328 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1916. 



(litions outside the organism, since it is these finally which decide 

 the fate of the variations. And one of the forms in which the oppo- 

 sition to the transformist ideas, at the time of Darwin, manifested 

 itself was the very argmnent that if organisms had varied it was 

 only because of an internal principle, as Kolliker and Niigeli have 

 more particularly explained. 



The biologists at the end of the nineteenth century were divided 

 with regard to the mechanism of evolution into two principal 

 groups, following either Lamarck or Darwin. Among the neo- 

 Lamarcldans some have accorded to natural selection the value of a 

 secondary factor, holding that the primary factors are the direct 

 modifying influences of the surroundings which according to them 

 cause the variations. Selection came in only secondarily, by sort- 

 .ing out these variations and especially by eliminating some of them. 

 Such was the particular doctrine developed by my master, A. Giard, 

 at the Sorbonne. Others have more or less absolutely refused to 

 ^zrant any value to selection. Such was the case of the philosopher 

 Ilerbeit Spencer. We must also recognize that, since the time of 

 Darwin, natural selection has remained a purely speculative idea and 

 that no one has been able to show its efficacy in concrete indisputable 

 Cixamples. 



The neo-Darwinists, on their side, have in a general wa}^ gone 

 further than Darwin because they see in selection the exclusive factor 

 v)f evolution and deny all value to Lamarckian factors. This was the 

 doctrine of Wallace, and has been especially that of Weismann. I 

 will digress a moment to speak of the ideas of these last-mentioned 

 authors, because of the influence which they have exerted and still 

 exert, correctly in some respects, incorrectly in others, at least as I 

 think. 



Weismann attacked the doctrine of the inheritance of acquired 

 characteristics and has incontestably shown the weakness of the facts 

 which had been cited before his time in support of this kind of 

 lieredity. But he went too far when he tried to show the impossi- 

 l>ility of this form of heredity. In so doing, he starts from a concep- 

 tion which meets with great favor — the radical distinction between 

 the cells of the body proper, or soma^ and of the reproductive ele- 

 ments, or germ cells. He saw in these two categories distinct and in- 

 dependent entities, the one opposed to the other. Som-a, which con- 

 Sititutes the individual, properly speaking, is only the temporary 

 and perishable envelope of the ger^n, which is itself a cellular 'auton- 

 omous immortal line, which is continuous through successive genera- 

 tions and forms the substratum of hereditary properties. The germ 

 alone has some kind of absolute value. The soma is only an epiphe- 

 nomenon, to use the language of philosophers. The sotna is, of 



