ACCOUNT OF THE GERM-CELL CYCLE 35 
4. PeRiop or MUuLTIPLIcATION. Soon after the 
germ cells aggregate to form more or less rounded 
groups lying in the position of the definitive germ 
glands mitotic division is resumed. At about this 
time also, the sex of the individual can often be 
determined by the shape of the germ-gland. Then 
both the testes and the ovaries acquire envelopes 
of the follicular cells, and frequently testicular cysts 
and ovarian tubes or chambers develop. The ques- 
tion of the origin of the follicular cells is still un- 
settled, but the evidence in most cases seems to 
favor the view that they are mesodermal. 
The multiplication of the germ cells by mitosis 
continues rapidly from this time on. In only one 
case, so far as I am aware, do we know the actual 
number of germ cells produced by the primordial 
germ cell; this is in Miastor, where typically sixty- 
four odgonia are formed (Fig. 26). As the germ 
cells multiply they become smaller in size and the 
substances present in the primordial germ cell 
become divided among a large number of progeny. 
Thus at the beginning of the growth period each 
germ gland contains many odgonia or spermatogonia, 
and each of these contains a small fraction of the 
material present in the primordial germ cell, plus 
whatever substances may have been assimilated 
during the period of multiplication. 
5. Toe Oricin or Nurse CELLS AND SERTOLI 
Crtts. Germ cells receive nourishment during the 
growth period in many ways, e.g., from nurse cells, 
follicle cells, or directly from the blood. The origin 
