swallow up theother two. But it is proper to remark that each of the latter has keptalive the tradition of precious truths. 

CATASTROPHISM has insisted upon the existence of a practically unlimitedbank of force, on which the theorist might draw; and it has cherished theidea of the development of the earth from a state in which its form, andthe forces which it exerted, were very different from those we now know. That such difference of form and power once existed is a necessary partof the doctrine of evolution. 

UNIFORMITARIANISM, on the other hand, has with equal justice insistedupon a practically unlimited bank of time, ready to discount any quantityof hypothetical paper. It has kept before our eyes the power of theinfinitely little, time being granted, and has compelled us to exhaustknown causes, before flying to the unknown. 

To my mind there appears to be no sort of necessary theoreticalantagonism between Catastrophism and Uniformitarianism. On the contrary, it is very conceivable that catastrophes may be part and parcel ofuniformity. Let me illustrate my case by analogy. The working of a clockis a model of uniform action; good time-keeping means uniformity ofaction. But the striking of the clock is essentially a catastrophe; thehammer might be made to blow up a barrel of gunpowder, or turn on adeluge of water; and, by proper arrangement, the clock, instead ofmarking the hours, might strike at all sorts of irregular periods, nevertwice alike, in the intervals, force, or number of its blows. Nevertheless, all these irregular, and apparently lawless, catastropheswould be the result of an absolutely uniformitarian action; and we mighthave two schools of clock-theorists, one studying the hammer and theother the pendulum. 

Still less is there any necessary antagonists between either of thesedoctrines and that of Evolution, which embraces all that is sound in bothCatastrophism and Uniformitarianism, while it rejects the arbitraryassumptions of the one and the, as arbitrary, limitations of the other. Nor is the value of the doctrine of Evolution to the philosophic thinkerdiminished by the fact that it applies the same method to the living andthe not-living world; and embraces, in one stupendous analogy, the growthof a solar system from molecular chaos, the shaping of the earth from thenebulous cub-hood of its youth, through innumerable changes andimmeasurable ages, to its present form; and the development of a livingbeing from the shapeless mass of protoplasm we term a germ. 

I do not know whether Evolutionism can claim that amount of currencywhich would entitle it to be called British popular geology; but, more orless vaguely, it is assuredly present in the minds of most geologists. 

Such being the three phases of geological speculation, we are now inposition to inquire which of these it is that Sir William Thomson callsupon us to reform in the passages which I have cited. 

It is obviously Uniformitarianism which the distinguished physicist takesto be the representative of geological speculation in general. And thus afirst issue is raised, inasmuch as many persons (and those not the leastthoughtful among the younger geologists) do not accept strictUniformitarianism as the final form of geological speculation. We shouldsay, if Hutton and Playfair declare the course of the world to have beenalways the same, point out the fallacy by all means; but, in so doing, donot imagine that you are proving modern geology to be in opposition tonatural philosophy. I do not suppose that, at the present day, anygeologist would be found to maintain absolute Uniformitarianism, to denythat the rapidity of the rotation of the earth _may_ be diminishing, thatthe sun _may_ be waxing dim, or that the earth itself _may_ be cooling. Most of us, I suspect, are Gallios, "who care for none of these things, "being of opinion that, true or fictitious, they have made no practicaldifference to the earth, during the period of which a record is preservedin stratified deposits. 

The accusation that we have been running counter to the _principles_ ofnatural philosophy, therefore, is devoid of foundation. The only questionwhich can arise is whether we have, or have not, been tacitly makingassumptions which are in opposition to certain conclusions which may bedrawn from those principles. And this question subdivides itself intotwo:--the first, are we really contravening such conclusions? the second, if we are, are those conclusions so firmly based that we may notcontravene them? I reply in the negative to both these questions, and Iwill give you my reasons for so doing. Sir William Thomson believes thathe is able to prove, by physical reasonings, "that the existing state ofthings on the earth, life on the earth--all geological history showingcontinuity of life--must be limited within some such period of time asone hundred million years" (_loc. Cit. _ p. 25). 

The first inquiry which arises plainly is, has it ever been denied thatthis period _may_ be enough for the purposes of geology?

The discussion of this question is greatly embarrassed by the vaguenesswith which the assumed limit is, I will not say defined, but indicated, --"some such period of past time as one hundred million years. " Now doesthis mean that it may have been two, or three, or four hundred millionyears? Because this really makes all the difference. [15]

[Footnote 15: Sir William Thomson implies (_loc. Cit_. P. 16) that theprecise time is of no consequence: "the principle is the same"; but, asthe principle is admitted, the whole discussion turns on its practicalresults. ]

I presume that 100, 000 feet may be taken as a full allowance for thetotal thickness of stratified rocks containing traces of life; 100, 000divided by 100, 000, 000 = 0. 001. Consequently, the deposit of 100, 000 feetof stratified rock in 100, 000, 000 years means that the deposit has takenplace at the rate of 1/1000 of a foot, or, say, 1/83 of an inch, perannum. 

Well, I do not know that any one is prepared to maintain that, evenmaking all needful allowances, the stratified rocks may not have beenformed, on the average, at the rate of 1/83 of an inch per annum. Isuppose that if such could be shown to be the limit of world-growth, wecould put up with the allowance without feeling that our speculations hadundergone any revolution. And perhaps, after all, the qualifying phrase"some such period" may not necessitate the assumption of more than 1/166or 1/249 or 1/332 of an inch of deposit per year, which, of course, wouldgive us still more ease and comfort. 

But, it may be said, that it is biology, and not geology, which asks forso much time--that the succession of life demands vast intervals; butthis appears to me to be reasoning in a circle. Biology takes her timefrom geology. The only reason we have for believing in the slow rate ofthe change in living forms is the fact that they persist through a seriesof deposits which, geology informs us, have taken a long while to make. If the geological clock is wrong, all the naturalist will have to do isto modify his notions of the rapidity of change accordingly. And Iventure to point out that, when we are told that the limitation of theperiod during which living beings have inhabited this planet to one, two, or three hundred million years requires a complete revolution ingeological speculation, the _onus probandi_ rests on the maker of theassertion, who brings forward not a shadow of evidence in its support. 

Thus, if we accept the limitation of time placed before us by Sir W. Thomson, it is not obvious, on the face of the matter, that we shall haveto alter, or reform, our ways in any appreciable degree; and we maytherefore proceed with much calmness, and indeed much indifference, as tothe result, to inquire whether that limitation is justified by thearguments employed in its support. 

These arguments are three in number. --

I. The first is based upon the undoubted fact that the tides tend toretard the rate of the earth's rotation upon its axis. That this must beso is obvious, if one considers, roughly, that the tides result from thepull which the sun and the moon exert upon the sea, causing it to act asa sort of break upon the rotating solid earth. 

Kant, who was by no means a mere "abstract philosopher, " but a goodmathematician and well versed in the physical science of his time, notonly proved this in an essay of exquisite clearness and intelligibility, now more than a century old, [16] but deduced from it some of its moreimportant consequences, such as the constant turning of one face of themoon towards the earth. 

[Footnote 16: "Untersuchung der Frage oh die Erde in ihrer Umdrehung umdie Achse, wodurch sie die Abwechselung des Tages und der Nachthervorbringt, einige Veränderung seit den ersten Zeiten ihres Ursprungeserlitten habe, &c. "--KANT's _Sämmntliche Werke_, Bd. I. P. 178. ]

But there is a long step from the demonstration of a tendency to theestimation of the practical value of that tendency, which is all withwhich we are at present concerned. The facts bearing on this point appearto stand as follows:--

It is a matter of observation that the moon's mean motion is (and has forthe last 3, 000 years been) undergoing an acceleration, relatively to therotation of the earth. Of course this may result from one of two causes:the moon may really have been moving more swiftly in its orbit; or theearth may have been rotating more slowly on its axis. 

Laplace believed he had accounted for this phenomenon by the fact thatthe eccentricity of the earth's orbit has been diminishing throughoutthese 3, 000 years. This would produce a diminution of the mean attractionof the sun on the moon; or, in other words, an increase in the attractionof the earth on the moon; and, consequently, an increase in the rapidityof the orbital motion of the latter body. Laplace, therefore, laid theresponsibility of the acceleration upon the moon, and if his views werecorrect, the tidal retardation must either be insignificant in amount, orbe counteracted by some other agency. 

Our great astronomer, Adams, however, appears to have found a flaw inLaplace's calculation, and to have shown that only half the observedretardation could be accounted for in the way he had suggested. Thereremains, therefore, the other half to be accounted for; and here, in theabsence of all positive knowledge, three sets of hypotheses have beensuggested. 

