Upon coral blocks, which represent the skeletons of polyps in orderly and systematic profusion, other creatures more highly organised appear, having in one feature a family likeness to the polyps, upon whose hospitality they impose, that is, if the setting up of an establishment on the remains of innumerable ancestors of its host may be said to be merely an imposition. One is a species of mollusc which resembles, in some respects, that to which has been given the name of SURPULA. In its babyhood it attaches itself to the coral, and forthwith begins to build a home, which is nothing more than a calcareous tube, superficially resembling a corpulent worm, instantaneously petrified while in the act of a more or less elaborate wriggle or fantastic contortion. In this complicated tunnel the creature resides, presenting a lovely circular disc of glowing pink as its front door. A few inches beneath the water this operculum or lid is not unlike a pearl, but as you gaze upon it, it slips on one side, and five animated red rays appear, waving like automatic flag signals. Though well housed, it is almost as timorous as the coral polyps. Upon the least alarm the rays disappear in a twinkle, and the pink pearl trap-door glows again. Break off the end of the shelly tunnel in an attempt to secure the pearl, and it is as elusive as a sunbeam. It recedes as piece by piece is broken away, until the edge of the cylinder is flush with the surface of the coral in which the shell is embedded. There the pearly operculum glows in safety. The living rays or flower-like face are the features in which this encased worm resembles the coral polyps on the one hand and the houseless beche-de-mer on the other. Some of the numerous inhabitants of the reef, struggling to keep in the fashion, make the very best of five simple points. Others flaunt with no apparent vanity or pride quite a plume, of complex rays more or less beautifully coloured. A worm which occasionally swims like a water snake, and again reposes inertly on the sand, as does the beche-de-mer, sets off its brown naked body with a red nimbus--a flexible living nimbus, ruby red. The visible part of the organism of the coral polyps is composed of rays, from the sides of which spring secondary rays, the combination producing complex stars of great beauty and which call to mind the frost flowers, and the flowers into which some inorganic substances bloom as they crystallise.