STRUCTURE OF THE TESTICLE. 



205 



thelium, and their tails emerging into the lumen of the tubule (fig. 

 238, b). As they become matured they gradually pass altogether 

 towards the lumen, where they eventually become free (c). During 

 the time that this crop of spermatozoa has been forming, another set 

 of spermatoblasts has been produced by the division of the spermato- 

 genic cells, and on the discharge of the spermatozoa the process is 

 repeated as before. 



The straight tubules which lead from the convoluted seminiferous 

 tubes into the rete testis (fig. 237) are lined only by a single layer of 

 clear flattened or cubical epithelium. The tubules of the rete also have 

 a simple epithelial lining, but the basement-membrane is here absent, 

 the epithelium being supported directly by the connective tissue of the 

 mediastinum. 



FIG. 239. SECTION ACROSS THE COMMENCEMENT OF THE VA* 

 DEFERENS. (Klein. ) 



a, epithelium ; 6, mucous membrane ; c, d, e, inner, middle, and outer layers of the muscular 

 coat ; /, bundles of the internal cremaster muscles ; g, section of a blood-vessel. 



The efferent tubules which pass from the rete to the epididymis, 

 and the tube of the epididymis itself, are lined by columnar ciliated 

 epithelium, the cilia being very long ; these tubes have a considerable 

 amount of plain muscular tissue in their wall. 



The vas deferens (fig. 239) is a thick tube, the wall of which is 

 formed of an outer thick layer of longitudinal bundles of plain muscular 



