The Reproductive System 257 



It appears, however, that it is a necessary evil inasmuch as the sperm 

 are not viable at the higher temperatures of the body. This hypothesis 

 appears to be verified by the fact that the failure of the testes to descend 

 (cryptorchidisin) is almost always accompanied by sterility; temporary 

 sterility often follows fevers. Also those mammals which retain the 

 testes within the body cavity commonly have lower body temperatures. 



Due to the unusual descent of the testes, they are surrounded by a 

 double layer of peritoneum. The heavy connective tissue sheath is di- 

 rectly below this, while in direct contact with the surface of each testis 

 is a vascular laver of tissue. 



SPERMATOGONIUM. 



SPERMATOCYTE 



SPERMATOCYTE 



INTERSTITIAL 

 CELL 



B 



Fig. 76. — Testis and sperm. A, Semidiagrammatic section of 

 testis; B, human sperm. 



The Ducts of the Reproductive System. — The much-convoluted 

 seminiferous tubules of the lobules straighten out near the apex and pass 

 into the heavy posterior edge of the capsule where they anastomose with 

 other tubules to form irregular epithelial-lined spaces. These spaces with 

 their surrounding connective tissues are known as the rete testes. A 

 series of tubules, continuous with those of the rete testes, emerge to 

 form the vasa efferentia. Finally these tubules unite to form the epi- 

 didymis which in turn gives rise to the vas deferens. 



Closely adhered to the testis is the epididymis, a mass of connective 

 tissue and ducts. There are three portions to this structure : the head, 

 body, and tail. The head is formed of the many vasa efferentia and their 

 surrounding connective tissue, while the body and tail are composed 

 of the heavy coiled epididymis and its surrounding tissues. From 



