422 ROBERT W. HEGNER 



of radiating follicles containing cysts of spermatogonia, sper- 

 matocytes, or spermatozoa (cy). A transverse section through the 

 distal end of a testis is shown in figure 12 (position 12 in fig. 11). 

 In the center is the terminal cap (tx); surrounding this is a 

 mass of spermatogonia not yet formed into cysts (sg) ; and from 

 this the testicular follicles radiate out to the periphery. Wieman 

 ('10b, '10c) has traced the development of the testis through 

 the larval and pupal stages and I have nothing to add to his 

 account. I wish, however, to describe certain stages in the 

 divisions of the spermatogonia during cyst formation, since 

 Wieman has reported the occurrence of amitotic nuclear division 

 at this time, and I have discovered some cellular connections which 

 makes it possible to compare certain processes in the testis with 

 those known to take place during the differentiation of nurse 

 cells and oocytes in the ovaries of several insects. 



In that region of the testis surrounding and underlying the 

 terminal cap (figs. 11, 12, t.c) there are a large number of sperma- 

 togonia 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 68 shows a few cells of the 

 terminal cap (t.c.) some of the neighboring spermatogonia (spg), 

 and several of the epithelial cells (ep) which are scattered about 

 among the spermatogonia. Cysts are formed toward the edge 

 of the spermatogonial mass away from the terminal cap and 

 figures 69 to 74 represent certain of the stages observed. The 

 spermatogonia divide apparently 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. 69) unite into a compact 

 strand (fig. 70) which stains dense black in iron hematoxylin 

 after fixation in Carnoy's fluid. In many cases it was impossible 

 to distinguish an intervening cell wall between the daughter 

 nuclei (fig. 71). In either case, however, the spindle remains 

 persist, forming a basic-staining strand with enlarged ends 

 connecting the two nuclei. Since at this time and in all later 

 stages the two or more spermatogonia may be found surrounded 



