Sensory Discrimination: Hearing 127 



vowel sounds sung on notes ranging from C% to Ge, trans- 

 mitted through rubber tubes, the tests being made on eight 

 species. On the other hand, Bigelow found that the gold- 

 fish on which he experimented were sensitive in their 

 normal condition, but insensitive when the auditory nerves 

 were cut, and thinks that Kreidl's operation did not remove 

 the whole of the fish's ear (54) . Triplett thought both perch 

 and goldfish were excited by the sound of whistling, which 

 usually preceded their being fed (720). Parker tested the 

 killifish, a species of minnow, using the sustained slow vibra- 

 tions (40 complete swings per second) of a bass viol string 

 placed on one side of the aquarium as a sounding board. The 

 fish cage was suspended in the aquafium from an indepen- 

 dent support. Normal fish responded to the vibrations, 

 usually by movements of the fin, 96 per cent, of the time. 

 Fish in which the nerves to the ears had been cut responded 

 in 1 8 per cent, of the tests ; those in which the skin had been 

 made insensitive, but the ears left, in 94 per cent. Since 

 causing the string to vibrate jarred the whole aquarium 

 somewhat, these experiments were checked by others where 

 the stimulus was produced by placing the stem of a vibrat- 

 ing tuning fork against the sounding board. The results 

 were the same as in the first set of tests. Parker concludes 

 that the ears of the minnow are certainly organs for the 

 reception of sound ; but as he obtained no such reactions 

 from dogfish, he is inclined to think that different species 

 var y (535? 536). In later experiments (544) on the dogfish, 

 Parker finds that individuals with the " auditory " or eighth 

 nerve cut show diminished sensitiveness to the blow of a 

 pendulum, the force of whose impact on the walls of the 

 aquarium could be measured, while cutting the optic nerve 

 or cocainizing the skin has no effect on the responses to 

 these stimuli: his conclusion is that the reactions are 



