PLATE XL 



FIG. 20. A portion of the outer surface of a branchial arch of a yo-pound 

 Polyodon at the base of two filaments. The main efferent branchial artery, 

 which lies directly below the efferent filament arteries is not figured. The 

 efferent filament and the nutrient arteries are stippled ; while the branchial and 

 filament lymphatics (nutrient veins?) are drawn in outline. X 5- Reduced \. 



FIG. 21. Like Fig. 19, a dorsal view of the same filament taken nearer the 

 basal end of the filament. Introduced to show the character of the so-called 

 lymphatic network on the outer edge of the filament. X 5- Reduced \. 



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