210 THE SWIM-BLADDER OF FISHES 



large pharyngeal teeth. "While moving its grinders as I supposed 

 the fish had done during life," said Dr. Hamilton, "... an 

 exact imitation of the croaking of the perch was produced. I 

 produced tlie sounds in a similar manner within the hearing of 

 several Alleghany River raftsmen and Ohio River fishermen at 

 intervals during the day on which I experimented, without 

 allowing them to know how the noises were made, or that a 

 perch was used for the purpose and they all declared it w^as an 

 exact imitation of the croaking of the perch. ... I cannot 

 conceive of any way by which the sound could be produced by 

 the air-bladder of the fish, as its physiological functions and 

 anatomical structure do not indicate its use as a vocal organ." 

 Dufosse (No. 7) attributed to the extrinsic muscles vibrations 

 which produced sounds aided by the resonance of the swim- 

 bladder ; but in other cases he attributed the sound simply to 

 gas violently driven through the pneumatic duct of the organ. 

 The late Professor J. A. Rj^der combatted this view which had 

 been urged to account for the noise produced by Aiilodinotii8 : 

 " the usual view that the air is forced from one part of the air- 

 bladder to another in the Sciaenoids seems to me inadequate in 

 the absence of clearly worked out demonstrations. The group 

 is physoclistous, or has the air-bladder entirely closed " (see 

 note on p. 63, No. 9 a). Sorensen (No. 22) regards the organ 

 as a resounding device, and thinks that it would have disap- 

 peared had it not so functioned. Yet the fact remains that 

 most fishes are silent, and fish such as the cod and carp have 

 never been credited with any gifts of voice, notwithstanding 

 the size and high development in these fishes of the swim- 

 bladder. The vastly greater number of fishes, w^hich possess 

 the swim-bladder, more or less highly developed, produce no 

 sounds. They are silent and the organ occupying s > large 

 a space in the super-abdominal space is unutilised for that 

 purpose. It is also remarkable in the extreme that some of the 

 most active and buoyant fishes should be without this organ 

 (e. g. the sharks and the family Scombridaj, or Mackerels, for 



