GERM CELLS IN THE ARTHROPODA 129 
cells and odcytes from odgonia, 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 odgonia 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 odcyte 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 
kh 
