122 ALLEN 



With the Ganoids, especially in the branchial region, it is a 

 very difficult proposition to determine whether these subcutan- 

 eous vessels are lymphatics or veins or a common system that 

 may function for both. For the present, until after the embry- 

 ology has been studied, and this system has been worked out in 

 the Cyclostomes, it has seemed best to leave it as an open ques- 

 tion. These vessels have, however, in this paper been described 

 as lymphatics for the following reasons : In every part of the 

 head, excepting the branchial region, each of the main subcu- 

 taneous canals is accompanied by a corresponding artery and 

 vein, and frequently the arterial and venous branches are sur- 

 rounded on either side by branches of these subcutaneous ves- 

 sels. They receive a superficial network, which is distinctly 

 lymphatic in the character of its meshes, and which is often 

 continuous with another subcutaneous canal of the same class, 

 and never to my knowledge with a corresponding arterial trunk. 

 Excepting the branchial trunks, as far as could be ascertained, 

 all of the subcutaneous canals contain a predominance of 

 white corpuscles ; although in some of the trunks they may be 

 very scarce. If the longitudinal subcutaneous canals of the 

 trunk were considered as veins it would be necessary to treat 

 them as a separate venous system, that had no counterpart in 

 the arterial system. As in the Teleosts the principal arterial 

 trunks of this region are the aorta and the caudal artery which 

 are accompanied by the cardinal and caudal veins. From these 

 vessels are given off or received the neural, heemal, and the 

 lateral branches, which extend to the skin and fins to supply or 

 collect the blood from the region drained by the superficial 

 longitudinal trunks. 



So far as could be determined in the branchial region of the 

 Ganoids there is a nutrient branchial arterial system, but no nu- 

 trient venous system was observed unless the so-called branchial 

 lymphatic system functions for both veins and lymphatics. In 

 Lepisosteiis each arch had a dorsal and ventral branchial trunk, 

 the latter terminating below in the inferior jugular and the 

 former in a branchial sinus, which was in connection with the 

 cephalic and pericardial sinuses. With Polyodon but one 

 branchial lymphatic trunk travels between the branchial fila- 



