THE REPRODUCTIVE ORGANS. 



227 



interstitial tissue just mentioned contains large cytoplasmic cells 

 of connective-tissue origin, which frequently contain globules of 

 fat or granules of pigment, and in many instances, in man, have 

 been observed to contain crystalloids of proteid nature. It has 

 been surmised that these cells may serve for the storage of nutri- 

 ment required by the active proliferation of the cells that produce 

 the spermatozoa within the seminiferous tubes (Fig. 200). 



FIG. 200. 



x& v - v 



'^* <^>;w.v 

 -^^-^ 







* 



, 



Interstitial tissue in the testis of the cat. (Plato.) Three bloodvessels are shown in either 

 complete or partial section. Portions of two seminiferous tubules are represented at the 

 upper corners. Between these structures is the interstitial tissue, containing large cyto- 

 plasmic cells. This tissue is rather more abundant in this instance than in the human 

 subject. 



Each seminiferous tube is provided with a basement-membrane, 

 upon the inner surface of which are epithelial cells. These are di- 

 visible into three groups : first, a parietal layer of cells, the " sper- 

 matogonia," lying next to the basement-membrane ; second, a layer 

 of cells, often two or three deep, called the " spermatocytes," lying 

 upon and derived from the spermatogonia ; third, the " spermatids," 

 lying most centrally. The spermatids are derived from the spermato- 

 cytes, and are the elements from which the spermatozoa develop, 

 one spermatozoon being formed from each spermatid. 



The cells of the parietal layer, that containing the spermatogonia, 

 are not all alike. At intervals certain cells, called " sustentacular " 



