265 



WD.-y 



vc- 



V.S. i: 



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TO: 4 







it anastomoses with the opposite vessel, the anastomosis occurs dorsal 

 to the aorta. Since this vessel may form a part of the adult azygos 

 vein, and since in its re- 

 lation to the somatic 

 vessels it is morphologi- 

 cally a part of that vein, 

 I shall refer to it as azygos 

 or as m e s n e p h r i c 

 azygos. Heretofore both 

 subcardinal and azygos 

 have been called indiscri- 

 minately posterior cardinal 

 vein. The subcardinal is 

 also frequently named the 

 vena revehens, and the 

 azygos, the vena advehens 

 of the Wolffian body. Con- 

 necting them, there is a 

 net of sinusoids which may 

 be studied so advantage- 

 ously in fishes that its 

 development is here pre- 

 sented from the compara- 

 tive standpoint. 



In Torpedo embryos 

 the caudal part of the 

 posterior cardinal is for- 

 med from the subintestinal 

 branch of the vitelline 

 vein. This is shown in 

 Fig. 3, a reconstruction of 

 a 12.8 mm Torpedo, seen 

 from the ventral side. The 

 median caudal vein has 

 forked to pass around the 

 cloaca, ventral to which 

 its branches reunite to 

 form the subintestinal 

 vein. The mesonephric 

 portion of the posterior 

 cardinal vein, according to 



W.D- 



W.Dr[ 



V.Cau- 



Fig. 3. Fig. 4, 



Fig. 3. Reconstruction of the posterior 75 of 

 the Wolffian body and veins of a 12.8 mm Torpedo, 

 H. E. C. 688. X 50 diams. 



Fig. 4. Similar reconstruction of the left 

 Wolffian body of a 19.2 mm Torpedo, H. E. C. 682, 

 X 50 diams. V. C. Posterior cardinal vein. F. Cau. 

 Caudal vein. F. Äi. Subintestinal vein. W.B.,W.D., 

 W. T. Wolffian body, duct, and tubule respectively. 



