xxx v.j THE TESTIS. 385 



in its deeper part. From its under surface septa pass into the 

 gland at fairly regular intervals, thus dividing it into a series of 

 compartments or lobules. At the upper and back part is the 

 nitrous septum corpus Highmorianum or mediastinum testis. 

 Many of the septa are connected with it. 



(k,) In the lobules lie twisted or convoluted tubules the semi- 

 niferous tubules which converge towards the mediastinum arid 

 form near it a number of straight tubes the tubuli recti which 

 in their turn unite and form the rete testis in the mediastinum, 

 and from this proceed the vasa efferentia, which run to join the 

 canal of the epididymis (fig. 356). 



(c.) The tubules in a state of activity are distinguished from 

 the resting ones by the intensely stained heads of the young 

 spermatozoa. An active tubule is lined by several rows of poly- 

 gonal cells, some of which are larger than the others. Embedded 

 amongst the cells, near the lumen of the tube, are bunches or 

 tufts of spermatozoa, best seen in longitudinal sections of the 

 tubes. The heads are directed towards the wall, and the tails 

 towards the lumen of the tube. 



(d.) In some animals the interstitial tissue between the tubules 

 is chiefly formed by thin flattened membranes of connective tissue ; 

 but in others, e.g., boar, the matrix consists of numerous pigmented, 

 polygonal, very granular cells interstitial cells. 



2. Spermatogenesis (Rat}. In order to see the structure of 

 the seminiferous tubules to the best advantage, harden small 

 pieces of the testis of a rat, or a guinea-pig, as directed under 

 v. and ii. (p. 384). To keep the parts together, cut in paraffin. 

 The best stain is safranin. Fix a thin T S. of a tubule under a 

 high power. 



(a.) Observe the rather thick wall wembrana propria of the 

 tubule, composed of flattened cells, perhaps of a connective tissue 

 nature. This is lined by three or more layers of glandular cells, 

 which vary in appearance according to their condition of physio- 

 logical activity. In a state of rest each tube is lined by several 

 layers of large polygonal cells placed one inside the other. 



(/>.) In an active gland, known by the evidences of division of 

 cells and by the development of spermatozoa (fig. 357), there is an 

 outer layer of cubical-looking cells, and internal to it several layers 

 of round or ovoid cells, which are called spermatogenic cells. In 

 the latter may be seen nuclei undergoing mitotic division. The 

 lining epithelial cells seem to divide ; one part of each cell passes 

 into the second layer of cells, and becomes a sperm atogen or sper- 

 matogenic cell, while the remainder of the original cell enlarges and 

 grows up as a sustentacular cell. The spermatogenic cells divide 

 and redivide by mitosis, and yield the small daughter-cells or 

 34 2 B 



