These creatures are first-cousins, so to speak, of the acorn shells, and they are called “Ship Barnacles” because they are so very fond of fastening themselves to the bottoms of ships. Even after two or three months, indeed, the hull of a vessel is often quite covered with them below the water-line, and they check her speed so greatly that she has to be taken into dock to have them scraped off before she can set out upon another voyage. You may generally find quite a number of these barnacles on the pieces of timber which are so often flung up by the waves after a storm. And you will notice that each of them grows, as it were, upon a kind of stalk, instead of being fastened down to the surface of the wood, as the acorn shells are upon the rocks. This stalk consists of the pillar of cement with which the little animal covered its feelers just before it changed its form for the last time. There are a good many other kinds of barnacles, some of which are found in very odd places. There is one, indeed, which always lives on the backs of whales, and somehow manages to sink itself quite deeply into their skins! CHAPTER VI THE SEA WORMS PLATE XXXI THE SEA MOUSE (1) If you go down among the rocks when the tide is out, and hunt in the muddy pools near low-water mark, you will be almost sure to find a very odd-looking creature indeed. It is generally between three or four inches long, and although it is called a “Sea Mouse” it looks very much more like a hairy slug; for its whole body is covered with a matted coat of bristles. But it is really a kind of sea worm. And it looks just about as dull and dingy as any creature can possibly be. Yet in reality it is one of the most beautiful animals which are found in the sea, and if you want to see its beauty, all that you have to do is to wash it. For the bristly coat which covers its body is a kind of filter, which strains out the mud from the water which passes to the gills; and it soon becomes so choked with mud that you cannot see what the animal is really like at all. All that it wants, however, is a really good bath: so just take it to a pool of clear sea-water, and rinse it thoroughly. Then take it to another pool, and rinse it again. Then take it to a third pool, and rinse it again; and go on rinsing it till every atom of mud has been washed out of its hairy coating. And then, if you look at it in the bright sunshine, I am quite sure that you will be astonished to find what a lovely creature it really is. For all the colours of the rainbow, and ever so many more besides, seem to be chasing one another over its bristles, and altering with every movement and every change of light. Doesn’t it seem strange that an animal so beautiful as this should live with all its beauty covered up, so that hardly any eye can ever see it?