THOMAS H. MONTGOMERY. 



the inner border of the tubule; the other end, the distal, is the 

 one that grows out and forms branches ramifying around the 

 spermatocytes and spermatids. In the later history of the 

 Sertoli cells large spaces are found within them, as shown in 

 Fig. 50, which are cavities in which germ cells had been situated 

 before their transformation into spermatozoa. Boundaries be- 

 tween the Sertoli cells become indistinguishable, so that these 

 cells come to constitute a syncytial cytoplasmic net of extreme] v 

 vacuolar structure (Fig. 50). In the basal portions of the Sertoli 

 cells parallel bundles of fibrils may be seen at certain stages 



(Fig. 43). 



The nuclear changes are also characteristic, and represent a 

 gradual transformation of the structure of the resting nucleus 

 of an ultimate spermatogonium. The reticulum changes first 

 into microsomal masses (Fig. 25, PI. II.). Then takes place a 

 flowing of these masses together (Figs. 34-39, 41-43, PI. III., IV.) 

 until all the basichromatic substance of the nucleus becomes 

 concentrated into a mass or karyosphere, and the particles re- 

 maining without the mass are oxychromatic. Figs. 44 and 45, 

 PL Y., represent the result of this process. Then follow stages 

 of dissolution of the karyosphere into minute granules, all of 

 which become gradually oxyphilic (Figs. 46 and 48), Fig. 49 

 representing a degenerate nucleus at the close of the cell's cycle. 

 During all these stages the nuclei become very irregular, with 

 deep indentations and Jobations at their margins and grooves 

 passing along their lengths. This irregularity of form and the 

 central karyosphere are diagnostics by which these nuclei may 

 be readily distinguished from those of neighboring germ cells. 

 Further, the nuclei do not remain at the basal end of the cell, 

 as they do in certain other mammals, but move out beyond the 

 level of the spermatogonia (Fig. 50). 



After passing through the series of changes just described the 

 Sertoli cells degenerate, for there is no evidence that they go 

 through a second cycle. This is proven by the later stages of 

 these nuclei (Figs. 47-49) which gradually become wholly achro- 

 matic and then disappear from view. Their vacuolar substance 

 must at that time mingle with the fluid of the tubule. Fig. 25 

 (PI. II.) is interesting in this regard, for it exhibits a yom i^ Serioli 



