OLFACTORY REACTIONS OF MARINE SNAILS 189 
receptor within the mantle chamber to which the fluid was 
conducted. 
The results of the experiments reported above indicate that 
the skin of Alectrion is in general more or less sensitive to food 
materials, and that certain regions of it, such as those covering 
the tentacles, the siphon, and lateral foot processes, sometimes 
at least play a part in reactions to food, inasmuch as stimulation 
of these surfaces by its juices initiates a testing of the environ- 
ment by means of the siphon. Finally, appropriate stimulation 
of the under surface of the latter organ, or of one within the 
mantle chamber, induces a protrusion of the proboscis. ‘To 
further test these conclusions, and to localize more definitely 
the receptor associated with the siphon or mantle, -it became 
necessary to limit in some way the action of the siphon. This 
end was accomplished by tying and cutting off the organ. 
The following tests were made upon a snail with its tentacles 
removed, and a thread tied around the siphon, so that about 
one and a half millimeters of the organ were visible between the 
anterior margin of the shell and the thread. It was noted that 
the slit-like aperture on the under side of the siphon posterior 
to the thread opened and closed, indicating that water could 
still pass into the mantle chamber through the proximal portion 
of the organ. Less than half an hour after tying the siphon the 
‘snail was moving about with the organ extended in normal 
fashion. Fish extract and carmine applied to the lateral foot 
processes induced the proboscis reaction in five trials out of six. 
The proximal part of the siphon was bent down into the juice 
after the contraction of the foot process, and before the extension 
of the proboscis. In one trial the siphon was only slightly moved, 
and no further response ensued. 
A second thread was then tied around the siphon about one 
millimeter back of the first. Several tests made shortly after 
this operation, and on the following day, gave similar results. 
The proboscis.was extended when the base of the siphon was 
definitely moved into the fish extract. In an attempt to tie a 
third thread about the siphon, the organ was pinched off just 
back of the second thread. It was now slightly over one milli- 
