EYES, EARS, AND OTHER SENSE ORGANS OF THE DOGFISH. 
53 
tactile organs and penetrated by certain parts of the lateral-line system, it was necessary 
first of all to eliminate these sense organs before conclusive experiments could be made 
on the underlying ampullae. To effect this elimination, I painted the skin over a given 
patch of ampullae with a 2 per cent solution of cocaine, hoping thereby to destroy the 
receptiveness of the superficial tactile and lateral-line organs and leave that of the deep- 
seated ampullae. After half an hour I tried various stimuli on this surface and I found 
that pressure upon this spot was accompanied by a momentary slowing or cessation 
of the respiratory movements. As I had also obtained this reaction from the lateral- 
line organs and as these organs were possibly involved here, I abandoned this method of 
procedure for another. This consisted in dissecting off the skin over a patch of ampullae 
and thus removing the tactile and lateral-line endings completely. If, now, into the 
mass of ampullae thus exposed, a blunt glass rod is gently pressed, the same partial or 
complete respiratory inhibition takes place as was seen in the earlier experiment. As 
this ceased on cutting the bundle of fine nerves that supplied the cluster of ampullae, 
I conclude that pressure is a normal stimulus for the ampullae of Torenzini, and that 
these organs are in truth closely related to lateral-line organs. 
THE ORGANS OF TOUCH. 
The whole outer surface of a smooth dogfish, like that of many higher vertebrates, 
is open to stimulation from a deforming pressure, i. e., it is sensitive to touch. As a 
result of this stimulation no alteration in the respiratory rate has been observed, but 
movements of the nictitating membrane and fins have been called forth. The fin 
movements often appear in coordinated groups such as would result in normal loco- 
motion. Wherever tactile stimulation occurs, electrical stimulation is also usually 
effective, with this difference, however, that the electrical stimulation may call forth a 
much more vigorous response than the purely tactile does. 
The surface of the dogfish’s body may be divided into some five tactile regions char- 
acterized mainly by the responses that result from their stimulation. The first of these 
regions is the part of the head anterior to the hindermost limits of the orbit. So far as 
the fins are concerned tactile stimulation of this region results in only slight irregular 
movements. When the stimulus is applied to a considerable stretch in front of the eyes, 
or above or below them, or to a very restricted area behind them, quick closing move- 
ments of the nictitating membrane occur. These movements, which are the really 
characteristic ones of this region, are strictly homolateral in that mechanical stimulation 
of the appropriate region on one side of the head never calls forth movements in the 
nictitating membrane of the opposite side, but only in that of its own side. Since they 
originate from a stimulus that in most cases is anterior to the eye and result in a closure 
of the nictitating membrane, they may be regarded as primarily concerned with the 
protection of the corneal surface of the eye-ball. Strange to say, they do not occur with 
anything like the certainty when the cornea is touched as when the adjacent skin is 
stimulated. This protective winking movement can be called out so far as I am aware 
only by mechanical stimulation; the nictitating membrane is not moved when intense 
