58 William F. Allen 



with the L. tristoeclius from which Figs 3 and 4 were drawn the dorsal 

 trunk culminated in the left sinus (x), nearer its anterior extremity 

 than its posterior. In Figs. 1 and 2, especially the former, sinus (x) 

 extends some little distance caudad of its ventral comm^^nication with 

 the caudal sinus; while in Figs. 3-6, sinus (x) might be described as 

 discharging itself caudad and ventrad into the caudal sinus. As a 

 matter of fact, sinus (x) in Figs. 3-6 appeared to be merely a deep 

 continuation of the lateral trunk, which empties into the caudal sinus. 

 No valves were observed at the entrance of any of the suljcutaneous 

 trunks into sinus (x), or guarding the exit of the latter into the caudal 

 sinus. 



Some interesting observations should be recorded in connection with 

 the dorsal trunk and sinus (x) from a series of transverse sections 

 taken through the tail of a 90 mm. L. osseus: The right sinus (x) 

 (Figs. 11-16, x) in this larva or small adult had a lengih of 1.42 mm. 

 It began anteriorly as a blind sac, and upon following this series toward 

 the tail the right sinus (x) was found to receive the hsemal longi- 

 tudinal trunk .43 mm. and the lateral trunk .83 mm. caudad of its 

 origin. The left sinus (x) has about the same length as the right, but 

 is unlike it in that it is merely a continuation of the left hasmal trunk. 

 It receives the left lateral trunk .6 mm. and the dorsal trunk .28 mm. 

 cauded. The two sinuses (x) terminate in their respective caudal 

 sinuses, and in section (see Fig. 16, x) their walls are continued some 

 little distance into the caudal sinuses. Both sinus (x) and the dorsal 

 trunk are surrounded by a mass of connective tissue. They are com- 

 posed of a single layer of endothelium, and contain only a very few red 

 corpuscles. No leucocytes were observed. 



With the Selachians, Parker (op. cit.. p. 720), Sappey (op. cit., p. 

 38), and Mayer {op. cit., pp. 316-8, find a dorsal cutaneous vein or 

 lymphatic trunk extending from the head to the tail. Sappey states 

 with Squalus that it bifurcates anteriorly, each fork terniinating behind 

 the eye in the jugular vein. Parker describes the lateral cutaneous vein- 

 in Mustelus (p. 721) as anastomosing caudad with both the caudal and 

 the dorsal cutaneous vein; while Mayer portrays the vena dorsalis as 

 anastomosing caudad with the vena lateralis. Of these three writers, 

 Mayer gives us the most comprehensive description of the distribution 

 of the subcutaneous vessels in the dorsal fin. He sets forth the vena 

 dorsalis (pp. 333-4 and PL XVII, Fig. 17. v. d.) as separating into 

 two vencB circidares (Fig. 17, v, circ). which encircle the fin, collect 



