fSubcutaneous Vessels iu Tail of Lepisosteus 71 



and ventrad to anastomose with the dorsal and ventral trunks as in 

 ScorpcBnichtliys and in other fishes, but this point was not determined 

 for a certainty in Lepisosteus. Instead of emptying directly into the 

 caudal sinus as in Amiatus the lateral trunk in Lepisosteus unites with 

 a haemal trunk in forming sinus (x), which terminates in the caudal 

 sinus. In a 90 mm. L. osseus series a connecting canal Avas found 

 joining the right lateral trunk with the right haemal trunk. This com- 

 munication was in advance of the union of the lateral with the haemal 

 in forming sinus (x). It was not observed on the opposite side of this 

 series or in any of the dissections. 



Two longitudinal hsemal trunks were found above the caudal vein on 

 either side of the caudal artery in the hgemal canal of Lepisosteus. 

 They are undoulitedly homologous to what Mayer has described in the 

 Selachians as vasa vasorum and to a similar trunk in the hgemal canal 

 of the Teleosts. The cephalic distribution of this trunk was not traced 

 out. No hgemal vessels were found connecting it with the ventral trunk 

 as in the Teleosts, and, as stated above, it emptied into sinus (x). 



In Lepisosteus no longitudinal neural trunk was found in the neural 

 canal, as is the case with many Teleosts, and consequently there are no 

 neural vessels to communicate above with the dorsal trunk. 



Microscopic sections of a 90 mm. L. osseus showed the subcutaneous 

 trunks, the caudal sinus and the caudal vein to be composed of a single 

 layer of endothelium, surrounded by a mass of connective tissue. They 

 contained but few corpuscles, the red predominating over the white. 



No valves were found in the subcutaneous system of the tail region 

 of Lepisosteus. save two semi-lunar valves guarding the entrance of 

 each caudal sinus into the caudal vein. 



Resume. — From the above summary the subcutaneous system of 

 Lepisosteus should fall under the head of a lymphatic system, or a 

 separate subcutaneous venous system that has no counterpart in the 

 arterial system and which may function both for veins and lymphatics. 



In favor of the hypothesis that this system in the tail region of 

 Lepisosteus are veins, we find from microscopic sections of a 90 mm. 

 L. osseus that the structure of the subcutaneous vessels and the caudal 

 vein are almost identical, and while they contain but few corpuscles, 

 yet the red predominate. 



As opposed to this supposition and in favor of the hypothesis that 

 they are lymphatics, this study has revealed the subcutaneous system of 

 the tail region of Lepisosteus to be entirely separate from the blood- 



