PRODUCTION OF SOUND 407 



sound is a single short grunt which may be repeated but is not 

 a continuous sound. In these fishes it was shown that the 

 sound is produced by intrinsic muscles in the wall of the air- 

 bladder, and a grunt is caused by a single contraction of these 

 muscles ; it can be called forth by electric stimulation even in a 

 bladder which has been taken out of the fish. The sound was 

 not produced when the bladder was deflated, but returned when 

 a rubber bladder was put inside the natural one so that the 

 diaphragm is not necessary. In Opsanus tan, the common 

 toad-fish of the American coast, the mechanism was the same 

 as in the gurnards (Triglidae). 



The bladder functions as a vocal organ not only in marine but 

 in many fresh-water fishes, for instance in several South Ameri- 

 can cat-fishes (Silurida;) and Characinida;. The blind fish of 

 the Mammoth Cave of Kentucky is not also dumb but calls its 

 mates and companions by sounds, and the same power is pos- 

 sessed by Lucifuga, the blind fish of the subterranean waters of 

 Cuba, although the former species has an open air-bladder and 

 is allied to the Cyprinodonts, while the latter has a closed bladder 

 and is allied to the Blennies. 



In Doras and several other genera of South American cat- 

 fishes there is a special adaptation for the production of sound 

 consisting of an elastic spring mechanism by which the wall of 

 the bladder is thrown into vibration. The springs are formed of 

 the elongated transverse processes of the fourth vertebra, the 

 ends of which are expanded and attached to the wall of the air- 

 bladder. Two powerful muscles pass from the skull to the 

 springs, and the contractions of these muscles causes the springs 

 and with them the walls of the bladder to vibrate rapidly and 

 produce a sound. 



In some fishes sounds are produced by the movement of air 

 through the mouth or through the opening of the air-bladder, 

 but it is not proved that such sounds are naturally emitted by 

 the fish in its normal life. The conger is said by the fishermen 

 to bark like a dog when it is caught, but this seems to be merely 

 an exaggerated description of gurgling sounds certainly pro- 

 duced by the fish in its struggles to escape. The carp is said 

 to produce a sound in the same manner. 



It is curious to notice that the voice of fishes in the cases 

 we have mentioned is not produced by vibrations of solid parts 



