108 ALLEN 



between these so-called lymphatics and the nutrient arteries, 

 one might claim that these branchial lymphatics are nutrient 

 veins, which receive a network decidedly lymphatic in charac- 

 ter, that is continuous from the great trunk passing through the 

 gills to the main trunk of the branchial arch, and which may 

 function both for a venous and a lymphatic system, terminating 

 above in a lymphatic trunk and below in a vein. 



Possibly it should be noted here that the fourth or last 

 branchial arch has but one row of filaments, and is therefore a 

 hemibranch. Except for some variation in connection with the 

 efferent branchial artery, which will doubtless be fully noted in 

 a forthcoming paper, by Mr. E. P. Allis on the blood vessels of 

 Polyodon, the lymphatics and the blood-vascular systems of the 

 fourth arch correspond very closely to a hemibranch of one of 

 the other arches. 



Dorsal and Ventral Endings of the Branchial Lymphatic 

 Trunks (Nutrient Branchial Veins?). Great variation is 

 shown not only in the dorsal and ventral terminations of these 

 trunks in different specimens, but also on the opposite sides of the 

 same specimen. In tracing out the culmination of these vessels 

 I found it frequently useful to insert a canula into one of these 

 trunks and force water with the aid of a syringe into the trunk ; 

 and having previously removed a portion of the sinus or trunk 

 into which it is discharged, note the orifice through which the 

 water was ejected. 



Fig. i shows the dorsal endings of the branchial lymphatic 

 trunks, as seen from the left side of a 7o-pound Polyodon, and 

 Figs. 2 and 3 represent the dorsal mode of termination of these 

 trunks on the opposite sides of a 25-pound Polyodon. In every 

 case \htfirst branchial lymphatic trunk (Br.L. T^i)) bifurcates 

 when about to leave the arch. In Fig. i the ventral fork 

 (Br.L,. T.(i')) continues cephalad in about the same plane until 

 the hyo-opercularis sinus is reached, when it bends dorsad to 

 follow along the mesal surface of the hyo-opercularis sinus for 

 a short distance, and immediately after receiving the dorsal 

 fork (Br.L. T.(i")) 9 the combined trunk opens into the hyo- 

 opercularis sinus through the inner wall (Br.L. T.(i)O.). With 

 the specimen from which Figs. 2 and 3 were drawn, both of 