(_a_. ) M. Delaunay suggests that the earth is at fault, in consequence ofthe tidal retardation. Messrs. Adams, Thomson, and Tait work out thissuggestion, and, "on a certain assumption as to the proportion ofretardations due to the sun and moon, " find the earth may lose twenty-twoseconds of time in a century from this cause. [17]

[Footnote 17: Sir W. Thomson, _loc. Cit_. P. 14. ]

(_b_. ) But M. Dufour suggests that the retardation of the earth (which ishypothetically assumed to exist) may be due in part, or wholly, to theincrease of the moment of inertia of the earth by meteors falling uponits surface. This suggestion also meets with the entire approval of SirW. Thomson, who shows that meteor-dust, accumulating at the rate of onefoot in 4, 000 years, would account for the remainder of retardation. [18]

[Footnote 18: _Ibid. _ p. 27. ]

(_c_. ) Thirdly, Sir W. Thomson brings forward an hypothesis of his ownwith respect to the cause of the hypothetical retardation of the earth'srotation:--

"Let us suppose ice to melt from the polar regions (20° round each pole, we may say) to the extent of something more than a foot thick, enough togive 1. 1 foot of water over those areas, or 0. 006 of a foot of water ifspread over the whole globe, which would, in reality, raise the sea-levelby only some such undiscoverable difference as three-fourths of an inchor an inch. This, or the reverse, which we believe might happen any year, and could certainly not be detected without far more accurateobservations and calculations for the mean sea-level than any hithertomade, would slacken or quicken the earth's rate as a timekeeper by one-tenth of a second per year. "[19]

[Footnote 19: _Ibid. _]

I do not presume to throw the slightest doubt upon the accuracy of any ofthe calculations made by such distinguished mathematicians as those whohave made the suggestions I have cited. On the contrary, it is necessaryto my argument to assume that they are all correct. But I desire to pointout that this seems to be one of the many cases in which the admittedaccuracy of mathematical process is allowed to throw a whollyinadmissible appearance of authority over the results obtained by them. Mathematics may be compared to a mill of exquisite workmanship, whichgrinds you stuff of any degree of fineness; but, nevertheless, what youget out depends upon what you put in; and as the grandest mill in theworld will not extract wheat-flour from peascods, so pages of formulaewill not get a definite result out of loose data. 

In the present instance it appears to be admitted:--

1. That it is not absolutely certain, after all, whether the moon's meanmotion is undergoing acceleration, or the earth's rotationretardation. [20] And yet this is the key of the whole position. 

[Footnote 20: It will be understood that I do not wish to deny that theearth's rotation _may be_ undergoing retardation. ]

2. If the rapidity of the earth's rotation is diminishing, it is notcertain how much of that retardation is due to tidal friction, how muchto meteors, how much to possible excess of melting over accumulation ofpolar ice, during the period covered by observation, which amounts, atthe outside, to not more than 2, 600 years. 

3. The effect of a different distribution of land and water in modifyingthe retardation caused by tidal friction, and of reducing it, under somecircumstances, to a minimum, does not appear to be taken into account. 

4. During the Miocene epoch the polar ice was certainly many feet thinnerthan it has been during, or since, the Glacial epoch. Sir W. Thomsontells us that the accumulation of something more than a foot of icearound the poles (which implies the withdrawal of, say, an inch of waterfrom the general surface of the sea) will cause the earth to rotatequicker by one-tenth of a second per annum. It would appear, therefore, that the earth may have been rotating, throughout the whole period whichhas elapsed from the commencement of the Glacial epoch down to thepresent time, one, or more, seconds per annum quicker than it rotatedduring the Miocene epoch. 

But, according to Sir W. Thomson's calculation, tidal retardation willonly account for a retardation of 22" in a century, or 22/100 (say 1/5)of a second per annum. 

Thus, assuming that the accumulation of polar ice since the Miocene epochhas only been sufficient to produce ten times the effect of a coat of iceone foot thick, we shall have an accelerating cause which covers all theloss from tidal action, and leaves a balance of 4/5 of a second per annumin the way of acceleration. 

If tidal retardation can be thus checked and overthrown by othertemporary conditions, what becomes of the confident assertion, based uponthe assumed uniformity of tidal retardation, that ten thousand millionyears ago the earth must have been rotating more than twice as fast as atpresent, and, therefore, that we geologists are "in direct opposition tothe principles of Natural Philosophy" if we spread geological historyover that time?

II. The second argument is thus stated by Sir W. Thomson:--"An article, by myself, published in 'Macmillan's Magazine' for March 1862, on the ageof the sun's heat, explains results of investigation into variousquestions as to possibilities regarding the amount of heat that the suncould have, dealing with it as you would with a stone, or a piece ofmatter, only taking into account the sun's dimensions, which showed it tobe possible that the sun may have already illuminated the earth for asmany as one hundred million years, but at the same time rendered italmost certain that he had not illuminated the earth for five hundredmillions of years. The estimates here are necessarily very vague; butyet, vague as they are, I do not know that it is possible, upon anyreasonable estimate founded on known properties of matter, to say that wecan believe the sun has really illuminated the earth for five hundredmillion years. "[21]

[Footnote 21: _Loc. Cit. _ p. 20. ]

I do not wish to "Hansardise" Sir William Thomson by laying much stresson the fact that, only fifteen years ago he entertained a totallydifferent view of the origin of the sun's heat, and believed that theenergy radiated from year to year was supplied from year to year--adoctrine which would have suited Hutton perfectly. But the fact that soeminent a physical philosopher has, thus recently, held views opposite tothose which he now entertains, and that he confesses his own estimates tobe "very vague, " justly entitles us to disregard those estimates, if anydistinct facts on our side go against them. However, I am not aware thatsuch facts exist. As I have already said, for anything I know, one, two, or three hundred millions of years may serve the needs of geologistsperfectly well. 

III. The third line of argument is based upon the temperature of theinterior of the earth. Sir W. Thomson refers to certain investigationswhich prove that the present thermal condition of the interior of theearth implies either a heating of the earth within the last 20, 000 yearsof as much as 100° F. , or a greater heating all over the surface at sometime further back than 20, 000 years, and then proceeds thus:--

"Now, are geologists prepared to admit that, at some time within the last20, 000 years, there has been all over the earth so high a temperature asthat? I presume not; no geologist--no _modern_ geologist--would for amoment admit the hypothesis that the present state of underground heat isdue to a heating of the surface at so late a period as 20, 000 years ago. If that is not admitted we are driven to a greater heat at some time morethan 20, 000 years ago. A greater heating all over the surface than 100°Fahrenheit would kill nearly all existing plants and animals, I maysafely say. Are modern geologists prepared to say that all life waskilled off the earth 50, 000, 100, 000, or 200, 000 years ago? For theuniformity theory, the further back the time of high surface-temperatureis put the better; but the further back the time of heating, the hotterit must have been. The best for those who draw most largely on time isthat which puts it furthest back; and that is the theory that the heatingwas enough to melt the whole. But even if it was enough to melt thewhole, we must still admit some limit, such as fifty million years, onehundred million years, or two or three hundred million years ago. Beyondthat we cannot go. "[22]

[Footnote 22: _Loc. Cit. _ p. 24. ]

It will be observed that the "limit" is once again of the vaguest, ranging from 50, 000, 000 years to 300, 000, 000. And the reply is, oncemore, that, for anything that can be proved to the contrary, one or twohundred million years might serve the purpose, even of a thoroughgoingHuttonian uniformitarian, very well. 

But if, on the other hand, the 100, 000, 000 or 200, 000, 000 years appear tobe insufficient for geological purposes, we must closely criticise themethod by which the limit is reached. The argument is simple enough. _Assuming_ the earth to be nothing but a cooling mass, the quantity ofheat lost per year, _supposing_ the rate of cooling to have been uniform, multiplied by any given number of years, will be given the minimumtemperature that number of years ago. 

But is the earth nothing but a cooling mass, "like a hot-water jar suchas is used in carriages, " or "a globe of sandstone, " and has its coolingbeen uniform? An affirmative answer to both these questions seems to benecessary to the validity of the calculations on which Sir W. Thomsonlays so much stress. 

Nevertheless it surely may be urged that such affirmative answers arepurely hypothetical, and that other suppositions have an equal right toconsideration. 

For example, is it not possible that, at the prodigious temperature whichwould seem to exist at 100 miles below the surface, all the metallicbases may behave as mercury does at a red heat, when it refuses tocombine with oxygen; while, nearer the surface, and therefore at a lowertemperature, they may enter into combination (as mercury does with oxygena few degrees below its boiling-point), and so give rise to a heattotally distinct from that which they possess as cooling bodies? And hasit not also been proved by recent researches that the quality of theatmosphere may immensely affect its permeability to heat; and, consequently, profoundly modify the rate of cooling the globe as a whole?

I do not think it can be denied that such conditions may exist, and mayso greatly affect the supply, and the loss, of terrestrial heat as todestroy the value of any calculations which leave them out of sight. 

My functions as your advocate are at an end. I speak with more than thesincerity of a mere advocate when I express the belief that the caseagainst us has entirely broken down. The cry for reform which has beenraised without, is superfluous, inasmuch as we have long been reformingfrom within, with all needful speed. And the critical examination of thegrounds upon which the very grave charge of opposition to the principlesof Natural Philosophy has been brought against us, rather shows that wehave exercised a wise discrimination in declining, for the present, tomeddle with our foundations. 

XI

PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION

[1870]

It is now eight years since, in the absence of the late Mr. LeonardHorner, who then presided over us, it fell to my lot, as one of theSecretaries of this Society, to draw up the customary Annual Address. Iavailed myself of the opportunity to endeavour to "take stock" of thatportion of the science of biology which is commonly called"palaeontology, " as it then existed; and, discussing one after another thedoctrines held by palaeontologists, I put before you the results of myattempts to sift the well-established from the hypothetical or thedoubtful. Permit me briefly to recall to your minds what those resultswere:--

1. The living population of all parts of the earth's surface which haveyet been examined has undergone a succession of changes which, upon thewhole, have been of a slow and gradual character. 

2. When the fossil remains which are the evidences of these successivechanges, as they have occurred in any two more or less distant parts ofthe surface of the earth, are compared, they exhibit a certain broad andgeneral parallelism. In other words, certain forms of life in onelocality occur in the same general order of succession as, or are_homotaxial_ with, similar forms in the other locality. 

