620 



VETERINARY PHYSIOLOGY 



proliferated cells of the zona granulosa and forms the corpus 

 luteum. If the ovum is fertilised and pregnancy occurs the 

 corpus luteum goes on growing, attains a considerable size, 

 and plays an important part in the course of gestation 

 (p. 608). 



B. Testis. — The testis is enclosed in a dense fibrous capsule 

 — the tunica alhuginea. Posteriorly this is thickened, and 

 forms the corpus Highmori. Processes extend from this 



Fig. 236. — I, To show this development of spermatozoa from 

 spermatogonia ; II and III, heads of spermatozoa dipping 

 into cells of Sertoli ; IV, mature spermatozoa. Two inter- 

 stitial cells shown below. (Mott. ) 



and form a supporting framework. In the spaces are situated 

 the ser)iiniferous tubules, which open into irregular spaces in 

 the corpus Highmori — the rete estis. From these the efferent 

 ducts, vasa eferentia, pass away and join together to form the 

 vas deferens, which, after receiving the duct from a diverticulum 

 of the seminal vesicle, opens into the urethra. 



In the seminiferous tubules, the spermatozoa are produced. 

 Some of the lining cells divide into two, forming a siqjporting 

 cell next the membrane and a spermatogonium. The latter 

 divides and subdivides till a group of cells, the primary 

 spermatocytes, are formed. Each of these undergoes a division, 

 in which the number of chromosomes in each cell formed is 



