HORMONES AND REPRODUCTION 5I 



a few hours after treatment with pregnancy urine. In the 

 last year or two this test has been superseded by another 

 based on the use of male toads, ^^ frogs, and urodels,^^^ 

 which react by shedding their sperm. 



4. THE TESTIS 



The greater part of the vertebrate testis is made up of a 

 mass of spermatic tubules, which are bounded by 

 connective tissue. These tubules, which are woven and 

 twisted together are blind at one end while at the other 

 they converge on to the dorsal side of the testis. There 

 they open into the vasa efferentia, which lead to the vas 

 deferens and so to the exterior. In the teleost fishes the 

 testis is similar in structure, but the ducts are absent. 



In a maturing testis the lining cells of the spermatic 

 tubules divide to form spermatogonia, which in turn 

 produce primary and secondary spermatocytes, sperma- 

 tids, and spermatozoa. Thus a gradient is established 

 with the spermatogonia on the tubule wall and the 

 spermatozoa in the central lumen along which they move 

 slowly towards the ducts. In a rat the time taken for the 

 production of a spermatozoon from a spermatogonium 

 is estimated at about 20 days. 



The spaces between the spermatic tubules are filled 

 with blood vessels, lymphatics, connective tissue and 

 the glandular cells of the interstitial tissue. 



The testis remains in an immature condition until the 

 hormones of the anterior pituitary gland reach it through 

 the blood stream. Then it is generally thought that the 

 F.S.H. acts primarily by stimulating spermatogenesis 

 within the spermatic tubules, while the I.C.S.H. acts 

 primarily by stimulating the multiplication and growth 

 of the glandular interstitial cells. However, it must be 

 borne in mind that each of these hormones can appar- 

 ently exert little if any effect in the complete absence of 

 the other. «3 



When stimulated to activity the testis itself acts as an 



