154 



THE AMERICAN XA TURA LIS T. XXXVIII. 



'* In inspiration the stream enters at the mouth in response to 

 a dilation of the oral cavity produced by the outward lateral 

 movement of the opercular frames. 



" At the same time water is prevented from entering at the 

 gill openings by the brancheostegal valves which although they 

 are attached to the opercular frames, move independently of and 

 contrary to them ; so that, while this outward movement of the 

 frames extends the gill openings, the brancheostegal valves close 

 them automatically by the action of the water which tries to 



" In inspiration the water is forced out of the gill openings by 

 a corresponding contraction of the oral cavity. At the same 

 time the water is prevented from regurgitating through the 

 mouth, not by the contraction of the latter, but by the automatic 

 operation of the maxillary and mandibular breathing valves which 

 move as accurately and efficiently as any of the heart's valves. 

 Caught on their posterior edges by the first movement of regur- 

 gitation, they snap together and completely prevent the 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 

 fishes' ability to get along without their services until they are 

 repaired." 



In examining about 70 species of fishes, the writer finds two 

 types of valves. These she has called the crescentic and the U- 

 shaped types. (Fig. i.) There is a 

 third form which may. however, be 

 considered as a modification of eithei 

 type and will be described later, 

 lives, c, crescentic; The crcsccutic type of valve IS 

 typically shown in the catfishes, 

 Silurid£c, particularly in Schilbcodcs 

 This type of valve, as its name indicates, is in the 

 rescent with tapering ends, and may be broad or 

 lat of Euponiotiis gibbosns is also of this type. 1 h«i 



