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BULLETIN OE THE UNITED STATES EISH COMMISSION. 
It may be reasonably asked at this point, What constitutes hearing? Every- 
one will agree, I believe, that the sensation we get through the skin from a vibrating 
rod in water should not be called hearing, and what is true for us should hold for 
the lower vertebrates. Hearing in these animals may therefore be defined as that 
sensory activity resulting from a stimulation of the ear by material vibrations. This 
is in essential accord with the definition given by Kreidl (1895, p. 461) to the 
effect that hearing is that sensation which is mediated by the nerve that is homolo- 
gous with the auditory nerve of man. When, therefore, a fish responds to sound 
vibrations the question at once arises whether the stimulus is received by the skin, 
the lateral-line organs, or the ear. And until this question can be answered, at least 
so far as the ear is concerned, the query whether fishes hear or not must remain 
open. In dealing with this general subject I shall take up, first of all, the question 
whether fishes respond to sound vibrations through the ears. 
THE EARS. 
Introductory . — The internal ears of fishes were described as early as 1610 by 
Casserius, and were studied in some detail in the following century by Geoffroy, 
Scarpa, Comparetti, and Hunter. The attitude taken by many of these early 
workers on the question of the ability of fishes to hear or not is well illustrated by 
a quotation from Hunter (1782, p. 388), who at the conclusion of his paper on the 
organs of hearing in fishes made the following statement: 
As it is evident that, fish possess the organ of hearing, it becomes unnecessary to make or 
relate any experiment made with live fish which only tends to prove this fact; but I will mention 
one experiment to shew that sound affects them much and is one of their guards, as it is in other 
animals. In the year 1762, when I was in Portugal, I observed in a nobleman's garden, near 
Lisbon, a small fish-pond full of different kinds offish. Its bottom was level with the ground and 
was made by forming a bank all round. There was a shrubbery close to it. Whilst I was lying 
on the bank, observing the fish swimming about, I desired a gentleman, who was with me, to take 
a loaded gun and go behind the shrubs and fire it. The reason for going behind the shrubs was 
that there might not be the least reflection of light. The instant the report was made the fish 
appeared to be all of one mind, for they vanished instantaneously into the mud at the bottom, 
raising, as it were, a cloud of mud. In about five minutes after they began to appear, till the whole 
came forth again. 
This passage shows very clearly that in the opinion of Hunter the internal ears 
of fishes, like those of the higher vertebrates, are organs of hearing. Without further 
experimental evidence this view was accepted by Muller (1848, p. 1238) in his well- 
known chapters on the physiology of the senses, and by many other eminent authori- 
ties, such as Owen (1866, pp. 342 and 346), Gunther (1880, p. 116), and Romanes 
(1892, p. 250). To these investigators the presence of the internal ears seemed, as 
it did to Hunter, sufficient ground for concluding that these animals could hear. 
Within recent years, however, this opinion has been called in question, or even 
denied. Some of the grounds for this change of view may be stated as follows: 
Bateson (1890, p. 251), in some investigations on the sense organs and perception of 
fishes, observed that the report from the blasting of rocks caused congers to draw 
back a few inches, flat-fishes (like the sole, plaice, and turbot) to bury themselves, 
and pouting to scatter momentarily in all directions; other fishes seemed to take 
no notice of the report. When the side of a tank containing pollock or soles was 
struck witli a heavy stick, the fishes behaved as they did toward the report of the 
