344 HEREDITY AND ENVIRONMENT 



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, 

 as Weismann at one time held. There is no 

 doubt that the germ cells and the germ plasm 

 are physiologically related to other cells and 

 to other plasms, and similarly there is no doubt 

 that the germ plasm although very stable can 

 and does change its constitution under some 

 rare conditions. But in the main the germ 

 plasm theory is accepted by the great majority 

 of biologists to-day, and recent work in gen- 

 etics and cytology has brought many confir- 

 mations of this theory. 



As long as it was believed that the developed 

 characters of an organism could be transmit- 



