GENERATION AND DEVELOPMENT. 247 



tough, made up chiefly of longitudinal with some circular plain muscular 

 fibres. When followed back to its origin, the vas deferens is found to 

 pass to the lower-part of the epididymis, with which it is directly con- 

 tinuous (Fig. 402), and assumes there a much smaller diameter with an 

 exceedingly tortuous course. 



The epididymiSf which is lined, except at its lowest part, by columnar 

 ciliated epithelium (Fig. 400), is commonly described as consisting (Fig. 

 402) of a globus minor (g], the body (e), and the globus major (I). When 

 unraveled, it is found to be constructed of a single tube, measuring 

 about twenty feet in length. 



At the globus major this duct divides into ten or twelve small branches, 

 the convolutions of which form coniform masses, named coni vasculosi; 

 and the ducts continued from these, the vasa efferentia, after anastomos- 

 ing, one with another, in what is called the rete testis, lead finally as the 

 tubuli recti or vasa recta to the tubules which form the proper substance 

 of the testicle, wherein they are arranged in lobules, closely packed, and 

 all attached to the tough fibrous tissue at the back of the testicle. The 

 epithelium of the coni vasculosi and vasa eff'erentia is columnar and cili- 

 ated; that of the rete testis is squamous. 



Structure of Seminal Tubes. The seminal tubes, or tubuli sem- 

 iniferi, which compose the parenchyma of the testicle, are arranged in 

 lobules between the connective tissue septa. 



They are relatively large, very wavy, and much convoluted; and they 

 possess a few lateral branches, by which they become connected into a net- 

 work. They form terminal loops, and in the peripheral portion of the 

 testis the tubules are possessed of minute lateral caecal branchlets. 



Each seminal tubule in the adult testis is limited by a membrana pro- 

 pria, which appears as a hyaline elastic membrane containing oval flat- 

 tened nuclei at regular intervals. Inside this membrana propria are 

 several layers of epithelial cells, the seminal cells. These consist of an 

 inner and outer layer, the latter being situated next the membrana pro- 

 pria. These cells are of two kinds, those that are in a resting state and 

 those that are in a state of division. The latter are called mother cells, 

 and the smaller cells resulting from their division are called daughter 

 cells or spermatoblasts. From these the spermatozoa are formed. During 

 their development they lie in groups, but when fully formed they become 

 detached and fill the lumen of the seminiferous tubule (Fig. 401). 



Spermatozoa. On examining the spermatozoon of Triton cristatus, 

 one of the Amphibia which possess the largest of all Vertebrate animals, 

 Heneage Gibbes found that the organism (Fig. 404) consisted of (a) a 

 long pointed head, at the base of which is (), an elliptical structure join- 

 ing the head to (c), a long filiform body; (d), a fine filament, much longer 

 than the body, is connected with this latter by (e), a homogeneous mem- 

 brane. 



