OLFACTORY REACTIONS OF MARINE SNAILS 221 
after olfactory stimulation, it traveled in directions which carried 
it far from the direct course to the source of the odor. 
The arrangement of the olfactory receptors of the fish has 
at least one slight advantage over the scenting apparatus of the 
snail. In the fish there is always a receptor on both sides of the 
head ready to be stimulated, whereas in the snail the osphradium 
may not be affected by stimulating material present on one side 
of the body, when it would be of advantage to the animal if it 
were, because of the fact that at the appropriate moment the 
siphon may be directed in the wrong way to receive it. This, I 
believe, is exactly what happened when the mud snail, described 
a few pages back, first went by the piece of fish meat instead of 
finding it directly. This defect in the snail’s olfactory receptive 
apparatus, however, under most circumstances cannot be a 
serious one for a slowly moving animal, and it may be somewhat 
overcome by the acceleration in siphon movement which usually 
follows stimulation. In another respect, on the other hand, the 
snail’s scenting apparatus has a distinct advantage over that of 
most animals possessing paired organs, unless they exhibit 
greatly accentuated lateral head movements. The area over 
which a change in the stimulating material can be recorded on 
the receptor, when Busycon is moving in a straight course, is 
twice as wide as it would be if paired olfactory organs were situ- 
ated on the sides of the foot, which is about six or seven centi- 
meters broad and ten to twelve centimeters long, and four times 
as wide if they were on the sides of the head. The siphon ‘nos- 
tril’ of this snail has a side to side range of action which is three 
times greater than the distance between the paired nostrils of a 
dogfish about eighty centimeters long, one which is greater than 
that distance in a large sand shark, and equal to it in a dusky 
shark of medium size. 
2. Taste and smell 
Although a detailed study of the sense of taste in the snails 
was not attempted, some facts pertaining to their gustatory 
reactions and to the distribution of surfaces sensitive to taste 