3. Homotaxis is not to be held identical with synchronism withoutindependent evidence. It is possible that similar, or even identical, faunae and florae in two different localities may be of extremely differentages, if the term "age" is used in its proper chronological sense. Istated that "geographical provinces, or zones, may have been asdistinctly marked in the Palaeozoic epoch as at present; and thoseseemingly sudden appearances of new genera and species which we ascribeto new creation, may be simple results of migration. "

4. The opinion that the oldest known fossils are the earliest forms oflife has no solid foundation. 

5. If we confine ourselves to positively ascertained facts, the totalamount of change in the forms of animal and vegetable life, since theexistence of such forms is recorded, is small. When compared with thelapse of time since the first appearance of these forms, the amount ofchange is wonderfully small. Moreover, in each great group of the animaland vegetable kingdoms, there are certain forms which I termed PERSISTENTTYPES, which have remained, with but very little apparent change, fromtheir first appearance to the present time. 

6. In answer to the question "What, then, does an impartial survey of thepositively ascertained truths of palaeontology testify in relation to thecommon doctrines of progressive modification, which suppose thatmodification to have taken place by a necessary progress from more toless embryonic forms, from more to less generalised types, within thelimits of the period represented by the fossiliferous rocks?" I reply, "It negatives these doctrines; for it either shows us no evidence of suchmodification, or demonstrates such modification as has occurred to havebeen very slight; and, as to the nature of that modification, it yieldsno evidence whatsoever that the earlier members of any long-continuedgroup were more generalised in structure than the later ones. "

I think that I cannot employ my last opportunity of addressing you, officially, more properly--I may say more dutifully--than in revisingthese old judgments with such help as further knowledge and reflection, and an extreme desire to get at the truth, may afford me. 

1. With respect to the first proposition, I may remark that whatever maybe the case among the physical geologists, catastrophic palaeontologistsare practically extinct. It is now no part of recognised geologicaldoctrine that the species of one formation all died out and were replacedby a brand-new set in the next formation. On the contrary, it isgenerally, if not universally, agreed that the succession of life hasbeen the result of a slow and gradual replacement of species by species;and that all appearances of abruptness of change are due to breaks in theseries of deposits, or other changes in physical conditions. Thecontinuity of living forms has been unbroken from the earliest times tothe present day. 

2, 3. The use of the word "homotaxis" instead of "synchronism" has not, so far as I know, found much favour in the eyes of geologists. I hope, therefore, that it is a love for scientific caution, and not merepersonal affection for a bantling of my own, which leads me still tothink that the change of phrase is of importance, and that the sooner itis made, the sooner shall we get rid of a number of pitfalls which besetthe reasoner upon the facts and theories of geology. 

One of the latest pieces of foreign intelligence which has reached us isthe information that the Austrian geologists have, at last, succumbed tothe weighty evidence which M. Barrande has accumulated, and have admittedthe doctrine of colonies. But the admission of the doctrine of coloniesimplies the further admission that even identity of organic remains is noproof of the synchronism of the deposits which contain them. 

4. The discussions touching the _Eozoon, _ which commenced in 1864, haveabundantly justified the fourth proposition. In 1862, the oldest recordof life was in the Cambrian rocks; but if the _Eozoon_ be, as PrincipalDawson and Dr. Carpenter have shown so much reason for believing, theremains of a living being, the discovery of its true nature carried lifeback to a period which, as Sir William Logan has observed, is as remotefrom that during which the Cambrian rocks were deposited, as the Cambrianepoch itself is from the tertiaries. In other words, the ascertainedduration of life upon the globe was nearly doubled at a stroke. 

5. The significance of persistent types, and of the small amount ofchange which has taken place even in those forms which can be shown tohave been modified, becomes greater and greater in my eyes, the longer Ioccupy myself with the biology of the past. 

Consider how long a time has elapsed since the Miocene epoch. Yet, atthat time there is reason to believe that every important group in everyorder of the _Mammalia_ was represented. Even the comparatively scantyEocene fauna yields examples of the orders _Cheiroptera, Insectivora, Rodentia_, and _Perissodactyla_; of _Artiodactyla_ under both theRuminant and the Porcine modifications; of _Caranivora, Cetacea_, and_Marsupialia_. 

Or, if we go back to the older half of the Mesozoic epoch, how trulysurprising it is to find every order of the _Reptilia_, except the_Ophidia_, represented; while some groups, such as the _Ornithoseclida_and the _Pterosauria_, more specialised than any which now exist, abounded. 

There is one division of the _Amphibia_ which offers especially importantevidence upon this point, inasmuch as it bridges over the gap between theMesozoic and the Palaeozoic formations (often supposed to be of suchprodigious magnitude), extending, as it does, from the bottom of theCarboniferous series to the top of the Trias, if not into the Lias. Irefer to the Labyrinthodonts. As the Address of 1862 was passing throughthe press, I was able to mention, in a note, the discovery of a largeLabyrinthodont, with well-ossified vertebrae, in the Edinburgh coal-field. Since that time eight or ten distinct genera of Labyrinthodonts have beendiscovered in the Carboniferous rocks of England, Scotland, and Ireland, not to mention the American forms described by Principal Dawson andProfessor Cope. So that, at the present time, the Labyrinthodont Fauna ofthe Carboniferous rocks is more extensive and diversified than that ofthe Trias, while its chief types, so far as osteology enables us tojudge, are quite as highly organised. Thus it is certain that acomparatively highly organised vertebrate type, such as that of theLabyrinthodonts, is capable of persisting, with no considerable change, through the period represented by the vast deposits which constitute theCarboniferous, the Permian, and the Triassic formations. 

The very remarkable results which have been brought to light by thesounding and dredging operations, which have been carried on with suchremarkable success by the expeditions sent out by our own, the American, and the Swedish Governments, under the supervision of able naturalists, have a bearing in the same direction. These investigations havedemonstrated the existence, at great depths in the ocean, of livinganimals in some cases identical with, in others very similar to, thosewhich are found fossilised in the white chalk. The _Globigerinoe_, Cyatholiths, Coccospheres, Discoliths in the one are absolutely identicalwith those in the other; there are identical, or closely analogous, species of Sponges, Echinoderms, and Brachiopods. Off the coast ofPortugal, there now lives a species of _Beryx_, which, doubtless, leavesits bones and scales here and there in the Atlantic ooze, as itspredecessor left its spoils in the mud of the sea of the Cretaceousepoch. 

Many years ago[1] I ventured to speak of the Atlantic mud as "modernchalk, " and I know of no fact inconsistent with the view which ProfessorWyville Thomson has advocated, that the modern chalk is not only thelineal descendant of the ancient chalk, but that it remains, so to speak, in the possession of the ancestral estate; and that from the Cretaceousperiod (if not much earlier) to the present day, the deep sea has covereda large part of what is now the area of the Atlantic. But if_Globigerina_, and _Terebratula caput-serpentis_ and _Beryx_, not tomention other forms of animals and of plants, thus bridge over theinterval between the present and the Mesozoic periods, is it possiblethat the majority of other living things underwent a "sea-change intosomething new and strange" all at once?

[Footnote 1: See an article in the _Saturday Review_, for 1858, on"Chalk, Ancient and Modern. "]

6. Thus far I have endeavoured to expand and to enforce by fresharguments, but not to modify in any important respect, the ideassubmitted to you on a former occasion. But when I come to thepropositions touching progressive modification, it appears to me, withthe help of the new light which has broken from various quarters, thatthere is much ground for softening the somewhat Brutus-like severity withwhich, in 1862, I dealt with a doctrine, for the truth of which I shouldhave been glad enough to be able to find a good foundation. So far, indeed, as the _Invertebrata_ and the lower _Vertebrata_ are concerned, the facts and the conclusions which are to be drawn from them appear tome to remain what they were. For anything that, as yet, appears to thecontrary, the earliest known Marsupials may have been as highly organisedas their living congeners; the Permian lizards show no signs ofinferiority to those of the present day; the Labyrinthodonts cannot beplaced below the living Salamander and Triton; the Devonian Ganoids areclosely related to _Polypterus_ and to _Lepidosiren_. 

But when we turn to the higher _Vertebrata_, the results of recentinvestigations, however we may sift and criticise them, seem to me toleave a clear balance in favour of the doctrine of the evolution ofliving forms one from another. Nevertheless, in discussing this question, it is very necessary to discriminate carefully between the differentkinds of evidence from fossil remains which are brought forward in favourof evolution. 

Every fossil which takes an intermediate place between forms of lifealready known, may be said, so far as it is intermediate, to be evidencein favour of evolution, inasmuch as it shows a possible road by whichevolution may have taken place. But the mere discovery of such a formdoes not, in itself, prove that evolution took place by and through it, nor does it constitute more than presumptive evidence in favour ofevolution in general. Suppose A, B, C to be three forms, while B isintermediate in structure between A and C. Then the doctrine of evolutionoffers four possible alternatives. A may have become C by way of B; or Cmay have become A by way of B; or A and C may be independentmodifications of B; or A, B, and C may be independent modifications ofsome unknown D. Take the case of the Pigs, the _Anoplothcridoe_, and theRuminants. The _Anoplothcridoe_ are intermediate between the first andthe last; but this does not tell us whether the Ruminants have come fromthe Pigs, or the Pigs from Ruminants, or both from _Anoplothcridoe_, orwhether Pigs, Ruminants, and _Anoplotlicridoe_ alike may not havediverged from some common stock. 

