THE P^DOGENETIC FLY, MIASTOR 67 



embryonic development ; and (6) the contents of 

 the primordial germ cell consist of the nucleus 

 with undiminished chromatin and of all of the pole- 

 plasm and apparently no other part of the egg sub- 

 stance. 



The fact that only the primordial germ cell re- 

 ceives a complete amount of chromatin is of particu- 

 lar interest, since a similar condition has long been 

 known in the case of Ascaris as we shall see later. 

 It may also be noted in this place that the cyto- 

 plasmic substance in the primordial germ cell may 

 be recognized as the pole-plasm in the growing 

 oocyte. Attempts have been made to determine the 

 origin of this pole-plasm, but so far without success. 

 It may be distinguished from the rest of the egg con- 

 tents by its position at the posterior end and because 

 of its affinity for certain dyes. It appears shortly 

 before the maturation division is initiated, but no 

 transition stages have been discovered it has been 

 either present or entirely absent in the preparations 

 thus far studied. If we consider the history of this 

 substance from the formation of the primordial 

 germ cell to the growth period of the oocytes pro- 

 duced by this primordial germ cell, we may conclude 

 that at the time the multiplication period ends the 

 pole-plasm has become equally distributed among the 

 sixty-four oogonia. Then ensues the growth period 

 during which the pole-plasm cannot be distinguished. 

 Later, however, just before maturation, pole-plasm 

 substance reappears which is equal in amount to 

 that contained in the primordial germ cell of the 



