364 THE GENITOURINARY ORGANS. 



arise. The latter, at first straight, soon begin to wind in such a man- 

 ner that the various convolutions of each canal form an independent 

 system, invested by a fibrous sheath of its own coni vasculosi 

 Halleri. These lobules constitute the elements of the globus major 

 of the epididymis. In cross-section the vasa efferentia are seen to 

 be stellate in shape. The vasa efferentia gradually unite to form 

 one canal the vas epididymidis. This is markedly convoluted and 

 is situated in the body and tail of the epididymis itself. 



The epithelium of the convoluted seminiferous tubules consists 

 of sustentacular cells (cells or columns of Sertoli) and of sperma- 

 togenic elements. The former are high, cylindric structures (see 

 below), the basilar surfaces of which are in contact. They do not 

 form a continuous layer, but their basal processes are interwoven 

 to form a superficial network surrounding the epithelium of the 



Fig. 291. Fig. 292. 



Sustentacular cells (cells of Sertoli) of the guinea-pig (chrome-silver method). 

 Figure 291, surface view of the seminiferous tubules; figure 292, profile view ; X 220: 

 a, Basilar surface of a cylindric sustentacular cell ; l>, flattened sustentacular cell ; c, c, 

 depressions in the sustentacular cells due to pressure from the spermatogenic cells ; </, 

 basilar portion of sustentacular cells. 



seminiferous tubules. (Fig. 292.) In the meshes of the reticulum 

 are deposited numbers of plate-like cells, which lie in contact with 

 the basement membrane and also represent sustentacular elements 

 (vid. Merkel, 71). 



Between the sustentacular cells are found from four to six rows 

 of cells, possessing relatively large nuclei, rich in chromatin, and 

 derived from cells of the deeper strata by mitotic cell division. The 

 epithelium of the convoluted portion of the seminiferous tubules is, 

 therefore, a stratified epithelium. The cells of this epithelium 

 present various peculiarities according to their stage of development, 

 and will be considered more fully in discussing spermatogenesis. 

 Externally, the walls of the convoluted tubules are limited by a 

 single layer or several layers of spindle-shaped, epithelioid cells. A 

 basement membrane is present, but very thin, and in some cases 



