288 THOS. H. MONTGOMERY, 



10 nucleoli. These nucleoli are much more irregular in form, number 

 and volume than those of the resting spermatocytes. 



The cell membrane (Figs. 1 — 3) is more delicate than that of the 

 nucleus, and the cytoplasm very delicately granular in appearance 

 and faintly staining. Within the cytoplasm of many of the cells lie 

 one or more spherical, usually deeply-staining yolk globules (Yk.GJ). 

 These are less numerous, considerably larger, and show a greater 

 staining intensity than those of the spermatocytes; but their appearance 

 agrees with that of the globules in the nurse cells of the sheath of 

 the testis. 



I have not been able to find any centrosomes, idiozome substance 

 or attraction spheres within the spermatogonia in the rest stage. 



At no point in the testis are the spermatogonia arranged in 

 rosettes or other groupings, such as is frequently the case in Insects. 

 My observations give no points for deciding the position of the spermato- 

 gonia in very young testes, i. e. as to whether in an early stage 

 they fill the entire lumen of the testis, or whether they are limited 

 to the periphery. 



3. Spermatogoiiic Mitoses up to the Metakiiiesis. 



The point is a difficult one to decided, but two generations of 

 spermatogonia appear to be present in the testis. As in the rest 

 stage smaller and larger spermatogonia could be distinguished, so 

 smaller and larger mitotic figures can be seen , the smaller figures 

 being more peripheral. The difficulty lies in the fact that there are 

 intermediate sizes between the largest cells and mitotic figures and 

 the smallest. In both large and small mitotic figures we find the 

 same number of chromosomes, and the structural changes in the pro- 

 phases are the same. The smaller mitoses were found difficult to 

 study, so that the following descriptions apply to the larger mitoses 

 which undoubtedly, as the delineation will show, represent the last 

 spermatogonic mitoses. 



At the commencement of the prophase (Fig. 3, Plate 19) the 

 chromatin gradually takes on a reticular arrangement, leading to the 

 formation of a spirem. The linin threads thus gradually become 

 hidden or masked by the chromatin. Then, and while the nucleus 

 increases in volume, the chromatin loops gradually become all of ap- 

 proximate thickness, and take on the stains characteristic of pure 

 nucleic acid. So by gradual degrees the stage of the "dense spirem" 

 is attaine, witdh the slender, nearly smooth chromatin loops at the 



