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HISTORY OF THE HUMAN BODY 



secondary modification due to the needs of an aquatic life. In 

 all remaining mammals the process is connected with the for- 

 mation of an inguinal canal, a subcutaneous evagination of 

 the body wall involving muscles and peritoneum, and the 

 testes pass into this either periodically, in association with 

 sexual activity, or permanently. The former condition occurs 



among many insectivores and rodents, and in the bats; the 

 latter is characteristic of the land carnivora, ungulates, most 

 lemurs and the primates. 



In the majority of animals coming under this latter head, 

 that of permanent descent, the testes lie in a special integumen- 

 tal sac, the scrotum, but in some cases, as tapirs, rhinoceros, 

 etc., there is no definite scrotum, and the testes lie beneath the 



