LEPID0S1RP]N PARADOXA. 
115 
extend backwards, communicating round it by one or two 
vertical anastomoses (Stage 29). These post-anal vessels 
are remarkable for their width and form large vascular loops 
round the gut. With the development of the tail and the 
disappearance of the post-anal gut, the caudal vein lengthens 
and the hoop-like anastomoses with the aorta disappear, 
while the vein comes to lie immediately ventral to the aorta 
(Stage 31).^ In the region of the cloaca, therefore, the 
caudal vein bifurcates to reach the posterior cardinal veins, 
which are joined in the same region by the bifurcations of 
Text-fig. 25. 
Diagram of anastomoses between the dorsal aorta and the idos- 
terior cardinal and snbintestinal veins. Cau. V. Caudal vein. 
D. Ao. Dorsal aorta. P.Carcl. Posterior cardinal vein. Si. V. 
Snbintestinal vein. a. The anastomosis between the dorsal 
aorta and the posterior cardinal vein. 5. The anastomosis 
between the snbintestinal and posterior cardinal veins. 
the subintestinal vein. These latter vessels (the bifurcations 
of the subintestinal vein) presently lose their connections 
with the subintestinal vein and persist in the adult as the 
rectal veins (Text-fig. 24 e, if. V.). Alittle later (Stage ol-f) 
the iliac veins (Text-fig. 24 e., II V.) open into the renal 
portal vessels a short distance in front of the cloaca. 
Meanwhile, Avith the gradual absorption of the yolk, the 
archinephric ducts approach one another in the middle line, 
and, Avith the appearance of the mesonephros dorsal and 
^ A similar condition is described in the development of Poly terns. 
Kerr, J. Graham, “The Develoimient of Polypterus senegalus, 
Cnv.” The Avork of John Samuel Bndgett, Cambridge, 1907. 
