334 



HISTOLOGY 



recent papers have dealt with the subject. Bremer (191 1) concludes that the tubules 

 may end blindly; Huber and Curtis (1913) state that the seminiferous ubules in the 

 rabbit present no blind ends. 



The convoluted tubules are lined with a highly specialized stratified 

 epithelium (Fig. 332). The cells divide and differentiate as they pass 

 from the basal layer outward. Finally each outer cell produces a single 



Spermatids. 



Sustentacular cell. 



Spermatogonium 



Blood vessel with 

 blood corpuscles. 



Fat 

 granules- 



Spermatids. ' 

 PIG. 332. CROSS SECTIONS OF SEMINIFEROUS (CONVOLUTED) TUBULES OF A MOUSE. X 360. 



Sustentacular cell. Spermatogonia, beneath Sustentacular cells, 

 large spermatocytes. 



large cilium, or flagellum, projecting from the free surface, and becomes 

 detached as a spermatozoon. The process of transformation of the basal 

 cells, or spermatogonia, into spermatozoa is known as spermatogenesis. 

 Its cytological features, as observed in the testis of the grasshopper, 

 have already been described (p. 21). Ordinary sections of the human 

 testis present the following characteristics: 



Each tubule is composed of cells of two sorts sexual cells and susten- 

 tacular cells. At birth the cords and developing tubules contain relatively 

 few sexual cells (Fig. 333). These are characterized by their large size, 

 clear protoplasm, and round vesicular nuclei. It is said that they retain 

 a primitive granular arrangement of their mitochondria. These cells 

 multiply by ordinary mitosis, producing the spermatogonia. Thus the 

 sexual cells in various forms eventually far outnumber the Sustentacular 

 cells. 



