GERM CELLS IN THE ARTHROPODA 109 



at the four cell stage becomes separated from the 

 rest of the egg, together with all of the Keimbahn- 

 plasma as the primordial germ cell (Fig. 33 B, 

 p.g.c). The Keimbahnplasma is apparently equally 

 divided between the daughter cells when the 

 primordial germ cell divides. Later the nuclei 

 of the germ cells increase in number without an 

 accompanying division of the cell, thus producing 

 binucleated cells (Fig. 33, C). The history of the 

 pole cells during embryonic development will be 

 more fully described in the Coleoptera, since in 

 the beetles the Keimbahn is much more distinct. 

 The origin and nature of the Keimbahnplasma 

 was not determined by Hasper, but it was found to 

 persist in certain cases even until the larval stage 

 was reached (Fig. 33, D). 



In Calliphora Noack (1901) described a dark 

 granular disc at the posterior end of the egg (Fig. 34) 

 which he termed the " Dotterplatte " and which, 

 like the pole-plasm of Miastor and the Keimbahn- 

 plasma of Chironomus takes part in the formation of 

 the primordial germ cells. The eggs of the parasitic 

 fly, Compsilura concinnata, were also found by the 

 writer (Hegner, 1914a) to possess a granular pole- 

 disc, thus adding one more species to the list of 

 DiPTERA in which such a structure exists. 



Coleoptera. The origin of the germ cells in 

 beetles and their subsequent history are well known 

 only in certain species of the family Chrysomelid^ 

 of the genera Calligrapha and Leptinoiarsa. The 

 contributions of Wheeler (1889), Lecaillon (1898), 



