GERM CELLS IN THE ARTHROPODA 173 



Bigelow (1902) has described in Lepa.s cuiafifera 

 and L. fascicularis certain stages which may Ijring 

 the forms in which no early segregation of the germ 

 cells has been discovered into line with the apparently 

 more determinate species. In Lepas the yolk, 

 which at first is evenly distributed within the egg, 

 passes to the vegetative pole and becomes segregated 

 in one of the first two cleavage cells {cd~). At the 

 16-cell stage the yolk lies within the single entoblast 

 cell (d^-^), which occupies a position corresponding to 

 that of the primordial germ cell in Moina. In this 

 connection may be mentioned the fact that in many 

 animals the germ cells are supposed to come from the 

 entoderm and are characterized by the possession 

 of much yolk. 



