296 THE INHABITANTS OF THE SEA, 
humble sphere of existence. The organs of sight are generally 
situated either on a promi- 
nence at the base of the 
superior pair of tentacles 
or, as, for instance, in the 
Murex, at the extremity 
of these organs (a, b), a 
position which enables 
the animal to direct them 
readily to different ob- 
jects. 
Many of the Gasteropods 
are evidently capable of 
perceiving odours; thus, 
animal substances let down 
in a net to the bottom will 
attract thousands of Nass 
in one night. We also may 
infer that they are not de- 
ficient in taste from the presence of papille at the bottom of 
their mouth, analogous to those found on the tongue of other 
animals; but, of all their senses, that of touch is undoubtedly 
the most perfect. The whole soft surface of the body is indeed 
of exquisite sensibility, but more especially the vascular foot, 
and the tentacles, or horns, which vary both in number and in 
shape in different genera. Yet, in spite of this delicacy in 
the organisation of the skin, which makes it so sensible of 
contact, it appears to have been beneficently ordered that 
animals so helpless and exposed to injury from every quarter 
are but little sensible to pain. Although they are deprived of 
all higher instincts, we find among the Gasteropods a few 
examples of concealment under extraneous objects, which 
remind us of the masks and artifices frequently employed by 
the insects and crustaceans. 
The Agglutinating Top (Trochus agglutinans) covers itself 
with small stones and fragments of shells, and thus shielded 
from the view escapes the voracity of many an enemy but 
little suspecting the savoury morsel hidden under the mound of 
rubbish which he disdainfully passes by. 
Tn animals which are only provided with passive means of 
Tentacles and eye of Murex. 
e. Eye highly magnified. 
