MUNSON: SPERMATOGENESIS OF PAPILIO. 
77 
fig. 35 with fig. 24, pi. 13). A distinct reticular structure with cyto- 
mierosomes can be seen in the cytoplasm of the resting cell. In this 
respect, as in many others, these spermatocytes differ very markedly 
from the grandmother stem cell. From the latter up to the sperma¬ 
tocyte, there seems to be a gradual evolution of the cytoreticulum, 
as even the cytomicrosomes, practically'invisible in the grandmother 
stem cell, seem also to increase in size with the growth of the cell. 
While the cytoplasm is distinctly granular, there is nothing that could 
be compared to the yolk of eggs. 
The centrosome of spermatocyte. — Although often impossible to 
see, favorable preparations reveal a centrosome. Its position is some¬ 
what variable (compare pi. 13, fig. 35, a, b, c, d, e, with fig. 36, c). In 
the spermatocytes of Papilio rutulus, the centrosome, in the resting 
cell, is imbedded in the nucleus, causing an indentation in the latter, 
by which it can often be located (pi. 13, fig. 36, c; pi. 15, figs. 71, 
75). This, however, seems not to be the case in Grapta silenus (pi. 
13, fig. 35). In Papilio, it is usually found on the inner free pole of the 
nucleus. In material preserved as indicated in the “method,” it is a 
clear unstained vesicle or archoplasmic body very regularly spher¬ 
ical, but sometimes more irregular. In Grapta silenus, the centro¬ 
some or small sphere has a more variable position (pi. 13, fig. 35). 
Giant spermatocytes. — At the end of the growth period, the sperma¬ 
tocytes of the same cyst are remarkably uniform in size, though as 
already pointed out the size varies greatly in different cysts (compare 
pi. 13, figs. 29, 30, 31 with figs. 35, 36, 37). 
I have never found these giant spermatocytes in the larval testes. 
They occur in the mature butterfly chiefly late in the season, when, 
as already shown, the stalked cells and the free cells (pi. 15, figs. 
68, 69, 77, 83, 64, 85) are also found. Consequently there seems to be 
some correspondence between the growth of the spermatocytes and 
the general maturity of the insect. No such difference exists between 
the spermatogones of the larva and the adult. 
Period of Maturation. 
Having completed their growth, the spermatocytes enter on their 
two final divisions to form spermatids. The first indication of 
approaching division appears in the centrosome (pi. 13, fig. 35, a, 6). 
