242 THE MALE REPRODUCTIVE SYSTEM 



kidney and the ureter which runs along the outer margin of the 

 kidney. Thus, in the breeding season the ureter, or Wolffian duct, 

 acts as a sperm duct also. The testis shows seasonal variations in 

 size, being largest during the breeding season. 



In many Amphibia, the Miillerian duct, which is the functional 

 oviduct of the female, is still present in the male. It may be 

 without a lumen in some, but in others it has the features of the 

 resting oviduct of the female. 



MALE REPRODUCTIVE SYSTEM OF REPTILES. 



In reptiles and birds the mesonephros is an embryonic structure, 

 but is replaced by the metanephros, which is the functional kidney 

 of the adult, and ureters are new developments from the embryonic 

 cloaca. Each testis has associated with it an epididymis, a coiled 

 sperm-carrying duct, distally connected with the seminiferous tubules 

 and proximally connected with the Wolffian duct. The Wolffian 

 duct has become a vas deferens and is now solely a sperm-carrying 

 duct. In some male reptiles the IVIiillerian duct still remains, and 

 in Lacerta viridis is as large as in the female, where it is the 

 oviduct. In the epididymal region the duct is lined with cuboidal 

 or columnar epithelium, which may be ciliated; in the \'as deferens 

 the epithelium is columnar or may api)ear stratified with regions 

 of glandular cells alternating with ciliated cells. 



MALE REPRODUCTIVE SYSTEM OF MAMMALS. 



Among the mammals the testes are paired, o\o'u\, comi)act organs 

 which show some variation in their location, not only in different 

 species, but often in the same species at different periods. In such 

 animals as elephants and whales the testes remain permanently 

 within the body cavity, but in marsupials, rodents, bats, and some 

 insectivora they pass out of the body into scrotal sacs during the 

 breeding season. In primates, carnivora, and ruminants they 

 remain permanently outside in scrotal sacs. 



In the testes that have descended during the breeding season, or 

 in the case of primates wdiere they are permanently outside the body 

 cavity, the scrotal sac adds several tissue sheaths about the testes. 

 The scrotal sac, or scrotum, is formed by an evagination of the bod\- 

 wall. Externally it has a covering of skin with its stratified squa- 

 mous epithelium, glands, and hairs, su])])orted b\- layers of con- 

 nective tissue, and muscle. Internally it is lined w itli a tissue simi- 

 lar to the peritoneum and known as tunica Aaginalis parietalis. 

 The same type of tissue is reflected over the anterior and lateral 



