n6 The Animal Mind 



second) of a bass viol string placed on one side of the aquarium 

 as a sounding board. The fish cage was suspended in the 

 aquarium from an independent support. Normal fish re- 

 sponded 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 18 per cent of the tests; those in 

 which the skin had been made insensitive, but the ears left, 

 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 vibrating 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 reac- 

 tions from dogfish, he is inclined to think that different species 

 vary (305, 306). Tests by Zenneck on Leuciscus rutilus, L. 

 dobula, and Alburnus lucidus also led to the conviction that 

 these fish, at least, could hear. A bell was struck by elec- 

 tricity under water, and occasionally a piece of leather was 

 placed upon it at the point where the clapper struck. In the 

 latter case the mechanical vibrations produced were, it was 

 held, the same as those occasioned by the actual ringing of the 

 bell, but the sound vibrations were destroyed. The fish 

 reacted by swimming instantly away from the neighborhood 

 of the bell when it was rung, but not when the leather was 

 used; hence, apparently, they reacted to sound (475). 



Widely distributed among fishes is a curious set of structures 

 known as the lateral-line canals. Along each side of the fish, 

 extending from head to tail, there is a row of pores opening 

 into a long canal, which at the head divides into three branches, 

 one going upward above the eye, a second below the eye, and 

 a third down toward the lower jaw. The functions of these 

 canals have given rise to much discussion among zoologists, an 



