STRUCTURE OF A SEMINAL TUBULE. 



8 45 



[Arrangement of Tnbules. Each compartment contains several seminal tubules, long 

 convoluted tubules (^-^ in. in diam. ) which rarely branch except at their outer end ; they are 

 about 2 feet in length and exceed 800 in number. These tubules run towards the mediastinum, 

 those in one compartment uniting at an acute angle with each other, to form a smaller number 

 of narrower straight tubules tubuli recti (fig. 632). These straight tubules open into a net- 

 work of tubules in the mediastinum to form the rete testis, a dense network of tubules of 

 irregular diameter (fig. 632). From this network there proceed 12 to 15 wider ducts, the 

 vasa efferentia which after emerging from the testis are at first straight, but soon become 

 convoluted and form a series of coni- 

 cal eminences the coni vasculosi T - albu ginea- 

 which together form the head of the 

 epididymis. These tubes gradually 

 unite with each other and form the 

 body and globus minor of the epi- 

 didymis, which, when unravelled, is 

 a tube about 20 feet long terminat- 

 ing in the vas deferens (2 feet long), 

 which is the excretory duct of the 

 testis. ] 



[Structure of a Tubule. The 

 seminal tubules consist of a thick 

 well-marked basement membrane, 

 composed of flattened nucleated cells bi 00( j_ 

 arranged like membranes (fig. 637). vessels. 

 These tubes are lined by several 

 layers of more or less cubical cells ; 

 there is an outer row of such cells 

 next the basement membrane, and 

 often showing a dividing large 

 nucleus. Internal to these are 

 several layers of inner large clear 

 cells, with nuclei often dividing, so 

 that they form many daughter cells 

 which lie internal to them and next 

 the lumen. From these daughter 

 cells are formed the spermatozoa, 

 and they constitute the sperma- 

 toblasts. These several layers of 

 cells leave a distinct lumen. The 

 tubuli recti are narrow in diameter, 

 and lined by a single layer of 

 squamous or flattened epithelium 

 (fig. 633). The rete testis consists 

 merely of channels in the fibrous 

 stroma without a distinct membrana 

 propria, but lined by flattened epi- 

 thelium. The vasa efferentia and 

 coni vasculosi have circular smooth 

 muscular fibres in their walls, and 

 are lined by a layer of columnar ^buies. 

 ciliated epithelium with striated pro- 

 toplasm. At the bases of these cells 

 in some parts is a layer of smaller 

 granular cells. These tubules form 

 the epididymis, whose tubules have 

 the same structure (fig. 634). In the. 

 sheep, pigment cells are often found 

 in the basement membrane. The vas 



Rete 



testis. 



Fig. 632. 

 Transverse section of the testis (low 

 power view). 



deferens is lined by several layers of columnar epithelium resting on a dense layer of fibrous 

 tissue the mucosa. Outside this is the muscular coat, a thick layer of non-striped muscle 

 composed of a thick inner circular, and thick outer longitudinal layer, a thin submucous coat 

 connecting the muscular and mucous coats together ; outside all is the fibrous adventitia.] 



[The interstitial tissue (fig. 632), supporting the seminal tubules, is laminated and covered 

 by endothelial plates, with slits or spaces between the lamellae, which form the origin of the 

 lymphatics. These lymph-spaces are easily injected by the puncture method. In fact, if 

 Berlin blue be forced into the testis, the lymphatics of the testis and spermatic cord are readily 

 filled with the injection. In some animals (boar), and to a less extent in man, dog, there are 