But if it can be shown that A, B, and C exhibit successive stages in thedegree of modification, or specialisation, of the same type; and if, further, it can be proved that they occur in successively newer deposits, A being in the oldest and C in the newest, then the intermediatecharacter of B has quite another importance, and I should accept it, without hesitation, as a link in the genealogy of C. I should considerthe burden of proof to be thrown upon any one who denied C to have beenderived from A by way of B, or in some closely analogous fashion; for itis always probable that one may not hit upon the exact line of filiation, and, in dealing with fossils, may mistake uncles and nephews for fathersand sons. 

I think it necessary to distinguish between the former and the latterclasses of intermediate forms, as _intercalary types_ and _linear types_. When I apply the former term, I merely mean to say that as a matter offact, the form B, so named, is intermediate between the others, in thesense in which the _Anoplotherium_ is intermediate between the Pigs andthe Ruminants--without either affirming, or denying, any direct geneticrelation between the three forms involved. When I apply the latter term, on the other hand, I mean to express the opinion that the forms A, B, andC constitute a line of descent, and that B is thus part of the lineage ofC. 

From the time when Cuvier's wonderful researches upon the extinct Mammalsof the Paris gypsum first made intercalary types known, and caused themto be recognised as such, the number of such forms has steadily increasedamong the higher _Mammalia_. Not only do we now know numerous intercalaryforins of _Ungulata_, but M. Gaudry's great monograph upon the fossils ofPikermi (which strikes me as one of the most perfect pieces ofpalaeontological work I have seen for a long time) shows us, among thePrimates, _Mesopithecus_ as an intercalary form between the_Semnopitheci_ and the _Macaci_; and among the _Carnivora_, _Hyoenictis_and _Ictitherium_ as intercalary, or, perhaps, linear types between the_Viverridoe_ and the _Hyoenidoe_. 

Hardly any order of the higher _Mammalia_ stands so apparently separateand isolated from the rest as that of the _Cetacea_; though a carefulconsideration of the structure of the pinnipede _Carnivora_, or Seals, shows, in them, many an approximation towards the still more completelymarine mammals. The extinct _Zeuglodon_, however, presents us with anintercalary form between the type of the Seals and that of the Whales. The skull of this great Eocene sea-monster, in fact, shows by the narrowand prolonged interorbital region; the extensive union of the parietalbones in a sagittal suture; the well-developed nasal bones; the distinctand large incisors implanted in premaxillary bones, which take a fullshare in bounding the fore part of the gape; the two-fanged molar teethwith triangular and serrated crowns, not exceeding five on each side ineach jaw; and the existence of a deciduous dentition--its close relationwith the Seals. While, on the other hand, the produced rostral form ofthe snout, the long symphysis, and the low coronary process of themandible are approximations to the cetacean form of those parts. 

The scapula resembles that of the cetacean _Hyperoodon_, but the supra-spinous fossa is larger and more seal-like; as is the humerus, whichdiffers from that of the _Cetacea_ in presenting true articular surfacesfor the free jointing of the bones of the fore-arm. In the apparentlycomplete absence of hinder limbs, and in the characters of the vertebralcolumn, the _Zeuglodon_ lies on the cetacean side of the boundary line;so that upon the whole, the Zeuglodonts, transitional as they are, areconveniently retained in the cetacean order. And the publication, in1864, of M. Van Beneden's memoir on the Miocene and Pliocene _Squalodon_, furnished much better means than anatomists previously possessed offitting in another link of the chain which connects the existing_Cetacea_ with _Zeuglodon_. The teeth are much more numerous, althoughthe molars exhibit the zeuglodont double fang; the nasal bones are veryshort, and the upper surface of the rostrum presents the groove, filledup during life by the prolongation of the ethmoidal cartilage, which isso characteristic of the majority of the _Cetacea_. 

It appears to me that, just as among the existing _Carnivora_, thewalruses and the eared seals are intercalary forms between the fissipedeCarnivora and the ordinary seals, so the Zeuglodonts are intercalarybetween the _Carnivora_, as a whole, and the _Cetacea_. Whether theZeuglodonts are also linear types in their relation to these two groupscannot be ascertained, until we have more definite knowledge than wepossess at present, respecting the relations in time of the _Carnivora_and _Cetacea_. 

Thus far we have been concerned with the intercalary types which occupythe intervals between Families or Orders of the same class; but theinvestigations which have been carried on by Professor Gegenbaur, Professor Cope, and myself into the structure and relations of theextinct reptilian forms of the _Ornithoscelida_ (or _Dinosauria_ and_Compsognatha_) have brought to light the existence of intercalary formsbetween what have hitherto been always regarded as very distinct classesof the vertebrate sub-kingdom, namely _Reptilia_ and _Aves_. Whateverinferences may, or may not, be drawn from the fact, it is now anestablished truth that, in many of these _Ornithoscelida_, the hind limbsand the pelvis are much more similar to those of Birds than they are tothose of Reptiles, and that these Bird-reptiles, or Reptile-birds, weremore or less completely bipedal. 

When I addressed you in 1862, I should have been bold indeed had Isuggested that palaeontology would before long show us the possibility ofa direct transition from the type of the lizard to that of the ostrich. At the present moment, we have, in the _Ornithoscelida_, the intercalarytype, which proves that transition to be something more than apossibility; but it is very doubtful whether any of the genera of_Ornithoscelida_ with which we are at present acquainted are the actuallinear types by which the transition from the lizard to the bird waseffected. These, very probably, are still hidden from us in the olderformations. 

Let us now endeavour to find some cases of true linear types, or formswhich are intermediate between others because they stand in a directgenetic relation to them. It is no easy matter to find clear andunmistakable evidence of filiation among fossil animals; for, in orderthat such evidence should be quite satisfactory, it is necessary that weshould be acquainted with all the most important features of theorganisation of the animals which are supposed to be thus related, andnot merely with the fragments upon which the genera and species of thepalaeontologist are so often based. M. Gaudry has arranged the species of_Hyoenidoe, Proboscidea, Rhinocerotidoe_, and _Equidoe_ in their order offiliation from their earliest appearance in the Miocene epoch to thepresent time, and Professor Rütimeyer has drawn up similar schemes forthe Oxen and other _Ungulata_--with what, I am disposed to think, is afair and probable approximation to the order of nature. But, as no one isbetter aware than these two learned, acute, and philosophical biologists, all such arrangements must be regarded as provisional, except in thosecases in which, by a fortunate accident, large series of remains areobtainable from a thick and widespread series of deposits. It is easy toaccumulate probabilities--hard to make out some particular case in such away that it will stand rigorous criticism. 

After much search, however, I think that such a case is to be made out infavour of the pedigree of the Horses. 

The genus _Equus_ is represented as far back as the latter part of theMiocene epoch; but in deposits belonging to the middle of that epoch itsplace is taken by two other genera, _Hipparion_ and _Anchitherium_;[2]and, in the lowest Miocene and upper Eocene, only the last genus occurs. A species of _Anchitherium_ was referred by Cuvier to the _Paloeotheria_under the name of _P. Aurelianense_. The grinding-teeth are in fact verysimilar in shape and in pattern, and in the absence of any thick layer ofcement, to those of some species of _Paloeotherium_, especially Cuvier's_Paloeotherium minus_, which has been formed into a separate genus, _Plagiolophus_, by Pomel. But in the fact that there are only six full-sized grinders in the lower jaw, the first premolar being very small;that the anterior grinders are as large as, or rather larger than, theposterior ones; that the second premolar has an anterior prolongation;and that the posterior molar of the lower jaw has, as Cuvier pointed out, a posterior lobe of much smaller size and different form, the dentitionof _Anchitherium_ departs from the type of the _Paloeotherium_, andapproaches that of the Horse. 

[Footnote 2: Hermann von Meyer gave the name of _Anchitherium_ to _A. Ezquerroe_; and in his paper on the subject he takes great pains todistinguish the latter as the type of a new genus, from Cuvier's_Paloeotherium d'Orléans_. But it is precisely the _Paloeotheriumd'Orléans_ which is the type of Christol's genus _Hipparitherium_; andthus, though _Hipparitherium_ is of later date than _Anchitherium_, itseemed to me to have a sort of equitable right to recognition when thisAddress was written. On the whole, however, it seems most convenient toadopt _Anchitherium_. ]

Again, the skeleton of _Anchitherium_ is extremely equine. M. Christolgoes so far as to say that the description of the bones of the horse, orthe ass, current in veterinary works, would fit those of _Anchitherium_. And, in a general way, this may be true enough; but there are some mostimportant differences, which, indeed, are justly indicated by the samecareful observer. Thus the ulna is complete throughout, and its shaft isnot a mere rudiment, fused into one bone with the radius. There are threetoes, one large in the middle and one small on each side. The femur isquite like that of a horse, and has the characteristic fossa above theexternal condyle. In the British Museum there is a most instructivespecimen of the leg-bones, showing that the fibula was represented by theexternal malleolus and by a flat tongue of bone, which extends up from iton the outer side of the tibia, and is closely ankylosed with the latterbone. [3] The hind toes are three, like those of the fore leg; and themiddle metatarsal bone is much less compressed from side to side thanthat of the horse. 

[Footnote 3: I am indebted to M. Gervais for a specimen which indicatesthat the fibula was complete, at any rate, in some cases; and for a veryinteresting ramps of a mandible, which shows that, as in the_Paloeotheria_, the hindermost milk-molar of the lower jaw was devoid ofthe posterior lobe which exists in the hindermost true molar. ]

In the _Hipparion_, the teeth nearly resemble those of the Horses, thoughthe crowns of the grinders are not so long; like those of the Horses, they are abundantly coated with cement. The shaft of the ulna is reducedto a mere style, ankylosed throughout nearly its whole length with theradius, and appearing to be little more than a ridge on the surface ofthe latter bone until it is carefully examined. The front toes are stillthree, but the outer ones are more slender than in _Anchitherium_, andtheir hoofs smaller in proportion to that of the middle toe; they are, infact, reduced to mere dew-claws, and do not touch the ground. In the leg, the distal end of the fibula is so completely united with the tibia thatit appears to be a mere process of the latter bone, as in the Horses. 

