294 GERM-CELL CYCLE IN ANIMALS 



eight nuclei in the egg. As determined by Kahle 

 (1908) and confirmed by the writer (Hegner, 1912, 

 1914a), this primordial germ cell gives rise to sixty- 

 four oogonia and to no other cells. This is the nearest 

 approach to a complete morphological continuity 

 of the germ cells that has yet been described, and 

 since this primordial germ cell must contain the germ- 

 plasm of the succeeding generation, the condition 

 in this fly is really comparable to that of the hypo- 

 thetical case cited above, only in Miastor the cell 

 set aside for reproductive purposes is much less than 

 one-half of the egg, the somatic part of the egg being 

 not a single cell, but a syncytium containing seven 

 nuclei. 



We may therefore look for the germ-plasm of 

 Miastor in the primordial germ cell. So far as we 

 know there are only two sorts of materials in this 

 cell, that contained in the nucleus, and the darkly 

 staining part of the egg which becomes recognizable 

 just before maturation occurs, is situated at the pos- 

 terior pole, and has been termed the pole-plasm 

 (Fig. 13). If the primordial germ-cell multiplies by 

 simple division and if there is an equal distribution 

 of the contents at every mitosis, then the sixty- 

 four oogonia must each possess one sixty-fourth of 

 both the nucleus and the pole-plasm of the primordial 

 germ cell plus any materials that have been added 

 during the period of multiplication. An enormous 

 enlargement occurs during the growth period both of 

 the nucleus and of the cell. The pole-plasm cannot 

 be recognized at this time, but again becomes 



