THE HEART AND ARTERIES OF POLYODON 



433 



A B 



Fig. 14 Ventral (A) and dorsal (B) views of the ventricle showing distribu- 

 tion of the coronary artery. Branches with cut ends supply the investing lym- 

 phoid tissue. 



bution it is extremely variable. Figure 14 is from sketches of the 

 dorsal and ventral aspects of a typical ventricle. To bring the 

 arteries into view the surrounding lymphoid masses were removed. 

 Vessels represented with cut ends went to supply these structures. 

 The question as to the homology of the 'coronary artery' 

 in Polyodon is not easily disposed of. The morphological impor- 

 tance of it depends on the value that maybe attached to such 

 structures as units. The vessels of fishes are variable to a marked 

 degree and it does not seem difficult for new channels to be 

 established nor is it surprising to find related forms more or less 

 divergent in the matter of the distribution of minor arteries. 

 Carazzi (op cit.) states that in working with a single form (Scyli- 

 lium) he finds in various individuals the arrangements described 

 for different species and even different genera. He seems to 

 be inclined to emphasize the functional rather than the mor- 

 phological significance of the different plans. How far the 

 divergent arteries of Polyodon are new developments or to what 

 extent they are direct modifications of a more primitive condi- 

 tion cannot be judged with any assurance till their embryology 

 is known. 



