GONADS 



541 



tissue condenses as an outer wall, the theca. In most mammals all 

 the follicles have been formed soon after birth. 



The testis also consists largely of connective tissue, with a 

 strong fibrous coat. The essential part of it consists of many 



Fig. 424. — A diagrammatic representation of the spermatogenesis of the rat. — 



After Schafer. 



Each of the numbered sections of the diagram represents a portion of the circumference of a seminiferous 

 tubule at a certain stage of the process. In (i) the cells (spermatids) which result from the two successive 

 maturation divisions of the spermatocytes, and eventually become spermatozoa, are seen in their 

 earliest condition. In (2) thev have become attached in groups to supporting cells (cells of isertoh). 

 In (3) to (8) they are becoming spermatozoa, of which their nuclei constitute the heads. In (i) again, 

 they are ready to be set free. 



a and a' a". Lining epithelium cells of the tubules ; a are " spermatogonia." which bv division (seen in 6) 



' throw off spermatocytes ; a' and a" are cells of Sertoli, which support the spermatids ; b spermatocytes. 



These undergo the iwo maturation divisions (indicated in 5) whose ultimate products are c. the 



spermatids The latter, in the process of development into spermatozoa, which they undergo after 



attachment to cells of Sertoli, throw off s', portions of their cytoplasm which disintegrate (s). 



convoluted semmiferous tubules, the cells in the walls of which 

 form the spermatozoa (Fig. 424). The tubules join and pass 

 into vasa efferentia, which are lined with columnar ciliated 

 epithelium, and these in turn lead into the coiled epididymis, 

 which is continuous with the muscular vas deferens. Also in 

 the connective tissue are the interstitial cells, which produce 

 the sex hormones. 



