12 J. E. WODSEDALEK. 



crowded out, thus forming a second layer which is always very 

 irregular. There is considerable variation in the appearance and 

 some variation in the size of different spermatogonia. Very 

 frequently the cells are far apart, in which case they are flattened 

 out on the tubule wall. 



The amount of cytoplasm is small and in some of the earlier 

 stages the cell boundaries are very indistinct (Fig. 16). Later 

 the nuclei assume a round shape and the cell wall becomes 

 visible. The amount of chromatin material increases and the 

 nuclei at this stage resemble very much the nuclei of the large 

 interstitial cells both in appearance and size (Fig. 17). 



Two large nucleoli much alike in size seem to be present in all 

 stages of these cells. Even in the testes of young embryos the 

 two bodies are very conspicuous. Besides these large nucleoli a 

 varied number of smaller, similarly staining bodies are usually 

 present, two of which seem to occur most frequently, and evi- 

 dently make their appearance first (Figs. 16 and 17). Later 

 other small nucleoli appear. At present I am unable to attach 

 any meaning to them as their numbers are so varied in the various 

 cells. The two large nucleoli, however, are very constant, and 

 I have been able to trace them throughout the entire spermato- 

 genesis. From all appearances one is led to believe that these 

 nucleoli and the accessory chromosomes are one and the same, a 

 condition similar to that found by Guyer (*io) in man, and by 

 others in some of the lower forms. Jordan ('n), however, has 

 not been able to identify any such structures at this stage as the 

 future accessory chromosomes in the opossum. 



At the conclusion of the resting stage numerous chromatin 

 granules appear, which arrange themselves along fine threads in 

 an entangled mass. The two nucleoli come in close contact and 

 the nuclear membrane gradually disintegrates. Eighteen chro- 

 mosomes appear in the late prophase of the spermatogonial 

 division (Fig. 18). Sixteen of these are rod-shaped, variously 

 curved and somewhat different in size. Two, which are always 

 found close together, and frequently off to one side are slightly 

 larger and oval in shape. The sixteen ordinary chromosomse 

 or autosomes arrange themselves with the two accessory chromo- 

 somes in the equatorial plate (Fig. 19). The accessories, like 



