236 Vertebrate Embryology 



form the tubules and Malpighian bodies of the 

 permanent kidney, very much in the same way 

 that the tubules of the Wolffian body were 

 formed. 



The metanephros is very small, compared to 

 the Wolffian body, during a large part of the 

 period of incubation ; but shortly before hatch- 

 ing, it increases rapidly in size, and grows for- 

 wards, dorsal to the Wolffian body. Before 

 describing the origin of the reproductive 

 organs proper, the ovaries and testes, it will 

 be well to recapitulate briefly the changes 

 undergone by the urinary organs in changing 

 from the embryonic to the adult condition. 



The Wolffian body, in the male, almost 

 entirely disappears, but a small portion of it 

 persists in the adult, chiefly as the epididymis. 

 In the female a very small portion of the 

 Wolffian body persists in the adult, as the 

 parovarium, a body that lies in the mesentery 

 between the ovary and the kidney. The 

 Wolffian duct persists in the male as the 

 vas deferens : in the female it disappears. 



The head-kidney or pronephros is, in both 

 sexes, a very rudimentary and transient struct- 

 ure, and leaves no trace in the adult. 



The Miillerian duct never opens into the 



