262 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
is no constant reaction, however, and in fact the fishes act very much as they do 
when a jet of simple sea water is directed against them. They do not appear to 
dislike the acid intensely. Later I tested these fishes with a 1 per cent solution of 
hydrochloric acid in sea water. This is decidedly unpleasant and is uniformly 
avoided. 
The experiments recorded seem to show clearly that the hake receives both tac- 
tile and gustatory stimuli by means of the free fin rays and to some extent doubtless 
by other parts of the outer body surface. What role may be played by the sense of 
smell remains obscure. To test the powers of locating concealed food the following 
experiments were tried: 
In a tank containing two hake which were very hungry I placed a piece of fresh 
clam meat concealed between two small, old, and thoroughly clean clam shells which 
had been lying for some time in the bottom of the tank. The fishes did not seem to 
smell the meat at a distance and so be attracted to the spot where the shells were, but 
if in the course of their aimless movements along the bottom of the tank they passed 
over the shells, they generally stopped a moment, smelled around, and then passed on, 
first feeling over the whole area of the shell with their free fins. As time passed, 
this reaction became less clear until after some fifteen minutes they generally passed 
over the shells without paying any attention. They never found the meat. This 
experiment was many times repeated with the same result. The sense of smell can 
play no strong part in the locating of their food. It may play some small part, 
though I incline to believe that the interest which the fishes show in the concealed 
bait is excited by a vague stimulus to the terminal buds on the fins. Compare the 
experiments made after extirpation of the olfactory organs in the tomcod described 
below 
The tomcod (Microgcidus tomcod ). — These fishes are much less active than the 
hake, spending most of the time lying quietly on the bottom of their tank. They 
have not so keen sight as the hake and pollock, but still obtain much of their food by 
this sense, catching food thrown in before it reaches the bottom. They do not catch 
live prawns in captivity so well as the hake do, yet prawns and other active crusta- 
ceans are found in the stomachs of specimens taken with the seine. The dorsal fin 
lacks the free filamentous rays and is not especially sensitive to gustatory stimuli. 
The ventral fins are, however, very efficient in locating sapid substances lying on the 
bottom. They are shorter than those of the hake and are not thrust forward, but 
incline slightly backward. Like the hake, the tomeods spend much time in slowly 
exploring the bottom, though they assume a very different position, with the head 
directed downward at an angle of some 30° to 45° with the bottom, so that the tips 
of the barblet and ventral fins just drag the bottom. When food particles are located 
they are snapped up by a quick lateral movement similar to that of the cat-fishes. 
Sometimes, however, stimulus of the ventral fins is followed by a reversed swimming 
movement, the fish backing up to take the bait. At other times the fish when explor- 
ing the bottom swims slowly backward, so that no change of direction is necessary 
when food is located. 
I made a series of tests with cotton wool and cotton dipped in clam juice similar to 
those described for the hake, and with the same results. I also repeated the tests 
made with sea water and with strained clam juice by the aid of a pipette, with iden- 
