526 Natural History of Molluscous Animals : — 
stance of its being dissolved by boiling, a process not likely 
to destroy a vascular communication. The other fact, which, 
however, is anomalous, being peculiar to the oyster, I cannot 
explain. The cavity itself is difficult to find, and escaped my 
observation in some attempts made to discover it; but I am 
informed, by a very skilful anatomist, that it is to be found on 
the anterior part of the shell, at the edge. The communica- 
tion between it and the body of the fish must be exceedingly 
minute, perhaps impervious, for no oyster-eating acquaintance 
of mine has any knowledge of the fetid fluid. 
I should, however, have led you into error, were you, from 
these remarks, to conclude that there is no closer connection 
between the shell and its inmate than between the mason and 
the house he has built. On the contrary, the connection 
between them is inseparable during life, but it is made merely 
through the medium of muscles which go from the animal to 
be inserted in the parietes. of its dwelling. The Mollisca of 
bivalved shells are in this manner attached by one or two 
large and powerful muscles; called, sometimes, transverse, be- 
cause, passing through the body, they are inserted into both 
valves at opposite points ; and, sometimes, adductors, because 
their office is to close the valves and keep them so; and the 
astonishing force with which they act is well illustrated by the 
extreme difficulty of opening those of an oyster. In simple 
conical univalves, as the limpet (Patélla Zin.), the body * is 
fastened to the circumference of the shell by a ring of fibres, 
whichare attached all round the shell, and which, after piercing 
the outward covering or cloak, are inserted in the edges of 
the foot, and interlaced with its circular fibres. Anteriorly they 
leave a free space for the passage of the head. This muscle, by 
its contractions, brings the foot and the shell closer together, 
and compresses the body ; on relaxing, it allows the shell to be 
raised up by the elasticity of the body.” The snails of spiral 
shells are bound to them by two muscles, which arise from 
the pillar, and, having penetrated the body below its spiral 
part, run forward under the stomach, and spread their fibres 
in several slips, which interlace with those of the muscles pro- 
per to the foot, the substance of which they enter. It is ob- 
vious from this direction, that, on their contraction, the body 
of the snail must be drawn within the shell. When it wishes 
to reissue, the head and foot are forced out by circular fibres, 
which surround the body immediately above the foot.* 
Having yoked them to their shells, I will next direct your 
attention to the locomotion of the various tribes ; but it may be 
* These particulars are from Cuvier’s Comp. Anatomy. 
