chap, xiii.] ACCESSORY MALE ORGANS. 521 



On the course of the urethra there are developed 

 the prostate, and frequently also the Cowperian 



glands, the secretion of which appears to serve as a 

 vehicle for the semen ; the size of these, and espe- 

 cially of the former, varies not only greatly in 

 various species, but also at different ages, being 

 often much larger in advanced years. The glans 

 itself is also provided with preputial glands, and is 

 not unfrequently armed with spines. In Ornitho- 

 rhynchus it has a kind of claw at its end, and its 

 surface is covered with spiny hooks, which are 

 directed backwards, and serve as organs of attach- 

 ment. 



The penis arises as an outgrowth of the wall of 

 the cloaca, and is at first grooved along its upper 

 surface ; the sides of this groove grow over and unite 

 in the male. On either side there is a fold of skin, 

 which, in males, unites below with its fellow to form 

 the scrotum, in which the testes are carried in a 

 number of mammals. In the female the just-men- 

 tioned parts remain as the clitoris and labia majora, 

 and do not, as a rule, increase greatly in size ; in 

 some, however, like the hyaena, they are as large as 

 the corresponding or homologous parts in the male, 

 so that the sexes cannot, externally, be distinguished 

 from one another, and a belief in the hermaphroditism 

 of the hyaena is consequently not uncommon. The 

 clitoris is perforated by the urethra in some of the 

 lemurs ; and in the seal the female has an os 

 clitoridis, the homologue of the os penis of the 

 male. 



Internally the male ordinarily retains a small por- 

 tion only of the Miillerian duct. This uterus 

 masculiiius varies considerably in size; in the 

 rabbit, for example, it is of considerable extent. 



Of the organs connected with the care of the young, 

 the most important are the mammary glands and 



