COMPARATIVE ANATOMY OF THE UROGENITAL SYSTEM 



277 



mesonephroa 



Wolffian duct 



intestine 



cloaca 



B 



testis 

 vasa efferentia 



epididymis (vestige 

 of mesonephros) 



Wolffian duct _J 

 (vas deferens) 



metanephros 



cloaca 



urinary 

 bladder 



cloaca 



FIG. 62. Diagrams to illustrate the urogenital systems of male and female anamniotes and 

 amniotes. A, male elasmobranch or amphibian; the mesonephros is differentiated into anterior 

 genital and posterior excretory portions; the genital part is connected with the testis by means of the 

 vasa efferentia which are outgrowths from the mesonephros; the mesonephric or Wolffian duct serves as 

 both genital and excretory duct; the oviduct or Mullerian duct is vestigial. B, female elasmobranch 

 or amphibian; the ovary is not connected with the mesonephros; the mesonephros and mesonephric 

 duct serve only excretory functions; the oviduct is well developed and opens into the coelom by the 

 ostium near the ovary. C, male reptile, bird, or mammal; the excretory part of the mesonephros has 

 disappeared but the genital part persists as the epididymis (in part) which is connected as in anamniotes 

 with the testis by means of the vasa efferentia; the Wolffian duct is purely genital and is renamed the 

 vas deferens; the excretory function is served by metanephroi and ureters. D, female reptile, bird, or 

 mammal; the mesonephros and Wolffian duct have entirely vanished; the condition of the ovary and 

 oviduct is the same as in anamniotes; the excretory function is served by the metanephroi and ureters 

 exactly as in the male. (The changes in the relation of the urogenital ducts and cloaca which occur in 

 mammals are not indicated in these figures but are shown in Figs. 63 and 64.) (Slightly modified 

 from Wilder's History of the Human Body, courtesy of Henry Holt and Company.) 



