THE GERM-PLASM THEORY 301 



of the nature and reactions of the chemical constitu- 

 ents of protoplasm, for, as Wilson (1912, p. 66) says, 

 *'The essential conclusion that is indicated by cy to- 

 logical study of the nuclear substance is, that it is an 

 aggregate of many different chemical components 

 which do not constitute a mere mechanical mixture, 

 but a complex organic system, and which undergo 

 perfectly ordered processes of segregation and dis- 

 tribution in the cycle of cell life." 



Some of the strongest evidence that the germ- 

 plasm must include cytoplasmic constituents is 

 afforded by the observations and experiments dealing 

 with the differentiation of the germ cells, especially 

 during early embryonic development. The writer's 

 morphological and experimental studies of chrysom- 

 elid beetles seem to prove that the nuclei during 

 the cleavage stages are all potentially alike and that 

 it is the cytoplasm which decides their fate. Boveri's 

 experiments on the eggs of Ascaris likewise show 

 that the cytoplasm determines the initiation of the 

 chromatin-diminution process and controls the differ- 

 entiation of the germ cells. Furthermore, much of 

 the data in the preceding chapters indicates that the 

 non-nuclear substance which will become segregated 

 within the primordial germ cell is present in a more 

 or less definite region in the undivided egg, being 

 gradually localized and separated from the other egg 

 substances as cleavage progresses. The position of 

 this germ-cell substance can in many cases be deter- 

 mined because of the presence of inclusions of vari- 

 ous sorts, but whether these keimbahn-determinants 



