218 MANTON COPELAND 
siphon toward the food as it was passing, stopped, extended its 
proboscis and turned into it. When these tests were made 
there was no water running into the aquarium to aid the dis- 
persal of the odorous material, and accordingly the responses 
occurred withir a comparatively restricted area. By applying 
fish extract with a pipette so that it was taken into the siphon 
when directed to one side, a snail could be made to turn to the 
right or left at will. It is evident, therefore, that Alectrion, 
although more active than Busycon, and possibly more apt to 
turn from a straight course for reasons not apparent, is never- 
theless directed to distant food in the same way as the larger 
species. 
When the olfactory apparatus and the directed responses of 
the snail are contrasted with those of an animal organized on a 
plan of more general occurrence, the peculiarities of the former 
are readily appreciated. 
In 1911, Sheldon showed that the dogfish obtains its food 
principally, if not entirely, through the olfactory sense; and 
three years later Parker (14) demonstrated that this fish does 
not run upon food by accident after scenting it, but finds it 
through movements resulting from olfactory stimulations which, 
in part at least, are directed. The latter conclusion is based on the 
results of experiments upon dogfish with one of their two nostrils 
occluded. He found that an animal under the influence of 
olfactory stimulations ‘‘can be forced to assume either a pre- 
dominantly right-handed or left-handed course by occluding 
the appropriate nostril.’ The results are discussed in part as 
follows: 
The consistent and striking circular courses that these fishes can be 
forced to assume have, in my opinion, more than a superficial re- 
semblance to the so-called circus movements of the invertebrates. 
These movements are dependent on the differences of intensity of 
stimulation on the two sides of the body and this explanation holds, 
I believe, for the circular movements of the dogfish. When a dogfish 
first enters water permeated with odorous material from its food, it 
invariably makes a quick turn with its head which, if the conditions 
of the water have been disturbed by currents, is always toward the 
bait. This movement is followed by other movements of a like kind 
whereby the fish eventually reaches the bait. When the normal con- 
