SPERMATOGENESIS OF THE RABBIT. 297 



may be seen the ordinary arrangement of the spermatogonial 

 cells on the outer margin with the primary spermatocytes 

 adjacent to them. Further towards the center lie the secondary 

 spermatocytes while the spermatids, the transforming spermato- 

 somes, and the fully developed spermatozoa lie in the central 

 cavity. 



2. SPERMATOGONIAL STAGES. 



It has been difficult to obtain satisfactory preparations of 

 the spermatogonial cells showing all of the essential structures, 

 chromatic and achromatic. Nutritive cells were also compara- 

 tively scarce although a few may have been identified (Fig. i). 

 They are very similar to the resting stage of the spermatogonia 

 with which they may easily be confused and their identity is 

 never certain. The nuclei of these nutritive cells usually appear 

 oval or irregular in shape and contain masses of chromatin 

 scattered throughout This close resemblance to the nucleus 

 of the resting spermatogonia makes it not at all improbable 

 that the nutritive cells, if they are such, may be derived from the 

 spermatogonia. Montgomery (1912) has found this to be true 

 in man. He was able to trace directly the formation of the 

 Sertoli cells from the spermatogonia by the presence of a rod- 

 like body in the cytoplasm, which was, according to him, an 

 invariable indication of the Sertoli cells. Hegner (1914) takes 

 the view that the Sertoli cells arise from the primordial germ- 

 cells. This may also be true in the rabbit although there is 

 little direct evidence to support either view. The similarity of 

 the Sertoli cells and the spermatogonia and the relative number 

 of these cells affords the only evidence. 



During the earliest prophases of the spermatogonial stage 

 (Figs. 2, 3) the nucleus is somewhat elongated and irregular as 

 a rule, and contains two or more large, spherical karyosomes. 

 These may be the two accessory elements which can be traced 

 very accurately after the formation of the primary spermatocytes. 

 Small linin threads, somewhat granular in appearance, radiate 

 out towards the periphery of the nuclear wall (Figs. 4, 5). 

 Slender fibrilke extend throughout the cytoplasm (Fig. 2). 

 Between these are small areas of a granular appearing substance. 

 The centrosome and the other cytoplasmic structures cannot be 



