864 REPRODUCTION, DEVELOPMENT, GROWTH AND DEATH [CH. LIX. 



more) or mediastinum testis. Attached to this is a much convoluted 

 tube, which forms a mass called the epididymis. This receives the 

 ducts of the testis, and is prolonged into a thick -walled tube, the vas 

 deferens, by which the semen passes to the urethra. 



Each lobule of the testicle contains several convoluted tubes. 

 Every tube commences near the tunica albuginea, and terminates 

 after joining with others in a straight tubule, which passes into the 

 body of Highmore, where it ends in a network of tubes, the rete testis. 

 From the rete about fifteen efferent ducts (vasa efferentia) arise, 

 which become convoluted to form the coni vasculosi, and then pass 

 into the tube of the epididymis. 



The convoluted or seminiferous tubes (fig. 548) have the following 



^v 



7^ J>JI SS ^ . ^V 4 



FIG. 548. Diagram of a portion of a seminal tubule showing development of spermatozoa. 1, Primi- 

 tive germ cell ; 2, spermatogonia ; 3, primary spermatocytes ; 4, secondary spermatocytes ; 5, 

 spermatids, some with commencement of axial lilament ; C, a nurse cell with spermatids and 

 spermatozoa in various stages of development ; 7, free spermatozoa in lumen of tube ; 8, portions 

 of nurse cells. (After Waldeyer.) 



structure : each consists of (1) an outer boundary of flattened connec- 

 tive-tissue cells intermingled with elastic fibres ; (2) a fine membrana 

 propria; (3) a lining epithelium of many layers of germinal cells. 

 Next to the membrana propria is a layer of cells, some of which are 

 primordial germinal cells, others are spermatogonia produced from the 

 primordial germinal cells, but differing from them in structure, and 

 the remainder are supporting or nurse cells (Cells of Sertoli) which 

 provide nutriment for the developing spermatozoa. More internally, 

 between the projecting processes of the nurse cells, are large primary 

 spermatocytes, derived from the division of the spermatogonia. Still 

 nearer the lumen of the tube lie the secondary spermatocytes , which 

 are the daughter-cells of the primary spermatocytes; the secondary 



