No. 435.] SENSE OF HEARING IN FISHES. 



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experiments with the bass viol string the earless fishes responded 

 eighteen times in the hundred trials. I believe that the tuning 

 fork experiments, in which no earless fishes responded, make it 

 probable that these eighteen responses were due not to the 

 stimulating effect of sound on the skin of the fishes, as might 

 be inferred, but to some other cause such as the trembling of 

 the whole aquarium. I do not wish to imply, however, that the 

 skin of a fish may not he stimulated bv sound. 



Although the conclusion that a fish hears is directly contrary 

 to that arrived at by Lee, it is not at all necessary to suppose 

 that the observations of this investigator and those of Kreidl 

 should be regarded as incorrect. Neither Kreidl nor Lee 

 worked on the killifish and the ears in this species may be dif- 

 ferent from those in the fishes studied by these two investigators. 

 In fact, in my own work I tried on the smooth dogfish (Mustelus 

 canis) the same experiments as those that I have just described 

 for the killifish, but without obtaining the least evidence of hear- 

 ing in this species. I am, therefore, quite prepared to believe 

 that there are fishes in which the sense of hearing is undeveloped, 

 and these may have been the very forms with which Kreidl and 

 Lee worked ; but that there are fishes that do hear I feel per- 

 fectly certain. 



The ear is related to other sense organs in a way unusually 

 well seen in fishes, and before closing I wish to call attention 

 briefly to this aspect of the subject. The sense organs con- 

 cerned are the skin and the lateral-line organs. Kveryone is 

 familiar with the skin as an organ of touch, but the lateral-line 

 organs are less generally known for at least one obvious reason, 

 namely, that man possesses none. Lateral-line organs occur 

 only in the true aquatic vertebrates, the fishes and the amphib- 

 ians, and in the latter only in those stages in which the animals 

 inhabit the water. Thus in the frog, lateral-line organs are pres- 

 ent while this amphibian is a tadpole, but, as soon as it takes 

 on the adult form and emerges from the water, these organs 



associated with the water habit. 



These organs form regular lines on the skin of an amphibian 

 or a fish, though in the latter they are more frequently in grooves 



