To some extent the marine creatures which bore in rocks seem to be helped by chemical action, since they show a preference for chalk and limestone, easily dissolved by weak acid secreted by the borer, though, clearly enough, they are not dependent on such chemical aid since we find them also boring in insoluble granite rock and shale and clay. There is one true worm-borer which perforates hard limestone pebbles and chalk rocks, so as to give them the appearance which we call “worm-eaten” when caused by another sort of worm and observed in a very different material, namely, old furniture and woodwork. At Tenby, in South Wales, the limestone pebbles on the beach are quite commonly riddled with these worm-holes, truly “worm-eaten.” When they are not too abundant one can see that the holes are arranged in pairs like a figure 8, about half the size here printed. On splitting the rock or stone one finds a deeply-running U-shaped double tube excavated in the stone. In this the little worm lived. It is easiest to get at the worms in a fresh and living state on a coast where there are chalk-rocks and sea-washed lumps of chalk. The chalk is easy to split and cut at low tide, and then the little key-hole apertures can be broken across and the soft red worm extracted. It is a beautiful red-blooded little worm—little more than half an inch long—with two tactile horns on its head and little bristles and gills on the rings of its annulated body. It is a true “worm,” like the earth-worm, what naturalists call by the not displeasing name an “annelid.” It seems at first sight impossible that this delicate little thing should “worm-eat” the hardest limestone. It has no jaws, but one of the rings or segments of the front part of the body has two of its bristles swollen to relatively gigantic size, hard and black. These are its boring organs, but I have no doubt that it is helped, especially in its young state when commencing to bore, by an acid secretion from the surface of the body.