ORAL BREATHING VALVES OF TELEOSTS, 

 THEIR MODIFICATIONS AND RELATION 

 TO THE SHAPE OF THE MOUTH. 



EVELYN GROESBEECK MITCHELL. 



Although the oral breathing valves of teleost fishes are very 

 prominent and their function important, they have, strangely 

 enough, been almost wholly neglected. Owen ('66), suggests 

 that they " seem intended to prevent the reflux of the respiratory 

 stream." MacuUum ('84) mentions them in his article on Ami- 

 urus but ascribes to them no function. Stannius ('39) has 

 described them, as has also Cuvier ('36) who suggests that they 

 not only prevent the reflux of water but the escape of food. 

 Galton ('71), describes the valves and their workmg m detail, 

 much as Dahlgren ('98) did later. Howes ('83), refers to them 

 in the trout, explaining their function. ^ 



In 1898 Dahlgren, who knew nothing of Galton's article, 

 took up the subject in detail and describes the valves m the sun- 

 fish, Eupomotus gibbosus. The valves are sheets of membrane 

 composed of elastic connective tissue covered with a mucous 

 membrane continuous with that lining the mouth. 1 hey are sit- 

 uated in the oral cavity just caudad of the maxillary and mandib- 

 ular teeth. In this species of sunfish there is a mec lan muscu a 

 thickening. The valves "are placed with their ^^'-^'^ ^^.^^ 

 downward and backward at an angle of less '''^^^^^ 

 degrees to the axis of the body. This angle is . 

 about eighty degrees when the valves are struck by the ic-u ^ 



ThVf^rcZ^Tte lral valves is to aid in the act of breathmg, 

 which has hitherto been described as ''a kind of ^w^"---^;^ 



Dahlgren says, ''The respiratory stream enters the oral caMt> 

 by the mouth and leaves by the two gill openings 



