ON MOLLUSCA. 155 
The distinction of neck, breast, abdomen, and tail, is still 
less evident ; the body forming but a simple mass, or some~- 
times subdivided in a vertical direction, but never in a longi- 
tudinal. 
The body is but rarely provided with locomotive appendages 
properly so called, but sometimes presents cutaneous expan- 
sions, more or less extended, which serve to locomotion. It 
is only in some that the disposition of the appendages assumes 
a form a little analogous to that which takes place among the 
entomozoaria. 
The skin which envelopes the body of the malacozoaria 
presents a peculiar character in its softness, its sponginess, 
and especially in the manner in which the dermis is con- 
founded with the subjacent muscular fibre, so that it is con- 
tractile in all points and in all directions. This dermis, as to 
the rest, may either be tuberculous, or very smooth; the vas- 
cular net-work there, is moreover, very considerable. ‘The 
colouring pigmentum is often very lively. It is also probable 
that the nervous stratum may be tolerably complete, from the 
great quantity of nerves which repair thither. As for the epi- 
dermis, it is often reduced to a nullity. 
If we may judge from the great quantity of mucosity which 
is spread in general over the surface of the skin of the mol- 
lusca, we should believe that the mucous crypt there were 
very numerous; but it is often very difficult to demonstrate 
their presence. We find parts, however, where the mucous 
pores are evident, as at the thickened edge of the mantle, 
which constitutes the collar of the conchyliferous cephala, and 
probably at the place which often forms numerous folds in the 
bottom of the respiratory cavity, towards the anus, and which 
have been designated under the name of mucous folds. In 
effect, there issues from these places in the skin much more 
mucus than from all the others. 
We never observe genuine hairs in any animal of this type ; 
