208 MANTON COPELAND 
oyster, the snail began feeding and gave no further sign of 
agitation. Another animal, whose siphon was tied as in the 
preceding case, responded to oyster juice placed in front of the 
end of the siphon by circling to the left. Owing to the curvature 
of the shell all attempts to fasten the siphon to the right of its 
median position were unsuccessful. 
Before any further discussion of these results is undertaken, 
it seems desirable to give an account of an investigation demon- 
strating at least one function of the osphradium. 
3. The osphradium 
The study of the responses of Alectrion and Busycon reported 
in the preceding pages led to the belief that an olfactory receptor 
was situated somewhere within the mantle cavity, and accord- 
ingly an investigation of the part played by the osphradium in 
the scenting reactions of Busycon was finally undertaken. 
Although the osphradium on account of its peculiar structure 
was formerly called a ‘false gill,’ it more recently has been termed 
an olfactory organ, or one for testing the quality of the water 
entering the mantle chamber. The evidence in support of the 
latter designation appears to be principally of a morphological 
character. In the first place, it was found that the organ was 
richly supplied with nerve endings and was undoubtedly a 
receptor of some sort, and secondly, its position on the mantle 
at the base of the pallial siphon would necessitate water taken 
in through the siphon coming in contact with it before reaching 
the gill. In this connection a statement by Dakin (12) in 
his work on the morphology of Buccinum is of interest, since 
this genus possesses the same kind of osphradium in the same 
relative position as that found in Busycon. 
One would imagine from observation of the living animal that the 
siphon was connected with some important system of.sense organs. 
It is continually in motion from side to side, and extends much further 
from the animal and is more active than the tentacles. 
Examination of the mantle cavity in this light reveals an interesting 
series of organs. The osphradium, which is a darkly pigmented 
structure on the left side, is situated right across the end of the siphon 
(fig. 8, Osph.). Thus all water entering the pallial cavity must pass 
over it before reaching the other organs. 
