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DAHLGREN. 



[Vol. II. 



fish occasionally gave did not disturb the rate because they also 

 occurred at regular intervals. The fish was taken out in a 

 scoop-net and held gently in a wet cloth while both valves were 



Fig. 3. — Diagrammatic representation of the pump-like structure of the teleost oral cavity. The 

 anterior portion of each figure is represented in longitudinal verti(.al section, the posterior 

 portion in longitudinal horizontal section. A , inspiration ; A, expiration. Arrows represent 

 water pressures ; double arrows represent motions of opercular frames, a, branchiostegal 

 valves ; b, maxillary and mandibular breathing valves. 



cut in their median line from edge to line of attachment, thus 

 practically destroying their usefulness as valves. When returned 

 to the water the fish darted about, but soon settled down and 



