EYES, EARS, AND OTHER SENSE ORGANS OF THE DOGFISH. 
49 
severity of the operation these fishes were as sensitive to sounds as normal fishes are. 
I therefore believe that the loss of sensitiveness in dogfishes whose eighth nerve has 
been cut is not due to the severity of the operation, but to the actual loss of the ear as 
an effective sense organ. 
As it has often been maintained that the responses of fishes to sounds depend upon 
stimulation of the skin and not of the ears, I prepared another set of dogfishes in which 
I endeavored to render the nerves of the whole integument insensitive to mechanical 
stimulation. As in the case of Fundulus, so in the dogfish, I cut the fifth and seventh 
nerves as well as the lateral-line nerves. I also pithed the animals by cutting off the 
tail, plugging the caudal artery and vein with a ball of absorbent cotton so as to prevent 
excessive bleeding, and inserting a wire into the spinal canal and twirling it as far forward 
as the neck region so as to destroy the spinal cord. After recovery from these operations 
the skin of the dogfish was found insensitive to mechanical stimuli except in the region 
of the gills and pectoral fins. In my experiments on Fundulus this region was also of 
necessity left sensitive to mechanical stimulation and might therefore serve as a recep- 
tive surface for sound vibrations. In reporting my results on Fundulus I noted this 
fact with regret, and it has been used as an argument against the validity of my results 
by a recent critic, Korner (1905). It seemed to me therefore highly important to ascer- 
tain whether this region of the skin played any important part in the reception of sound, 
and for this purpose I attempted to render it insensitive without, however, interfering 
with the nervous control of its underlying muscles. 
To accomplish this end I endeavored to cut the dorsal roots of the spinal nerves 
of this region, but my efforts were unsuccessful. I finally found in cocaine a means 
of accomplishing my purpose. If a 2 per cent solution of cocaine is applied to a tactile 
area on a dogfish’s skin, in from fifteen to twenty minutes the area becomes somewhat 
mottled and loses its sensitiveness. I therefore placed, on a frame in the open air, 
a dogfish in which the appropriate nerves had been cut, and after having started a 
current of sea water through its mouth and gills for respiration I covered the remaining 
sensitive part of its skin in absorbent cotton soaked in 2 per cent cocaine. Before 
the application of the cocaine the dogfish responded by movements of the pectoral 
fins to mechanical stimuli applied to these fins, but after a quarter of an hour these 
responses ceased. After half an hour’s treatment the dogfish was taken from the 
frame and suspended by its anterior dorsal fin in the sea water of the wooden 
aquarium and subjected to sound stimuli. The animal occasionally responded by 
movements of the pectoral fins to the sound produced when the bob of the 
pendulum hit the side of the aquarium with a momentum of 1 and it invariably 
reacted when the momentum was 1.5 or more; in other words, the animal, so far 
as its responses to sound were concerned, differed in no essential respect from a 
normal dogfish. Three other dogfish were tested in like manner and gave similar 
results. I therefore conclude that the skin of a dogfish is not essential to its response 
to sound. 
To check these conditions in relation to the ear, two of the four dogfishes with 
insensitive skins were subjected to the further operation of having their eighth nerves 
48299° — Bull. 29 — 11 4 
