454 



NATURE 



{Sept. 8, 1 88 1 



old world, but also in those of the new fl'orld, although, at 

 present, neither elephants nor hippopotamuses occur in America. 

 Fifthly! in the middle of the continents, in regions most remnte 

 from the sea, we 6nd an infinite number of shells, of which the 

 most part belong to animals of those kinds which still exist in 

 southern seas, but of which ma-^y others have no living analogues ; 

 so that th2se species appear to be lost, destroyed by some unknown 

 cause. It is needless to inquire how far these statements are 

 strictly accurate ; they are sufficiently so to justify Buffon's con- 

 clusions that the dry land was once beneath the sea ; that the 

 formation of the fof^siliferous rocks must have occupied a vastly 

 greater lapse of time than that traditionally ascribed to the age 

 of the earth ; that fossil remains indicate different cliniatal 

 conditions to have obtained in former times, and especially that 

 the polar regions were once warmer ; that many species of 

 animals and plants have become extinct ; and that geological 

 change has had something to do wiih geographical distribution. 



But the-e propositions almost constitute the framework of 

 paljEontology. In order to complete it but one addition was 

 needed, and that was made, in the last years of the eighteenth 

 century, by William .Smith, whose work comes so near our own 

 times that many living men may have been personally acquainted 

 with him. This modest land surveyor, whose business took him 

 into many parts of England, profited by the peculiarly favr urable 

 conditions offered by the arrangement of our secondary strata 

 to make a careful examination and comparison of their fossil 

 contents at different points of the large area over which they ex- 

 tend. The result of his accurate and widely-extended oberva- 

 tions was to establish the important truth that each stratum 

 contained certain fossils which are peculiar to it ; and that the 

 order in w hich the strata, characterised by these fossils, are su- 

 perimposed one upon the other is always the same. This most 

 important gener.alisation was rapidly verified and extended to all 

 parts of the world accessible to geologists ; and, now, it rests 

 upon such an immense mass of observations as to be one of the 

 best established irulhs of natural science. To the geologist this 

 discovery was of infinite importance, as it enabled him to identify 

 rocks of the same relative age, however their continuity might be 

 interrupted or their composition altered. But to the biologist it 

 had a still deeper meaning, for it demonstrated that, throughout 

 the prodigious duration of time registered by the fos'iliferous 

 rocks, the living popiulation of the earth bad undergone continual 

 changes, not merely by the extinction of a certain number of the 

 species which at first existed, but by the continual generation of 

 new species, and the no less constant extinction of old ones. 



Thus, the broad outlines of palaeontology, in so far as it is the 

 common property of both the geologist and the biologist, were 

 marked out at the close of the last century. In tracing its sub- 

 sequent progress I must confine myself to the province ofbiology, 

 and, indeed, to the influence of palaeontology upon zor.logical 

 morphology. And I accept this limitation the more w illingly as 

 the no less important topic of the bearing of geology and of 

 palreontology upon distribution has been luminously treated in 

 the address of the Preident of the Geographical Section. 



The succession of the species of animals and plants in time 

 being established, the first question which the zoologist or the 

 botanist had to ask himself was. What is the relation of these 

 successive species one to another ? And it is a curious circum- 

 stance that the most important event in the history of pateonto- 

 logy which immediately succeeded William Smith's generalisation 

 was a discovery which, could it have been rightly appreciated at 

 the time, w ould have gone far towards suggesting the answer, 

 which was in fact delayed for more than half a century. I refer 

 to Cuvier's investigation of the Mammalian fossils yielded by 

 the quarries in the older Tertiary rocks of Montmartre, among 

 the chief results of which was the bringing tolight of two genera 

 of extinct hoofed quadrupeds, the Anoplotkerhim and the PaUvo- 

 theriitm. The rich materials at Cuvier's disposition enabled 

 him to obtain a full knowledge of the osteology and of the denti- 

 tion of these two forms, and consequently to compare their 

 structure critically with that of existing hoofed animals. The 

 effect of this comparison was to prove that the Anoplotheriiim, 

 though it I Tesente I many points of rcemblance with the pigs on 

 the one hand, and with the ruminants on the other, differed from 

 both to such an extent that it could find a place in neither group. 

