GERM CELLS IN THE ARTHROPODA 129 



cells and oocytes from oogonia, and there can be 

 little doubt but that the process of cyst formation 

 in the male as described above is similar to the differ- 

 ential divisions in the female. 



Thus the discovery of these distinct spindle re- 

 mains in the spermatogonial divisions enables us 

 to homologize one more period in the cycle of the 

 male germ cells with a corresponding period in the 

 cycle of the female germ cells. 



According to this view the ultimate spermato- 

 gonium passes through a certain number of divisions 

 — probably five or six — which correspond to the 

 differential divisions so clearly exhibited by the 

 ultimate oogonia of Dytiscus. Just as in the matura- 

 tion processes, however, where only one female cell 

 but all of the male cells are functional, so these 

 earlier divisions result in the female in the pro- 

 duction of a single oocyte and a number of nurse 

 cells which may be considered abortive eggs, whereas 

 in the male every daughter cell is functional. The 

 limited period of division in the cycle of the male 

 germ cells in man (Montgomery, 1911 ; von Wini- 

 warter, 1912) is also similar to those in Dytiscus and 

 Leptinotarsa. The Sertoli cells are intimately con- 

 nected with the germ cells in the mammalian testis 

 and probably perform three functions : (1) they 

 nourish the spermatocytes ; (2) they provide the 

 spermatic fluid ; and (3) they exert some chemico- 

 tactic stimulus which serves to orient the spermato- 

 zoa into bundles. The origin of the Sertoli cells has 

 been for many years in doubt. Many investigators 



