No. 3] VALVES OF TELEOST FISHES. 121 



A number of young black bass, Micropteriis salmoidcs (Lac), 

 were carefully kept in aquaria with running water, and when 

 they had become perfectly tame, in some weeks' time, observa- 

 tions were made on the rate and manner of breathing, with 

 particular reference to the valves under consideration. 



Each breath requires two acts : one of inspiration and one 

 of expiration. During inspiration the oral cavity is enlarged 

 by moving the opercular frames outward, thus requiring an 

 incoming stream of water to fill the extra space produced. 

 This stream enters the oral cavity at the mouth, which at the 

 beginning of inspiration is open about one-fourth of its normal 

 maximum extent. During inspiration the mouth is opened 

 about ten per cent more, this motion being due only to the 

 connection of the jaws with the opercular frames. 



The mandibular and maxillary breathing valves are flattened 

 back against the top and bottom of the oral cavity by the 

 entrance of this stream of water. Meanwhile water would 

 enter at the gill openings, which are widening, was it not 

 for the branchiostegal membranes which, although they are 

 attached to the opercular frames, move independently of and 

 contrary to them, closing the entrance automatically by the 

 action of the water that tries to enter. (See Fig. 3.) 



The opposite act of expiration now takes place, the opercular 

 frames moving inward to reduce the space in the oral cavity. 

 The water tries to leave at the mouth, but catching on the 

 edges of the breathing valves and then striking their posterior 

 surfaces it forces them up into such a position that their edges 

 meet and all further progress is stopped. The water then leaves 

 at the gill openings. 



During expiration the mouth is slightly shut, both this and 

 its opening during inspiration being unavoidably due to the 

 attachment of the jaws to the opercular frames, and not to an 

 effort to retain or let out the water. 



One fish of this lot was six and one-half inches long. When 

 at rest and free from recent excitement, the number of breaths 

 each minute was forty, with the temperature of the water at 

 10^ ° Centigrade. 



This rate was very constant, and the half-yawns which the 



