GERM CELLS IN THE ARTHROPODA 171 



this nurse cell is confined to one cell (Fig. 50, C-E) 

 which gives rise during the third cleavage (8- to 16- 

 cell stage) to the primordial germ cell, containing 

 the remains of the nurse cell (Fig. 50, E, K), and to 

 the primordial entoderm cell which does not receive 

 any part of the nurse cell (Fig. 50, E, e). The pri- 

 mordial germ cell and primordial entoderm cell do not 

 divide as quickly as the other blastomeres during 

 the succeeding cleavage stages a fact that aids 

 in their identification. While the egg is undergoing 

 cleavage the nurse cell is gradually changing, so that 

 when the sixteen-cell stage is reached it has become 

 disintegrated into dark staining granules and frag- 

 ments of various forms and sizes (Fig. 50, E} . Dur- 

 ing the division of the " Keimbahnzelle " (from 16- 

 32-cell stage) these granules and fragments are about 

 equally distributed between the daughter cells (Fig. 

 50, F). A similar distribution takes place in suc- 

 ceeding divisions of the primordial germ cells, and 

 this is accompanied by a further decrease in the size 

 of the dark staining granules. A blastula of 236 

 cells is figured by Kiihn which shows at the vegeta- 

 tive pole four primordial germ cells lying next to 

 eight entoderm cells and bordered by twelve meso- 

 derm cells. During gastrulation this group of twenty- 

 four cells becomes surrounded by the ectoderm cells, 

 and the primordial germ cells may then be recognized 

 as the anlage of the reproductive organs. 



Kiihn discusses the origin and significance of the 

 "Nahrzellenkern" and compares this body with 

 similar bodies which have been found in the primor- 



