PROBLEM OF EVOLUTION — CAULLERY. 329 



course, modified by external conditions, but for one to speak of the 

 inheritance of acquired characteristics, the local modifications of the 

 soma would have to be registered in the germ and reproduced in the 

 same form in the soma of following generations in the absence of the 

 external cause which produced them in the first place. Now, says 

 Weismann, the possibility of such an inscription, as it were, upon the 

 germ of a modification undergone by the sOTna is not evident a priori, 

 and when we go over the facts we find none supporting this con- 

 clusion. There are, indeed, modifications which appear in one gen- 

 eration and which are reproduced in the following generations; but 

 Weismann goes on to attempt to proA^e that at their first appearance 

 they were not the effect of external factors on the soma, but that 

 they proceeded from the very constitution of the germ; that they 

 w^ere not really acquired and somatic, but were truly innate or 

 germinal. 



Such, reduced to its essential points, is the negative contention of 

 the doctrine of Weismann. It rests upon the absolute and abstract 

 distinction between the soma and the germ. In spite of the support 

 which this conception has had and still has, I consider it, for my part, 

 as unjustifiable in the degree of strictness which Weismann has attrib- 

 uted to it. It is true that the advance in embryology and cytology 

 often allows us to identify the reproductive tissue and to follow it 

 almost continuously through successive generations, but the concep- 

 tion of its autonomy is at least a physiological paradox. Though 

 the continuity of the germ cells is sufficiently evident in many organ- 

 isms, it is more than doubtful in others, particularly in all those 

 which reproduce asexually; that is to say, many large groups of 

 animals like the Ccelenterata, the Bryozoa, the Tunicata, and many 

 plants. This has more than the force of an exception ; it is a general 

 principle of the life of species. One can not, then, say that the con- 

 ception of Weismann carries full conviction. But this conception 

 exercised a tyrannical influence upon the minds of contemporaneous 

 biologists, and it is exclusively through it that most of them look at 

 the facts. 



Weismann, besides, exercised a considerable influence by champion- 

 ing a theory of heredity based at the start on the preceding ideas. 

 This theory, built with undoubted ingenuity and adapted to the 

 loiowledge gained from the study of cell division, turns out on the 

 other hand to agree wdth the recent works on heredity. 



Lamarckism and Darwinism shared the support of biologists up to 

 the end of the nineteenth century, discussion being in general re- 

 stricted to speculation. The controversy begun in 1891 between Weis- 

 mann and Spencer, who represented the two extremes, gives an idea 

 of the extent to which one could go in this direction. 



