HEARING AND ALLIED SENSES IN FISHES. 
51 
obtaining fishes in these conditions and the responses that they showed will be 
described for each class of fishes. 
Normal fishes . — When a normal fish is first liberated in the cage it swims vigor- 
ously about for a few moments, after which it may, sooner or later, come to rest on 
or near the bottom. The animals are extremely quick-sighted, and, if after they 
have come to rest the observer makes any sudden movements near the aquarium, 
they are very likely to begin active swimming anew. It is, therefore, extremely 
necessary to work in such a way that all movements, and particularly quick ones, 
are made out of sight of the fish. When the fish is resting on the bottom of the 
cage, two sets of motions will usually be observed : first, the respiratory movements 
of the operculum; and secondly, the alternate vibratory movements of the pectoral 
fins. The opercular movements, as might be expected, always continue, but the 
movements of the pectoral fins, which seem to be connected also with the respiratory 
function, often cease entirely. 
When a fish has become quiet, except for the respiratory movements, the vibra- 
tions from the string may call forth any of four kinds of responses. The first of 
these is the vibratory movement of the pectoral fins, either a few slight beats, if the 
fins were previously at rest, or an increased rate or extent of swing if they were 
previously in motion. The vibration of the string at the intensity ordinarily 
employed almost invariably called forth this reaction; thus, in ten observations 
taken from each of ten fishes at a distance of about 25 cm. (10 in. ) from the sounding- 
board there were 96 pectoral-fin responses and 4 failures. Since this response is so 
readily observed, it has afforded one of the most satisfactory criteria of stimulation. 
The second form of response is a change in the rate of the respiratory movements. 
In a quiescent fish measuring 8 cm. (3.2 in.) in length the respiratory rate was 114 
per minute. On stimulating by sound this rate rose suddenly to 138 per minute for 
some ten or a dozen movements and then fell rapidly to about the former number. 
This is probably a very usual form of response, perhaps quite as much so as the 
movement of the pectoral fins, but the shortness of its duration and its inconspicu- 
ousness make it less satisfactory as an indication of stimulation than that afforded 
by the pectoral fins. If the sound from the string is of considerable intensity, the 
third form of response may appear, a slight motion of the caudal fin, beginning 
usually at the dorsal edge and proceeding as a wave ventrally. Finally, with strong 
stimulation, the fish may make a short but quick spring forward. 
All these reactions have been obtained from fishes even at 75 cm. (30 inches) 
from the sounding-board, although the springing movements are more frequently 
observed when the animals are not so far from the source of sound. One very inter- 
esting fact about these reactions is that they can not be repeated rapidly for even a 
short period. A fish that responds to the first stimulus by a spring, may react to the 
second or to the third only by moving the pectoral fins, and to the fourth in no 
observable way. It is only when a considerable period of rest intervenes that the 
reactions may be repeatedly obtained; and I have found that the minimum period 
of rest is not far from one minute, though, even then, reactions may sometimes fail 
to appear. 
Earless fishes . — The removal of the ears from a fish is a serious operation, but it 
is one which, after a little practice, may be accomplished with success and from 
which the fishes generally recover. These animals are easily etherized by putting 
