Development of Excretory Organs. 141 



becomes the oviduct in the female, and grows back to open 

 into the cloaca. It is present, but rudimentary, in the cock 

 bird. 



The mesonephros is the permanent excretory organ of the 

 frog, but not of the fowl. Hence it is inaccurate to speak of 

 both as kidney. In the fowl, on the fourth day, the archi- 

 nephric duct gives oflf a diverticulum, from which is formed, 

 by its elongation, the ureter of the adult. With this com- 

 municates a third set of tubules, also formed in the mesoblast, 

 but without peritoneal openings. These tubules, with the duct, 

 form the kidneys or metanepkros of the adult. 



The original duct, the archinephric duct, persists in the cock 

 bird as the vas deferens ; it acquires connection with the testis, 

 and carries off the sperm. In the hen the mesonephric duct 

 disappears, the Miillerian duct, as already stated, being the 

 oviduct. 



A tabular statement of the above facts may aid the memory. 



Tadpole. Chick. 



Archinephric duct = Archinephric duct. 



Functional pronephros of threej ^ ^^^^^^^^^^^^ p^^„^p^,.„^^ 3 f^„„,l3_ 



Mesonephric tubes = Mesonephric tubes. 



Mesonepliric duct (persistent pro-\ 



nephric duct itself persistent ,„,,„„ ^ric (archinephric) or Wolf- 



archmephnc duct, ;.««« most = I fi^„ /„,(. 



anterior section), or Woltnanl ^ 



duct ' 



Miillerian duct (independent (?)\ _ fMullerian duct (a growth backwards 



of pronephric duct) j \ of rudimentary pronephric duct). 



Frog. Fowl. 



Excretory organ, mesonephros \ 



Ureter of male (also functioning I _ y^^ deferens ( = mesonephric duct). 



as sperm duct) = mesonephric 



duct ) 



No structure present ' = Ureter. 



Oviduct (Miillerian duct) = Oviduct minus funnel. 



Funnel of oviduct = No structure present. 



No structure present = Excretory organ, metanephros. 



Before leaving the excretory organs, their correspondence 

 in the embryo with the typical excretory organs of inverte- 

 brates must be pointed out. We have already seen that the 



