XH] DTTISCUS 185 



going a differential division, and the process is repeated in 

 all four times, giving rise to a group of sixteen cells, of which 

 one contains the chromatic ring and the other fifteen are 

 without it. All the cells remain connected together by short 



Antepenultimate 

 Spermatogonium 



Penultimate 

 Speraatogonia 



Ultimate 

 Spermatogonia 



Sertoli / 

 cell 



FIG. 22. Diagram of differential division of a Sertoli cell from spermatogonia 

 in Man, after MONTGOMERY (1911 b}. 



stalks, due to incomplete division. The cell with the chro- 

 matic ring is the oocyte, and the fifteen others become 

 nutritive cells which supply nourishment to the oocyte 

 during its subsequent growth. In the later oogenesis of 

 Dytiscus, therefore, as in Ascaris and Miastor, a true germ- 

 cell is separated from cells that will not become germ-cells 



