214 MANTON COPELAND 
three trials each. In each of these seventeen trials the oyster 
juice was squirted over the siphon tip frequently for ten minutes. 
The end of the siphon sometimes flared, or was momentarily 
contracted, indicating a local skin stimulation, but it was quite 
impossible to induce the animals to leave the sand. That water 
was being drawn into the siphons in a normal way was determined 
for each individual by tests with carmine and sea water. 
The failure of the snails to respond to oyster extract was 
closely paralleled by their behavior, while resting or moving 
on the bottom of the aquarium, when pieces of oyster were given 
them. Three of them took the food once, but these responses 
were the only ones recorded in over thirty trials. It was taken 
three times when the animals were on, or partly on the side of 
the aquarium near the bottom. After having fed individually 
over eighty snails upon oysters and noted what often appeared 
to be an insatiable appetite for them, it was perhaps not strange 
that this falling off in feeding activity was first attributed to 
some unrecognizable physiological disturbance resultant of the 
operations. That this interpretation was incorrect, however, 
was made evident when the snails were removed from the water 
and pieces of oyster were dropped under their heads. All five 
snails ate oysters under these conditions. They also took food, 
while resting on the side of the aquarium at the surface of the 
water, when it was placed on their feet close by the head and 
tentacles. All but one were fed in this position. 
Two important facts are brought out by these responses to 
food. First, the animals were ready to eat, which supports the 
coriclusion drawn from other aspects of their behavior that they 
were physiologically fit for experimental study. Secondly, as 
already noted, a concentrated food stimulus is the effective one 
for causing the feeding reaction when the osphradium is elimi- 
nated. The snails without doubt failed in most instances to 
respond to the food on the bottom of the aquarium because the 
strength of the stimulating substance was considerably reduced 
by the rinsing the oyster underwent before it could be directed 
under the head of the animal, and because of the difficulty in 
keeping it in contact with the body surface for any length of time. 
