OLFACTORY REACTIONS OF MARINE SNAILS 207 
that if the siphon were fastened to one side, so that it could not 
be swung over to the opposite side, the snail should move in 
a circle when reacting to food juices generally distributed in 
front of it. Accordingly, the following experiment was tried: 
One end of a string was fastened to the tip of the shell siphon, 
and the other end tied around the operculum, which lies behind 
the shell on the dorsal surface of the foot when the latter is 
expanded for locomotion. The string was adjusted so that the 
end of the siphon was drawn forty-five degrees to the left of its 
median position. It could be swung still farther to the left 
but not to the right. The right tentacle pointed directly for- 
ward, the left one in the same direction as the siphon. Con- 
trary to expectation, restricting the movement of the siphon in 
this way did not seriously disturb the animal or cause it to 
circle in any abnormal manner. The test was begun by squirt- 
ing oyster juice from a pipette over the right tentacle in front 
of the foot. The snail moved forward slowly a short distance, 
scented the juice and extended its proboscis. ‘The extract was 
then placed alternately in front of the siphon tip, on the right 
tentacle and on the right anterior border of the foot. By this 
procedure the stimulating material was about equally distributed 
in front of the animal and on both sides. The snail began 
immediately to turn to the left, and soon completed a circle of 
about twenty to twenty-five centimeters in diameter. There 
was very little tendency shown to turn to the right, whereas 
siphon stimulation always brought about active locomotion 
to the left. The proboscis was extended somewhat during the 
test, indicating conclusively that the animal was sensing food 
and was not disturbed by the presence of the string limiting 
siphon movement. Stimulation was finally discontinued, and 
the snail promptly moved forward in a straight line for about 
twenty-five centimeters. Then for the first time it showed 
disturbance over the tied siphon, and began stretching upward 
and tugging on the string. As a result of this activity, it turned 
ninety degrees to the right and stopped moving. In the absence 
of the oyster extract, therefore, the only decided deviation from 
a straight course was one to the right. When given a piece of 
