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. 



Metabolic Products. 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 Korper" 

 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 " Aussenkornchen " 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 egg is respon- 

 sible for the segregation of the primordial germ cells, 

 whereas the visible substances simply furnish evi- 



