OLFACTORY REACTIONS OF MARINE SNAILS Pere 
found in Busyeon, where the two form an apparatus by means 
of which the snail under the influence of olfactory stimulation 
is directed toward food with remarkable precision. <A close 
inspection of the mud snail’s behavior in the presence of food 
showed clearly that the animal did not find it by wandering 
about until it happened to be encountered. When the snail 
is crawling, the right and left siphon movements predominate. 
The organ is not held at the same level throughout its course, 
but usually the distal end is depressed at the termination of the 
lateral movement, often so as to touch the bottom, and is lifted 
as it returns to the opposite side. Frequently it is waved about, 
is directed upward or even turned backward. The free condition 
of the siphon in the mud snail thus allows many irregular changes 
in its position, which may tend to make less evident the right 
and left ones which in Busycon, on account of the restriction 
of siphon movement by the shell, are directly recognized. 
A small piece of butterfish, a little over a centimeter in diam- 
eter, was placed on the bottom of a glass aquarium containing 
several mud snails. The animals after scenting the food found 
it by movements which unquestionably were directed by ol- 
factory stimulations. They were seen to turn into the fish 
when headed in a direction which, if followed, would take them 
by it. Sometimes after circling about, they drew away from 
the meat, but then proceeded to it in a fairly straight course. 
All the time their siphons were swung from one side to the 
other, often being raised betweed the lateral movements, and 
their proboscides were extended when they were several centi- 
meters away from the fish. One snail, which scented the food 
when five to eight centimeters off, circled about rapidly extending 
and swinging its siphon in the characteristic manner. It then 
‘moved toward the fish but, when closest to it, the siphon hap- 
pened to be directed away, although the organ would have 
touched the food if it had been swung to the opposite side at 
that moment. Asa result the snail missed the mark by a slight 
margin and went beyond it about five centimeters, when it turned 
and took a straight course back to it. Another snail, which 
was moving in a direction comparable to the last, stretched its 
