156 SUPPLEMENT 
sometimes, however, the epidermic mucous part of the shell is 
prolonged, as it were, externally, and is rounded or flatted, 
so as to present a pilose aspect, as may be seen in certain spe- 
cies of helix, and of bivalve shells. 
In the oscabrions, this disposition is still more marked upon 
the skin itself, and sometimes we find in certain species bun- 
dles of corneo-calcareous hairs on each side of the body. 
As it happens pretty often that the skin of the mollusca is 
larger than necessary to surround the body exactly, or the 
mass of the viscera, and that the folds which it forms seem to 
envelope it, as our body might be in a mantle or cloak, this 
name (pallium) has been generalized to designate the skin of 
the mollusca, though in reality this disposition does not 
always exist. 
~The general disposition of the mantle of the mollusca pre- 
sents so great a number of differences, that it would be almost 
tiresome to enumerate them; we shall therefore confine our- 
selves to the principal ones. In octopus, sepia, and loligo, it 
forms a sort of purse or very thick sheath, open at the lower 
circumference of the neck, and it is through this aperture that 
the water penetrates into the branchial cavity which it consti- 
tutes. In the conchyliferous acephaia, the part of the skin 
which covers the viscera is excessively slender; it thickens 
gradually towards the edges of the mantle, and forms round 
the pedicle which joins the foot to the visceral mass a sort of 
ring, more slender behind, much thicker in front, and to which 
the name of collar is often given. Itis in the thick part of 
this free edge of the mantle that are found in the greatest 
abundance the mucous pores which produce the shell, and it 
is into the middle of these edges that the head and foot of the 
animal re-enter when it is desirous of a complete shelter in its 
shell. The extent and form of the aperture of the mantle are 
always in relation with the bulk of the pedicle of the feet ; ac- 
cordingly, very much contracted in the buccina and the neigh- 
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