30 THEORY OF ORGANIC EVOLUTION. 



visible characters involved in it, the soma-plasm and 

 the non-plasmic substances experience, by the influ- 

 ence of nutrition and climate, greater or less varia- 

 tions, which constitute nutrition varieties, and since 

 the idioplasm remains unaffected in general, last 

 only so long as the causes which called them forth.* 

 If we have in mind the inner nature of the organ- 

 ism, there is, properly speaking, no such specific 

 phenomenon as heredity, since the phylogenetic line 

 is a continuous idioplasmic individual. In this sense 

 heredity is nothing more than the persistence of 

 organized substance in a movement in which varia- 

 tions are automatically induced, or the necessary 

 transition of one idioplasmic configuration into the 

 next following. It is present, not only among plant 

 and animal individuals which are ontogenetically 

 separated, but also everywhere within these individ- 

 uals, where individual parts (cells, organs) follow 

 each other in time. Hereditary phenomena are 

 those that necessarily pass over to following genera- 

 tions, and in general those that are located in the 

 idioplasm, since non-idioplasmic substance can be 

 hereditary only through a limited number of cell 

 generations. 



* Nageli, like Weismann, arrives at the conclusion that acquired 

 characters are not inherited. He was not content, however, to rest the 

 generalization upon purely speculative grounds, but undertook the experi- 

 mental demonstration. After seventeen years of work by himself and son, 

 especially upon several species of HIeracium, he satisfied himself that his 

 theory was true to the facts. We all know now how far he fell short of set- 

 tling the question. Trans. 