 In fact, it held, in some respects, an intermediate position, tend- 

 ing to bridge over the interval between these two groups, which 

 in the existing fauna are so distinct. In the same way, the 

 Palmotherium tended to connect forms so different as the tapir, 

 the rhinoceros, and the horse. Subsequent investigations have 



brought to light a variety of facts of the same order, the most 

 curious and striking of which are those w hich prove the existence, 

 in the mesozoic epoch, of a seiies of forms intermediate between 

 birds and reptiles — two classes of vertebrate animals wdiich at 

 present appear to be moi'e widely separated than any others. 

 Yet the interval between them is completely filled, in the meso- 

 zoic fauna, by birds which have reptilian characters on the one 

 side, and reptiles which have ornithic characters, on the othe-. 

 So, again, while the group of fishes termed ganoids is at the 

 present time so distinct from that of the dipnoi, or mudfishes, 

 that they have been reckoned as distinct orders, the Devonian 

 strata present us with forms of which it is impossible to say with 

 certainty whether they aie dipnoi or whether they are ganoids. 



Agassiz's long and elaborate researches upon fossil fishes, pub- 

 hshed between 1833 and 1842, led him to suggest the existence 

 of another kind of relation tjetween ancient and modern forms 

 of life. He observed that the oldest fishes presented many 

 characters which recall the en bryonic conditions of existing 

 fishes ; and that, not only among fishes, but in several groups of 

 the invertebrata which have a long pateontological history, the 

 latest forms are more modified, more specialised, than the earlier. 

 The fact that the dentition of the older tertiary ungulate and 

 carnivorous mammals is always complete, noticed by Prof. 

 Owen, illustrated the same generalisation. 



Another no less suggestive observation was made by Mr. 

 Darwin, whose personal investigations during the voyage of the 

 Beagle led him to remark upon the singular fact, that the fauna 

 which immediately precedes that at present existing in any geo- 

 graphical province of distribution presents the same peculiarities 

 as its succes or. Thus, in South America and in Australia, the 

 later tertiai y or quaternary fossils show that the fauna w hich 

 immediately pireceded that of the present day was, in the one 

 case, as much characterised by edentates and in the other by 

 marsupials as it is now, although the species of the older are 

 largely different from tho^e of the newer fauna. 



However clearly these indications might point in one direction, 

 the question of the exact relation of the successive forms of 

 animal and vegetable life could be satisfactorily se'tled only in 

 one way — namely, by comparing, stage by stage, the series of 

 forms presented by one and the same type throughout a long 

 space of time. Within the last few years this has been done 

 fully in the case of the horse, less completely in the case of the 

 other principal types of the ungulata and of the carnivora, and 

 all the'e investigations tend to one general result — namely, that 

 in any given series the successive members of that series present 

 a gradually increasing specialisation of structure. That is to 

 say, if any such mammal at present existing has specially modified 

 and reduced limbs or dentition and complicated brain, its pre- 

 decessors in time show less and less modification and reduction 

 in limbs and teeth and a less highly developed brain. The 

 labours of Gaudry, Marsh, and Cope furnish abundant illustra- 

 tions of this law from the marvellous fossil wealth of Pikermi 

 and the vast uninterrupted series of tertiary rocks in the territories 

 of North America. 



I will now sum up the results of this sketch of the rise and 

 progress of palaeontology. The whole fabric of palaeontology is 

 based upon two propositions : the first is, that fossils are the 

 remains of animals and plants ; and the second is, that the 

 stratified rocks in which they are fotmd are sedimentary deposits ; 

 and each of these propositions is founded upon the same axiom 

 that like effects imply like causes. If there is any cause compet- 

 ent to produce a fossil stem, or shell, or bone, 'except a living 

 being, then pala;ontology has no foundation ; if the stratification 

 of the rocks is not the effect of such causes as at present produce 

 stratification, we have no means of judging of the duration of 

 past time, or of the order in which the forms of life have succeed- 

 ed one another. But, if these two propositions are granted, 

 there is no escape, as it appears to me, from three very important 

 conclusions. The first is that living matter has existed upon the 

 earth for a vast length of time, certainly for millions of years. 

 The second is that, during this lapse of time, the forms of living 

 matter have undergone repeated changes, the effect of which has 

 been that the animal and vegetable population at any period of 

 the earth's history contains some species which did not exist at 

 some antecedent period, and others w hich ceased to exist at some 

 subsequent period. The third is that in the case of many groups 

 of mammals and some of reptiles, in which one type can be 

 followed through a considerable extent of geological time, the 

 series of different forms by which the type is represented at 

 successive intervals of this time is exactly such as it would be if 



