OLFACTORY REACTIONS OF MARINE SNAILS 223 
terminated in the obtainment of food, it is reasonable to conelude 
that external taste receptors were stimulated, and the designation 
of. certain reactions as gustatory is, In my opinion, justified. 
When the stronger extracts were applied to certain parts of the 
body such as the mantle edge, a slight local contraction of the 
stimulated region was the only response noted; the proboscis 
was not extruded. In such cases there was no conclusive phys- 
iological evidence that taste receptors were the ones stimulated. 
After the removal of the osphradium, Busycon responded to 
strong stimulating material derived from oysters in contact 
with certain skin areas by protruding their proboscides and, if 
food was present, by seizing it, but extract further diluted by its 
entrance into sea water in nearly all cases in many trials failed 
to initiate this feeding response. In the one or two instances 
where the proboscis reaction occurred, the snails were not moving 
and I believe that the extract, forced from the pipette, settled 
over especially sensitive skin surfaces in strong enough concen- 
tration to stimulate its taste receptors over an extent sufficient 
to cause the reaction. Snails, however, whose osphradia were 
operative, habitually showed this reaction in the presence of 
dilute food juices. The proboscis reaction, therefore, is called 
forth by either gustatory or olfactory stimuli; in the latter case 
notably more often when the receptor is under strong or fre- 
quently repeated stimulations, and is obviously serviceable in 
the later stages of obtaining food. The surfaces of the head 
near the false mouth, the tentacles, and the anterior end of the 
foot appear to be the external receptive areas most sensitive to 
the more concentrated stimuli derived from food, although all 
the regions tested were found to be somewhat so. Taste in 
the snail, therefore, is a diffused sense as compared with olfaction. 
Certain complex reactions, noted particularly in the more 
active mud snail, now become readily explainable. When 
fish extract was applied to a tentacle or foot process of a moving 
snail, the organ contracted and the animal stopped, turned its 
siphon into the extract, perhaps moved into it, and finally 
extended its proboscis. When the extract issued from the mouth 
of the pipette, it was strong enough to stimulate momentarily 
