Il8 DAHLGREN. [Vol.11. 



of the respiratory stream rather than the escape of food from 

 the mouth." 



Gunther ^ makes no mention of the organs in question, and 

 states that "the water used by fishes for respiration is received 

 by the mouth and by an action similar to that of swallowing is 

 driven to the gills and expelled by the gill openings." I have 

 found several differences between the acts of swallowing" and of 

 breathing in the teleost fishes. 



Wiedersheira ^ states that " fishes breathe by taking in water 

 through the mouth and, by the contraction of the latter, forcing 

 it out again through the gill slits." 



The use of the word " through " in the above quotation leads 

 me to infer that the mouth opening is meant, and not the oral 

 cavity. 



A. B. Macallum ^ has mentioned these structures in his 

 article on the " Anatomy of Amiurus," where he says: " Behind 

 the pads of teeth and running concentrically with them are 

 folds, one above and one below, arising from a relaxation of the 

 lining membrane; that behind the maxillae is largest, but both 

 may be absent. In one specimen of AmijiriLS nigricans the 

 fold reached downward and backward into the cavity of the 

 mouth fully one-half inch." No mention of the function of these 

 folds of membrane is made. 



These valves have been observed in operation by the writer 

 in over fifty species of fresh-water and marine fishes, and no 

 teleost has been found which does not possess them. Since no 

 accurate description of them and of their function has become 

 part of our recent manuals or text-books, and since, on the 

 other hand, for want of such knowledge it has been impossible 

 to clearly describe the act of breathing in fishes, I take this 

 opportunity of calling attention to these valves and of demon- 

 strating their value as organs of breathing. 



These valves will first be described as they appear in the 

 common sunfish, Enpomotis gibbosns (Linn.). (See Fig. i.) 



1 Gunther, Introduction to Study of Fishes, p. 136. Edinburgh. 1880. 



2 W^iedersheim (translated by W. N. Parker), Comparative Anatomy of Verte- 

 brates, p. 278. London. 1896. 



^ Proc. of Canadian Inst., N.S., vol. ii. No. 3, p. 387. Toronto. 



