346 REPRODUCTION 



tubules are united posteriorly in groups to form the straight 

 tubules which lead into the rete testis — a network of canals 

 situated in the mediastinum. From the rete about twenty 

 vessels known as the vasa efferentia lead into the canal of 

 the epididymis. For part of their course the vasa effer- 

 entia are convoluted — tfie coni vasculosi. The epididymis, 

 a tube much coiled and of great length, serves as a store 

 for spermatozoa, and its cells contribute to the seminal 

 fluid. It leads into the vas deferens. The vasa efferentia 

 and epididymis are cihated internally and their walls 

 contain unstriated muscle fibres. The wall of the vas 

 contains three muscular layers; its epithelium is not 

 ciliated. The vas opens into the prostatic portion of the 

 urethra. Shortly before its termination the seminal vesicle 

 opens into it. 



The Formation of Spermatozoa 



Each seminiferous tubule is composed of several layers 

 of cells enclosed in a basement-membrane. The layer 

 next to the basement-membrane consists of cubical epi- 

 thehal cells — the spermatogonia. These by division are 

 continually giving rise to the next layer of much larger 

 cells — the spermatocytes. Each spermatocyte divides into 

 two daughter-cells, and each of these again into two sperma- 

 tids. In this last division there is a reduction of the 

 number of chromosomes {heterotype mitosis). The sperma- 

 tids elongate, the nucleus passes to one end and a tail 

 develops at the other. The spermatozoa as they are thus 

 being formed he in groups on the inner part of the tubules, 

 their tails occupying the lumen. Accompanying each 

 group is a cell of Sertoh, an elongated cell derived from the 

 epithehum at the periphery of the tubule. The cells of 

 Sertoh are beheved to take part in the nutrition of the 

 spermatozoa. The last stage is the hberation of the 

 spermatozoa in the seminal fluid. 



The various stages in the formation of the spermatozoa 

 are represented in Fig. 64, p. 348. 



