People sometimes say that the curious substance which we call “coral” is made by “coral insects.” But the little animals which make it are not related in any way to the true insects. They are really tiny polyps, very much like those of the sea finger; and they suck up lime out of the water, and build it up underneath and round their own bodies, just as the madrepores do.
If you were to place one of these tuft corals in a vessel of clear sea-water, and to watch it carefully, you would soon see the little polyps poking themselves out, and spreading their tiny fleshy feelers, or “tentacles.” The coral which they make is pearly white in colour, with just a faint tinge of rosy red, and the polyps themselves are partly white, and partly fawn, and partly chestnut brown.
One does not often find a tuft coral, however, for the polyps like to live in rather deep water. But when there is a very high spring-tide, as there generally is about the end of March and the end of September, the waves retreat afterwards a good deal farther than usual. And then, if you go right down to the water’s edge, you may perhaps find a tuft coral fastened to the rocks.
PLATE XLIV
THE BREAD-CRUMB SPONGE (2)
I dare say that you will be rather surprised to hear that nearly three hundred different kinds of sponges have been found in the British seas. You will not be able to find very many of these, however, for they nearly all live in deep water, and have to be scooped up by means of the dredge. But the Bread-crumb Sponge is easily found, for it lives in shallow water, and you are nearly sure to find it if you look for it in the rock-pools.
1. THE TUFT CORAL.2. THE BREAD-CRUMB SPONGE.
3. THE GRANTIA SPONGE.4. FORAMINIFERA.