In _Equus_, finally, the crowns of the grinding-teeth become longer, andtheir patterns are slightly modified; the middle of the shaft of the ulnausually vanishes, and its proximal and distal ends ankylose with theradius. The phalanges of the two outer toes in each foot disappear, theirmetacarpal and metatarsal bones being left as the "splints. "

The _Hipparion_ has large depressions on the face in front of the orbits, like those for the "larmiers" of many ruminants; but traces of these areto be seen in some of the fossil horses from the Sewalik Hills; and, asLeidy's recent researches show, they are preserved in _Anchitherium_. 

When we consider these facts, and the further circumstance that theHipparions, the remains of which have been collected in immense numbers, were subject, as M. Gaudry and others have pointed out, to a great rangeof variation, it appears to me impossible to resist the conclusion thatthe types of the _Anchitherium_, of the _Hipparion_, and of the ancientHorses constitute the lineage of the modern Horses, the _Hipparion_ beingthe intermediate stage between the other two, and answering to B in myformer illustration. 

The process by which the _Anchitherium_ has been converted into _Equus_is one of specialisation, or of more and more complete deviation fromwhat might be called the average form of an ungulate mammal. In theHorses, the reduction of some parts of the limbs, together with thespecial modification of those which are left, is carried to a greaterextent than in any other hoofed mammals. The reduction is less and thespecialisation is less in the _Hipparion_, and still less in the_Anchitherium_; but yet, as compared with other mammals, the reductionand specialisation of parts in the _Anchitherium_ remain great. 

Is it not probable then, that, just as in the Miocene epoch, we find anancestral equine form less modified than _Equus_, so, if we go back tothe Eocene epoch, we shall find some quadruped related to the_Anchitherium_, as _Hipparion_ is related to _Equus_, and consequentlydeparting less from the average form?

I think that this desideratum is very nearly, if not quite, supplied by_Plagiolophus_, remains of which occur abundantly in some parts of theUpper and Middle Eocene formations. The patterns of the grinding-teeth of_Plagiolophus_ are similar to those of _Anchitherium_, and their crownsare as thinly covered with cement; but the grinders diminish in sizeforwards, and the last lower molar has a large hind lobe, convex outwardsand concave inwards, as in _Palueotherium_. The ulna is complete and muchlarger than in any of the _Equidoe_, while it is more slender than inmost of the true _Paloeotheria_; it is fixedly united, but not ankylosed, with the radius. There are three toes in the fore limb, the outer onesbeing slender, but less attenuated than in the _Equidoe_. The femur ismore like that of the _Paloeotheria_ than that of the horse, and has onlya small depression above its outer condyle in the place of the greatfossa which is so obvious in the _Equidoe_. The fibula is distinct, butvery slender, and its distal end is ankylosed with the tibia. There arethree toes on the hind foot having similar proportions to those on thefore foot. The principal metacarpal and metatarsal bones are flatter thanthey are in any of the _Equidoe_; and the metacarpal bones are longerthan the metatarsals, as in the _Paloeotheria_. 

In its general form, _Plagiolophus_ resembles a very small and slenderhorse, [4] and is totally unlike the reluctant, pig-like creature depictedin Cuvier's restoration of his _Paloeotherium minus_ in the "OssemensFossiles. "

[Footnote 4: Such, at least, is the conclusion suggested by theproportions of the skeleton figured by Cuvier and De Blainville; butperhaps something between a Horse and an Agouti would be nearest themark. ]

It would be hazardous to say that _Plagiolophus_ is the exact radicalform of the Equine quadrupeds; but I do not think there can be anyreasonable doubt that the latter animals have resulted from themodification of some quadruped similar to _Plagiolophus_. 

We have thus arrived at the Middle Eocene formation, and yet have tracedback the Horses only to a three-toed stock; but these three-toed forms, no less than the Equine quadrupeds themselves, present rudiments of thetwo other toes which appertain to what I have termed the "average"quadruped. If the expectation raised by the splints of the Horses that, in some ancestor of the Horses, these splints would be found to becomplete digits, has been verified, we are furnished with very strongreasons for looking for a no less complete verification of theexpectation that the three-toed _Plagiolophus_-like "avus" of the horsemust have had a five-toed "atavus" at some earlier period. 

No such five-toed "atavus, " however, has yet made its appearance amongthe few middle and older Eocene _Mammalia_ which are known. 

Another series of closely affiliated forms, though the evidence theyafford is perhaps less complete than that of the Equine series, ispresented to us by the _Dichobune_ of the Eocene epoch, the_Cainotherium_ of the Miocene, and the _Tragulidoe_, or so-called "Musk-deer, " of the present day. 

The _Tragulidoe_; have no incisors in the upper jaw, and only sixgrinding-teeth on each side of each jaw; while the canine is moved up tothe outer incisor, and there is a diastema in the lower jaw. There arefour complete toes on the hind foot, but the middle metatarsals usuallybecome, sooner or later, ankylosed into a cannon bone. The navicular andthe cuboid unite, and the distal end of the fibula is ankylosed with thetibia. 

In _Cainotherium_ and _Dichobune_ the upper incisors are fully developed. There are seven grinders; the teeth form a continuous series without adiastema. The metatarsals, the navicular and cuboid, and the distal endof the fibula, remain free. In the _Cainotherium_, also, the secondmetacarpal is developed, but is much shorter than the third, while thefifth is absent or rudimentary. In this respect it resembles_Anoplotherium secundarium_. This circumstance, and the peculiar patternof the upper molars in _Cainotherium_, lead me to hesitate in consideringit as the actual ancestor of the modern _Tragulidoe_. If _Dichobune_ hasa fore-toed fore foot (though I am inclined to suspect that it resembles_Cainotherium_), it will be a better representative of the oldest formsof the Traguline series; but _Dichobune_ occurs in the Middle Eocene, andis, in fact, the oldest known artiodactyle mammal. Where, then, must welook for its five-toed ancestor?

If we follow down other lines of recent and tertiary _Ungulata_, the samequestion presents itself. The Pigs are traceable back through the Mioceneepoch to the Upper Eocene, where they appear in the two well-marked formsof _Hyopopotamus_ and _Choeropotamus_; but _Hyopotamus_ appears to havehad only two toes. 

Again, all the great groups of the Ruminants, the _Bovidoe, Antilopidoe, Camelopardalidoe_, and _Cervidoe_, are represented in the Miocene epoch, and so are the Camels. The Upper Eocene _Anoplotherium_, which isintercalary between the Pigs and the _Tragulidoe_, has only two, or, atmost, three toes. Among the scanty mammals of the Lower Eocene formationwe have the perissodactyle _Ungulata_ represented by _Coryphodon, Hyracotherium_, and _Pliolophus_. Suppose for a moment, for the sake offollowing out the argument, that _Pliolophus_ represents the primarystock of the Perissodactyles, and _Dichobune_ that of the Artiodactyles(though I am far from saying that such is the case), then we find, in theearliest fauna of the Eocene epoch to which our investigations carry us, the two divisions of the _Ungulata_ completely differentiated, and notrace of any common stock of both, or of five-toed predecessors toeither. With the case of the Horses before us, justifying a belief in theproduction of new animal forms by modification of old ones, I see noescape from the necessity of seeking for these ancestors of the_Ungulata_ beyond the limits of the Tertiary formations. 

I could as soon admit special creation, at once, as suppose that thePerissodactyles and Artiodactyles had no five-toed ancestors. And when weconsider how large a portion of the Tertiary period elapsed before_Anchitherium_ was converted into _Equus_, it is difficult to escape theconclusion that a large proportion of time anterior to the Tertiaryperiod must have been expended in converting the common stock of the_Ungulata_ into Perissodactyles and Artiodactyles. 

The same moral is inculcated by the study of every other order ofTertiary monodelphous _Mammalia_. Each of these orders is represented inthe Miocene epoch: the Eocene formation, as I have already said, contains_Cheiroptera, Insectivora, Rodentia, Ungulata, Carnivora_, and _Cetacea_. But the _Cheiroptera_ are extreme modifications of the _Insectivora_, just as the _Cetacea_ are extreme modifications of the Carnivorous type;and therefore it is to my mind incredible that monodelphous _Insectivora_and _Carnivora_ should not have been abundantly developed, along with_Ungulata_, in the Mesozoic epoch. But if this be the case, how muchfurther back must we go to find the common stock of the monodelphous_Mammalia_? As to the _Didelphia_, if we may trust the evidence whichseems to be afforded by their very scanty remains, a Hypsiprymnoid formexisted at the epoch of the Trias, contemporaneously with a Carnivorousform. At the epoch of the Trias, therefore, the _Marsupialia_ must havealready existed long enough to have become differentiated intocarnivorous and herbivorous forms. But the _Monotremata_ are lower formsthan the _Didelphia_ which last are intercalary between the_Ornithodelphia_ and the _Monodelphia_. To what point of the Palaeozoicepoch, then, must we, upon any rational estimate, relegate the origin ofthe _Monotremata?_

The investigation of the occurrence of the classes and of the orders ofthe _Sauropsida_ in time points in exactly the same direction. If, asthere is great reason to believe, true Birds existed in the Triassicepoch, the ornithoscelidous forms by which Reptiles passed into Birdsmust have preceded them. In fact there is, even at present, considerableground for suspecting the existence of _Dinosauria_ in the Permianformations; but, in that case, lizards must be of still earlier date. Andif the very small differences which are observable between the_Crocodilia_ of the older Mesozoic formations and those of the presentday furnish any sort of approximation towards an estimate of the averagerate of change among the _Sauropsida_, it is almost appalling to reflecthow far back in Palaeozoic times we must go, before we can hope to arriveat that common stock from which the _Crocodilia, Lacertilia, Ornithoscelida_, and _Plesiosauria_, which had attained so great adevelopment in the Triassic epoch, must have been derived. 

