OLFACTORY REACTIONS OF MARINE SNAILS 201 
way. The oyster extract was next applied whenever the sinhon 
was swung downward, that is, at the end of its dextral movement, 
and the foot responded by turning in the same direction. After 
the animal had definitely changed its course in this manner, the 
juice was squirted over the siphon tip when at the end of its 
swing to the left. The reaction was striking. The snail again 
headed upward, and on continuing the stimulation in the same 
way, circled: to the left until the siphon actually pointed down- 
ward and the foot nearly so. In that position the foot slipped 
on the glass, and the animal slid to the bottom. By appropriate 
stimulation, therefore, a snail can be made to circle on a vertical 
surface as readily as on a horizontal one. 
When Busycon was crawling on the glass side of the aquarium, 
it was comparatively easy to observe the details of its reactions. 
The turning of the anterior end of the foot was seen to occur 
very quickly after the application of the extract to the siphon 
tip at or near the end of its lateral movement. If, for example, 
stimulation took place when the siphon was swung to the left, 
the foot was turning in the same direction synchronously with 
the return of the siphon to the right. It appeared also as if 
the return swing of the siphon was somewhat shortened as a 
result of the preceding stimulation, or possibly the turning of the 
foot in the opposite direction. 
Whether the eyes or chemical receptors of the tentacles or 
foot play a part in these responses may next be considered. The 
contention might be raised that some of the oyster extract passed 
back along the sides of the siphon and by stimulating the tentacles 
directed locomotion. To remove the tentacles, bearing the eyes 
at their bases, is a simple operation which, as in Alectrion, seems 
to have no injurious effect on the snail. Soon after the opera- 
tion the animal will take food and its behavior appears quite 
normal. A snail, whose tentacles and eyes had been eliminated 
by severing the tentacle bases close to the head, was tested with 
oyster juice squirted from a pipette in front of the siphon. Its 
scenting reactions were identical with those of animals possessing 
tentacles. It was led about the aquarium and up the side by 
the same method used in directing the movements of other 
