52 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
them in sea water containing enough ether to give it a strong ocjor. On being trans- 
ferred to pure sea water they quickly recover, and an individual that I etherized six 
times in the course of one afternoon finally recovered without showing any ill effects. 
The first method I used in operating on the etherized fishes was to open the cranium 
in the region of the ears and, after cutting the auditory nerves, to remove those 
nerves and the attached ear-sacs. These parts were easily identified from the fact 
that the auditory nerve emerges from the medulla almost exactly ventral to the cleft 
between that organ and the optic lobe, and the ear-sac, which is only partly sur- 
rounded by cartilage, lies in the cranial cavity only slightly peripheral to the point 
where the nerve leaves the medulla (pi. 9, fig. 3). After the operation the fishes 
were returned to pure sea water and, notwithstanding the exposure of the brain, a 
considerable number recovered and survived. One of these I kept for more than six 
weeks, and, though its swimming was characteristically irregular, it was alert and 
active and, except for a brief intervening period, it fed normally. 
From the operation just described about one fish in ten recovered. This pro- 
portion was greatly increased by a second form of operation in which the auditory 
nerve was cut without opening the cranium (fig. 4). After a little practice I found 
that this could be done with great certainty and about eight out of ten fishes usually 
recovered. All fishes that had been operated on were kept at least twenty-four 
hours before they were subjected to experimentation. 
Fishes in which the auditory nerves have been cut have very characteristic 
reactions. When resting or when swimming slowly they behave for the most part 
as normal fishes do, and, in fact, are often undistinguishable from individuals upon 
which no operation has been performed. When, however, they are stimulated to 
rapid locomotion, they swim either in irregular spirals, the same individual revolving 
sometimes to the right and sometimes to the left, or they turn over and over in 
irregular circles without accomplishing much real progression. This loss of 
orientation on attempting rapid locomotion has for some time been recognized as 
indicative of one of the chief functions of the ears in fishes — i. e., equilibration. 
It is probable that in resting or in swimming slowly the fish depends upon the eye 
for orientation, but in quick movements the ears come more into play, and hence 
after their loss quick movements are accompanied with lack of orientation. The 
forced movements thus observed may be taken with perfect certainty, so far as my 
experience goes, as evidence of the successful outcome of an attempt to cut the 
auditory nerves, for in the few cases where these movements failed to appear, 
subsequent dissection showed that the nerves had not been cut, and in all instances 
where the movements were observed and the animals afterwards dissected, the 
nerves were found severed. 
A second feature of interest that generally characterized fishes with severed 
auditory nerves was the color that they finally assumed. Under ordinary circum- 
stances the color of this species is a light greenisli-gray. When etherized the fishes 
become very dark, with a mottling of blue-green on the sides and belly. After 
recovery from cutting the auditory nerves, the dark coloration disappears and the 
fish assumes a tint even paler than that of a normal individual. This tint is retained 
throughout life. Etherizing probably influences the chromatophores of the skin 
directly, but cutting the auditory nerves introduces changes that are probably 
dependent upon the nervous control of the chromatophores. 
