STUDIES ON GERM CELLS 399 



there is a primary cellular differentiation similar to that already 

 described in other Diptera. Figures 41 and 42 represent two 

 stages in the formation of the primordial germ cells at the pos- 

 terior end of the egg. The granules of the pole-disc are en- 

 countered by the cleavage nuclei which chance to reach the 

 posterior pole; they surround these and are distributed about 



Fig. 6 Compsilura concinnata; reproductive organs of a female, a.g, accessory 

 gland; o, ovary; od, eviduct; s.r, seminal receptacle; u, uterus full of eggs in vari- 

 ous stages of development. 



within the cytoplasm of the germ cells when they are cut off by 

 cell walls. The further history of the germ cells does not seem 

 to differ in any way from that described in other Diptera. 



Cecidomyia strobiloides. A pole-disc was also found in the 

 eggs of the willow-cone gall just before deposition (fig. 43), and 

 an attempt was made, as in Miastor, to trace this structure 

 to its place of origin. The growth of the egg of this species 

 resembles that of Miastor and all efforts to connect the pole- 

 disc with substances within the oocyte previous to its appearance 

 at the posterior end were futile. 



