CORAL, a calcareous secretion or deposit of many kinds of zoophytes (q.v.) of the class antkozoa, which assumes very various, and often beautiful forms, according to the different laws which govern the gemmation of the polyps of the different species. The C. producing zoophytes are compound animals, which increase by gemmation, young polyp buds springing from the original polyp, sometimes indifferently from any part of its surface, sometimes only from its upper circumference, or from its base, and not separating from it, but remaining in the same spot, even when tho original or parent polyp has ceased to exist, and producing buds in their turn. The calcareous deposi tion begins when the zoophyte is still a simple polyp—owing its existence to oviparous reproduction—adhering to a rock or other substance, to which the calcareous matter becomes affixed, and on which the C. grows or is built up, the hard deposits of former generations forming the base to which those of their progeny are attached. One layer of the calcareous polyp cells of which the greater number of corals are composed, oc casionally surrounds another like the concentric circles in the wood of exogenous trees; one layer is sometimes deposited above another; the whole structure sometimes branches like a shrub, spreads like a fan, or assumes the form of a cup, a flower, or a mushroom. Under the common name C. are included many species, also designated madrepores (q.v.), and sonic have received other names derived from peculiarities of their form and appearance, as brainstone C. (q.v.), etc. In the greater number of kinds, besides the calcareous plates which form and separate the polyp cells, and which are variously ar ranged according to the form and structure of the polyps themselves, there is a more solid internal or central calcareous part, formed by the additional deposition of calcare ous matter at the bottom of each polyp cell, or from the common living part in which the polyps are united. The calcareous framework is further strengthened by a greater or less mixture of horny animal matter with the pure calcareous substance. This cal careous framework is analogous to the cartilaginous, leathery, or fibrous framework of many other compound zoophytes, as aleyonnint (q.v.), or dead man's fingers. The polyps of the common RED C. (eorallium rubrum) indeed very much resemble those of alcgonium; but the central axis in this and other corals forming the family corallicke is quite solid, being produced in concentric layers by the living gelatinous substance, which envelops it like the bark of a tree, and from which the polyps project like buds, or, when their tentacula are expanded, like little flowers. In the madreporidce,
the general structure more nearly resembles that of aleyonium. Many of them, how ever, have the whole calcareous framework covered as in the corallithr, by a gelatinous living substance which unites all the polyps. The whole living part soon decomposes and disappears, when the C. is taken out of the water; in some species, almost imme diately running from the calcareous part as a watery slime.
Corals chiefly abound in the seas of the warmer latitudes, where they form extensive banks at no very great depth, and their various and bright colors present the appearance of submarine flower-gardens. Numerous species are usually combined in the formation of a single C. reef, and respectively occupy different places in it. Corals of the branch ing genus porites usually occupy the exposed edge of the reef, and with them is asso ciated millepora eomplanata, a species which forms thick vertical united at different angles by their edges, the outer plates only being tenanted by living polyps. In the stiller water within are many more delicate kinds, and in the quiet sheltered depths. brainstone corals and flower-like forms appear.
The C. of commerce, or common RED C.—so much admired for its fine color, suscepti ble of a high polish, and much used for ornamental purposes—is chiefly obtained from the Mediterranean, in some parts of which extensive " coral fisheries " are carried on. It is brought up from considerable depths by means of a sort of grappling apparatus dragged after a boat or boats: the pieces being broken from the bottom by beams of wood which are sunk by weights, and then entangled among hemp. Red C. has a shrub-like branching form, and grows to the height of about one foot; with a thickness like that of the little finger. Much of the C. of the Mediterranean is exported to but red C. is also obtained in the Red sea, the Persian gulf, etc.—BLACK C. (anti'pathes), the axis of which is rendered still more solid by the greater mixture of horny with cal careous matter, is still more highly prized. C. was known to the ancients, and was used for ornamental purposes by the Gauls.