EXPERIMENTS ON HEARING. 103 



From the evidence at hand it is very probable that some fishes hear and that 

 others do not. The following experiments have been made on the blind fish 

 Amblyopsis spelaus. Various opinions have been expressed about the hearing of this 

 fish. 



Wyman states: 



It is said that the blind fishes are acutely sensitive to sounds as well as to undulations produced 

 by other causes in the water. In the only instance in which I have dissected the organ of hearing 

 (which I believe has not before been noticed), all its parts were largely developed. 



The following words of Professor Cope are frequently quoted : 



If these Amblyopsis be not alarmed, they come to the surface to feed and swim in full sight, 

 like white, aquatic ghosts. They are then easily taken by the hand or net, if perfect silence is pre- 

 served, for they are unconscious of the presence of an enemy except through the medium of hearing. 

 This sense is, however, evidently very acute; at any noise they turn suddenly downward and hide 

 beneath stones, etc., on the bottom. 



Subsequent writers have generally disagreed with Cope. Dr. Sloan (in Packard, 

 1884) wrote: 



I tested their hearing by hallooing, clapping my hands, and striking my tin bucket when they 

 were in easy reach and near the surface. In no instance did they change their course or notice the 

 sound. 



Miss Hoppin (Garman) failed to get any response from Troglichthys as long 

 as noises only were resorted to. She says: 



I may scream or strike metal bodies together over him, as near as possible, yet he seems to take 

 no notice whatever. 



Blatchley states that noises do not attract them. 



Eigenmann's observations (Proc. Brit. Ass. A. Science, Toronto Meeting) on 

 Amblyopsis confirm those of Miss Hoppin on Troglichthys. No ordinary noises 

 produced had any effect on Amblyopsis. Whistles, tuning-forks, clapping of hands, 

 shouting in the reverberating caves, were alike disregarded. 



Amblyopsis, since it is blind, does not require precautionary methods to exclude 

 sight as a possible disturbing element. 



If there are sounds in the water of the caves that concern the blind fishes and 

 the ears are sound-perceiving organs, we might expect the ear to be better de- 

 veloped along with the tactile organs as a compensation for the loss of sight. But 

 if there are no sounds, we might expect them to degenerate along with the eye 

 unless the function is something else than sound perception. Amblyopsis has few, 

 if any, enemies in the caves. There are certainly none that make sounds, so the 

 ears of the fishes would not be kept on the alert for them. There is less variety 

 of sounds in the air of the caves than on the outside. This may make but little 

 difference, as sound generated in the air does not penetrate readily into the water. 

 Rippling of the water is certainly perceived more readily by the tactile organs than 

 b/the ear. Besides, the fishes are confined to the quiet pools. 



My methods of experimenting were practically the same as those of Parker 

 and Bigelow. I used a heavy slate-bottomed aquarium, 24 inches long, 14.5 

 inches high, and 12.5 inches wide. I removed the glass from one end and substi- 

 tuted a board 2 inches thick. This served as a sounding board. The fishes were 

 confined in a smaller aquarium (4x5x8 inch) suspended in the larger. The end 

 of the smaller aquarium was covered with cheese-cloth toward the sounding board. 



