. Natural history. Zoology. Fig, 17.—Oegan-Fitb CoaAL (Tubipora musica). chalk and horn alternately. The fleshy crust which covers the axis, and out of which the individual polypa protrude, is supported by chalky spicules or plates scattered through its substance (see Fig. 18). There are, however, massive forms produced by the eight-rayed polyps which have no central skeletal axis, such as the Blue Coral (Heliopora) and the Organ Pipe Coral (Fig. 17). In the latter, the polyps grow up side by side in separate tubes which result from the fusion of coloured chalky spicules. Those tubes, from whi
. Natural history. Zoology. Fig, 17.—Oegan-Fitb CoaAL (Tubipora musica). chalk and horn alternately. The fleshy crust which covers the axis, and out of which the individual polypa protrude, is supported by chalky spicules or plates scattered through its substance (see Fig. 18). There are, however, massive forms produced by the eight-rayed polyps which have no central skeletal axis, such as the Blue Coral (Heliopora) and the Organ Pipe Coral (Fig. 17). In the latter, the polyps grow up side by side in separate tubes which result from the fusion of coloured chalky spicules. Those tubes, from which the coral takes its name, are, at regular intervals, joined together by platforms. It is from these platforms, where the interval between two tubes is considerable, that new buds arise to grow up alongside of the older polyps. Both the skeleton and the soft parts of this colony are of a deep crimson, the tentacles of the polyps being of an emerald green. The coral we probably know best in its skeletal condition, the Red Coral of commerce, is also the product of one of the eight-rayed corals. Some idea of the structure of this coral in its living condition may be gained from the diagram- atic section of it given in Fig. 18. The central hard (chalky) axis answers to the smooth red branch with which we are familiar. This is covered by a layer of soft tubes, some of which, in the illustration, are thrown back in order to reveal the hard axis, the grooved markings on which show where the canals ran. These tubes convey the nourishing fluid through the whole colony, receiving it from the polyps and giving it off through branches connecting them with the soft crust that lies over them. Throughout this crust star or plate-like spicules are scattered, which give it some degree of firmness. Three polyps are seen in the illustration: the one to the right has its fringed tentacles extended in search of prey, the middle one is in a retracted condition, and that to the left is cut across
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