392 FISHES 



however, difficult to reconcile with the fact that many fishes 

 not only produce sounds but have special organs for its produc- 

 tion, and that in some cases the voice is limited to the males as 

 in the squeteague, Cynoscion regalis. These sounds are not of 

 the kind which the experimenters above-mentioned found to 

 be perceived by the skin. Accordingly G. H. Parker 

 carried out a further investigation of the subject in America. 

 He used an aquarium of which one end consisted of a deal board 

 and confined the fish under experiment in a small cage in the 

 middle of the aquarium, the side of the cage towards the sounding- 

 board being closed only by a fine net. Outside the sounding- 

 board was stretched a bass viol string giving forty vibrations per 

 second. The fish chiefly used for the experiments were speci- 

 mens of the kilifish, Fundulus heteroclitus, one of the marine 

 Cyprinodonts common on the east coast of the United 

 States. Comparisons were made between normal fishes, others 

 in which the auditory nerves had been divided, and others in 

 which these nerves were intact and the skin had been rendered 

 insensitive by division of the spinal cord. When the string was 

 set in vibration the fishes responded by movements of the 

 pectoral fins and by other movements. It was found that en- 

 tire fishes regularly responded to the sound, and also those in 

 which the sensibility of the skin was destroyed but the auditory 

 nerves were intact, while those in which the auditory nerves 

 had been destroyed gave no response. On the other hand, 

 Parker was unable to obtain any evidence of the perception of 

 true sounds in the smooth dog-fish, Mustelus cam's. Zenneck 

 in Germany found that three fresh- water species of fish, namely, 

 the roach, the dace, and the bleak, showed distinct evidence 

 of the perception of sound vibrations. At Parker's suggestion 

 Bigelow repeated the experiments on the gold-fish, on which 

 species Kredl had obtained only negative results. Bigelow used 

 as source of sound a tuning-fork vibrating one hundred times 

 per second and used great precautions to eliminate all other 

 shocks or disturbances in the experiments. He found that the 

 fish responded to the sound by characteristic movements, and 

 gave the same response even after the auditory nerve of one 

 side had been cut, but when both nerves were cut the responses 

 disappeared. 



In a large number of fishes the air-bladder has remarkable 



