124 DAHLGREN. 



which move as accurately and efficiently as any of the heart's 

 valves. Caught on their posterior edges by the first movement 

 of regurgitation, they snap together and completely prevent 

 any water from leaving the oral cavity by the mouth which, 

 meanwhile, is left partly open, almost as much open as during 

 inspiration. 



That these valves are of value as breathing organs is evident 

 upon casual observation; that they are of much importance is 

 shown by the compensatory action brought about by injury; 

 that they are not of immediate vital importance is proved by 

 the fish's ability to get along without their services until they 

 are repaired. 



