224 NOTE ON A YOUNG MALE FROG. 



which in great part made u[> the inter-renal portion of the post- 

 caval arose from it. 



This connection of the renal-portals with the post-caval has some 

 significance from a developmental point of view. Hochstetter has 

 shown"*^ that the post-caval vein of amphibia is to be regarded as 

 a compound vessel and due to the fusion of an unpaired pre-renal 

 portion formed independently of the cardinals, with an inter-renal 

 portion formed by the fusion of the posterior portions of the 

 posterior cardinals ; and he figures the stages in the development 

 of these and other parts of the venous system in Salamandra atra. 

 In the youngest condition the posterior cardinals are shown as 

 arising from the bifurcation of the caudal vein. Then in the 

 region of the kidneys the cardinal of each side splits into a loop 

 of two longitudinal vessels. On the fusion of the undivided 

 portions of the cardinals anterior to the kidneys, the two inner 

 vessels lose their posterior connection and form, together with 

 the fused cardinals, the inter-renal portion of the post-caval. The 

 outer limbs of the two loops lose their anterior connection with 

 the cardinals and form two longitudinal vessels ( Jacobson's veins), 

 which constitute the renal-portals. Jacobson's veins are later 

 joined posteriorly by the iliacs in the frog, and the renal-portal of 

 the adult is thus constituted. 



The condition in the specimen under consideration is thus seen 

 to be due to the persistence in the adult of the original anterior 

 connection between Jacobson's veins and the posterior cardinals, 

 now fused to form the posterior part of the post-caval. 



Howes has described! a specimen of Ranct temporaria in which 

 the anterior portion of the posterior cardinal persisted on the left 

 side, forming an azygos vein, with which the renal-portal of that 

 side was in direct communication. In my specimen no traces of 

 azygos veins were present, and since it shows in the adult the 

 persistence by arrested growth of a condition usually passed 

 through in the larval state, I have thought it worth recording. 



* Morph. Jahrb. Bd. xiii. p. 160. 

 t Proc. Zool. Soc. Lond. 1888, p. 122. 



