240 GERM-CELL CYCLE IN ANIMALS 



so far as the segregation of the keimbahn-determi- 

 nants in cleavage cells is concerned, but the move- 

 ment of the egg contents seems to be a more probable 

 cause of localization. 



C, The Fate of the Keimbahn-determinants 



It is unfortunately impossible to trace the keim- 

 bahn-determinants throughout the entire germ-cell 

 cycle. The question of their fate, however, is an 

 important one. As we have seen, they become vis- 

 ibly apparent shortly before or just after the inaugu- 

 ration of the maturation divisions, and remain intact 

 for a brief period during the early cleavage stages. 

 They persist in insects as definitely recognizable 

 granules (Fig. 37, F) for some time after the primor- 

 dial germ cells are segregated ; then they gradually 

 break up into finer particles, leaving no trace of their 

 existence behind except in so far as they give the 

 cytoplasm of the germ cells a greater afiinity for 

 certain dyes. In Chironomus they may still form 

 distinct masses after the definitive germ glands 

 have been formed (Fig. 33, D). The ectosomes in 

 the copepods are temporary bodies which appear 

 to rise de novo during the formation of each mitotic 

 figure in the early cleavage stages, then break down 

 and disappear. Practically all of the other keim- 

 bahn-determinants persist during early cleavage and 

 then disappear as distinct visible bodies as soon as the 

 primordial germ cells are definitely segregated. What 

 becomes of them during the comparatively long 

 period between their disappearance in the primordial 



