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.

The congested state of a coral reef, and the inevitable result thereof—­perpetual war of species and shocking cannibalism—­have been referred to.  Another result of the overcrowding has yet to be mentioned.  Possibly there may be those who are disinclined to credit the statement that some of the denizens take in lodgers.  But the fact remains.  Having ample room and to spare within their own walls, they offer hospitality to homeless and unprotected strangers, whom graceless Nature has not equipped to take part in the rough-and-tumble struggle for existence outside.  A tender-hearted mollusc (Pinna) accepts the company of a beautiful form of mantis-shrimp—­tender, delicate and affectionate—­which dies quickly when removed from its asylum, as well as a singular creature which has no charm of character, and must be the dullest sort of lodger possible to imagine.  It is a miniature eel, which looks as if it had been drawn out of rock crystal or perfectly clear glass.  There is no apparent difference between the head and the tail, save that one end tapers more gradually than the other.  Very limited power of motion has been bestowed upon it.  It cannot wriggle.  It merely squirms in the extremity of laziness or lassitude.  These two keep the Pinna company—­the lively shrimp, pinkish brown and green with pin-point black eyes, and the little eel as bright and as transparent yet as dull and insipid as glass.  One of the oysters attracts the patronage of a rotund crab, which in some respects resembles a tick, and a great anemone a brilliant fish—­scarlet and silver defined with purple hair lines—­which on alarm retires within the ample folds of its host.

The flowers of a coral reef live.  A bouquet of lavender-coloured, tender, orderly spikes has a gentle rhythmical, swaying movement.  A touch, and by magic the colour is gone—­naught remains but a dingy brown lump on the rock, whence water oozes.  Another form of plant-like life takes the colour of rich green—­the green of parsley, and faints at the touch, as does the sensitive plant of the land.  Another strange creature, roughly saucer-shaped, but deep grey mottled with white and brown, continuously waves its serrated edges and pulsates at the centre.  It starts and stops, contracts and withdraws steadily into the sand upon interference.