We may number the sea mouse amongst our treasures of the sea-side. Though called a mouse, on account of its curious movements and partly perhaps because of its appearance, it is really a worm. It does not appear to have the slightest resemblance to the common earth worm, nor to the liver fluke which is described on another page, nevertheless, it is related to both these creatures. The raiment of the sea mouse is gorgeous in the extreme; on its back is soft brownish hair, its sides are clothed with yellow and green hair, displaying a wonderful iridescence and amongst the hair on the sides there are many stiff brown bristles. Of the covering of the sea mouse it has been said: “It is as if all the hues of the rainbow were collected there, making this remarkable animal a living jewel, and truly worthy of the name of Aphrodite, the Queen of Beauty.” The bristles of this creature we must examine microscopically, they vary in structure according to the kind of sea mouse, for there are several kinds, but in some of them they are formidably barbed, in all of them they act as a protection. Many other worms, a number of them un-wormlike in appearance will claim our attention but we cannot devote more space to them here. There is the common shell-binder, a curious worm, which builds for itself a still more curious shelter of broken shells. Another worm, _Serpula_ by name, also lives in tube-like structures of its own manufacture and is remarkable in that a row of nearly two thousand seven-toothed hooks run along its back and all these thirteen thousand odd teeth are there merely for the purpose of holding _Serpula_ in its tubular home. Much interesting work may be done at the seaside in studying the young stages of various familiar creatures. This work, however, necessitates the keeping of the adults in an aquarium; for the young ones, in most cases, are so unlike their parents that, if found swimming about on their own account, they would never be recognised. Young barnacles, for instance, have six legs, a tubular mouth and a single eye. At a later stage they might be mistaken for young shell fish; they possess a shell, not unlike that of the mussel, containing, however, not a soft, fleshy mollusc but a six legged creature which swims through the water in jerks, after the manner of a water flea. Strangely enough, it is now provided with two stalked eyes like those of a crab, whilst of mouth parts it has none, or they are so imperfectly developed as to be useless for feeding. Soon this active youngster settles down for the rest of its life and becomes a sedate and sedentary barnacle, with one imperfectly developed eye and a mouth capable of feeding to good purpose.