You will have noticed that there are various kinds of Sponges in the market; some are large and flat, others small and cup-shaped; some are soft, and others rather hard. They are all somewhat horny and elastic. This "spongy" material is the skeleton of the Sponge animal, cleaned and dried for your use. Some kinds of Sponge would tear your skin if you tried to use them, for they have a hard skeleton. It is made of lime, and sometimes of flint, which the Sponge obtains from its food. Of course we use only those sponge-skeletons which are soft; but the cheaper kinds do often contain little flinty needles. The best washing-sponges live in warm seas, attached to the rocks on the sea-bed. Divers go down and obtain them; or else they are dredged up, cleaned, dried, and sorted, and then sent to the market. Some Sponges, called Slime Sponges, have no skeleton, being merely a living mass of slime. Coral is also the hard skeleton of a little animal, known as the Coral Polyp. The rest of the polyp's body is soft jelly, which many fish regard as good food. The Sea Anemone--another jelly-animal--is first cousin to the Coral Polyp. And we may call the Jellyfish second cousin to these two, for it is in the same big division of the animal kingdom. The pretty red Coral, then, is really the hard part of a little jelly-animal. This animal is much like a Sea-anemone, with a hard skeleton of lime. Coral, as you know, looks like a solid rock; it is really made of needles of lime, fastened together into a solid mass by the little Coral Polyp. Now, many of the Coral animals have the strange habit of budding. The buds become perfect polyps, and then they, too, begin to bud. In this way, those marvellous _coral-reefs_ and _coral-islands_ have been made. Branch by branch, layer by layer, the hard Coral is built up by myriads of the small, soft-bodied creatures. This kind of polyp can live only in warm, clear water. So it is not found in the cold depths of the sea, nor in the seas near our islands, but in the warm shallow waters near tropical lands it flourishes so well that it builds up most wonderful Coral walls. So strong are they that they can defy the terrific force of the waves. [Illustration: THE PICTURE STORY OF A CORAL ISLAND.] Some coral-reefs are of immense size and strength. One, near the coast of Australia, is nearly a thousand miles in length. These marvellous works of the polyp are of great use, for they break the force of the waves, and so make a calm shelter for vessels. The brilliant masses of Coral make a world of colour in the clear seas of the tropics, a gay garden inhabited by fishes of gaudy hues. In dull seas we have, as a rule, dull creatures to match. And in bright, warm, sunny seas the fishes are also brightly coloured. A dull fish would show up amid such rich colours, so it is easy to know why Coral fish wear such fine clothes.