964 



GENERATIVE APPARATUS. 



Fig. 519. 



The seminiferous tubes in the lobules are from -20 mm. to -25 mm. in diameter. 

 Their walls are composed of two membranes — an internal, which is thin, amor- 

 phous, and formed of cells joined border to border as in an endothelium ; and 

 an external, thicker, lamellar, and containing nuclei. The walls are lined by a 

 stratified epithelium, which is constantly undergoing evolution in the adult. 

 The external layer is named the basal epithelium. It contains two kinds of cells : 

 ordinary, indifferent cells, named the " cells of Sertoli ; " and thin, round, 



granular cells (^spermatogonia) mixed with, 

 these. The latter are the male ova of 

 Robin, and it is they alone which exhibit 

 the phenomena of spermatogenesis. Before 

 the manifestation of this process, the male 

 ova proliferate, join the cells of Sertoli, and 

 form on the face of each of these elegant 

 radial series. 



Spermatogenesis is the name given to 

 the epithelial evolution which leads to the 

 formation of spermatozoids. In spermato- 

 genesis, there are two periods : 1. The 

 period of the proliferation of the tubular 

 epithelium resulting in the production of 

 the spermatoblasts. 2. The period of dif- 

 ferentiation, in which the spermatoblasts 

 are transformed into spermatozoids. This- 

 change involves the nucleus of the sperma- 

 toblast, which becomes the head of the 

 spermatozoid ; then the protoplasm, from 

 which is produced the tail of the sperma- 

 tozoid. 



Between the seminiferous tubules is a 

 stroma composed of somewhat peculiar 

 connective tissue, in which are numerous 

 cells filled with yellowish granules. Blood- 

 vessels and lymphatics course through this 

 stroma. 



Vessels and nerves. — The blood is carried 

 to the testicle by the spermatic arteryy 

 which is almost exclusively appropriated ta 

 it ; this vessel, after describing a great 

 number of very remarkable flexions, enters the upper border of the gland, a 

 little behind the epididymis. It does not immediately plunge into its sub- 

 stance, however, but passes within the texture of the tunica albuginea, along the 

 borders of the testicle, and forms a complete circle around it. From this circle 

 it sends oif divisions, which spread over the sides of the organ, detaching fine 

 arterial ramifications that penetrate its proper tissue in accompanying the inter- 

 lobular septa. (There is generally described a tunica vasctdosa., which forms one 

 of the coverings of the testicle. This, in reality, is not a distinct coat, but 

 merely the fine ramifications of the spermatic artery spreading beneath the 

 tunica albuginea, and held together by delicate connective tissue.) 



The veins are very voluminous and frequently varicose ; they comport them- 



VERTICAL SECTION OF THE TESTICLE 

 (horse's), passing THROUGH THE CORPUS 

 HIGHMORIANUM. 



1 Spermatic cord, with its serous covering; 

 2, sections of the flexuous vessels of the 

 cord; 3, head of the epididymis, or globus 

 major ; 4, tail of the epididymis, or globus 

 minor; 5, vas deferens; 6, corpus High- 

 morianum ; 7, rete testis ; 8, tunica 

 albuginea sending prolongations from its 

 inner face, and which divide the testicle 

 into lobules , 9, surface of the tunica 

 albuginea. 



