THEORIES OF WEISMANN AND DE VRIES 395 



the same stuff. The rise of the idea of .i^erminal continuity 

 has been indicated in Cha])ter XI \', where it was pointed out 

 that Weismann was not the originator of the idea, but he is nev- 

 ertheless the one who lias developed it the most extensively. 



Complexity of the Germ-Plasm. — The germ-plasm has 

 been molded for so many centuries by external circum- 

 stances that it has accjuired an organization of great com- 

 plexity. This appears from the following considerations: 

 Protoplasm is impressionable; in fact, its most characteristic 

 feature is that it responds to stimulation and modifies itself 

 accordingly. These subtle changes occurring within the 

 protoplasm affect its organization, and in the long run it is 

 the summation of experiences that determines w^hat the pro- 

 toplasm shall be and how it will behave in development. 

 Two masses of protojjlasm differ in capabilities and poten- 

 tialities according to the experiences through which they have 

 passed, and no two will be absolutely identical. All the time 

 the body was being evolved the protoplasm of the germinal 

 elements was being molded and changed, and these ele- 

 ments therefore possess an inherited orgnization of great 

 complexity. 



When the body is built anew from the germinal ele- 

 ments, the derived cjualities come into play, and the whole 

 process is a succession of responses to stimulation. This is 

 in a sense, on the part of the protojjlasm, a repeating of its 

 historical experience. In building the organism it does not 

 go over the ground for the first time, but repeats the activities 

 which it took centuries to acquire. 



The evident complexity of the germ-plasm made it 

 necessary for Weismann, in attempting to explain inheritance 

 in detail, to assume the existence of distinct vital units within 

 the protoplasm of the germinal elements. He has invented 

 names for these particular units as bio|)hors, the elementary 

 vital units, and their com])ination mto determinants, the 