The _Amphibia_ and _Pisces_ tell the same story. There is not a singleclass of vertebrated animals which, when it first appears, is representedby analogues of the lowest known members of the same class. Therefore, ifthere is any truth in the doctrine of evolution, every class must bevastly older than the first record of its appearance upon the surface ofthe globe. But if considerations of this kind compel us to place theorigin of vertebrated animals at a period sufficiently distant from theUpper Silurian, in which the first Elasmobranchs and Ganoids occur, toallow of the evolution of such fishes as these from a Vertebrate assimple as the _Amphioxus, _ I can only repeat that it is appalling tospeculate upon the extent to which that origin must have preceded theepoch of the first recorded appearance of vertebrate life. 

Such is the further commentary which I have to offer upon the statementof the chief results of palaeontology which I formerly ventured to laybefore you. 

But the growth of knowledge in the interval makes me conscious of anomission of considerable moment in that statement, inasmuch as itcontains no reference to the bearings of palaeontology upon the theory ofthe distribution of life; nor takes note of the remarkable manner inwhich the facts of distribution, in present and past times, accord withthe doctrine of evolution, especially in regard to land animals. 

That connection between palaeontology and geology and the presentdistribution of terrestrial animals, which so strikingly impressed Mr. Darwin, thirty years ago, as to lead him to speak of a "law of successionof types, " and of the wonderful relationship on the same continentbetween the dead and the living, has recently received much elucidationfrom the researches of Gaudry, of Rutimeyer, of Leidy, and of AlphonseMilne-Edwards, taken in connection with the earlier labours of ourlamented colleague Falconer; and it has been instructively discussed inthe thoughtful and ingenious work of Mr. Andrew Murray "On theGeographical Distribution of Mammals. "[5]

[Footnote 5: The paper "On the Form and Distribution of the Landtractsduring the Secondary and Tertiary Periods respectively; and on the Effectupon Animal Life which great Changes in Geographical Configuration haveprobably produced, " by Mr. Searles V. Wood, jun. , which was published inthe _Philosophical Magazine_, in 1862, was unknown to me when thisAddress was written. It is well worthy of the most careful study. ]

I propose to lay before you, as briefly as I can, the ideas to which along consideration of the subject has given rise in my mind. 

If the doctrine of evolution is sound, one of its immediate consequencesclearly is, that the present distribution of life upon the globe is theproduct of two factors, the one being the distribution which obtained inthe immediately preceding epoch, and the other the character and theextent of the changes which have taken place in physical geographybetween the one epoch and the other; or, to put the matter in anotherway, the Fauna and Flora of any given area, in any given epoch, canconsist only of such forms of life as are directly descended from thosewhich constituted the Fauna and Flora of the same area in the immediatelypreceding epoch, unless the physical geography (under which I includeclimatal conditions) of the area has been so altered as to give rise toimmigration of living forms from some other area. 

The evolutionist, therefore, is bound to grapple with the followingproblem whenever it is clearly put before him:--Here are the Faunae of thesame area during successive epochs. Show good cause for believing eitherthat these Faunae have been derived from one another by gradualmodification, or that the Faunae have reached the area in question bymigration from some area in which they have undergone their development. 

I propose to attempt to deal with this problem, so far as it isexemplified by the distribution of the terrestrial _Vertebrata_, and Ishall endeavour to show you that it is capable of solution in a senseentirely favourable to the doctrine of evolution. 

I have elsewhere[6] stated at length the reasons which lead me torecognise four primary distributional provinces for the terrestrial_Vertebrata_ in the present world, namely, --first, the _Novozelanian_, orNew-Zealand province; secondly, the _Australian_ province, includingAustralia, Tasmania, and the Negrito Islands; thirdly, _Austro-Columbia_, or South America _plus_ North America as far as Mexico; and fourthly, therest of the world, or _Arctogoea_, in which province America north ofMexico constitutes one sub-province, Africa south of the Sahara a second, Hindostan a third, and the remainder of the Old World a fourth. 

[Footnote 6: "On the Classification and Distribution of theAlectoromorphoe;" _Proceedings of the Zoological Society_, 1868. ]

Now the truth which Mr. Darwin perceived and promulgated as "the law ofthe succession of types" is, that, in all these provinces, the animalsfound in Pliocene or later deposits are closely affined to those whichnow inhabit the same provinces; and that, conversely, the formscharacteristic of other provinces are absent. North and South America, perhaps, present one or two exceptions to the last rule, but they arereadily susceptible of explanation. Thus, in Australia, the laterTertiary mammals are marsupials (possibly with the exception of the Dogand a Rodent or two, as at present). In Austro-Columbia, the laterTertiary fauna exhibits numerous and varied forms of Platyrrhine Apes, Rodents, Cats, Dogs, Stags, _Edentata_, and Opossums; but, as at present, no Catarrhine Apes, no Lemurs, no _Insectivora_, Oxen, Antelopes, Rhinoceroses, nor _Didelphia_ other than Opossums. And in the widespreadArctogaeal province, the Pliocene and later mammals belong to the samegroups as those which now exist in the province. The law of succession oftypes, therefore, holds good for the present epoch as compared with itspredecessor. Does it equally well apply to the Pliocene fauna when wecompare it with that of the Miocene epoch? By great good fortune, anextensive mammalian fauna of the latter epoch has now become known, infour very distant portions of the Arctogaeal province which do not differgreatly in latitude. Thus Falconer and Cautley have made known the faunaof the sub-Himalayas and the Perim Islands; Gaudry that of Attica; manyobservers that of Central Europe and France; and Leidy that of Nebraska, on the eastern flank of the Rocky Mountains. The results are verystriking. The total Miocene fauna comprises many genera and species ofCatarrhine Apes, of Bats, of _Insectivora_; of Arctogaeal types of_Rodentia_; of _Proboscidea_; of equine, rhinocerotic, and tapirinequadrupeds; of cameline, bovine, antilopine, cervine, and tragulineRuminants; of Pigs and Hippopotamuses; of _Viverridoe_ and _Hyoenidoe_among other _Carnivora_; with _Edentata_ allied to the Aretogaeal_Oryeteropus_ and _Manis_, and not to the Austro-Columbian Edentates. Theonly type present in the Miocene, but absent in the existing, fauna ofEastern Arctogaea, is that of the _Didelphidoe_, which, however, remainsin North America. 

But it is very remarkable that while the Miocene fauna of the Arctogaealprovince, as a whole, is of the same character as the existing fauna ofthe same province, as a whole, the component elements of the fauna weredifferently associated. In the Miocene epoch, North America possessedElephants, Horses, Rhinoceroses, and a great number and variety ofRuminants and Pigs, which are absent in the present indigenous fauna;Europe had its Apes, Elephants, Rhinoceroses, Tapirs, Musk-deer, Giraffes, Hyaenas, great Cats, Edentates, and Opossum-like Marsupials, which have equally vanished from its present fauna; and in NorthernIndia, the African types of Hippopotamuses, Giraffes, and Elephants weremixed up with what are now the Asiatic types of the latter, and withCamels, and Semnopithecine and Pithecine Apes of no less distinctlyAsiatic forms. 

In fact the Miocene mammalian fauna of Europe and the Himalayan regionscontains, associated together, the types which are at present separatelylocated in the South-African and Indian sub-provinces of Arctogaea. Nowthere is every reason to believe, on other grounds, that both Hindostan, south of the Ganges, and Africa, south of the Sahara, were separated by awide sea from Europe and North Asia during the Middle and Upper Eoceneepochs. Hence it becomes highly probable that the well-knownsimilarities, and no less remarkable differences between the presentFaunae of India and South Africa have arisen in some such fashion as thefollowing. Some time during the Miocene epoch, possibly when theHimalayan chain was elevated, the bottom of the nummulitic sea wasupheaved and converted into dry land, in the direction of a lineextending from Abyssinia to the mouth of the Ganges. By this means, theDekhan on the one hand, and South Africa on the other, became connectedwith the Miocene dry land and with one another. The Miocene mammalsspread gradually over this intermediate dry land; and if the condition ofits eastern and western ends offered as wide contrasts as the valleys ofthe Ganges and Arabia do now, many forms which made their way into Africamust have been different from those which reached the Dekhan, whileothers might pass into both these sub-provinces. 

That there was a continuity of dry land between Europe and North Americaduring the Miocene epoch, appears to me to be a necessary consequence ofthe fact that many genera of terrestrial mammals, such as _Castor, Hystrix, Elephas, Mastodon, Equus, Hipparion, Anchitherium, Rhinoceros, Cervus, Amphicyon, Hyoenarctos_, and _Machairodus_, are common to theMiocene formations of the two areas, and have as yet been found (exceptperhaps _Anchitherium_) in no deposit of earlier age. Whether thisconnection took place by the east, or by the west, or by both sides ofthe Old World, there is at present no certain evidence, and the questionis immaterial to the present argument; but, as there are good grounds forthe belief that the Australian province and the Indian and South-Africansub-provinces were separated by sea from the rest of Arctogaea before theMiocene epoch, so it has been rendered no less probable, by theinvestigations of Mr. Carrick Moore and Professor Duncan, that Austro-Columbia was separated by sea from North America during a large part ofthe Miocene epoch. 

