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HANDBOOK OF PHYSIOLOGY. 



which compose the parenchyma of the testicle, are loosely 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 

 propria, which appears as a hyaline elastic membrane, but which is 

 really made up of several incomplete layers of flattened cells, containing 

 oval flattened nuclei at regular intervals. Inside this membrana propria 

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

 two or more layers, the outermost being situated next the membrana 

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



FIG. 431. 



432. 



FIG. 431. A section of a dog's testicle, highly magnified, showing three " tubuli seminiferi," 

 lined and largely occupied by a spheroidal epithelium, the numerous nuclei of which are well seen; 



c, connective tissue surrounding and supporting the tubuli; sp, masses of spermatozoa occupying 

 the centre of tubuli; the small black bodies scattered about are the heads of the spermatozoa. 

 (Schofield.) 



FIG. 432. Section of a tubule of the testicle of a rat, to show the formation of the spermatozoa, 

 a, spermatozoa; 6, seminal cells; c, spermatoblasts to which the spermatozoa are still adherent; 



d, membrana propria; e, fibro-plastic elements of the connective tissue. (Cadiat.) 



which generally form a complete layer, and those that are in a state of 

 division, of which there may be two layers. 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, their head corresponding with the nuclei of the daughter cells; 

 and during their development they lie in groups (Fig. 432), and are sup- 

 ported by irregular masses of so-called nutritive cells; but when fully 

 formed, they become detached, and fill the lumen of the seminiferous 

 tubule (Fig!! 431). 



