PLATE X. 



Fig. iS. Microscopic preparation of an injected branchial filament of a 70- 

 pound Polyodon as seen from above. The respiratory filament vessels are 

 stippled and the lymphatic network (nutrient filament veins.'), which are shown 

 only in part, are drawn in outline. X SO- Reduced \. 



Fig. i8a. A portion of the filament respiratory network. X450' Reduced^. 



Fig. 19. Dorsal view of the lymphatic (nutrient venous.'') network of a 70- 

 pound Polyodon. This network is superficial to the septa that contains the res- 

 piratory network, and for the most part the transverse vessels run parallel to the 

 spaces separating the respiratory septa. Its meshes are more irregular and very 

 much coarser (compare with Fig. 18). A longitudinal filament lymphatic 

 trunk (nutrient filament vein.') receives the network from the two opposite fila- 

 ments. X50- Reduced f, 



144 



