142 



THE URINOGENITAL ORGANS OF VERTEBRATES. 



into two parts, according to the duct by which their secretion is 

 carried off. 



In the male the following parts are present : 



(1) The Miillerian duct (fig. 5, md.}, consisting of a small 

 remnant, attached to the liver, which represents the foremost 

 end of the oviduct of the female. 



(2) The Wolffian duct (fig. 5, wd], which precisely corre- 

 sponds to the Wolffian duct of the female, except that, in ad- 

 dition to functioning as the duct of the anterior part of the 

 kidneys, it also serves to carry away the semen. In the female 

 it is straight, but has in the adult male a very tortuous course 

 ^vide fig. 5). 



FIG. 5. DIAGRAM OF THE ARRANGEMENT OF THE URINOGENITAL ORGANS IN 

 AN ADULT MALE SELACHIAN. 



md. rudiment of Miillerian duct ; ivd. Wolffian duct, which also serves as vas 

 deferens ; st. segmental tubes. The ends of three of those which in the female 

 open into the body-cavity, have in the male united with the testicular follicles, and 

 serve to carry away the products of the testis ; d. duct of the posterior segmental 

 tubes; t. testis. 



(3) the duct (fig. 5, d.} of the posterior portion of the kid- 

 neys, which has the same relations as in the female. 



(4) The segmental tubes (fig. 5. .$/.) . These have the same 

 relations as in the female, except that the most anterior two, 

 three or more, unite with the testicular follicles, and carry away 

 the semen into the Wolffian duct. 



The mode of arrangement and the development of these 

 parts suggest a number of considerations. 



In the first place it is important to notice that the seg- 

 mental tubes developc primitively as completely independent 



