WEISMANN'S THEORY 143 



its sexual cells some germ plasm, not only of its par- 

 ents, but of its grandparents and of all its ancestors. 

 Hence it consists of numberless ancestral plasms, rep- 

 resented by ids whose number corresponds to that of 

 its ancestors. 



Heredity as well as atavism are accounted for by 

 the faithful transmission of those parental and ances- 

 tral plasms. Another conclusion to be drawn from 

 these premises is that an individual can only inherit 

 _sucJhLcharacters as wercTinnate in the parent, for the 

 transmission only takes place from germ cell to germ 

 cell, and only the elements existing in the ovum which 

 produced the parent can exist in the ovum which pro- 

 duces the progeny. The differentiated tissues, or 

 soma cells, are from the very beginning of ontogen- 

 esis, absolutely separated from the germen and no 

 force which bears upon the former can exercise any 

 influence on the latter. Consequently, characters ac- 

 quired in the course of an individual's life cannot in 

 any way be transmitted to its progeny. This is one 

 of the most important conclusions reached by Weis- 

 mann; it defines very clearly his attitude towards the 

 Lamarckian doctrine and constitutes the main tenet 

 of Neo-Darwinism of which he is the recognised ex- 

 ponent. 



How then can a species evolve ? As we said before, 

 Weismann and his followers explain evolution by in- 

 nate variations, preserved and fostered by natural 



