56 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
a whole and also without producing any ripple. The fork, moreover, produced atone 
much purer than that obtained from the string. It had a pitch of 128 vibrations per 
second. 
Earless fishes, when subjected to sound waves from the tuning-fork, showed 
nothing that I could identify as a reaction. Normal fishes and fishes with normal 
ears but insensitive skins very usually reacted by pectoral -fin movements. The 
occasional failure to respond was attributed by me to the faintness of the vibrations, 
for the most intense sound obtained from the fork was much less than that produced 
by the bass-viol string. That the fishes, however, always did react, even to this 
relatively faint tone, was pointed out to me by my friend Dr. F. S. Lee, who while 
watching one of the experiments thought lie detected an increase in the respiratory 
rate even when no pectoral-fin reaction occurred. Subsequent study showed this to 
be entirely correct, for, irrespective of pectoral-fin responses, at each sounding from 
the tuning-fork an increase of the respiratory rate did take place for a very short 
period. There is, then, no question but that these fishes respond to sound waves, 
and, since this response is through the ear, I conclude that Fundulus heteroclitus 
may be said to hear. Since I never succeeded in getting reactions of any kind to 
the tuning-fork from earless fishes with skins and lateral lines intact, I have no reason 
for believing that these parts are stimulated by true sound waves, and I attribute 
the responses that earless fishes occasionally showed to the vibrating bass-viol string 
not to the action of its sound waves on the skin or the lateral-line organs, but, as 
will be shown later, to the influence of the accompanying movement of the whole 
aquarium and its contained water on these parts. 
Although the experiments already described remove every reasonable doubt 
from my mind as to the ability of these fishes to hear, the objection may still be 
raised that the conditions under which they were carried out were so artificial that 
they may be said to have almost no bearing on the ordinary habits of Fundulus, and 
it must be admitted that the relatively small volume of water in the aquarium and 
the character of its walls as reflecting surfaces for sound, may possibly have 
introduced factors to which the fishes, in their natural surroundings, were not 
accustomed. To ascertain how much weight should be given to this objection the 
following experiment was tried. The sounding apparatus, consisting of the sounding- 
board and the bass-viol string, was taken from the aquarium and set up in the open 
water of the outer pool at the Fish Commission wharf. The fish cage was hung at a 
distance of 50 centimeters (20 inches) from the sounding-board and toward the center 
of the pool, which is about 100 feet wide. The sound, therefore, was as unrestricted 
as that which naturally reaches these fishes. On experimenting with normal fishes, 
fishes without ears, and those with insensitive skins, results were obtained essentially 
like those observed in the aquarium, and I therefore concluded that the restriction 
of the water in the aquarium played no essential part in the results obtained from 
that apparatus. There is, thus, good reason to believe that Fundulus heteroclitus 
not only hears, but that for it hearing is a normal process. 
Having determined that hearing was one of the normal functions of the ears in 
Fundulus, I had hoped to be able to ascertain by experiment the particular part of 
the ear, if such there be, that was concerned with this sense. The internal ear in 
Fundulus heteroclitus is like that in most teleosts. It consists of the usual three 
semicircular canals and a large sacculus, at whose posterior end a well-developed 
lagena is present. The sacculus is a thin-walled chamber, vertically flattened and 
