THE SENSE OP SMEEE IN FISHES. 37 
these reactions that the fishes sensed the difference between the wad of cloth with 
worms and that without worms. 
To ascertain what receptive organs were concerned in the reactions just described, 
two sets of 5 fishes each were taken from among the 15 normal fishes already tested, and 
each set was prepared differently by subjecting its members to a special operation. One 
set was etherized, and, through a small incision between the eyes, their olfactory tracts 
were cut, thus rendering their olfactory apparatus functionless. From fishes of the 
other set all the barblets were removed, whereby their external gustatory organs were 
partly, though not wholly, eliminated. After these operations both sets of fishes were 
liberated in the large aquarium, where they remained for over two days. At the expira- 
tion of this time, they were carefully inspected and tested. They swam about in an 
essentially normal way and members of both sets snapped bits of worm from the end of 
a hooked wire much as a normal fish does. Presumably they were in a satisfactory 
condition for experimentation. 
The tests were begun by introducing into the large aquarium containing the 10 fishes 
a wad of cheesecloth within which were hidden some minced earthworms and recording 
the kind of fish that visited it and the nature of their reactions. During the first hour 
the wad was seized 34 times by fishes without barblets but with normal olfactory organs 
and, though often passed by fishes with cut olfactory tracts, it was “nosed” only once 
by one of these. A wad of cheesecloth without worms was next substituted for that 
with worms and the reactions of the fishes were recorded for a second hour. Though 
members of both sets frequently swam by this wad, none at any time during the hour 
seized it or even nosed it. These tests were repeated on the same fishes for two succeed- 
ing days and with essentially similar results. On the second day the wad with worms 
was seized 16 times during the test hour by fishes with normal olfactory organs and on 
the third day 54 times. On both these days the fishes with their olfactory tracts cut 
made no attempts on the wad with worms nor did any fish at any time nose the worm- 
less wad. The movements of the two sets of fishes when in the neighborhood of the wad 
containing minced worms were characteristically different. The fishes with their 
olfactory tracts cut swam by the wads without noticeable change; those without barb- 
lets, but with their olfactory apparatus intact almost always made several sharp turns 
when near the wad as though seeking something, and then either moved slowly away or 
swam more or less directly to the wad and began to nose and nibble it. These reactions 
were so clear and so characteristic that when taken in connection with the conditions 
of the fishes, they lead inevitably to the conclusion that the olfactory apparatus of the 
catfish is serviceable in sensing food at a distance much beyond that at which the organs 
of taste are capable of acting; in other words, catfishes truly scent their food. 
EXPERIMENTS WITH MUSTELUS. 
The experiments here recorded were performed on the smooth dogfish, Mustelus 
canis (Mitchell). This was selected owing to its great abundance in Buzzard’s Bay 
near Woods Hole, and also because previous experimentation (Sheldon, 1909) rendered 
many of its habits and reactions familiar. 
