Coral (Gr.Coral 0500126 ; Lat. coralium, curalium, or corallum). The derivation and use of tbis term are discussed by Theophrastus in his work on plants. Such were these stony products of the ocean naturally believed to be, from their growth resembling that of the productions of the garden. Imitating the forms of trees and flowering shrubs, they rivalled them in gracefulness and delicacy; and the brilliant hues of the blossoms that crowned them made permanently beautiful these gardens in the depths of the sea. And when at last Peyson-nel, in an elaborate memoir sent to the royal society in 1751, supported the opinion (first advanced by the Neapolitan naturalist Fer-rante Imperato in 1599) that the coral blossoms, les fieurs du corail (so described in 1706 by Marsigli), belonged to the animal and not to the vegetable kingdom, his views met with a cool reception among naturalists, and were pronounced even by Reaumur too absurd to be discussed. The power of vegetation to produce stately forests and the minutest plants was familiar to naturalists. To ascribe still greater power and as elaborate skill to "poor, helpless, jelly-like animals," seemed like an insulting demand upon their credulity.

The controversy was continued through the greater part of the last century. The coral animals were shown in form resembling blossoms, sending forth their petal-like tentacles in series around the mouth, and drawing into this their prey. Still Linnaeus would admit their possession only of a nature intermediate between plants and animals, and the word zoophyte (Gr.Coral 0500127 j animal, andCoral 0500128 to grow like a plant) was applied by him to the organic bodies, with reference to their supposed relation to both kingdoms. The word is still in use with naturalists as a distinctive term for the division of animals in which the sponges are included. The whole compound animal mass produced by budding is called by Prof. J. D. Dana a zoothome (Gr.Coral 0500129 animal, andCoral 0500130 a heap), and the single animal is called by him a polyp. - Coral is the stony frame which belongs to these animals, as a skeleton belongs to an individual of the higher orders of the animal kingdom. It is called by Prof. Dana the corallum, and the coral of a single polyp in the mass is called a corallet. It is formed within the mass of them by animal secretion, each individual adding to the common structure, not by actual effort directed to this purpose, but by the involuntary secretion of calcareous matter. Hence it will be seen that corals are not, as formerly supposed, the products of the labor of the coral animals, but are the results of a growth analogous to that of the bones in other animals. A single polyp of the genus astrma (see fig. 1), for instance, has a disk above surrounded with tentacles, like the actinia or sea anemone, to which it is closely allied; the mouth at the centre of the disk opens into a stomach, and is the passage for the food and for the exit of refuse matters. Below and around the stomach space is divided radi-ately by a series of pairs of fleshy plates, the larger of which extend from the stomach to the sides of the polyp.

The coral is secreted between the plates of these several pairs, as well as through the tissues; and hence comes the radiate character of the interior of the cells over the surface of a coral, that is, the star-like interior of each corallet. The material of the coral is carbonate of lime, or the same that constitutes limestone, and it is taken by the polyp from the sea water or from its food. Fig. 2 represents the coral of a single polyp, one of the larger simple kinds, reduced to one fourth its natural size. When alive the whole corallum was concealed by the fleshy exterior; the mouth was situated over the middle portion of the median furrow from which the calcareous plates radiate outward; and these radiating calcareous plates of the coral were secreted between pairs of fleshy plates, as stated above. Fig. 3 represents one of the branching corals; in the living state each little prominence was the interior of a separate flower-like polyp. - Coral polyps, besides producing eggs and young like other animals, generally multiply also through a process of budding which is closely like growth by buds in the vegetable kingdom.

A new polyp commences as a mere prominence on the side of an old one; soon the mouth and tentacles appear; then both continue growing, each adding to the calcareous accumulation within, and each sending forth new buds to be developed into new polyps. According to the manner in which the buds develop the mass receives its shape. In some species they branch out into tree-like forms from the buds putting forth laterally. In many species of the madrepore family each branch terminates in what is called the parent polyp, this terminal polyp continuing to grow on and at the same time making new polyps for the sides of the branch by the process of budding. In a few species of other kinds each polyp forms a separate branch, at the termination of which it is seated; at these extremities the growth goes on, while the stem below is left behind dead. Other species, in which the polyps form massive corals, put forth the young polyps in the spaces which are produced between the older ones as these extend upward, or they make new ones by a subdividing of an old polyp; thus keeping the hemispherical form symmetrical, till in a single astrsea dome a diameter of even 12 ft. has been attained, and the polyps, each occupying a square half inch only, have increased to more than 100,000 in number.