It is unfortunate that we have no knowledge of the Miocene mammalianfauna of the Australian and Austro-Columbian provinces; but, seeing thatnot a trace of a Platyrrhine Ape, of a Procyonine Carnivore, of acharacteristically South-American Rodent, of a Sloth, an Armadillo, or anAnt-eater has yet been found in Miocene deposits of Arctogaea, I cannotdoubt that they already existed in the Miocene Austro-Columbian province. 

Nor is it less probable that the characteristic types of AustralianMammalia were already developed in that region in Miocene times. 

But Austro-Columbia presents difficulties from which Australia is free;_Cantelidoe_ and _Tapirdoe_ are now indigenous in South America as theyare in Arctogaea; and, among the Pliocene Austro-Columbian mammals, theArctogaeal genera _Equus, Mastodon, _ and _Machairodus_ are numbered. Arethese Postmiocene immigrants, or Praemiocene natives?

Still more perplexing are the strange and interesting forms _Toxodon, Macrauchenia, Typotherium_, and a new Anoplotherioid mammal(_Homalodotherhon_) which Dr. Cunningham sent over to me some time agofrom Patagonia. I confess I am strongly inclined to surmise that theselast, at any rate, are remnants of the population of Austro-Columbiabefore the Miocene epoch, and were not derived from Arctogaea by way ofthe north and east. 

The fact that this immense fauna of Miocene Arctogaea is now fully andrichly represented only in India and in South Africa, while it is shrunkand depauperised in North Asia, Europe, and North America, becomes atonce intelligible, if we suppose that India and South Africa had but ascanty mammalian population before the Miocene immigration, while theconditions were highly favourable to the new comers. It is to be supposedthat these new regions offered themselves to the Miocene Ungulates, asSouth America and Australia offered themselves to the cattle, sheep, andhorses of modern colonists. But, after these great areas were thuspeopled, came the Glacial epoch, during which the excessive cold, to saynothing of depression and ice-covering, must have almost depopulated allthe northern parts of Arctogaea, destroying all the higher mammalianforms, except those which, like the Elephant and Rhinoceros, could adjusttheir coats to the altered conditions. Even these must have been drivenaway from the greater part of the area; only those Miocene mammals whichhad passed into Hindostan and into South Africa would escape decimationby such changes in the physical geography of Arctogaea. And when thenorthern hemisphere passed into its present condition, these lost tribesof the Miocene Fauna were hemmed by the Himalayas, the Sahara, the RedSea, and the Arabian deserts, within their present boundaries. 

Now, on the hypothesis of evolution, there is no sort of difficulty inadmitting that the differences between the Miocene forms of the mammalianFauna and those which exist at present are the results of gradualmodification; and, since such differences in distribution as obtain arereadily explained by the changes which have taken place in the physicalgeography of the world since the Miocene epoch, it is clear that theresult of the comparison of the Miocene and present Faunae is distinctlyin favour of evolution. Indeed I may go further. I may say that thehypothesis of evolution explains the facts of Miocene, Pliocene, andRecent distribution, and that no other supposition even pretends toaccount for them. It is, indeed, a conceivable supposition that everyspecies of Rhinoceros and every species of Hyaena, in the long successionof forms between the Miocene and the present species, was separatelyconstructed out of dust, or out of nothing, by supernatural power; butuntil I receive distinct evidence of the fact, I refuse to run the riskof insulting any sane man by supposing that he seriously holds such anotion. 

Let us now take a step further back in time, and inquire into therelations between the Miocene Fauna and its predecessor of the UpperEocene formation. 

Here it is to be regretted that our materials for forming a judgment arenothing to be compared in point of extent or variety with those which areyielded by the Miocene strata. However, what we do know of this UpperEocene Fauna of Europe gives sufficient positive information to enable usto draw some tolerably safe inferences. It has yielded representatives of_Insectivora_, of _Cheiroptera_, of _Rodentia_, of _Carnivora_, ofartiodactyle and perissodactyle _Ungulata_, and of opossum-likeMarsupials. No Australian type of Marsupial has been discovered in theUpper Eocene strata, nor any Edentate mammal. The genera (except perhapsin the case of some of the _Insectivora, Cheiroptera_, and _Rodentia_)are different from those of the Miocene epoch, but present a remarkablegeneral similarity to the Miocene and recent genera. In several cases, asI have already shown, it has now been clearly made out that the relationbetween the Eocene and Miocene forms is such that the Eocene form is theless specialised; while its Miocene ally is more so, and thespecialisation reaches its maximum in the recent forms of the same type. 

So far as the Upper Eocene and the Miocene Mammalian Faunae arecomparable, their relations are such as in no way to oppose thehypothesis that the older are the progenitors of the more recent forms, while, in some cases, they distinctly favour that hypothesis. The periodin tine and the changes in physical geography represented by thenummulitic deposits are undoubtedly very great, while the remains ofMiddle Eocene and Older Eocene Mammals are comparatively few. The generalfacies of the Middle Eocene Fauna, however, is quite that of the Upper. The Older Eocene pre-nummulitic mammalian Fauna contains Bats, two generaof _Carivora_, three genera of _Ungulata_ (probably all perissodactyle), and a didelphid Marsupial; all these forms, except perhaps the Bat andthe Opossum, belong to genera which are not known to occur out of theLower Eocene formation. The _Coryphodon_ appears to have been allied tothe Miocene and later Tapirs, while _Pliolophus_, in its skull anddentition, curiously partakes of both artiodactyle and perissodactylecharacters; the third trochanter upon its femur, and its three-toed hindfoot, however, appear definitely to fix its position in the latterdivision. 

There is nothing, then, in what is known of the older Eocene mammals ofthe Arctogaeal province to forbid the supposition that they stood in anancestral relation to those of the Calcaire Grossier and the Gypsum ofthe Paris basin, and that our present fauna, therefore, is directlyderived from that which already existed in Arctogaea at the commencementof the Tertiary period. But if we now cross the frontier between theCainozoic and the Mesozoic faunae, as they are preserved within theArctogaeal area, we meet with an astounding change, and what appears to bea complete and unmistakable break in the line of biological continuity. 

Among the twelve or fourteen species of _Mammalia_ which are said to havebeen found in the Purbecks, not one is a member of the orders_Cheiroptera, Rodentia, Ungulata_, or _Carnivora_, which are so wellrepresented in the Tertiaries. No _Insectivora_ are certainly known, norany opossum-like Marsupials. Thus there is a vast negative differencebetween the Cainozoic and the Mesozoic mammalian faunae of Europe. Butthere is a still more important positive difference, inasmuch as allthese Mammalia appear to be Marsupials belonging to Australian groups, and thus appertaining to a different distributional province from theEocene and Miocene marsupials, which are Austro-Columbian. So far as theimperfect materials which exist enable a judgment to be formed, the samelaw appears to have held good for all the earlier Mesozoic _Mammalia_. Ofthe Stonesfield slate mammals, one, _Amphitherium_, has a definitelyAustralian character; one, _Phascolotherium_, may be either Dasyurid orDidelphine; of a third, _Stereognathus_, nothing can at present be said. The two mammals of the Trias, also, appear to belong to Australiangroups. 

Every one is aware of the many curious points of resemblance between themarine fauna of the European Mesozoic rocks and that which now exists inAustralia. But if there was this Australian facies about both theterrestrial and the marine faunae of Mesozoic Europe, and if there is thisunaccountable and immense break between the fauna of Mesozoic and that ofTertiary Europe, is it not a very obvious suggestion that, in theMesozoic epoch, the Australian province included Europe, and that theArctogaeal province was contained within other limits? The Arctogaealprovince is at present enormous, while the Australian is relativelysmall. Why should not these proportions have been different during theMesozoic epoch?

Thus I am led to think that by far the simplest and most rational mode ofaccounting for the great change which took place in the livinginhabitants of the European area at the end of the Mesozoic epoch, is thesupposition that it arose from a vast alteration of the physicalgeography of the globe; whereby an area long tenanted by Cainozoic formswas brought into such relations with the European area that migrationfrom the one to the other became possible, and took place on a greatscale. 

This supposition relieves us, at once, from the difficulty in which wewere left, some time ago, by the arguments which I used to demonstratethe necessity of the existence of all the great types of the Eocene epochin some antecedent period. 

It is this Mesozoic continent (which may well have lain in theneighbourhood of what are now the shores of the North Pacific Ocean)which I suppose to have been occupied by the Mesozoic _Monodelphia_; andit is in this region that I conceive they must have gone through the longseries of changes by which they were specialised into the forms which werefer to different orders. I think it very probable that what is nowSouth America may have received the characteristic elements of itsmammalian fauna during the Mesozoic epoch; and there can be little doubtthat the general nature of the change which took place at the end of theMesozoic epoch in Europe was the upheaval of the eastern and northernregions of the Mesozoic sea-bottom into a westward extension of theMesozoic continent, over which the mammalian fauna, by which it wasalready peopled, gradually spread. This invasion of the land was prefacedby a previous invasion of the Cretaceous sea by modern forms of molluscaand fish. 

