414 



PERSISTENCE OF A VEIN IN XENOPUS LAEVIS. 



Other Cases of the Persistent Post car dial Vein in Anura. — 

 More or less similar cases to the above have been described 

 in a female Ra>ia temporaria by Howes (1888), and in a male of, 

 the same species by Parker (1889). In the specimen described 

 by Howes, the postcaval is present, and the postcardinal ( azygos) 

 joins it at the anterior extremity of the kidneys, just after having 

 received a vein from the renal portal. In that described by 

 Parker, a case practically identical with that described in A'. 

 Icevis was found, except that in the former it was the left post- 

 cardinal which persisted, and not the right, as in X. I'cevis. 



Probable Significance of this Persistence. — Hochstetter, in 

 1887 advanced the view that the inferior vena cava (post caval) 



RPC 



HV == Hepatic vein; Kd = kidney; Li =: liver; PrC = precaval vein; 

 ReP = renal portal ; RPC = right postcardinal vein ; Sc = sciatic 

 vein ; Scl = subclavian vein ; SV = sinus venosus ; Ur =: ureter. 



of vertebrates had its origin partly independently and partly 

 from the fusion of the two postcardinal veins of iishes ; whilst 

 Balfour distinguishes the venous system of Amphibia and 

 Amniota from that of fishes by the presence of a new vessel — 

 the inferior vena cava (postcaval) — which vessel replaces the 

 postcardinals of fishes. 



The persistence of one of these postcardinals in this speci- 

 men of X. Icevis is, therefore, of interest, because it shows the 

 retention of an ancestral character, and at the same time seems 

 to afford further support towards Hochstetter's view as to the 

 origin of the post caval. The inter-renal portion may be con- 

 sidered as being comparable with the corresponding region of 



