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 séminiferous tubules into’ lobules. From the 
Fic. 340.—Modifications of female urogenital structures in J, monotreme; JJ, 
Orycteropus (uterus duplex); JI, many monodelphs (uterus bipartitus); 7V, most mono- 
delphs; V, Bradypus; VI, Dasypus; b, bladder; c, urinary canal, cu, urogenital sinus; g, 
genital sinus; 0, oviduct, u, uterus; v, vagina. 
lobules the sperm is carried outward by numbers of small 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 
Wolffian 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 
