s produced by a secretion peculiar to the Molusca, and chiefly employed in the formation of their shells. (See MOLLUSCA.) In a few species pearl attains an economic importance, and gives rise to considerable branches of industry. Its normal development is as a slimy excretion from the exterior surface of the mantle, which being applied to the inner surface of the shell increases its thickness by the deposition of successive layers. It is abnormally developed for the purpose of covering grains of sand or other foreign bodies, which, by getting accidentally between the delicate mantle and the shell, would, but for this protection, cause irritation and disease to the former. Man takes advantage of both circumstances. By the former process he is supplied with mother-of-pearl, and by the latter with the precious pearls used in jewellery. These are generally spherical in form, and unconnected with the shell of the animal. Linnaeus showed that by perforating a living pearl oyster, and introducing a grain of sand, a nucleus is formed for the development of a pearl.

Precious pearls have been ranked as gems from a very early period; and then, as well as now, the finest both in size and colour were obtained from the Indian Ocean, and are produced by the bivalve *Meleagrina margaritifera*, Lam. The famous wager between Cleopatra and Marc Antony gives us an insight into the value of pearls. At that time the two pearl ear-drops which the luxurious queen proposed to dissolve in vinegar, and serve up at the promised costly repast, were valued at 10,000,000 of sesterces, or about L76,000. The pearl belonging to A. J. B. Hope, Esq. M.P., the largest known in modern times, and far too large to be used as an ear-drop, is not worth a fourth of that sum. It weighs 1800 grains, or 3 ounces, and has a circumference of 4½ inches, and a length of 2 inches. The most usual dimensions of good oriental pearls is from the size of a pea to about three times that size. When much below the size of a pea they are called seed pearls. These seed pearls, as well as the larger kinds, were in great request in the time of Pliny; for he says, "And now at the present day the poorer classes are even affecting them, as people are in the habit of saying that a pearl worn by a woman in public is as good as a lictor walking before her" (the size bespeaking the importance of the person). "Nay, even more than this, they put them on their feet, and that not merely on the laces of their sandals, but all over the shoes; it is not enough to wear pearls, but they must tread upon them, and walk with them under foot as well." (Bohn's edit.) Small pearls are also yielded by other bivalves, as the common oyster, mussel, and more particularly by the pearl-mussel (*Unio margaritiferus*), which was also known to the Romans; for Pliny says, "It is a well-ascertained fact that in Britannia pearls are found, though small and of a bad colour; for the deified Julius Caesar wished it to be distinctly understood that the breast-plate which he presented to Venus Genetrix, in her temple, was made of British pearls." (Bohn's edit.) They are also mentioned by Tacitus in his Life of Agricola as indigenous products of Britain; he describes them "as not very orient, but pale and wan." (See MOLLUSCA.) Strangely enough, these seed pearls, the collection of which was eagerly pursued as a branch of profitable industry by the ancient Britons, is still followed by their descendants in the principality. The traveller who sojourns in the neighbourhood of Conway is sure to be solicited to purchase British pearls, which may be obtained from 5s. to 10s. per ounce. They are of little value except as curiosities.

The finest oriental pearls are obtained from Ceylon and the Persian Gulf; the seed pearls chiefly from Kurrachee, on the Bombay coast, where they are washed ashore, and are collected by coolies, under contractors, who pay 40,000 rupees (£4000) to the Jalpore government for the privilege. The seed pearls are chiefly used by the natives of India and Persia, who attribute important medicinal virtues to them. Pearls of good size and colour are sometimes collected in the West Indies and on the coast of South America. Imports were received from the following places in 1856:—Egypt, value L32,570; St Thomas, L20,744; New Granada, L1,000; British West India Islands, L500; other parts, L348.

The same animal (*Meleagrina margaritifera*) which yields the precious pearl produces also the mother-of-pearl shells of commerce. They are often very large, nearly circular in form, and very slightly convex externally. Specimens are occasionally seen 12 inches in diameter. Generally the *nacre*, or pearly material, constitutes the chief part of the shell, only a thin, worn, dark-coloured crust forming the outside coating or epidermis. They are principally collected on the shores of Madagascar, Ceylon, Manila, Panama, &c. There are three principal kinds:—1st. The silver-lipped. These have a yellowish pearly lustre, generally very clear and bright. The largest shells also occur amongst them. Their value ranges from L80 to L130 per ton. They are imported chiefly from Manila and China. 2d. Blue-edged or black-lipped, from South America or other places, worth from L30 to L40 per ton. 3d. The Panama or bullock-shell, a small kind from Panama, worth from L18 to L21 per ton. The quantity imported in 1856, of all sorts, was 2102 tons, of the value of L76,544. They are used for a variety of purposes—for the manufacture of buttons, for knife-handles, for inlaying, &c. Great numbers are sent to the Holy Land, where the monks carve upon them religious pictures, often of great artistic merit, which are sold to visitors as souvenirs of their visits to the holy places. Many tons are annually consumed in this way, and in making rosary beads and other small articles. The beautiful opalescence of these shells appears to depend upon "minute undulations of the layers, which has been successfully imitated upon steel buttons." (Woodward, Manual of Mollusca.) Other shells are occasionally imported and used by the button-maker and inlayer in consequence of the brilliancy of their nacreous layers, as Turbo marmoratus, Linn., from China, and the beautiful Haliotis gigas from the Indian Seas.