Acquired Modifications Heritable ? 107 



this cell (fertilized egg) gives rise to the rest 

 of the cells that make up the animal or plant. 

 Most of these cells differentiate as they assume 

 different functions. Thus in the animal we 

 have muscle cells, nerve cells, gland cells, and 

 corresponding differentiations in the tissues of 

 plants. But those ceUs that are going to give 

 rise to the eggs and sperm are relatively undif- 

 ferentiated, maintaining more or less completely 

 their embryonic character. To these cells 

 Weismann gave the name of germ ceUs, to 

 distinguish them from the cells which go to 

 make up the rest of the body, which he called 

 the somatic cells. The protoplasm of the germ 

 cells he designates germ plasm, that of the 

 somatic cells, soma plasm, and Weismann's 

 contention is that the germ plasm is continuous 

 generation after generation. It is the gerni 

 plasm that gives rise to the soma plasm, not the 

 reverse, or, to put it in more concrete form, it is 

 the egg which gives rise to the chick, and to the 

 eggs which its body contains, rather than the 

 chick which gives rise to the egg. The dia- 

 gram (Fig. 7) AviU make this plainer. The 



