270 



The relation between the subcardiucals and azygos in the adult Necturus 

 is shown in Fig. 7, except that here also the sinusoidal network has 

 been omitted ^). It shows more clearly than the Torpedo the con- 

 tinuity of the azygos vein from the caudal vein forward. 



In the reconstruction of a 5 mm Lacerta embryo, Fig. 8, the net 

 of sinusoids has been represented as completely as possible. The 

 caudal vein is here continuous with the subcardinal. Both azygos and 

 subcardinal serve as venae advehentes posteriorly, and both are venae 

 revehentes anteriorly. The intimacy of the relation between them is 

 further shown by the shifting of the caudal vein from the subcardinal 

 to the azygos vein, which occurs in an older stage, and is brought 

 about by the enlargement of some sinusoids and the reduction of 

 others. 



In the forms now described. Torpedo, Necturus, and Lacerta, the 

 renal portal system of sinusoids exists throughout life. The veins in 

 the posterior part of the body remain paired. The vena cava inferior 

 is merely a subcardinal which has acquired connection with the liver; 

 sinusoids intervene between it and the mesonephric azygos. 



In the mammals, the Wolffian sinusoids exist only in the embryo. 

 The veins on the left side of the body are broken into small sections 

 which largely disappear. The vena cava inferior is the right subcar- 

 dinal anterior to the renal vein, but incorporates the mesonephric 

 azygos posteriorly. By means of anastomoses dorsal to the aorta it 

 comes to receive the vertebral vessels from both sides. A detailed 

 account of this transformation is found in the American Journal of 

 Anatomy, Vol. 1, p. 229 — 244, where, however, the mesonephric azygos 

 is referred to as the posterior cardinal. The development and dis- 

 appearance of the Wolffian sinusoids is the only portion of the subject 

 with which we are here concerned, and this has not previously been 

 figured. 



In a rabbit 6.6 mm long, there are no sinusoids in the meso- 

 nephros, as shown in the cross section, Fig. 5B. The cardinal vein is 

 seen to be on the dorsal side of the Wolffian body, in the azygos po- 

 sition, whereas in the Torpedo it was ventral, in the place of the sub- 

 cardinal. As in the Torpedo it soon becomes dissected into sinusoids 

 which are drawn in Fig. 5 D. It gives rise to azygos and subcardinal 

 divisions, separated by mesonephric arteries. Fig. 9 A pictures the 



1) This figure is from a celloidin injection of a male Necturus. 

 For the use of it I am much indebted to Dr. C. W. Prentiss, of 

 Western Reserve University, who made both the injection and the 

 drawing. 



