MOLLUSCS, 767 
The organs of sense are more developed, as a rule, in this than 
in the two preceding classes. The head is usually furnished (in 
most G‘asteropoda) on the upper surface with two feelers, on the 
outer margin of which the eyes, sometimes on two little tubercles 
or pedicles, are situated. When the eye-supporting pedicles are 
developed independently, two pairs of feelers are present. In 
some these feelers are hollow and can be everted like the finger of 
a glove after they have been drawn in, as may be seen in the com- 
mon snail. Besides these feelers situated on the head, different 
productions of the mantle are probably the seat of a finer sense of 
touch, as the cerr¢ round its margin in Patella and Haliotis. The 
folded and indented fringe or circular lip in the Cephalopoda, the 
various feelers round the mouth in Nautilus, may also be regarded 
as organs of tact. 
Taste cannot be very highly developed, since the tongue, as we 
stated above, is horny. Of the organ of smell nothing certain is 
known, although in Nautilus a part, first pointed out by VALEN- 
CIENNES, situated close to the eyes, may probably be regarded as 
such. That, however, many molluscs possess the sense of smell 
seems to be demonstrated by observations; thus SwAMMERDAM 
found that vineyard snails, when he brought fresh food near them, 
came out of their house and crept quickly towards it. According 
to Cuvrer the entire mantle that covers these animals may be 
analogous to the pituitary or mucous membrane of the nasal cavities, 
and thus very appropriately the organ of smell?. 
The auditory organ was known in the Cephalopods alone a few 
years ago. In the cartilage of the head two small cavities are 
found, which enclose a sacculus filled internally with a fluid, whilst 
it is surrounded also by a fluid substance and attached to the larger 
cavity, in which it is suspended by numerous fibrous threads. In 
this sac, in most species, there lies a calcareous round or conical 
little stone. The auditory nerve penetrates the saccule, and divides 
into fine branches on its inner surface. There are neither apertures, 
also GARNER in Linn. Transact. Tom. xvi. cited above, p. 716. For the nervous 
system of the Cephalopoda see below on this order. 
1 Legons d’ Anat. comp. i. p. 676. BuAINVILLE, who regards the antennz of insects 
as olfactory organs, ascribes similarly to the feelers of molluscs the capacity of smell. 
Principes @ Anat. comp. 
