i8 7 



upon wave lengths. Thus, the keys of a piano when struck in 

 sequence give rise to a series of tones that differ one from 

 another much as the colors of the spectrum do, namely, in the 

 lengths of their waves. Although a trained eye cannot distin- 

 guish between white lights made by mixing different pairs of 

 colored lights, even the unpracticed ear can distinguish between 

 any pairs of tones when sounded on the keyboard, and, while 

 the person may not be able to name the keys, the actual dis- 

 crimination is easily accomplished. Thus white light is a meas- 

 ure of the deception due to our eyes, a deception that the ear 

 ordinarily never gives rise to. Could we see the colors in 

 ordinary light as we hear the tones in sound, the work of the 

 most extreme French colorists would be dull in comparison with 

 reality. The eye, therefore, fails to give much information 

 about light that is obtained from the ear about sound. 



The occurrence of well-developed organs of hearing only among 

 the insects and higher vertebrates suggests, since these animals 

 are air-inhabiting forms, that possibly the sense of hearing is 

 capable of development only in an organism surrounded by air. 

 To test this supposition one naturally turns to the nearest aquatic 

 relatives of the groups possessing this sense. With the insects 

 these relatives are probably the somewhat distantly related crus- 

 taceans, but with the vertebrates they are the fishes, a class 

 closely allied to the other members of the vertebrate group. If 

 the sense of hearing can originate only in air-inhabiting animals, 

 no traces of it should be found among fishes. If it can arise in 

 other situations, the fishes are probably the class in which its 

 beginnings in the vertebrate series are to be sought for. The 

 problem of hearing in fishes, therefore, is a general one dealing 

 with the possible origin of one of the most important senses of 

 vertebrates, a sense probably the most recently developed of all 

 and yet in many respects the most efficient. 



Hearing in fishes can best be approached from the standpoint 



composed of three parts, the external, the middle, and the inter- 

 known as the concha and a somewhat twisted tube leading 

 inward to the ear-drum. The middle ear is a cavity in the head 



