UROGENITAL SYSTEM. 



341 



fold of integument (fig. 341) and in the former group may be provided 

 with a common sphincter muscle. 



The testes are relatively small and the outer surface is smooth as 

 the result of the development around them of a fibrous envelope, the 

 tunica albuginea. This sends inward partitions (trabeculae) which 

 separate groups of seminiferous tubules into lobules. From the 



FIG. 340. Modifications of female urogenital structures in 7, monotreme; 77, 

 Orycteropus (uterus duplex); 777, many monodelphs (uterus bipartitus) ; 7 V, most mono- 

 delphs; V, Bradypus; VI, Dasypus; b, bladder; c, urinary canal, cu, urogenital sinus; g, 

 genital sinus; o, oviduct, u, uterus; r, vagina. 



lobules the sperm is carried outward by numbers of smalt tubules, the 

 homologues of the efferent ductules of the lower vertebrates, and 

 like them connected together by vessels which correspond to the longi- 

 tudinal canals. The ductules empty into the anterior end of the 

 Wolfnan duct, the upper end of which is greatly coiled, the coiled por- 

 tion and the ductules forming the epididymis. From the entrance 

 of the ductules to its entrance into the urogenital sinus or canal the 

 duct is called the vas deferens. From this point the urogenital canal 

 is provided with muscular walls and forms an ejaculatory duct. 



In the female the Wolffian duct and the mesonephros are largely lost in the 

 adult, the mesonephros forming a small collection of tubules near the anterior 

 end of the ovary which are known as the parovarium. In the male the Miillerian 



