STRUCTURE OF THE TESTICLE 



175 



uniting- with the other straight tubules, a network of intercom- 

 municating vessels, which is known as the rete testis. From the rete 

 a certain number of efferent tubules arise, and after a few convolutions 

 pass into the tube of the epididymis. 



Structure of the tubules. The seminiferous tubules are formed of 

 a basement-membrane, and contain several layers of epithelium-cells. 

 Of these layers, the one next the basement-membrane is a uniform 

 layer of clear cubical cells (lining epithelium), the nuclei of which, for 

 the most part, exhibit the irregular network which is characteristic of 



FIG. 212. SECTION OF PARTS OF THKEE SEMINIFEROUS TUBULES OF THE RAT. 



a, with the spermatozoa least advanced in development ; 6, more advanced ; c, containing 

 fully developed spermatozoa. Between the tubules are seen strands of interstitial cells 

 with blood-vessels and lymph-spaces. 



the resting condition. Here and there these epithelium-cells appear 

 enlarged and to project between the more internal layers. 



Next to this layer of cubical epithelium there is seen a layer of 

 larger cells (spermatogenic cells), the nuclei of which have the skein- 

 like aspect which is typical of commencing division ; these cells may 

 be two, three, or more deep (as in the tubule a, fig. 212). Next to them, 

 and most internal, are to be seen in some tubules (b and c) a large 

 number of small protoplasmic corpuscles with simple circular nuclei 

 (spermatoblasts). In other tubules these corpuscles are elongated, 

 and the nucleus is at one end, and in others again these elongated 

 cells are converted into evident spermatozoa, which lie in groups with 

 their heads projecting between the deeper cells and connected with one 

 of the enlarged cells of the lining epithelium, and their tails emerging 

 into the lumen of the tubule (fig. 212, 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 



