236 GERM-CELL CYCLE IN ANIMALS 



an insect has a similar occurrence been noted, namely, 

 in Polyphemus, where, according to Kiihn (1911, 

 1913), the keimbahn-determinants consist of the 

 remains of one or more nurse cells (Fig. 50). In the 

 DAPHNID.E (Weismann and Ischikawa, 1889) the 

 " Paracopulationszelle " arises from material cast out 

 by the germinal vesicle ; in JEquora (Haecker, 1892) 

 the " Metanucleolus " is likewise derived from the 

 germinal vesicle ; in Ascaris (Boveri, 1892) chroma- 

 tin-diminution occurs during the two- to four-cell 

 stage; in Cyclops (Haecker, 1897, 1903) and other 

 copepods (Amma, 1911) the " Aussenkornchen " or 

 "Ectosomen" become visible soon after fertiliza- 

 tion (Diaptomus) , but usually not until the pro- 

 nuclei fuse (other species) ; in Sagitta the "be- 

 sondere Korper" (Elpatiewsky, 1909, 1910) or 

 " Keimbahnchromidien " (Buchner, 1910) appear to 

 arise de novo after fertilization, although if Buchner's 

 contention that they are the remains of the accessory 

 fertilization cells is correct, they should be classed 

 with the " Nahrzellenkern " described by Kiihn 

 (1911, 1913) in Polyphemus. 



It is thus evident that the keimbahn-determinants 

 become visible, wherever they have been described, 

 either just before or just after the eggs are fertilized, 

 or, in parthenogenetic forms, shortly before matura- 

 tion and cleavage are inaugurated. 



The localization of the keimbahn-determinants at 

 the time of their appearance seems to be predeter- 

 mined. In insects the posterior end of the egg is 

 invariably the place where these bodies occur. In 



