IO2 ALLEN 



but distad of it. The latter is undoubtedly the principal trunk, 

 for it often receives the former, and it is collected above by either 

 the hyo-opercularis sinus or the cephalic trunk, and below by 

 the inferior jugular. Considerable variation, however, is shown 

 in both the dorsal and ventral endings, and as many deviations 

 are to be found on the opposite sides of the same specimen as 

 on the same sides of different specimens. Both the branchial 

 trunks and the branchial arch trunks are connected by a very 

 coarse network of capillaries, which are distinctly lymphatic in 

 the character of their meshes. Transverse sections through the 

 branchial trunk disclosed it to be full of red corpuscles, but at 

 no point was a definite peripheral connection between a nutrient 

 branchial artery established ; although at several places hypo- 

 thetical communications might occur. 



The distribution of these branchial canals is practically the 

 same for the first three arches ; hence a description of the first 

 arch of a 7o-pound Polyodon, as shown by Fig. 17 will answer 

 for all. As stated above the main branchial lymphatic trunk 

 (nutrient branchial vein f) (Br.L. T.) travels in the connective 

 tissue, midway between the two rows of filaments, parallel with, 

 but distad of, the efferent branchial artery. For every pair of 

 branchial filaments, a rather large filament lymphatic trtmk 

 (nutrient vein?) (Figs. 17, 18, 19, and 27, Fil.L.T.) is re- 

 ceived from the connecting tissue lying between the two rows 

 of filaments. A cross-section through these filaments (Fig. 

 27) reveals the fact that these branches do not lie opposite each 

 pair of filaments as the two corresponding afferent filament 

 arteries do (Figs. 17 and 27, A.Ftl.A.}, but rather about 

 midway in the space separating one pair of filaments from the 

 next, and Fig. 27 represents each of these filament vessels as 

 being about equidistant from four afferent filament arteries. 

 Numerous transverse filament lymphatic vessels (nutrient veins f) 

 (Figs. 18 and 19, Tr.F.L. V.) entwine in various ways with the 

 roots from which the corresponding afferent filament transverse 

 arteries (Fig. 18, A.F.Tr.A.) take their origin, and form a very 

 coarse plexus-like network between them. These vessels col- 

 lect a very rich network from the outer surface of the filament 

 (Fig. 19, T^'/.Z.TV^.), which in the region of the respiratory septa 



