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 Mollusca 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 (Patella Lin.\ the body " is 

 fastened to the circumference of the shell by a ring of fibres, 

 which are 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 yo'ked 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 Cuvicr's Comp. Anatomy. 



