296 GERM-CELL CYCLE IN ANIMALS 
One of the distinguishing features of many primor- 
dial germ cells is the presence within their cytoplasm 
of certain stainable bodies to which I have applied 
the term “keimbahn-determinants.”’ Although, as 
pointed out in Chapter VIII, these inclusions do not 
appear to consist of the same sort of material in 
the eggs of different species and hence their signif- 
icance is problematical, still they seem to be asso- 
ciated with that particular part of the egg sub- 
stance which becomes the cytoplasm of the primor- 
dial germ cells. For this reason, if for no other, 
the keimbahn-determinants are of the greatest 
value, since they enable us to determine the position 
of this germ-cell substance during the stages before 
the primordial germ cells are established. It is 
therefore possible to trace the germ-cell substance 
in such eases as Sagitia (Fig. 54), where there is no 
morphological continuity of the germ cells. What 
relation the keimbahn-determinants have to the germ- 
plasm is not yet definitely known. 
There have, of course, been many objections to 
the germ-plasm theory. The history of the germ 
cells in the Ccelenterata, upon which Weismann 
(1882) based a large part of his argument, is consid- 
ered by Hargitt (see p. 95) to be directly opposed 
to the hypothesis. According to some zodlogists 
there is no essential difference between the repro- 
ductive cells and the various sorts of somatic cells; 
they have all arisen as the result of division of labor, 
and the germ cells have been differentiated for pur- 
poses of heredity just as the muscle cells have been 
