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 cyto- 
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 
