May 6, iS8o] 



jVA TURE 



reptiles, which showed the nature of the modifications in 

 virtue of M'hich the type of the quadrupedal reptile 

 passed into that of the bipedal bird ; and abundant con- 

 firmatory evidence of the justice of the conclusions which 

 1 then laid before you has since come to light. 



In 187s, the discovery of the toothed birds of the 

 cretaceous formation in North America, by Prof. Marsh, 

 completed the series of transitional forms between birds 

 and reptiles, and removed Mr. Darwin's proposition that 

 " many animal forms of life have been utterly lost, 

 through which the early progenitors of birds were for- 

 merly connected with the early progenitors of the other 

 vertebrate classes," from the region of hypothesis to that 

 of demonstrable fact. 



In 1S59, there appeared to be a very sharp and clear 

 hiatus between vertebrated and invertebrated animals, 

 not only in their structure, but, what was more important, 

 in their development. I do not think that we even yet 

 know the precise links of connection between the two : but 

 the investigations of Kowalewsky and others upon the 

 development of Amphioxus and of the Tiitikata prove 

 beyond a doubt that the differences which were supposed 

 to constitute a barrier between the two are non-existent. 

 There is no longer any difficulty in understanding how 

 the vertebrate type may have arisen from the inverte- 

 brate, though the full proof of the manner in which the 

 transition was actually effected may still be lacking. 



Again, in 1859, there appeared to be a no less sharp 

 separation between the two great groups of flowering and 

 flowerless plants. It is only subsequently that the series 

 of remarkable investigations inaugurated by Hofmeister 

 has brought to light the e.xtraordinary and altogether 

 unexpected modifications of the reproductive apparatus 

 in the Lycopodiacca, the Rhizocarpca, and the Gymnosper- 

 mca-, by which the ferns and the mosses are gradually 

 connected with thePhanerogamicdivisionof the vegetable 

 world. 



So, again, it is only since 1859 that we have acquired 

 that wealth of knowledge of the lowest forms of life which 

 demonstrates the futility of any attempt to separate the 

 lowest plants from the lowest animals, and shows that 

 the two kingdoms of living nature have a common 

 borderland which belongs to both or to neither. 



Thus it will be observed that the whole tendency of 

 biological investigation since 1859 has been in the direc- 

 tion of removing the difficulties which the apparent 

 breaks in the series created at that time ; and the recog- 

 nition of gradation is the first step towards the acceptance 

 of evolution. 



As another great factor in bringing about the change 

 of opinion which has taken place arjong naturalists, I 

 count the astonishing progress which has been made in 

 the study of embryology. Twenty years ago, not only 

 were we devoid of any accurate knowledge of the mode of 

 development of many groups of animals and plants, but 

 the methods of investigation were rude and imperfect. 

 At the present time there is no important group of 

 organic beings the development of which has not been 

 carefully studied, and the modern methods of hardening 

 and section-making enable the embryologist to deter- 

 mine the nature of the process in each case, with a degree 

 of minuteness and accuracy which is truly astonishing to 

 those whose memories carry them back to the beginnings 



of modern histology. And the results of these embryo- 

 logical investigations are in complete harmony with the 

 requirements of the doctrine of Evolution. The first 

 beginnings of all the higher forms of animal life are 

 similar, and however diverse their adult conditions, they 

 start from a common foundation. Moreover the process 

 of development of the animal or the plant from its 

 primary egg or germ is a true process of evolution— a 

 progress from almost formless to more or less highly 

 organised matter, in virtue of the properties inherent in 

 that matter. 



To those who are familiar with the process of develop- 

 ment all a priori objections to the doctrine of biological 

 evolution appear childish. Any one who has watched the 

 gradual formation of a complicated animal from the pro- 

 toplasmic mass which constitutes the essential element of 

 a frog's or a hen's egg has had under his eyes sufficient 

 evidence that a similar evolution of the animal world from 

 the like foundation is, at any rate, possible. 



Yet another product of investigation has largely con- 

 tributed to the removal of the objections to the doctrine 

 of Evolution current in 1859. It is the proof aff'orded by 

 successive discoveries that Mr. Darwin did not over- 

 estimate tha imperfection of the geological record. No 

 more striking illustration of this is needed than a com- 

 parison of our knowledge of the mammalian fauna of the 

 Tertiary epoch in 1859 with its present condition. M. 

 Gaudry's researches on the fossils of Pikermi were pub- 

 hshed in 1868, those of Messrs. Leidy, Marsh, and Cope 

 on the fossils of the Western Territories of America, 

 have appeared almost wholly since 1870 ; those of M. 

 Filhol, on the phosphorites of Quercy, in 1S7S. The 

 general effect of these investigations has been to intro- 

 duce us to a multitude of extinct animals, the existence 

 of which was previously hardly suspected; just as if 

 zoologists were to become acquainted with a country, 

 hitherto unknown, as rich in novel forms of life, as Brazil 

 or South Africa once were to Europeans. Indeed the 

 fossil fauna of the Western Territories of America bids fair 

 to exceed in interest and importance all other known 

 Tertiary deposits put together ; and yet, with the excep- 

 tion of the case of the .American tertiaries, these investi- 

 gations have extended over very limited areas, and at 

 Pikermi were confined to an extremely small space. 



Such appear to me to be the chief events in the history 

 of the progress of knowledge, during the last twenty years, 

 which account for the changed feeling with which the 

 doctrine of Evolution is at present regarded by those who 

 have followed the advance of biological science in respect 

 of those problems which bear indirectly upon that doctrine. 



But all this remains mere secondary evidence. It may 

 remove dissent, but it does not compel assent. Primary 

 and direct evidence in favour of Evolution can be furnished 

 only by paleontology. The geological record, so soon as 

 it approaches completeness, must, when properly ques- 

 tioned, yield either an affirmative or a negative answer ; 

 if evolution has taken place, there will its mark be left ; 

 if it has not taken place, there will lie its refutation. 



What was the state of matters in 1859? Let us hear 

 Mr. Darwin, who may be trusted always to state the case 

 against himself as strongly as possible. 



'■ On this doctrine of the extermination of an infinitude 

 of connecting links between the living and extinct inhabi- 



