THE SENSE OF SMEEE IN FISHES. 
43 
on a vigorous competition as to which would have possession of the packet. Fre- 
quently the first comer would not only seize the packet and tussle with it, but would 
often attempt to drive off other fish that had approached the region, attracted appar- 
ently by the movements of the first fish. These preliminary tests showed quite con- 
clusively that the normal killifish responds very quickly and in a characteristic way to 
hidden food. 
It was also quite evident from these tests that the killifish, in strong contrast with 
the catfish and dogfish, uses its eyes as well as its chemical senses in seeking and retain- 
ing its food. If a small piece of dogfish flesh is dropped into an aquarium in which there 
are hungry killifish, one is almost sure to pounce upon the fragment and swallow it 
quickly. This action is so sudden and begins when the fish is at such a distance from 
the bit of flesh that it is evidently controlled through the eye. That it is not entirely 
so, however, is seen from the fact that if a small ball of filter paper is thrown into the 
water, this too is pounced upon and taken into the mouth but soon discharged. Thus 
the sight of an object must be followed by an appropriate stimulus of smell or taste, 
if the object is to be swallowed. 
It is the eye, apparently, that leads killifish to swim to a packet of plain cloth and 
seize it, even though it contains no food. The fact that the fishes do not remain about 
such a packet long, however, shows how clearly they distinguish it from a packet in 
which meat is hidden and around which they will gather and tussle for long periods 
of time. The use of the eye in the preliminary steps of search for food is shown in the 
amusing habit that these fish have of chasing drops of water down the glass face of an 
aquarium as if they were bits of food. The eye, then, in Fundulus is serviceable in the 
initial stages of procuring food, but whether the material is to be persistently nibbled 
and finally swallowed depends, as the preceding tests show, on senses other than sight. 
The part played by the olfactory organs in reactions to hidden food can be deter- 
mined by first eliminating these organs and then testing the fishes. The olfactory appa- 
ratus can be rendered inoperative by cutting the olfactory tracts in a position where 
they are easily accessible as, for instance, between the eyes. In this situation a small 
incision can be made through the thin bony roof of the skull and the two tracts can be 
cut by a single movement of a narrow blade. Twenty-four hours after such an opera- 
tion the fish were fully active, took food, and in all obvious ways seemed normal. 
When two packets of cloth, one with dogfish meat hidden in it and the other without 
this food, were suspended in the aquarium in which the operated fishes were, these 
animals nibbled temporarily both packets in a way that made it impossible for an 
uninformed observer to distinguish one packet from the other. When these two 
packets were transferred to an aquarium of normal fish, the one containing the food 
was soon surrounded by a vigorously contesting assembly of fishes, whereas the packet 
without food was only occasionally nibbled. The evidence from these experiments 
favors the view that the olfactory organs are necessary to Fundulus in sensing hidden 
food. The severity of the operation, however, renders this evidence not wholly con- 
clusive. 
