REMOVAL OF WHORLS. 121 



the animal be wounded. In this instance, calcareous 

 matter exudes, and a pearly deposit is produced. The 

 worn edges of shells and their fractures are never re- 

 paired, except so far as they can be by the addition of 

 materials from the secreting surfaces of the mantle. 

 Still, it were erroneous to suppose that there is no closer 

 connexion between the shell and its inmate, than be- 

 tween the mason and the house he has built. On the 

 contrary, the connexion 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 or walls of its dwelling. The mollusca 

 of bivalved shells are thus attached by one or two 

 large and powerful muscles ; sometimes called trans- 

 verse, because, passing through the body, they are in- 

 serted into both valves at opposite points ; and some- 

 times adductions, because their office is to close the 

 valves, and keep them shut ; and the astonishing force 

 with which they act is felt whenever there is extreme 

 difficulty in opening those of an oyster. 



In some univalves, as the limpet, 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 



