THE SIIOHES OF Bi;[TAIN. 91 



butcd ; and tliough the last two agree in being in- 

 vested with what is, in common parlance, called " a 

 shell," yet the crust of the one bears no analogy in 

 form, structure, or composition, to the shell of the 

 other. Again : those animals which, like the Oyster, 

 are covered with true calcareous shells, differ greatly 

 from each other : some, as the Periwinkle and the 

 "Whelk, being animals of much higher grade in the 

 scale of development than others, as the Oyster or 

 Scallop. The former crawl with ease on a broad 

 fleshy disk, as we have all seen in the case of the 

 garden Snail, an animal closely allied to them ; they 

 have a distinct head, with tentacles, jaws, and often 

 with eyes ; but the latter have no power of crawling, 

 being, for the most part, confined to one spot, no 

 liead, and no jaws, but are shut up within their two 

 shells, which can be opened only to a small extent 

 during the life of the animal. Yet we must not for 

 a moment suppose that these creatures are unhappy, 

 or that the meanest occupant even of a bivalve shell 

 is not supplied with everything that could conduce to 

 its welfare. It is SEsr alone that is the source of 

 unhappiness. I will just point out one or two par- 

 ticulars in which the Divine care for these creatures 

 is manifest. All of them have the vital parts of the 

 body protected by a thick fleshy coat, somewhat pro- 

 jecting at the edges, called the mantle : the surface 

 of this organ has the power of forming the shell, by 

 depositing stony matter in a sort of glutinous cement, 

 which soon hardens into a thin layer of shell. If a 

 little piece were broken otF the edge of the shell oi 

 a "WTiielk, when alive, the animal would press the 



