MUNSON: SPERMATOGENESIS OF PAPILIO. 
53 
14. In the stages of Papilio rutulus that I have studied there is 
no true germinal epithelium, but as will be pointed out farther on, the 
original germinal material from which primary spermatogones arise, 
has the character of a large primordial germ cell (pi. 12, figs. 4, Sb; 
pi. 15, fig. 56), which I have called the grandmother stem cell. 
15. The grandmother stem cell has connected with it numerous 
smaller cells (pi. 15, fig. 57a), which I have called the mother branch 
cells. 
16. The grandmother stem cell and the mother branch cells are 
surrounded by minute nuclei which I have called cortical nuclei. 
17. Finally, I have distinguished two kinds of spermatocytes, 
the ordinary and the giant spermatocytes, and ordinary and giant 
spermatids .' 
Growth Zones of the Follicles. 
In the youngest larva which I have studied, and while the right and 
left testes are still separated, the gonoeysts are already formed. They 
practically fill each follicle, the spermatocysts not yet having been 
formed. In the pupa of about the 15th of February, four months 
before the last moult, cytocysts are formed, some having even passed 
the maturation period and entered on the spermatocyst stage (pi. 12, 
fig. 6). But no fully formed spermatozoa exist. These appear about 
one month before the last moult. 
In the mature testis the larger portion of each follicle is filled with 
spermatocysts in various stages of development (pi. 12, fig. 5, sp. c.). 
In such a testis, therefore, there is at the periphery, next to the pig¬ 
mented inner lining of the testis, a series of variously developed gono- 
cysts. This is the multiplication zone of the follicle. Within these 
there is usually a zone of cytocysts, the growth zone, and scattered 
within that again are cysts in which maturation is taking place, matur¬ 
ation zone. Finally within these, and next to the opening into the 
vas deferens, are the variously developed spermatocysts, the mature 
ones being nearest the vas deferens. 
While it is possible, therefore, to distinguish, in a very general way, 
these various zones, they are not distinctly separated. It follows that 
as the spermatozoa become mature and are discharged, the inner zones 
encroach more and more on the outer ones. Hence late in the season 
