168 THE PHYSIOLOGY OF REPRODUCTION 



unite in their turn, giving rise to a network of vessels called the 

 rete testis. From the rete the vasa efferentia are given off. 

 Between the tubules is a loose connective tissue containing a 

 number of yellow epithelioid interstitial cells. The connective 

 tissue also contains numerous lymphatics and blood-vessels 

 (branches of the spermatic artery). The nerves of the testis 

 are derived from the sympathetic system, but a few filaments 

 come from the hypogastric plexus. 



In embryonic development the tubules arise from the 

 primitive germinal epithelium. According to Allen 1 the inter- 

 stitial cells are derived from connective tissue. 



The straight tubules, and the tubules of the rete, are lined by 

 a single layer of cubical or flattened epithelium without a base- 

 ment membrane. The seminiferous tubules, on the other hand, 

 contain several layers of epithelial cells supported by a thick 

 basement membrane. The layer nearest the membrane con- 

 sists of clear cubical cells, a few of which show evidence 

 of division. These are the spermatogonia. Certain of the 

 epithelial cells between the spermatogonia are enlarged, and 

 project among the more internal cells in association with de- 

 veloping sperms. These are the cells of Sertoli. On the inside 

 of the spermatogonia are certain larger cells, known as sperma- 

 tocytes. These are products of division of spermatogonia, each 

 of which on dividing into two gives rise to a cell like itself, 

 and another cell, which grows larger, passes into the second layer, 

 and becomes a spermatocyte. 



The spermatids, which in some seminiferous tubules lie on the 

 inside of the spermatocytes, are the double products of division 

 of the latter. The spermatids so formed may be seen as small 

 cells with spherical nuclei, and forming irregular clumps on the 

 inner surface of the tubule. Often, however, the spermatids 

 are elongated, being partially converted into spermatozoa. As 

 this process of transformation proceeds, the developing sperms 

 become arranged in little groups. Associated with each group 

 is a foot-cell, or a cell of Sertoli, which probably serves as a 



1 Allen, "The Embryonic Development of the Ovary and Testis," Amer. 

 Jour, of Anat., vol. iii., 1904. As already mentioned, Allen regards the in- 

 terstitial cells of the ovary as being developed from connective tissue, thus 

 differing from Miss Lane- Clay pon. 



