OLFACTORY REACTIONS OF MARINE SNAILS 211 
could be seen by inserting a small dental mirror into the mantle 
chamber after the animal had been anaesthetized with magnesium 
sulphate. This discovery made possible at least the complete 
elimination of the osphradium without injury to surrounding 
parts. 
The osphradia of four snails, whose olfactory responses had 
been carefully studied, were cauterized. All four subsequently 
failed to show scenting reactions when oyster extract was taken 
into their siphons, whereas they had been decidedly responsive 
to it before. They also paid no attention to pieces of oyster 
when offered after testing them with the extract. If, however, 
a snail was removed from the water, and a piece of oyster placed 
beneath the head near the false mouth,! or in one case, between 
its lips, the proboscis was usually extended and the oyster eaten. 
One of the snails also took this food when it was dropped be- 
tween the head and foot while resting on the side of the aquarium 
at the surface of the water. Only one test was made with the 
snail in this position. In short, when a concentrated food stimu- 
lus was applied to the skin in the rhynchostome region or to its 
lips the feeding reaction occurred. 
Although highly suggestive, these results were not considered 
conclusive, as all four animals, at times at least, showed more or 
less contraction of the mantle or siphon. When, after anaes- 
thetizing three of them, an examination of the osphradia was . 
made, one or two large holes were found in the mantles. Since, 
at the most, only traces of the osphradia appeared, the organs 
undoubtedly had been rendered non-functional. 
It was evident that the last cauterization method employed 
was directly injurious to the mantle, and led to undesirable 
conditions of the siphon. Accordingly, the original procedure 
of scraping away the osphradium was again undertaken, this 
time with the aid of a mirror. The lamellae of the organ are 
delicate and offer little resistance to the flattened tip of a wire, 
' The so-called false mouth or rhynchostome, which is the opening of the 
cavity about the proboscis, should be distinguished from the true mouth at the 
free end of the proboscis. The former is the aperture which is visible on the 
under surface of the head through which the proboscis is protruded. 
