_Nacre_ or _mother-of-pearl_ is the inner part of the shell of the pearl muscle. This is of a brilliant and beautifully white colour, and is usually separated from the external part by aqua-fortis, or the lapidary's mill. Pearl muscle shells are on this account an important article of traffic to China and many parts of India, as well as to the different countries of Europe. They are manufactured into beads, snuff-boxes, buttons, and spoons, fish and counters, for card-players, and innumerable other articles. The pearl muscles are not considered good as food; though, after having been dried in the sun, they are sometimes eaten by the lower classes of people in the countries near which they are found. 274. _The COMMON or EDIBLE MUSCLE_ (Mytilus edulis, Fig. 79) _is a testaceous animal, with a smooth double or bivalve shell of oblong oval form, pointed, and slightly keel-shaped at the beak, flatted and somewhat curved on one side._ _The colour is generally blackish, and the length about three inches._ _This species of muscle is found adhering to sub-marine rocks by certain silky threads, which it forms from its own body; and it is common both in the Indian and European seas._ In many parts of Europe muscles are nearly as much in request for the table as oysters; and at Rochelle, and some other places, modes are adopted of increasing their excellence, by placing them, after they are taken from the sea, in pools or ditches where the sea-water is stagnant, and introduced only at particular periods as it is wanted. Muscles are caught nearly through the whole year, though they are considered best in the autumn. To some constitutions they are an unwholesome food, producing inflammation, eruptions on the skin, and an intolerable itching over the whole body; the best remedies for which are said to be a liberal use of oil, emetics, or milk. 275. _The OYSTER_ (Ostrea edulis, Fig. 77) _is a testaceous animal, too well known to need any description._ _It is found affixed to rocks, or in large beds, both in the European and Indian seas._ The use of oysters as food has rendered them celebrated in all ages. The ancient Roman writers speak of them as in great request by that luxurious people. Pliny relates that in his time they were considered so exquisite as, when in perfection, to have been sold for enormous prices; and that Apicius, the notorious epicure or glutton, invented a peculiar method of preserving and fattening them.