INFLUENCE OF ENVIRONMENT 335 



win also held this view and proposed his hy- 

 pothesis of pangenesis in order to explain the 

 process of the transmission of such characters 

 to the germ cells. 



Weismann introduced a new era in biology 

 by denying the inheritance of acquired char- 

 acters, by showing the weakness of the evi- 

 dence for such inheritance and by challenging 

 the world to produce evidence that would stand 

 a rigorous analysis. But Weismann's great- 

 est service lay in his constructive theories 

 rather than in destructive criticism ; he forever 

 disposed of theories of pangenesis and the like 

 by showing that the germ cells are not built 

 up by contributions from the body and that 

 characters are not transmitted from genera- 

 tion to generation ; but on the other hand that 

 there is transmitted a germ plasm which is rela- 

 tively independent of the body and which is 

 relatively very stable in organization. This 

 epoch-making theory of Weismann's has 

 naturally undergone some changes, as the re- 

 sult of new discoveries. It is no longer be- 

 lieved that the germ plasm is really independ- 

 ent of the body, nor that it is absolutely stable, 



