126 GERM-CELL CYCLE IN ANIMALS 
lying the terminal cap (Fig. 39, ¢. c) there are a large 
number of spermatogonia not yet contained in cysts. 
All stages in cyst formation may be observed here 
not only in larval testes but also in those of pups 
and adults. The youngest spermatogonia are those 
lying near the terminal cap. Figure 40, A shows a 
7 few cells of the 
OO terminal cap (t.c), 
; sg some of the neigh- 
boring spermato- 
gonia (spg), and 
cy several of the epi- 
thelial cells (ep) 
ie that are scattered 
about among the 
sd spermatogonia. 
Fic. 39.— Leptinotarsa decemlineata. Longi- Cysts are formed 
tudinal section through testis of full-grown toward the edge 
larva. c=cavity; cy=region of cysts; 
s.d = sperm duct; sg =region of spermato- of the spermato- 
gonia; sp=region of spermatozoa; t.c = gonial mass away 
terminal cap. . 
from the terminal 
cap, and Fig. 40, A to G represent certain of the 
stages observed. The spermatogonia divide ap- 
parently exclusively by mitosis. A well-developed 
spindle is formed and this persists after the cell wall 
has separated the two daughter cells. The spindle 
fibers which are at first perfectly distinct (Fig. 40, B) 
unite into a compact strand (Fig. 40, C) which 
stains dense black in iron hematoxylin after fixa- 
tion in Carnoy’s fluid. In many cases it was im- 
possible to distinguish an intervening cell wall 
