206 MANTON COPELAND 
lated to activity with oyster extract, which was then swept away 
with a current of sea water flowing from the end of a rubber 
tube, the swinging of the siphon was more pronounced, and 
there was more tendency shown to move out of a straight course. 
Finally, it was conceivable that some difference in the weight 
of the cheese cloth packet and the one containing oyster meat 
was a controlling factor in the responses described. Accordingly, 
samples of both types were weighed after taking up sea water, 
and it was found that the one composed entirely of cheese cloth 
was about one hundred and fifty milligrams heavier than the 
other. Tests were then made as follows: A pebble, weighing 
nearly three grams, was tied up in cheese cloth and fastened to 
the end of one of the sticks projecting from the shell siphon, 
whereas the other stick was left free. The difference in weight 
of the two was now nearly twenty times as great as in the orig- 
inal trials, yet the snail tested moved in a straight course irre- 
spective of the side on which the pebble was suspended. The 
same apparatus was fastened to a second individual, the pebble 
being on the left stick. The snail crawled in an approximately 
straight line for about forty centimeters, when it was returned to 
the starting point. Oyster juice was then squirted in front of 
the siphon when it was moved to the left, and the snail responded 
by turning a half circle in the same direction. Again it was 
placed in the middle of the tank, and this time stimulated when 
the siphon was swung to the dextral side, after which it moved 
a half circle to the right. The snail made long sweeps with its 
siphon and was affected in no way discernible by the attached 
weight. These control tests show conclusively that the circling 
reactions of the snails described above were wholly due to the 
directive influence of olfactory stimulation. 
The results of the experiments on Busycon support the con- 
clusion that the animal, when moving in response to olfactory - 
stimulation, is not directed toward food by juices falling upon 
external body surfaces such as those of the tentacles and foot, 
but that it takes a course in the direction indicated by the siphon 
when it receives the effective stimulating substance from a dis- 
tant source. Assuming this conclusion to be correct, it is clear 
