72 ^Yilliam F. Allen 



vascular system, save at the points where the caudal sinuses empty 

 into the caudal vein. This system of vessels collects a network 

 which is decidedly lymphatic in the character of its meshes, is coarser 

 than the blood capillaries, and so far as observed had no connection 

 with the arteries. Furthermore, the peripheral regions are sufficiently 

 supplied with veins. For most of the smaller subcutaneous vessels are 

 accompanied by corresponding arterial and venous branches; the lateral 

 arteries and veins supply the peripheral region of the trunk, the dorsal 

 fin artery and vein nourish the dorsal fin, and the caudal artery and 

 vein do the same for the caudal fin. If the subcutaneous vessels are 

 classed as veins it would be necessary to consider them as a distinct 

 venous system that had no counterpart in the arterial system. 



We are compelled to admit that the evidence is insufficient to warrant 

 anv sweeping statement as to the exact nature of this system of vessels 

 in fishes. The little data we have, when considered in the light of 

 certain recent studies on the embryology of the lymphatics in mammals, 

 supports the supposition that, in the more primitive Selachians, certain 

 subcutaneous vessels, probably veins, have become separated to some 

 extent from the main venous system. , According to Sappey, in the 

 skates the communications of this system with the veins are quite 

 numerous. In Mustehis and Squahis, Parker and Mayer found these 

 points of union less abundant, but in addition to the connections of the 

 subcutaneous vessels with the caudal vein in the tail region of the 

 Ganoids and Teleosts, they note that the so-called dorsal cutaneous vein 

 anastomoses behind the dorsal fin with a deep dorsal fin vein. Such a 

 vein was found in Lepisosteus, but no anatomosis Avith the dorsal sub- 

 cutaneous trunk occurred, indicating, of course, that in Lepisosteus the 

 separation of this subcutaneous system had become more complete. 



In the head region we find that the same differentiation of the 

 subcutaneous system has gone on as we pass from the Selachians to the 

 Ganoids, and from the Ganoids to the Teleosts and Batrachians, but in 

 this region it is more obscure. In an earlier paper it was pointed out 

 that each of the branchial lymphatic trunks (nutrient branchial veins?) 

 of Poh/odon anastomosed above with the subcutaneous system and below 

 with the inferior jugular vein ; that they received a coarse network from 

 the branchial arches and from their filaments, which, so far as could 

 be ascertained, had no capillary connections with the arterial system. 

 In Lepisosteus these branchial trunks were separated into dorsal and 

 ventral l:)ranchial lymphatic trunks (nutrient branchial veins?), whicJi 



