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SCIENCE 



[N. S. Vol. XLIII. No., Ilia 



at the very foundation of evolution. One 

 of my compatriots, an ardent disciple of 

 Lamarck, F. Le Dantec, wrote even as far 

 back as eight years ago a book bearing the 

 significant title "La Crise du Transform- 

 isme"- in which he brought out the contra- 

 dictions in question, contradictions which, 

 according to him, were to result in the ruin 

 of the very idea of transformism. Since 

 that time opposition has become even more 

 marked and at the present day, either 

 tacitly or explicitly, certain of the most 

 authoritative men, by their works, have ar- 

 rived very near to a conception which would 

 be the negation of transformism rather than 

 its affirmation. 



The term "evolution," in French at least, 

 has had historically two contrary meanings. 

 In the eighteenth century, it was the expres- 

 sion of the theory of the preformation or 

 "emboitement" of the germs, according to 

 which the lot of every organism was deter- 

 mined from the beginning. The succession 

 of generations was only the unfolding 

 (evolutio) of parts that existed from the 

 beginning. In the nineteenth century, and 

 it is in this sense that it is always used now, 

 it had an opposite sense; it is the synonym 

 of transformism and it signifies the succes- 

 sive transformation of animal or vegetable 

 organic types, not realized beforehand, in 

 the course of the history of the earth, under 

 the influence of external causes. Now, if 

 one admits the general value of certain of 

 the ideas recently expressed, evolution 

 would be only the unfolding of a series of 

 phases completely determined in the germs 

 of primitive organisms. It is a reversion, 

 under a modern form, to the idea which the 

 word evolution represented in the eight- 

 eenth century. It is unnecessary to say 

 that I use the word evolution in its nine- 

 teenth-century sense, which is synonymous 



2 ' ' Nouvelle collection scientifique, ' ' Paris, 

 Alcan. 



with transformism. It is evident then that 

 all is far from being clear in the present 

 conception of transformism and that, in 

 consequence, an exposition of its various 

 aspects and an effort to coordinate them is 

 not a useless thing in a course of lectures. 

 Furthermore a comprehensive glance at the 

 principal questions which we shall have to 

 examine will make my meaning clear and 

 will give me the chance to indicate the gen- 

 eral plan of the course. 



In spite of the contradictions to which I 

 have just alluded, the reality of transform- 

 ism as an accomplished fact is no longer 

 seriously questioned. We can make the 

 statement that, in the unanimous opinion 

 of biologists, evolution, that is to say, the 

 gradual differentiation of organisms from 

 common ancestral forms, is the only ra- 

 tional and scientific explanation of the 

 diversity of fossil and living beings. All the 

 known facts come easily under this hypoth- 

 esis. All morphology in its different as- 

 pects, comparative anatomy, embryology, 

 paleontology, verifies it. By virtue of this 

 same hypothesis, these different branches 

 of morphology have made an enormous 

 progress since Darwin's day. The signif- 

 icance of certain categories of facts, espe- 

 cially in the domain of embryology, may 

 have been exaggerated. Scientific men have 

 certainly overworked the idea that the devel- 

 opment of the individual, or ontogeny, was 

 an abridged repetition of phylogeny, that 

 is to say, of the several states through which 

 the species had passed, an idea which 

 Haeckel raised to the fundamental law of 

 biogenesis and which a whole generation of 

 naturalists accepted almost as a dogma. 

 Without doubt, ontogeny, in certain cases, 

 shows incontestable traces of previous 

 states, and for that reason embryology fur- 

 nishes us with palpable proofs of evolution 

 and with valuable information concerning 

 the afSnities of groups. But there can no 



