164 GERM-CELL CYCLE IN ANIMALS 



it united with one of the first eight cells. Further- 

 more, it apparently always fused with a certain 

 definite cleavage cell. The authors conclude that the 

 Copulationszelle has some important relation to the 

 history of the germ cells. 



The keimbahn of Cyclops and some closely allied 

 forms has been very carefully investigated by Haecker 



ak- 



Fig. 48. — Cyclops. A. Egg showing " Aussenkornchen " (ak) at one 

 end of first cleavage spindle. B. Thirty-two-cell stage showing 

 " Aussenkornchen " {ak) in the primordial germ cell {Kz). Rk = 

 polar bodies. {From Haecker, 1897.) 



(1897), Amma (1911), and Fuchs (1913) with results 

 which are of particular interest. In Cyclops, accord- 

 ing to Haecker, "Aussenkornchen" arise at one pole 

 of the first cleavage spindle (Fig. 48, A, ak) ; these 

 are derived from disintegrated nucleolar material 

 and are attracted to one pole of the spindle by a dis- 

 similar influence of the centrosomes. During the 

 first four cleavage divisions the granules are segregated 

 always in one cell (Fig. 48, B, Kz) ; at the end of the 

 fourth division these "Aussenkornchen" disappear, 

 but the cell which contained them can be traced by 

 its delayed mitotic phase and is shown to be the 

 primordial germ cell. 



