TESTES. 227 



the septa. This interstitial connective tissue is characterized 

 by the presence of numerous large cells, known as interstitial 

 cells (Figs. 175 and 176). They are rounded, coarsely granu- 

 lar cells, with abundant protoplasm, containing fat droplets, 

 pigment granules, or crystalline bodies. They lie usually in 

 groups or columns situated in the spaces between adjacent semi- 

 niferous tubules. The origin and significance of these cells are 

 not known definitely. It is to be assumed that they are of 

 connective-tissue origin. A few authors hold that they are de- 

 rived from epithelial cells. J. Plato ascribes to them a trophic 

 function, claiming that the fat-like inclusions wander through 

 pores in the membrana propria to reach the cells of Sertoli, 

 and thus serve as a nourishment for the spermatozoa that are 

 in process of formation. 



The test.es are supplied with blood by branches of the inter- 

 nal spermatic artery, which enter the septa partly from the 

 mediastinum and partly from the tunica vasculosa. They form 

 networks of capillaries around the seminiferous tubules, and 

 send off branches to the interstitial cell group. The veins col- 

 lect in the interstitial tissues and leave the organ by the path 

 taken by the arteries in entering. 



The lymph-vessels run partly superficially in the tunica 

 albuginea, and partly in the deeper parts, where they form 

 plexuses surrounding the seminiferous tubules. 



The nerves accompany the blood-vessels, and send fine 

 branches between the epithelial cells, where they end in small 

 enlargements. 



The semen consists of a fluid part produced mainly by 

 the accessory sexual glands arid the spermatozoa, which are a 

 product of the testes themselves. There are about 60,000 

 .spermatozoa in 1 cu. mm. of semen. 



The spermatozoon of man may be divided into three parts : 

 the head, the middle piece, and the tail (Fig. 177). The head 

 (Fig. 178, k. Sk.} is flattened, 3-5 fi long, and 2-3 ^ wide. Its 

 flat surface is oval, and shows depressions in its anterior part. 

 Seen from the side, it is pear-shaped. The whole head consists of 

 chromatin substance (nuclein), and represents the cell nucleus. 



