188 



ESSENTIALS OF ZOOLOGY 



the testis, and thus the mesonephric duct is in the male also a 

 vas defer ens. 



As growth proceeds the anterior mesonephric tubules are 

 gradually reduced, except those which in the male form the 



Male. 



Female. 



Pronephric 

 nephrostome 



Mesoneph. tubules 

 which are con- 

 nected to vasa 

 efferentia 



Pronephric duct 



^ 



Bowman's capsule 



Nephrostome' ^4 

 *t 



1 



loom * 



Int. opening 

 Miillerian duct 



Degenerating 

 'mesoneph. tubules 



.Miillerian duct 



.Mesoneph. duct 



Cloaca 



FIG. 95. Diagram of mesonephros of male and female Pristiurus. 

 After Rabl. 



vasa efferentia and the mesonephric duct which functions as 

 a vas deferens. The posterior tubules are directed more and 

 more backwards before fusing with the mesonephric duct, and 

 ultimately the functional kidney part of the mesonephros is 

 separated by a duct or ducts, the ureter or ureters, connected 

 only with the mesonephric duct at its termination. 



The germ cells appear over a great part of the same 

 area as the pronephros and the mesonephros. They are 



