OLFACTORY REACTIONS OF MARINE SNAILS 199 
of the vertical sides of the aquarium, in which position they were 
often fed. These tests were made on over seventy individuals. 
An analysis of the snail’s movements, when responding to ol- 
factory stimuli, shows clearly that the swinging of the siphon 
precedes stimulation, and the latter precedes change in the 
direction of locomotion. 
In the experiment already described, where the odor was 
distributed through the aquarium by a current of water flowing 
over an oyster held to the end of a tube, the same sequence of 
muscle activity and stimulation was noted. One of the snails, 
for example, was moving somewhat diagonally across the current 
when the siphon was swung to the right and held into the stream. 
The anterior end of the foot then turned to the right, and the 
snail circled in the same direction to the bag containing the oyster. 
A study of the reactions which occurred when a snail was 
directed from the bottom to the side of the aquarium, and its 
responses in the latter position, were particularly instructive. 
Certain trials, therefore, may be described in some detail. 
A snail was moving slowly over the floor of the aquarium. 
When oyster extract was liberated in front of the siphon by the 
use of a pipette, so that the end of the organ passed through the 
extract in the middle of its path from one side to the other, the 
animal took a straight course across the aquarium. The siphon 
was swung rather close to the bottom of the aquarium, so that 
its tip, bent downward, touched at the right and left terminations 
of its movements. Upon arriving at the side of the aquarium 
the left surface of the end of the siphon struck the glass first, 
and while it was in that position the stimulating material was 
applied. The animal tried to force the siphon to the left, but 
meeting an obstruction, raised it higher on the glass. Again 
the oyster Juice was squirted over the siphon tip while in contact 
with the glass. The anterior end of the foot was next applied 
to the glass, and the snail began crawling upward. At the same 
time the siphon was swung far off the glass to the right. When 
it returned, it hit the glass still higher, as all the time the foot 
was moving upward. In the last position it was again stimu- 
lated, and the animal continued its upward course. The aper- 
