THE SENSE OF HEARING IN FISHES. 81 



fishes with skin and lateral-line organs intact but ears eliminated : 

 fourth, fishes with only skin intact; fifth, fishes with only lateral- 

 line organs and ears intact ; sixth, fishes with only ears intact ; 

 seventh, fishes with only lateral-line organs intact; and eighth and 

 last, fishes with none of the three sets of sense organs intact. 



The fishes were tested in an aquarium of glass and stone, measur- 

 ing 75 cm. by 35 cm. by 40 cm. This was supported on an in- 

 flated bicycle tire that rested on a table each leg of which pressed 

 on a mass of excelsior wood chippings spread on a tile which in turn 

 had under it a pad of rubber i.S cm. thick. The whole apparatus 

 was set up on the concrete floor of a basement room in the labora- 

 tory and proved to be remarkably free from extraneous vibrations. 



Of the several kinds of sounds to which the fishes were sub- 

 jected, that from a watchman's whistle^ blown vigorously in the 

 air gave most striking results. Of the four classes of fishes in 

 which the ears were intact all responded with clearness and cer- 

 tainty by swimming at once from the upper surface of the water 

 into deeper positions in the aquarium. Those in which the eighth 

 nerve had been cut did not respond at all to the whistle, though they 

 responded to other stimuli, such as currents of water, water dropped 

 on the surface of that in the aquarium, and pendulum strokes on 

 the wall of the aquarium. Incidentally it may be mentioned that the 

 currents of water and the drops of water proved to be stimuli for 

 the skin only, but that the strokes of the pendulum affected not only 

 the skin but also the ear (compare Table I., Parker and Van Heusen, 

 1917, p. 472). 



Another means of stimulating Aminrns consisted in a series of 

 tones from a telephone submerged in the water of the aquarium. 

 This telephone was enveloped in a tightly stretched thin rubber bag. 

 By means of a piece of apparatus consisting of a series of seven 

 alternating-current generators with their armatures on a common 

 shaft driven by a ten-horse-power electric motor, currents of 43, 

 86, 172, 344, 688, 1,376, and 2,752 cycles per second were produced. 

 By appropriate switches any one of these could be thrown into the 



2 The sound produced by this whistle consisted of at least two elements : 

 a low vibration probably due to the rapid oscillation of the small ball con- 

 tained in the whistle, and a shrill piping note. 



