THE SENSE OF HEARING IN FISHES. 85 



affairs does not militate against the use of this class of sounds as 

 stimuli for the ear. It is, therefore, entirely appropriate to use such 

 sounds in testing hearing in fishes, but the experimenter must show 

 beyond a doubt that they do stimulate the ear, otherwise evidence 

 derived from such tests fails to touch the problem. The test for 

 hearing in fishes is the proved presence of a response mediated by 

 the ear and dependent upon some vibratory physical disturbance in 

 the water which disturbance may vary from the extreme regularity 

 of a pure tone to the extreme irregularity of a noise such as the 

 report of a gun or other like explosion. 



In discussing hearing in fishes, Lang (1903, pp. 44, 48) ex- 

 pressed the opinion that these animals probably possess through the 

 ear a sense of trembling (Erschiitterung, Erzitterung) rather than 

 one of true hearing and that this sense of trembling is a forerunner 

 of hearing. In distinguishing the sense of trembling from that of 

 hearing he states that in the former the pressure waves are per- 

 ceived as a series of more or less distinct and separate entitles, 

 whereas in hearing the impression is more homogeneous. This 

 distinction is one that pertains to sensation and, therefore, it can 

 hardly be made the basis of experimental tests in fishes. It, more- 

 over, implies that we cannot be said to hear sound vibrations whose 

 note is so low that the single beats fail to fuse. But that we hear 

 these beats as well as we do tones is beyond dispute and Lang's dis- 

 tinction, therefore, is in reality without support. Something of the 

 same view has been expressed by Bernoulli (1910, p. 639) who, 

 however, assumes the receptor for such beats to be the skin not 

 the ear. 



Lang (1903, p. 48) and a few other workers have also intimated 

 that hearing is a process that probably cannot be carried out in 

 water, but is necessarily associated in some way with the air. A 

 little thought, however, will show that this position is quite unten- 

 able, for watery fluids bathe the end organs of the internal ears of 

 all vertebrates whether they be inhabitants of the air or of the 

 water. If fishes hear, sounds normally reach their ears much more 

 simply and directly than in the case of air-inhabiting forms, for 

 such disturbances pass at once through fishes' bodies and require no 



PROC. AMER. PHIL. SOC, VOL. LVII, G, JUNE I4, I918. 



