OLFACTORY REACTIONS OF MARINE SNAILS allay 
osphradia, is well supported by the condition and behavior of the 
animals about to be described. 
The fragmentary and inconclusive results obtained from four 
of the snails were in striking contrast to those derived from the 
study of the remaining five, which were under observation 
from twenty to twenty-five days after the operations. An 
examination of the anaesthetized animals with the aid of a 
mirror after all the tests had been made, showed that the osphra- 
dia had been removed without apparent injury to the mantles. 
The general behavior of the snails was like that of animals which 
had not been operated upon. They were active in the aquarium, 
buried themselves’ characteristically in sand, and there was no 
abnormal contraction of mantles or siphons. Both morphologi- 
cally and physiologically they gave every appearance of healthy 
animals. The earlier experiments demonstrated that the ex- 
tirpation of a considerable portion of the osphradium produced 
no observable shock effects, the reactions after the operation 
being the same as before, and it was exceedingly unlikely, there- 
fore, that the successful removal of the whole of it would do so. 
When oyster extract was applied to the siphon tips of these 
snails no reaction of the usual type ensued. Sometimes the 
siphon was raised somewhat, or the end flared a bit, but the 
response so characteristic of a snail scenting food and so clearly 
shown by these individuals before the osphradia were removed 
no longer appeared, and not once was the proboscis extended 
after the application of the extract, although they were tested 
many times. This cessation of olfactory response was very 
striking when the snails were buried in the sand. Before ‘the 
operations four of them were tested once, and one three times 
in this position. In these seven trials there was not a single 
failure in the response to oyster extract taken into the siphon. 
The snails were entirely out of the sand in the maximum time 
of three minutes, and the average time of less than two minutes 
after stimulation. After the removal of the osphradia, however, 
there was complete lack of response under similar conditions. 
The animal which was given three trials before the operation 
was tested five times afterward, and the other four were given 
