HEAKING AND ALLIED SENSES IN FISHES. 
55 
earless fishes is due to the loss of the ear as a sense organ and not to secondary 
complications accompanying the operation. 
Although some of the observations recorded on the preceding pages make it 
certain that in these fishes the ears are stimulated by disturbances such as those 
set up in the water by the sounding apparatus, it may still fairly be asked whether 
these disturbances are in the nature of sounds. When the bass-viol string attached 
to the aquarium was plucked, a series of sound waves of diminishing intensities 
was delivered to the water. To ascertain something of the nature of this sound I 
immersed my head in the water of the aquarium and had an assistant pluck the 
string in the usual way. The sound that I thus heard was, so far as I could judge, 
of nearly the same pitch as that which the string gave to the air and of only slightly 
greater intensity. This sound certainly reached the fishes. 
The sounding apparatus, however, did more than give rise to this sound. When 
the string was plucked two things besides the production of sound certainly happened : 
First, the whole aquarium, including its supporting table, trembled slightly, and, 
probably as a consequence of this, ripples started from the ends and sides of the 
aquarium and proceeded toward the center. These ripples, though chiefly surface 
effects, indicated a wave motion that penetrated the water to some extent, and that 
was doubtless the cause of the very slight swaying movement of the fish cage occa- 
sionally noticed after the string had been vigorously plucked. Moreover, a distinct 
tremor could be felt in the water when the hand was held 5 to 8 cm. (2 to 3 inches) 
from the sounding-board and the string was plucked. The question naturally arose 
whether the fishes did not respond to the movement of the aquarium as a whole or 
to the wave movement indicated by the ripples rather than to the true sound waves. 
To answer this question, at least so far as the ripple movement was concerned, 
I was led to study the reaction time of the fishes. Unfortunately circumstances 
prevented me from reducing this to a very accurate process ; but, by listening to the 
beat of a chronometer and at. the same time watching the fish, I am confident that 
the fin reactions occurred in less than 0.2 second after the string had been plucked. 
The sound waves and ripples mentioned above traveled from the sounding-board 
toward the fish at very different rates. The sound waves must have passed over 
the 25 cm. of water between the sounding-board and the fish almost instantly. The 
surface ripple traveled much less rapidly and its rate could be easily measured. 
This proved to be a meter (39f inches) in t.8 seconds; hence, to traverse 25 cm. (10 
inches) the ripple required about 1.2 seconds. Since the fishes responded in less 
than 0.2 second, they must have reacted to something other than the disturbance 
indicated by the ripples. 
Having eliminated the ripples as the initial stimulus for the fishes, it remained 
to be shown whether this stimulus was the movement of the whole aquarium or the 
sound waves proper. I succeeded in doing this by substituting an electric tuning- 
fork for the bass-viol string. The tuning-fork was placed so that its base was within 
about a millimeter (d T inch) of the sounding-board. The iron frame holding the fork 
rested on supports made of rubber bottle-stoppers. These flexible supports allowed 
the fork to be moved enough to bring its base into contact with the sounding-board 
without moving the supports over the surface on which they rested. As this could 
be done without any initial jar, it was possible to communicate to the water in the 
aquarium a sound of uniform intensity and pitch without moving the aquarium as 
