Tubipora Musica.
The Tubiporidæ are confined to the narrow limits of a single genus containing but few species. Here the polypary is composed of distinct calcareous tubes rising from a fleshy or membranaceous basis, and arranged in successive stages. These tubes are separated from each other by considerable intervals, but mutually support each other by the interposition of external horizontal plates, formed of the same dense substance as themselves, by which they are united together, so that a mass of these tubes exhibits an arrangement something like that of the pipes in an organ, whence the beautiful Indian species, Tubipora musica, has derived its name. From the upper ends of the tubes the polyps are protruded, and being, when alive, of a bright grass-green colour, they contrast very beautifully with the rich crimson of the tubes they inhabit.
Caryophyllia.
In our seas, the coralligenous Zoophytarians, distinguished by the hard calcareous skeletons they deposit within their tissues are but feebly represented by a few straggling Caryophylliæ, but in the tropical ocean they branch out into numerous families, genera, and species, and play a highly important part in the economy of the maritime domain. Originally proceeding from single ova, which at first freely move by means of vibratile ciliæ, and become fixed after a short period of erratic existence, they multiply by gemmation, and grow into an immense variety of forms, of which the following description by one who has long and attentively studied them in their native haunts may serve to give an idea. "Trees of coral," says Professor Dana, "are well known; and although not emulating in size the oaks of our forests—for they do not exceed six or eight feet in height—they are gracefully branched, and the whole surface blooms with coral polyps in place of leaves and flowers. Shrubbery, tufts of rushes, beds of pinks, and feathery mosses, are most exactly imitated. Many species spread out in broad leaves or folia, and resemble some large-leaved plant just unfolding; when alive, the surface of each leaf is covered with polyp-flowers. The cactus, the lichen clinging to the rock, and the fungus in all its varieties, have their numerous representatives. Besides these forms imitating vegetation, there are gracefully modelled vases, some of which are three or four feet in diameter, made up of a network of branches and branchlets, and sprigs of flowers. There are also solid coral hemispheres like domes among the vases and shrubbery, occasionally ten or even twenty feet in diameter, whose symmetrical surface is gorgeously decked with polyp-stars of purple and emerald-green."
Under such aspects appear the living organisms whose combined efforts have mainly constructed those reefs and islands of coral origin which now lie scattered far and wide over the surface of the equatorial ocean. Words are inadequate to express the splendour of the submarine gardens with which the lithophytes clothe the rocky shores of the tropical seas.
"There are few things more beautiful to look at," says Captain Basil Hall, "than these corallines when viewed through two or three fathoms of clear and still water. It is hardly an exaggeration to assert that the colours of the rainbow are put to shame on a bright sunny day by what meets the view on looking into the sea in those fairy regions." And Ehrenberg was so struck with the magnificent spectacle presented by the living polyparia in the Red Sea that he exclaimed with enthusiasm, "Where is the paradise of flowers that can rival, in variety and beauty, these living wonders of the ocean!"
Besides the charms of their own growth, the tropical coral gardens afford a refuge or a dwelling-place to numberless animals clothed in gorgeous apparel. Fishes attired in azure, scarlet, and gold, crustaceans, sea-urchins, sea-stars, sea anemones, annelides, of a brilliancy of colour unknown in the northern seas, glide or swim along through their tangled shrubberies; and frequently the gigantic tridacna, embedded in their calcareous parterres, discloses, on opening her ponderous valves, her violet mantle tinted with emerald-green. The enchanted naturalist lingers for hours over the magnificent spectacle, and forgets the lapse of time, as wonders upon wonders crowd on his enraptured gaze.
But the tropical coral-gardens serve not only as a harbour of refuge to the numberless creatures that frequent their labyrinthine recesses, for many annelides, crustaceans, asterias, and even fishes, feed upon their animal flowrets. Among these, the Scari are provided with a very remarkable dental apparatus to protect their mandibles from injury while biting the calcareous corals. These fishes have their jaws, which resemble the beak of a parrot (whence they receive their usual appellation "parrot fishes"), covered externally with a kind of pavement of teeth, answering the same purpose as the horny investment of the mandibles of the bird. The teeth that form this pavement are perpetually in progress of development towards the base of the jaw, whence they advance forward, when completed, to replace those which become worn away in front by the constant attrition to which they are subjected. Thus armed, the Scari browse without difficulty on the newest layers of the stony corals, digesting the animal matter therein contained, and setting free the carbonate of lime in a chalky state. Many of the Diodons, Chætodons, and Balistæ or file-fishes, of which Kittlitz saw some new species, one still more splendid than the other, in every lagoon-island he visited in the long range of the Carolines, likewise feed upon corals, and possess a dental apparatus fit for masticating their refractory aliment. The Diodons have grooved teeth, excellently adapted to crush and bruise, and the Balistæ have eight strong conical teeth in every jaw, with which they easily nip off the shoots of the coral bushes.
Of the reef-building corals it may well be said that they build for eternity. The bones of the higher animals vanish after a few years, but the stony skeleton of the polyp remains attached to the spot of its formation, and serves as a basement or stage for new generations to build upon. Life and death are here in concurrent or parallel progress; generally the whole interior of a corallum is dead. The large domes of the astræas are in most species covered with a hemispherical living shell, about half an inch thick; and in some porites of the same size the whole mass is lifeless, except the exterior for a sixth of an inch in depth.