DISTRIBUTION OF SUBCUTANEOUS VESSELS IN GANOIDS 93 



lymphatic heart was found in the tail of Anguilla^ but its con- 

 nections with the lymphatic system were not made clear. A 

 specimen of Anguilla was said to have lived several days in an 

 aquarium after its tail had been cut off, without seeming to 

 suffer from the operation. 



From what we know of the development of the lymphatics in 

 mammals * it would not be surprising to find in the embryos of 

 the lower forms, if not in the adults also, even closer relation- 

 ships between these two systems. For example, it might be 

 possible to find a vessel that functioned both as a vein and a 

 lymphatic trunk, and, again, an homologous vessel or system 

 of vessels might exist, which functioned as veins in the more 

 generalized forms, but which had their exact counterpart in 

 lymphatic canals in the higher or more specialized forms. It 

 is very evident from the above discussion that the last word has 

 not been said on this subject. What is most needed is not more 

 generalizations, but more anatomical and embryological data on 

 many different groups, and especially in the Cyclosomes. It is 

 not therefore my intention to make what might be considered 

 a dogmatic statement as to whether these subcutaneous vessels 

 in the Ganoids are veins or lymphatics. The chief aim will be to 

 give an accurate description of the distribution of these vessels. 

 They will, however, be described as lymphatics because the 

 balance of evidence (such as size and arrangement of capillaries, 

 and the fact that except in the branchial region the main ducts 

 in the head region always accompany venous trunks), seems 

 to warrant thjs view. Yet, on the contrary, it must be admitted 

 that if these vessels are termed lymphatics in the branchial region 

 no corresponding nutrient branchial veins were found ; further, 



!In an especially interesting paper Miss. Sabin (27) found a stage in the 

 embryo pig that about corresponded with the lymphatic system of the adult frog. 

 Here there were two cervical hearts or sacs that received the lymph from the neck 

 region and emptied into the cardinal vein at its junction with the subclavian, the 

 opening being guarded by a valve. Similar posterior hearts were found to dis- 

 charge themselves in the common vein formed by the union of the sciatic with 

 the femoral, and their orifices were likewise said to be protected by valves. It 

 was not until considerable later that the thoracic duct and the right lymphatic 

 duct were formed from the anterior heart. To begin with, the lymphatic system 

 of the pig is said to have its origin from two blind ducts that arise from the car- 

 dinal at its junction with the subclavian. 



