7.8 PARKER— A CRITICAL SURVEY OF 



the eel so that he could demonstrate a demarcation current on these 

 parts. On producing sounds in the water in which the prepara- 

 tions were, an action current was identifiable that lasted as long as 

 the sound did. Such a current was also produced by tapping the 

 walls of the containing vessel, but it did not result from a noise- 

 less jarring of the preparation, nor from a stirring of the water 

 around the preparation. From these results Piper (1906a, p. 296) 

 concluded that fishes responded to sounds by means of their ears. 



Parker (1909, 1911a) attempted to ascertain if there was any 

 evidence for hearing in the dogfish, Mnstehis canis, which, as previ- 

 ous study (1903a, p. 62) had shown, was not responsive to ordinary 

 sound vibrations in water. It was found, however, that if the 

 wooden wall of a tank containing a dogfish was struck by a heavy 

 swinging pendulum, the dogfish within would respond by a sudden 

 jump forward or at least by a waving of the posterior edges of the 

 pectoral fins. The pendulum consisted of a bob weighing 3,800 

 grams and a suspending wire, the whole apparatus having a length 

 of 260 centimeters. This device was calibrated so as to strike the 

 wall of the tank with a momentum of 83,600 centimeter-gram-second 

 units or more. The minimum stroke was taken as unity and strokes 

 of greater magnitude could be conveniently delivered up to about 

 five times that of the assumed unit. Normal fishes when swimming 

 freely in the water occasionally responded by pectoral-fin movement 

 to a stroke of magnitude i and invariably to a stroke of 1.5. After 

 their eighth nerves had been cut. they did not respond to a stroke 

 of less than 3 and invariably only to one of 4. To ascertain if this 

 reduction in sensitivity was due to the operation they had suffered, 

 a second set, in which for other purposes the optic nerves had been 

 cut, were tested with the pendulum. These fishes responded regu- 

 larly to a stroke of magnitude 2. To eliminate the skin and lateral- 

 line organs, the fifth, seventh, and lateral-line nerves were cut, the 

 spinal cord destroyed up to the neck region and the skin around the 

 pectoral fin cocainized. Notwithstanding the extent of their prep- 

 arations, these fishes responded by movements of the pectoral fins to 

 strokes of the pendulum of magnitude i to 1.5. Without question 

 their ears were receptive for these vibrations. Parker, therefore, 



