How the Frenchmen have learned the habits of this well-known little spinner, and cultivated him, and made of him a cheap and nutritious article of diet for the French nation, is fairly well known. How the little fellow builds his house and weaves his ropes, is not quite so well known. The house itself, with its black outside, and the beautiful sky-blue, pearly inside, is a work of the greatest skill, while the mechanism by which it is opened and closed forms a chapter in the world’s wonder-lore. The little spinner lives in a soft, fleshy ‘mantle,’ inside of his stony house. On the edge of this mantle are tiny fingers (_cilia_) and little pigment cells with which he builds. The material—carbonate of lime—is extracted from the clear sea-water by a simple process in the life of the animal. Just as our food goes to form blood and bone, muscle and sinew, so does the food of the little spinner go to form his delicate tissues and his hard shelly house. The mussel-house is as much a part of the mussel’s life as our homes are part of our lives, and the processes of building are not so very different either; both are simple, both are mysterious. To watch this little spinner make his thread is very interesting. From one side of his house protrudes a curious little pad of flesh, a quaint, pointed sort of a tab. This is called his ‘foot,’ though it might just as well have been called his hand. He touches the rock, or whatever he desires to attach himself to, with this foot, then withdraws it, leaving a tiny thread, which he has made by some mystic process, in his own body, just as a spider makes her silken cord. The foot comes out again and again, always leaving a thread, until a strong rope is woven, which binds him securely to his chosen home. He can shorten or lengthen this cable by a simple contractile motion, which allows him a little play; but he may be said to be fixed for life, once he settles down. After a severe storm, some of them will generally be found on the shore, driven from their moorings, helpless and homeless on the strand; but they can stand the storm as well as the ships of more skilful people, and their disasters at sea are probably less numerous in proportion than ours are. I had one little fellow in an aquarium, who had been gathered from a spot where the tide left him for a long period every day. He did not care to be under water all the time, so, by the aid of his foot and his wonderful home-made thread, he climbed up the glass to the surface of the water. There he attached some threads above water to the glass, leaving some below. When the little spinner felt like having a breath of fresh air, he ‘hauled in’ on his upper guys, and rose above the surface. When tired of that, he ‘slacked off,’ and took a turn underneath, thus making something like his accustomed tidal habit.