AUGUST WEIS MANN 335 



tures to its offspring with such precisicm. And the immediate an- 

 swer to such a question must be given in the following terms : — *^A 

 single cell out of the millions of diversely differentiated cells which 

 compose the body, becomes specialized as a sexual cell ; it is thrown 

 off from the organism and is- capable of reproducing all the peculiari- 

 ties of the parent body, in the new individual which springs from it 

 by cell-division and the complex process of differentiation." Then 

 the more precise question follows : "How is it that such a single 

 cell can reproduce the tout ensemble of the parent with all the faith- 

 fulness of a portrait?" 



The answer is extremely difficult ; and no one of the many attempts 

 to solve the problem can be looked upon as satisfactory; no one of 

 them can be regarded as even the beginning of a solution or as a 

 secure foundation from which a complete solution may be expected in 

 the future. Neither Haeckel's 'Terigenesis of the Plastidule," nor 

 Darwin's "Pangenesis," can be regarded as such a beginning. The 

 former hypothesis does not really treat of that part of the problem 

 which is here placed in the foreground, viz., the explanation of the 

 fact that the tendencies of heredity are present in single cells, but it is 

 rather concerned with the question as to the manner in which it is 

 possible to conceive the transmission of a certain tendency of develop- 

 ment into the sexual cell, and ultimately into the organism arising from 

 it. The same may be said of the hypothesis of His, who, like Haeckel 

 regards heredity as the transmission of certain kinds of motion. On 

 the other hand, it must be conceded that Darwin's hypothesis goes to 

 the very root of the question, but he is content to give, as it were, a 

 provisional or purely formal solution, which, as he himself says, does 

 not claim to afford insight into the real phenomena, but only to give us 

 the opportunity of looking at all the facts of heredity from a common 

 standpoint. It has achieved this end, and I believe it has uncon- 

 sciously done more, in that the thoroughly logical application of its 

 principles has shown that the real causes of heredity cannot lie in the 

 formation of gemmules or in any allied phenomena. The improba- 

 bilities to which any such theory would lead are so great that we can 

 affirm with certainty that its details cannot accord with existing facts. 

 Furthermore, Brooks' well-considered and brilliant attempt to modify 

 the theory of Pangenesis cannot escape the reproach that it is based 

 upon possibilites, which one might certainly describe as improbabiHties. 



