126 



GERM-CELL CYCLE IN ANIMALS 



lying the terminal cap (Fig. 39, t. 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 pupae 

 and adults. The youngest spermatogonia are those 

 lying near the terminal cap. Figure 40, A shows a 



few cells of the 

 terminal cap {tx), 

 some of the neigh- 

 boring spermato- 

 gonia {spg), and 

 several of the epi- 

 thelial cells {ep) 

 that are scattered 

 about among the 

 spermatogonia. 

 Cysts are formed 

 edge 

 of the spermato- 

 gonial mass away 

 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 hsematoxylin after fixa- 

 tion in Carnoy's fluid. In many cases it was im- 

 possible to distinguish an intervening cell wall 



Fig. 39. — Leptinotarsa decemlineata. Longi 



tudinal section through testis of full-grown tOWard the 

 larva. c = cavity ; cy = region of cysts ; 

 s.d = sperm duct ; sg = region of spermato- 

 gonia ; sp = region of spermatozoa ; t.c = 

 terminal cap. 



