54 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
having so little of the normal locomotor apparatus intact, the fishes often swim ven- 
tral side up, for the action of the pectoral fins is not always sufficient to overcome 
the physical effects of the specific gravity of the fish’s body. 
Fishes that have recovered from the operation just described have intact the 
ears, the central nervous organs from the anterior end of the brain caudad to the 
fourth or fifth vertebra, and the sensory and motor apparatus for the region of 
the gills and the pectoral fins. Excepting in these two rather restricted regions, the 
whole integument is insensitive, at least so far as its capacity to originate impulses 
to movements in the gills or pectoral fins is concerned. Such fish, therefore, are in 
a condition to receive stimuli through the ears and to respond by respiratory or 
pectoral-fin movements. 
The reactions that these fishes showed to the sound apparatus were surprisingly 
clear and decisive. From the nature of the operation one would not expect them to 
be able to give the sudden spring that the normal fishes often showed, and, as a 
matter of fact, such responses were never observed. Were the skin of the trunk 
sensitive, it is conceivable that the caudal-fin reaction might occur, for the cord, 
though severed from the rest of the central nervous organs, was in itself intact. 
Caudal-fin reactions were, however, also never observed. The respiratory reactions 
and the pectoral-fin responses occurred with great regularity. When the bass-viol 
string was made to vibrate, the respiratory rate increased for a very brief period. 
In a fish 7 cm. (2f inches) long the rate previous to stimulation was 120 per minute; 
immediately after stimulation it was 156. The reactions of the pectoral fin were also 
well marked. In ten observations on each of ten animals at a distance of about 25 
cm. (10 inches) from the sounding-board the pectoral- fin responses occurred 94 times 
in the total hundred. This is in close agreement with the normal fishes and in strong 
contrast with the earless ones. So far, then, as reactions to the vibrating chord are 
concerned, these fishes show the essential characteristics of normal individuals. 
Discussion of the results of the experiments . — It is clear from the experiments 
described in the preceding sections that fishes whose ears were rendered functionless, 
but whose skins were normally sensitive, reacted only slightly to the stimulus from 
the sound-producing apparatus, whereas those with insensitive skins but functional 
ears responded to this stimulus, as far as their conditions would permit, almost exactly 
as normal fishes did. It might be assumed that the failure to respond on the part of 
earless fishes was due not to the loss of the ear, but to the shock of the operation 
they had undergone. This, however, does not seem to be the case, for, after the 
fishes had recovered from the immediate effects of the operation, they were active, 
fed well, and sometimes lived many weeks. Moreover, if the operation were as 
severe as is implied in the above assumption, one might expect some indications of 
this in fishes in which only one auditory nerve had been cut. As a matter of fact, 
immediately after this operation fishes with only one ear intact did swim irregularly, 
but in from six to eight hours this tendency disappeared entirely, and the fish in its 
quickness, precision, and normality of response became, so far as my obsei’vations 
went, absolutely indistinguishable from a normal individual. Further, fishes with 
the fifth, seventh, and lateral-line nerves and spinal cord cut have without doubt 
suffered a more severe shock than those that have had only the eighth nerve cut, 
and yet the pectoral- fin reactions of the former were essentially normal. It therefore 
seems, to me that the great reduction in the number of pectoral-fin reactions of 
