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bodies the mesonephric cardinal veins have fused, producing a single 

 vessel unnecessarily set apart by Rabl as the interrenal vein. In 

 Fig. 3 it is seen that the tributaries of the cardinal alternate regularly 

 with the Wolffian tubules. 



In a Torpedo of 19.2 mm the cardinal veins have lost their con- 

 nection with the subintestinal vessels. A median caudal vein divides 

 into two mesonephric cardinals. One of these is shown in Fig. 4, 

 which represents the posterior three fifths of the left Wolffian body 

 with its related veins. The somatic veins branch and anastomose, 

 spreading over the surface of the coils of tubule. In the cross section, 

 Fig. 5 A, taken from this embryo, it is evident that no sinusoids have 

 formed. Neither arteries nor glomeruli have developed. A section 

 from an older embryo, 27.8 mm, is drawn in Fig. 5C. The growing 

 tubules and enlarging vein have here become involved in a typical 

 sinusoidal system, extending through all but the ventro-lateral part of 

 the Wolffian body. There is a distinct line of separation between the 

 sinusoidal and non-sinusoidal portions. Along this line a small artery, 

 A.M., passes to the glomerulus, Gl. This vessel is a branch of the 

 vertebral artery which it leaves opposite Balfour's suprarenal gland 

 (a clump of coarse dots in the figure). Thence it proceeds, without 

 branches, among the sinusoids to the line of uninvaded tissue just de- 

 scribed. The corresponding artery in the rabbit. Fig. 5D, leaves the 

 aorta and pursues a shorter course to the glomeruli. In both the 

 rabbit and the Torpedo these mesonephric arteries are dorsal to the 

 main venous stems, the subcardinal veins. In both also they are ventral 

 to the veins receiving the vertebrals, the mesonephric azygos veins. 

 In the posterior part of the Wolffian body of older Torpedos a 

 complication arises, the development of which is shown in Fig. 5C. 

 The vein which receives the vertebrals, V. a., becomes reduced to 

 sinusoids, which the vertebrals then enter directly. It is a temporary 

 mesonephric azygos. The permanent mesonephric azygos, V. A., is 

 formed by the enlargement of other sinusoids. It receives somatic 

 tributaries, but not the vertebral veins. The important fact is that 

 all these vessels are subdivisions of the single vein shown in Fig. 5 A. 

 The veins of a 51 mm Torpedo are seen in the reconstruction, 

 Fig. 6. The single caudal vein, receiving the vertebrals, bifurcates 

 and each fork encounters a Wolffian body. There it is resolved into 

 an intricate network of sinusoids, not figured, which empty into the 

 subcardinal and azygos veins. The azygos is reduced to sinusoids 

 toward the cephalic end of the Wolffian body. It receives somatic 

 and iliac veins, and in part of its course the vertebrals. Caudally as 



