These closed cups are concerned in the reproduction of the creature, for after a few weeks the substance inside them is seen to collect into bunches of round or oval bodies, often yellow in color, or of other tints. By and by the cup bursts, or a sort of trap-door opens at the top, and these things escape. They are small, covered with cilia, or moving hairs, and resemble the planulas of the jelly-fish in shape, and they swim freely, and finally settle down on a stone or weed. They become environed by a horny coat, the stomach having been formed first by simple bending in of the outside of the creature, and tentacles grow. The planula thus founds a new colony. But there are other phases in this curious life-story; for instead of the little round balls in the closed cups getting free as planulas, some in certain kinds grow there, and resemble excessively minute jelly-fish stuck fast by the back, and exposing the mouth, feet, and the fringed umbrella. These Medusæ, as they may be called, die on the parent, and never wander. There is one kind of these Garland polypes called Lafœa in which the round bodies produced in the closed cups burst forth, and not in the shape of planulas. They come forth like tiny bells, furnished with minute eye-spots on the edge, and they have an umbrella shape, and long tentacles arising from the edge near the eye-spots. They are jelly-fish, to all intents and purposes, and swim freely about, and in time produce planulas which develop into a parent Garland polype again. There is a very interesting kind of these allies of the sea-jellies which, from its feathery shape, has been called Plumularia. Specimens are common, and there is a stem, and it has branches, and the cups are in one row on the branchlets. Moreover, there are openings in the horny envelope of the soft pith of the branches, which do not give exit to a polype-looking thing with its mouth surrounded with tentacles, but to a simple pith with many threads or stinging cells in it. It is more or less like a long tongue, and is placed among the cups with polypes, and it is evidently an instrument for capturing minute creatures. The Sickle-beard is one of them. But one of the most singular of these delicate creatures lives in very numerous colonies, on such an unexpected place as the outside of the shell tenanted within by a wandering hermit-crab. It is called Hydractinia. The Hydractinia has a kind of crust for its formation, with tubes in it, and out from them comes a white film, which, under a magnifying-glass, presents a number of stems and polypes. Each one has at its free part a club-shaped end, which has several rows of tentacles around it. These, often twenty-five in number, are, like the stem, very irritable, flexible, and are covered with a sticky matter. The club is hollow within, for the stomach, and food gets in by the top, where the horny skin appears to be absent.