HEARING AND ALLIED SENSES IN FISHES. 
53 
When the earless fishes were tested in the sounding apparatus, they yielded 
very interesting results. Unlike the gold-fishes experimented on by Ivreidl (1895), 
they differed markedly from normal fish. In an extended series of observations on 
over 20 fishes I never once observed with certainty the springing reflex as a result 
of sounding the bass-viol string. The fishes were usually very active, and I was 
never able to ascertain with certainty whether they showed a change in the respira- 
tory rate on stimulation. The pectoral-fin movements, however, were observed with 
much certainty. On 10 earless fishes I succeeded in getting 10 observations each 
to sound stimuli at about 25 cm. (10 inches) from the sounding-board. The total 
result was that in 82 observations there were no reactions and in the remaining 18 
the reactions were at best slight ones. As the fishes often moved the pectoral fins 
without apparent cause, some of the 18 reactions may have been accidental coinci- 
dences, but others were so precise and typical that I am convinced they were due to 
stimulation. Earless fishes, therefore, differ from normal ones in that their pectoral- 
fin responses to vibrations from the bass-viol string are enormously reduced, though 
not entirely obliterated. 
Fishes with insensitive skins . — For reasons already given it is imperative, before 
drawing conclusions from the condition of earless fishes, to examine the evidence 
afforded by those whose general surface has been rendered insensitive. In this way 
it is possible to ascertain what part the integument plays in the reception of sound 
vibrations. I had hoped that the integument of Fundulus lieteroclitus could be 
rendered insensitive by immersing the fish for a short time in a solution of cocaine, 
but all attempts in this direction proved failures, since the drug acted much more 
vigorously as a poison than as an anaesthetic, and I was finally obliged to abandon 
this method altogether and resort to nerve-cutting. 
The following operation performed on etherized fishes insures an almost complete 
insensibility of the surface. The fifth and seventh cranial nerves can be cut just 
posterior to the eyeball (pi. 9, figs. 3 and I), the lateral-line branch of the tenth nerve 
can next be cut at the posterior edge of the pectoral girdle (fig. 5), and finally the 
spinal cord can be severed at the fourth or fifth vertebra. Severe as this operation 
is, almost all fishes recover from it and respire and feed normally, though they 
seldom live beyond two weeks after the operation. 
Fishes that have recovered from this operation show certain well-marked charac- 
teristics. The integument, particularly l.hat of the dorsal surface, is unusually 
dark, as a result of the expanded condition of the chromatophores. The fish’s 
mouth is gaping and motionless in consequence of the motor portion of the fifth 
nerve having been cut. This condition, however, does not interfere with respiration 
or with the sucking in of pieces of food, an act which the fish performs with avidity. 
Since in cutting the fifth and seventh nerves, the three small nerves to the muscles 
of the eyeballs, the third, fourth, and sixth, must also be cut, the eyes are motion- 
less and usually protrude somewhat. Finally, as a result of cutting the spinal cord, 
the whole trunk of the animal is, as a rule, passive and is drawn after the head, the 
swimming being performed by the pectoral fins. Since the greater part of the cord 
is intact, a more or less vigorous stimulus applied to the trunk is followed by move- 
ments in the dorsal, anal, and caudal fins, or even by a locomotor response of the 
whole trunk, but such movements are made only after special stimulation, and the 
trunk is ordinarily carried passively, like a paralyzed appendage. As a result of 
