368 Grant Sherman Hopkhis 



fishes, among which are the absence of lymphatic glands and 

 the incomplete development or entire absence of valves within 

 the lymphatic vessels. According to Robin (17) Monro was 

 the first anatomist to investigate the lymphatic system of 

 selachians. Bnt many of his statements are incorrect as in 

 several instances he mistook veins for lymphatics. It was 

 a mistake of this kind that led him to believe that the 

 lymphatic vessels commenced by free extremities provided 

 with small orifices. He saw the injected material ooze out 

 upon the surface of the skin and enteric mucosa without ex- 

 travasation into the underlying connective tissue and con- 

 cluded that they commenced by these free openings. The 

 general arrangement of the large lymphatic vessels in fishes, 

 as given by Milne-Edwards (12) corresponds with the state- 

 ments of most anatomists who have written upon this subject. 

 He divides the system into two portions, one belonging to the 

 abdominal viscera, the other to the skin, muscles and 

 neighboring parts. Concerning the latter he says, " the sub- 

 cutaneous lymphatic system constitutes, in general, three 

 principal trunks which have a longitudinal direction, and 

 which are situated, one on the ventri-meson, the two others 

 on the sides, in the groove which separates the muscular 

 masses of the dorsal and ventral portions of the body, and 

 which can be recognized, externally, because it corresponds 

 in position to the lateral line. This system of vessels receives 

 a multitude of secondary branches which ramify under the 

 skin, and it opens into the veins at its two extremities, i. e., 

 near the base of the cranium and at the base of the caudal 

 fin. " At the caudal end each laterallymph vessel terminates 

 in a sinus ; these sinuses communicate not only with the 

 caudal vein but with each other as well. 



The investigations of Hyrtl (9) upon the cephalic and cau- 

 dal sinuses of fishes, and the lateral vessels with which they 

 are connected, led him to the conclusion that these vessels 

 formed no part ot the blood- vascular system but were lym- 

 phatics. He examined the fluid of the caudal sinus and 

 found it " clear as water, having the same properties as the 

 liquid contained in the lymphatic vessels of other parts of the 

 body." 



