228 GERM-CELL CYCLE IN ANIMALS 
employed by students who are studying mitochondria 
give us good reason to hope that other substances 
may be made visible which will help to clear up the 
problem of primary cellular differentiation. 
Merapo.tic Propucts. Among the most difficult 
cases to explain are those of Sagitta and certain cope- 
pods, since here the keimbahn-determinants ap- 
parently arise de novo in the cytoplasm. Buchner’s 
(1910) contention that the ‘“‘besondere Kérper”’ 
of Sagitta is the remains of the “‘accessory fertiliza- 
tion cell” of Stevens (1904) is not sustained by either 
Stevens (1910) or Elpatiewsky (1910). The idea of 
the nucleolar nature of the “‘Aussenkérnchen”’ in 
Cyclops has been discarded by Haecker (1903) 
and the conclusion reached that these granules are 
similar to nucleoli in one respect, namely, they are 
by-products of activities within the cell. Amma 
(1911) has considered this subject at some length, 
and after rejecting the possibilities of these being 
of (1) chromatic, (2) nucleolar, (3) chromidial, and 
(4) mitochondrial origin likewise concludes that 
they are transitory by-products. In this way 
the keimbahn-determinants in copepods are satis- 
factorily explained, and a similar explanation may 
be applied to Sagitta, although with less certainty. 
c. Discussion. A review of the literature on the 
keimbahn-determinants and the investigation of these 
substances in the eggs of insects force me to conclude 
that the fundamental organization of the eggis respon- 
sible for the segregation of the primordial germ cells, 
whereas the visible substances simply furnish evi- 
