256 The Vertebrate Organ Systems 



Many mammals, such as man, retain the testes permanently in the 

 scrotum, and normally the inguinal canals close. If the inguinal canal 

 does not obliterate, portions of the intestine at times slip into the canal 

 to produce inguinal hernias. Other animals whose testes remain per- 

 manently descended are cats, dogs, ungulates, seals, marsupials, and most 

 primates. 



body cavity 



ureter 



vas deferens 



symphysis 

 pubis 



ureth 



testis 



scrotum 



large 

 intestine 



seminal 

 vesicle 



_ prostate 

 gland 



corpora 

 cavernosa 



onus 



Fig. 75. — The male reproductive system. (By permission from Man and the 

 Biological World, by Rogers, Hubbell, and Byers, 1952. McGraw-Hill Book Com- 

 pany, Inc.) 



Another group of mammals includes those whose testes descend only 

 during periods of sexual activity. The rats, bats, camels, otters, and 

 some apes are included here. A third group consists of those mammals 

 whose testes remain permanently within the body cavity. Such animals 

 as the elephants, whales, and the duck-billed platypus represent this type. 

 All vertebrates other than the mammals have their testes located within 

 the body cavity. 



At first it appears relatively unfavorable to have important organs 

 such as the testes in such an exposed position outside the body cavity. 



