CORAL (OF. coral, Lat. eorallum, corallius, from Gk. KopaXXiov, korai/ion, coral; of uncer tain origin, possibly a loan-word from Heb. Oral, small stone). A calcareous or horny secretion or deposit of many kinds of polyps of the class Anthozoa, which assume various and often beau tiful forms. Millepore 'coral' is produced by polyps of the class Ilydrozoa- (See MILLEponE.) The coral-producing polyps form colonies which increase by gemination, young polyp-buds spring ing from the original polyp, sometimes indiffer ently 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 the original or parent polyp has ceased to exist, and producing buds in their turn. The calcareous or horny deposition begins when the polyp is single, ad hering to a rock or other surface, on which the coral 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 chambers, of which the greater number of corals are composed, occasionally surrounds an other like the concentric circles in the wood of exogenous trees; one layer is sometimes de posited 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 coral are included many species, also designated madre pores (q.v.), and some have received other names derived from peculiarities of their form and ap pearance, as brain coral. etc. This last forms into large rounded masses furrowed with wind ing depressions like the convolutions of a 1119111 malian brain or a meadow brook, hence its tech nieal name is Meandrina. In the greater num ber of kinds, besides the plates which form and separate the polyp-cells, and which are variously arranged, there is a more solid internal or cen tral part, formed by the additional deposition of matter at the bottom of each polyp-cell, or from the common living part in which the polyps are united. The calcareous framework is sometimes further strengthened by a greater or less mixture of horny animal matter with the purely calcareous substance.
Kinds of are roughly classed under two heads, the horny corals and the lime or stone corals. The former consist chiefly of a horny secretion from the polyps. which may in clude also separate particles of lime, while the stone corals consist almost wholly of lime firmly united in a solid mass. No sharp line can be drawn between these two groups, for all possible gradations can be found. The Antipatharia and Aleyonaria as a rule have a horny skeleton. while the millepores and madrepores are almost wholly limestone. The polyps of the common red or precious coral (CoraMuni nibruni) be long to the suborder Al•yonaria (q.v., for illus
tration) ; but the central axis in this and other corals forming the family CoraMake is quite solid, and is 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 tentacles are expanded, like little flowers. Another aleyona rian coral of more than usual interest is the •organ-pipe' coral (Tubipora) in which no cen tral axis fills in behind the polyps, but the chambers in which they live remain as open, elongated tubes, crowded together side by side to form a solid mass. Its polyps are violet or grass-green, but the coral itself is red or purplish. These corals are found in the Indian and Pacific oceans. Many of the madrepores have the whole calcareous framework covered, as in the Coral by a gelatinous living substance which unites all the polyps. The whole living part soon decomposes and disappears, when the coral is taken out of the water, in some species almost immediately running from the calcareous part as a watery slime.
Utilization.—Red coral—so much admired for its fine color and susceptibility to a high polish. and much used for ornamental purposes—is chiefly obtained from the Mediterranean, in some parts of which extensive 'fisheries' are carried on. It is brought up from consider able 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 coral 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 coral of the Mediterranean is exported to India, but red coral is also obtained in the Red Sea, the Persian Gulf, etc. Black coral (Antipathes) , the axis of which is more solid, is still more highly prized. Coral was known to the ancients, and was used for ornamental purposes by the Gauls.
formation of coral reefs and is lands is one of the most noteworthy results of the action of coral polyps. Many kinds of polyps are concerned in the building of a reef, but the growth is mainly dependent on the stone corals. Reef-building corals only flourish in clean, fresh sea-water, which is not over 125 feet in depth and never is cooler than GS° F. They are con sequently confined to the tropics and to shallow water, and never thrive near the mouths of rivers. Although reef-building corals are not found on the coast of the United States north of Florida, some species of coral occur much further north. Even on the coast of New England there is to lie found quite commonly a true stone coral gia Dane), the polyps of which when expanded are large and very beautiful.