Many polyps are of still smaller dimensions. A porites of the same size should contain, according to Prof. Dana, more than 5,500,000 individuals. The genus is often met with over the coral reefs, in rudely shaped hillocks sometimes measuring 20 ft. across. Fig. 4 represents a kind, related to the astrms, called brain coral, in allusion to the meandering furrows over the surface. Here, instead of each polyp having a separate cell with its mouth over the centre of it, there are a large number of polyps coalesced along a single furrow, many mouths being visible in the living meandrina along the bottom of the furrow, and a row of tentacles along either side. In addition to the hemispherical forms seen in the star coral (astrcea) and the brain coral (meandrina), and the madrepore shrubs and trees, Prof. Dana remarks that "some species grow up in the form of large leaves rolled around one another like an open cabbage, and cabbage coral would be no inapt designation for such species. Another foliated kind consists of leaves more crisped and of more delicate structure, irregularly grouped; lettuce coral would be a significant name. Each leaf has a surface covered with polyp flowers, and was formed by the growth and secretion of these polyps.

Clustered leaves of the acanthus and oak are at once called to mind by other species; a sprouting asparagus bed by others. The mushroom is here imitated in very many of its fantastic shapes, and other fungi, with mosses and lichens, add to the variety. Vases of madrepores are common about the reefs of the Pacific; they stand on a cylindrical base, which is enveloped in flowers when alive, and consist of a network of branches and branchlets, spreading gracefully from the centre, covered above with crowded sprigs of tinted polyps. The actinise may well be called the asters, carnations, and anemones of the submarine garden; the tubipores and alcyonia form literally its pink beds; the gor-gonise and melitseas are its flowering twigs; the madrepores its plants and shrubbery; and astrseas often form domes amid the grove a dozen feet or more in diameter, embellished with green or purple blossoms which stud the surface like gems, while other hemispheres of meandrina appear as if enveloped in a network of flowering vines." Over the surface of all these corals each depression is the site of a polyp; and the radiated form of this cell corresponds in its plates to the similar structure of the animal.

As young polyps are produced, they communicate for a time or permanently with the parent stock, through the internal cavity, in some species each having in the early period of growth nothing externally to mark its separate existence but a new mouth and incipient tentacles. In a living polyp, the tentacles are expanded and made rigid by injection with sea water. When disturbed, the water is ejected, the tentacles contract and disappear beneath the margin of the disk which is rolled inward over them, and conceals also the mouth. In many even of the larger corals the living portion is but a thin outer part of the mass, the rest having become dead by the drying up of the tissues as growth went on. The various forms of coral are produced by as many species of polyps. A large number of kinds are described and figured by Prof. Dana in his great work "On Zoophytes," and a general review of the subject, illustrated by many figures, is given in his "Coral and Coral Islands" (New York, 1872). - Among the tribes of corals, some species or other are found in all oceans from the equator to the polar regions, and to the lowest depths explored by man. But the range of individual species and families is limited by the physical conditions of light, heat, pressure, etc, appropriate to their organization.

Those tribes which produce the great coral reefs, as the astreeas, madrepores, meandrinas, etc, are developed with peculiar luxuriance in the warmest parts of the Pacific, where the temperature varies from 75° to 85°; but they are also found in waters the temperature of which during the coldest winter months does not fall below 68°, and in other oceans and seas. Two isothermal lines of 68°, one N., the other S. of the equator, near the parallel of 28°, but varying therefrom according to the marine currents and the vicinity of continents, will include all the growing coral reefs of the world. The higher the temperature, the greater is the profusion and variety of the coral reefs. The range in depth of the reef-forming corals appears to be limited to 120 ft., and comparatively few are found below half that depth. This statement may at first sight seem inconsistent with the fact that coral is often found extending from a few feet to hundreds and even thousands of. feet below the surface of the sea. Various theories have been advanced to account for this, but they have all been rejected, and the explanation first offered by Mr. Darwin is now very generally adopted by the scientific world.

