230 



NORMAL HISTOLOGY. 



As seen in sections of the mature human testicle (Fig. 281), the epithelial 

 lining of the seminiferous tubules includes two chief varieties of cells, the sup- 

 porting and the spermatogenelic. The former, the Sertoli cells, take no active 

 part in the production of the spermatozoa, but serve as temporary supports 

 for the more essential elements during certain stages of spermatogenesis. 

 They are elongated irregularly pyramidal in form and rest by expanded 

 bases upon the membrana propria, projecting between the surrounding sper- 

 matogenetic cells towards the lumen of the tubule. Their large oval nuclei 

 are meagre in chromatin and often lie at some distance from the bases. 

 The outer part of the cytoplasm contains fat- droplets, the inner zone being 



Tunica propria 



Secondary spermatocyte 



Spermatids being 

 transformed into spermatozoa. 



Secondary spermatocyte 

 Spermatozoa 



Sertoli cell 

 Resting spermatogone 



Primary spermatocyte 



FIG. 281. Portion of a seminiferous tubule, cut transversely, showing the lining cells in various stages of 



spermatogenesis. X 350. 



granular or longitudinally striated. Where the convoluted tubules pass into 

 the straight ones, the Sertoli cells become reduced in height and form a layer 

 of simple columnar cells continuous with the low cuboidal epithelium that 

 lines the rete testis in the mediastinum. 



The spermatogenetic cells are concerned in the cytological cycle, 

 known as spermatogenesis, whereby the spermatozoa are produced from 

 the cells lining the seminiferous tubules. They include four forms that 

 stand in the relation of succeeding generations to one another, those repre- 

 senting the oldest lying nearest the membrana propria and the youngest, 

 from which the spermatozoa are directly derived, next the lumen of the 

 tubule. 



The first generation, the spermatogones, lie at the periphery between the Sertoli 

 cells and, although small round elements, possess nuclei exceedingly rich in chromatin. 



