THE GERM-CELL CYCLE 



271 



concerning this process in certain insects, crustaceans, nema- 

 todes, and in Sagitta. Furthermore, in almost every thoroughly 



Fig. I.— Diagrams illustrating the origin and history of the keimbahn-determinants 



in parasitic Hymenoptera. 



A-E, the chromatin in the nucleus of the lower (older) oocyte condenses to form keimbahn-chromatin (E, k); 



a spindle is organised in the upper oocyte, but disintegrates to form a nucleus, and the two oocytes 



unite (D and E), producing a single egg. (After Hegner.) 

 The diagram below indicates the history of the keimbahn-chromatin as described by Silvestri. Sexual 



larva: (s.l.) develop from groups of cells, including one or more cells containing keimbahn-chromatin. 



Asexual larvae (a.l.) arise from groups without any cells provided with keimbahn-chromatin. (After 



Silvestri.) 



studied case inclusions in the cytoplasm enable us to identify 

 the germ-cell substance in the undivided egg and to trace it 

 until it becomes localised in the primordial germ cells. Such 