Mention has already been made in the article Atoll of the coral reefs of the Pacific, where they are traced in barriers for hundreds of miles; and also of the annular form of many of them, the reef surrounding shallow basins, while the waters outside are often of unfathomable depth. According to Mr. Darwin's theory, which is supported and more fully developed by Prof. Dana in his recent work above mentioned, the bottom of the ocean where these atolls are found has been for ages slowly subsiding, while the coral reef has pari passu been growing upward. Hence, while the living coral has never existed more than 50 or 100 ft. below the surface of the water, the coral rock, the product of former ages, exists at immeasurable depths. The dead corals and shells of the coral seas become ground up by the waves as they sweep over the reef, and thus the beds of coral debris are made which become by consolidation the coral reef rock. This reef rock differs in no important particular from the great limestone strata which are spread over large portions of the western states, and which testify by the corals they contain, and the other fossils associated with them, to a similar mode of production.

The fine white mud which is made by trituration much resembles when dried the ordinary white chalk of Europe. It is often spread over the bottoms of the lagoons or channels, and is also drifted over the shallow seas outside of the reefs by currents. Throughout the long series of the geological formations produced by aqueous deposition, back to those of the Silurian era, the agency of the marine polyps is traced in the production of limestones. At one period, in the lower Devonians, there were true coral reefs of great extent over the Mississippi basin, and along the northern borders of New England; and the corals of those old reefs may be now seen making the old reef rock at the falls on the Ohio near Louisville, and near Lake Memphremagog, in northern Vermont. Unmistakable coral rocks of recent production are met with in the islands of the Pacific and Indian oceans, sometimes hundreds of feet above the level of the sea. In the tertiary and cretaceous formations ranging along our own coast, corals of various species, as perfect as specimens brought from the East Indies, are occasionally taken from the marl pits, together with multitudes of shells, such as now belong to warmer latitudes.

Teeth of sharks and of other fishes are scattered with the shells throughout the rocks of these districts, precisely as they are now left by the fishes whose remains lie entangled among the reefs which were their pastures. Most fossiliferous groups thus contain in their calcareous strata evidences that corals have contributed more or less to their origin. Even limestones that are now crystalline and without a trace of a fossil (owing to alteration through the action of heat and other metamorphic agencies) are in some cases, largely of coral formation. Thus part of the material of the solid marbles quarried from the midst of granitic rocks, and apparently as far removed in their origin as these from the agency of organic bodies, are traced back to the digestive and secretory operations of the coral polyps. By analyses of different varieties of coral, they are found to consist almost solely of carbonate of lime (95 to 98 per cent.). There is a small proportion, usually from 1 1/2 to 4 per cent., of animal matter, and according to Sharpies 0.27 to 0.90 per cent, of phosphate of lime.

Prof. B. Silliman found fluorine in some corals, and Sharpies the "slightest traces of it." Forchhammer obtained 2.1 per cent. of magnesia from the precious coral of the Mediterranean, and 6.36 per cent. from an Isis. The soluble salts of sodium, which form the greater part of the solid matters contained in sea water, are rejected by the polyps, and only those materials are made use of which are best fitted for producing the most substantial structures. By their removal, the waters of the ocean are kept of uniform composition. The soluble impurities poured into them by every river, but for some such provision, would accumulate, as the fresh water alone is carried off by evaporation. The coral insects and marine shells are the agents appointed to keep pure the waters of the great deep, to take up and store away the excess of the lime salts, and preserve the balance in this department of nature, as the vegetable growth performs a similar office in keeping down the excess of carbonic acid in the atmosphere. The great ocean currents spread all the waters among the coral groves, as the winds convey the air through the forests.

The mightiest forces of nature are thus made to administer food to the tiny polyp and the other life of the coral reef. - The coral which is used in jewelry is known as precious coral (coral-lum rubrum). It is mostly obtained in the Mediterranean, the Barbary coast furnishing the dark red, Sardinia the yellow or salmon color, and the coast of Italy the rose-pink; in Europe and in this country the latter is most valued, while in the East the dark red is preferred. Torre del Greco, near Naples, is the residence of many of the coral fishers, and the place from which boats are fitted out for the business. The coral obtained by them is sold to the merchants of Naples, who have it manufactured into various articles of ornament for the European market.

Coral Animals (Astraea pallida).

Fig. 1. - Coral Animals (Astraea pallida).

Fungia echinata.

Fig. 2. - Fungia echinata.

Branching Coral.

Fig. 3. - Branching Coral.

Meandrina (Diploria) cerebriformis.

Fig. 4. - Meandrina (Diploria) cerebriformis.