It is easy to imagine how an analogous change might come about in theexisting world. There is, at present, a great difference between thefauna of the Polynesian Islands and that of the west coast of America. The animals which are leaving their spoils in the deposits now forming inthese localities are widely different. Hence, if a gradual shifting ofthe deep sea, which at present bars migration between the easternmost ofthese islands and America, took place to the westward, while the Americanside of the sea-bottom was gradually upheaved, the palaeontologist of thefuture would find, over the Pacific area, exactly such a change as I amsupposing to have occurred in the North-Atlantic area at the close of theMesozoic period. An Australian fauna would be found underlying anAmerican fauna, and the transition from the one to the other would be asabrupt as that between the Chalk and lower Tertiaries; and as thedrainage-area of the newly formed extension of the American continentgave rise to rivers and lakes, the mammals mired in their mud woulddiffer from those of like deposits on the Australian side, just as theEocene mammals differ from those of the Purbecks. 

How do similar reasonings apply to the other great change of life--thatwhich took place at the end of the Palaeozoic period?

In the Triassic epoch, the distribution of the dry land and ofterrestrial vertebrate life appears to have been, generally, similar tothat which existed in the Mesozoic epoch; so that the Triassic continentsand their faunae seem to be related to the Mesozoic lands and their faunae, just as those of the Miocene epoch are related to those of the presentday. In fact, as I have recently endeavoured to prove to the Society, there was an Arctogaeal continent and an Arctogaeal province ofdistribution in Triassic times as there is now; and the _Sauropsida_ and_Marsupialia_ which constituted that fauna were, I doubt not, theprogenitors of the _Sauropsida_ and _Marsupialia_ of the whole Mesozoicepoch. 

Looking at the present terrestrial fauna of Australia, it appears to meto be very probable that it is essentially a remnant of the fauna of theTriassic, or even of an earlier, age[7] in which case Australia must atthat time have been in continuity with the Arctogaeal continent. 

[Footnote 7: Since this Address was read, Mr. Krefft has sent us news ofthe discovery in Australia of a freshwater fish of strangely Palaeozoicaspect, and apparently a Ganoid intermediate between _Dipterus_ and_Lepidosiren_. [The now well-known _Ceratodus_. 1894. ]]

But now comes the further inquiry, Where was the highly differentiatedSauropsidan fauna of the Trias in Palaeozoic times? The supposition thatthe Dinosaurian, Crocodilian, Dicynodontian, and to Plesiosaurian typeswere suddenly created at the end of the Permian epoch may be dismissed, without further consideration, as a monstrous and unwarranted assumption. The supposition that all these types were rapidly differentiated out of_Lacertilia_ in the time represented by the passage from the Palaeozoic tothe Mesozoic formation, appears to me to be hardly more credible, to saynothing of the indications of the existence of Dinosaurian forms in thePermian rocks which have already been obtained. 

For my part, I entertain no sort of doubt that the Reptiles, Birds, andMammals of the Trias are the direct descendants of Reptiles, Birds, andMammals which existed in the latter part of the Palaeozoic epoch, but notin any area of the present dry land which has yet been explored by thegeologist. 

This may seem a bold assumption, but it will not appear unwarrantable tothose who reflect upon the very small extent of the earth's surface whichhas hitherto exhibited the remains of the great Mammalian fauna of theEocene times. In this respect, the Permian land Vertebrate fauna appearsto me to be related to the Triassic much as the Eocene is to the Miocene. Terrestrial reptiles have been found in Permian rocks only in threelocalities; in some spots of France, and recently of England, and over amore extensive area in Germany. Who can suppose that the few fossils yetfound in these regions give any sufficient representation of the Permianfauna?

It may be said that the Carboniferous formations demonstrate theexistence of a vast extent of dry land in the present dry-land area, andthat the supposed terrestrial Palaeozoic Vertebrate Fauna ought to haveleft its remains in the Coal-measures, especially as there is now reasonto believe that much of the coal was formed by the accumulation of sporesand sporangia on dry land. But if we consider the matter more closely, Ithink that this apparent objection loses its force. It is clear that, during the Carboniferous epoch, the vast area of land which is nowcovered by Coal-measures must have been undergoing a gradual depression. The dry land thus depressed must, therefore, have existed, as such, before the Carboniferous epoch--in other words, in Devonian times--andits terrestrial population may never have been other than such as existedduring the Devonian, or some previous epoch, although much higher formsmay have been developed elsewhere. 

Again, let me say that I am making no gratuitous assumption ofinconceivable changes. It is clear that the enormous area of Polynesiais, on the whole, an area over which depression has taken place to animmense extent; consequently a great continent, or assemblage ofsubcontinental masses of land must have existed at some former time, andthat at a recent period, geologically speaking, in the area of thePacific. But if that continent had contained Mammals, some of them musthave remained to tell the tale; and as it is well known that theseislands have no indigenous _Mammalia_, it is safe to assume that noneexisted. Thus, midway between Australia and South America, each of whichpossesses an abundant and diversified mammalian fauna, a mass of land, which may have been as large as both put together, must have existedwithout a mammalian inhabitant. Suppose that the shores of this greatland were fringed, as those of tropical Australia are now, with belts ofmangroves, which would extend landwards on the one side, and be buriedbeneath littoral deposits on the other side, as depression went on; andgreat beds of mangrove lignite might accumulate over the sinking land. Let upheaval of the whole now take place, in such a manner as to bringthe emerging land into continuity with the South-American or Australiancontinent, and, in course of time, it would be peopled by an extension ofthe fauna of one of these two regions--just as I imagine the EuropeanPermian dry land to have been peopled. 

I see nothing whatever against the supposition that distributionalprovinces of terrestrial life existed in the Devonian epoch, inasmuch asM. Barrande has proved that they existed much earlier. I am aware of noreason for doubting that, as regards the grades of terrestrial lifecontained in them, one of these may have been related to another as NewZealand is to Australia, or as Australia is to India, at the present day. Analogy seems to me to be rather in favour of, than against, thesupposition that while only Ganoid fishes inhabited the fresh waters ofour Devonian land, _Amphibia_ and _Reptilia_, or even higher forms, mayhave existed, though we have not yet found them. The earliestCarboniferous _Amphibia_ now known, such as _Anthracosaurus_, are sohighly specialised that I can by no means conceive that they have beendeveloped out of piscine forms in the interval between the Devonian andthe Carboniferous periods, considerable as that is. And I take refuge inone of two alternatives: either they existed in our own area during theDevonian epoch and we have simply not yet found them; or they formed partof the population of some other distributional province of that day, andonly entered our area by migration at the end of the Devonian epoch. Whether _Reptilia_ and _Mammalia_ existed along with them is to me, atpresent, a perfectly open question, which is just as likely to receive anaffirmative as a negative answer from future inquirers. 

Let me now gather together the threads of my argumentation into the formof a connected hypothetical view of the manner in which the distributionof living and extinct animals has been brought about. 

I conceive that distinct provinces of the distribution of terrestriallife have existed since the earliest period at which that life isrecorded, and possibly much earlier; and I suppose, with Mr. Darwin, thatthe progress of modification of terrestrial forms is more rapid in areasof elevation than in areas of depression. I take it to be certain thatLabyrinthodont _Amphibia_ existed in the distributional province whichincluded the dry land depressed during the Carboniferous epoch; and Iconceive that, in some other distributional provinces of that day, whichremained in the condition of stationary or of increasing dry land, thevarious types of the terrestrial _Sauropsida_ and of the _Mammalia_ weregradually developing. 

The Permian epoch marks the commencement of a new movement of upheaval inour area, which dry land existed in North America, Europe, Asia, andAfrica, as it does now. Into this great new continental area the Mammals, Birds, and Reptiles developed during the Palaeozoic epoch spread, andformed the great Triassic Arctogaeal province. But, at the end of theTriassic period, the movement of depression recommenced in our area, though it was doubtless balanced by elevation elsewhere; modification anddevelopment, checked in the one province, went on in that "elsewhere";and the chief forms of Mammals, Birds and Reptiles, as we know them, wereevolved and peopled the Mesozoic continent. I conceive Australia to havebecome separated from the continent as early as the end of the Triassicepoch, or not much later. The Mesozoic continent must, I conceive, havelain to the east, about the shores of the North Pacific and IndianOceans; and I am inclined to believe that it continued along the easternside of the Pacific area to what is now the province of Austro-Columbia, the characteristic fauna of which is probably a remnant of the populationof the latter part of this period. 

Towards the latter part of the Mesozoic period the movement of upheavalaround the shores of the Atlantic once more recommenced, and was veryprobably accompanied by a depression around those of the Pacific. TheVertebrate fauna elaborated in the Mesozoic continent moved westward andtook possession of the new lands, which gradually increased in extent upto, and in some directions after, the Miocene epoch. 

It is in favour of this hypothesis, I think, that it is consistent withthe persistence of a general uniformity in the positions of the greatmasses of land and water. From the Devonian period, or earlier, to thepresent day, the four great oceans, Atlantic, Pacific, Arctic, andAntarctic, may have occupied their present positions, and only theircoasts and channels of communication have undergone an incessantalteration. And, finally, the hypothesis I have put before you requiresno supposition that the rate of change in organic life has been eithergreater or less in ancient times than it is now; nor any assumption, either physical or biological, which has not its justification inanalogous phenomena of existing nature. 

I have now only to discharge the last duty of my office, which is tothank you, not only for the patient attention with which you havelistened to me so long to-day, but also for the uniform kindness withwhich, for the past two years, you have rendered my endeavours to performthe important, and often laborious, functions of your President apleasure instead of a burden.