The question of protective coloration in fishes has of late received some light which compels a revision of our former theories on the subject. It has usually been held that the color of fishes is of the mimicry order--that is, it has been acquired for the purpose of deceiving their enemies. Trout will very commonly take the hue of the river bottom over which they swim, and, as every one knows, it is difficult to detect a flounder or other flat fish at rest, though when it turns over the white under surface of its body instantly reveals the creature’s presence. The hue of the upper surface is due to the action of light. For when a sole was kept in a raised glass case, with light directed upward from below, pigment formed on the white side, and began to be absorbed on the one hitherto exposed to the same agent. DWELLINGS --FRÉDÉRIC HOUSSAY Animals construct dwellings either to protect themselves from the cold, heat, rain, and other chances of the weather, or to retire to at moments when the search for food does not compel them to be outside and exposed to the attacks of enemies. Some inhabit these refuges permanently; others only remain there during the winter; others, again, who live during the rest of the year in the open air, set up dwellings to bring forth their young, or to lay their eggs and rear the offspring. We shall find every stage, from that of beings provided for by nature, and endowed with a special organ which secretes for them a shelter, up to those who are constrained by necessity to seek in their own intelligence an expedient to repair the forgetfulness of nature. Nearly all the Mollusca are enveloped by a very hard calcareous case, secreted by their mantle: this shell, which is a movable house, they bear about with them and retire into at the slightest warning. Caterpillars which are about to be transformed into chrysalides weave a cocoon, a very close dwelling in which they can go through their metamorphosis far from exterior troubles. It is an organic form of dwelling, or produced by an organ. It is not necessary to multiply examples of this kind; they are extremely numerous. In the same category must be ranged the cells issuing from the wax-glands which supply bees with materials for their combs in which they inclose the eggs of the queen with a provision of honey. I do not wish to insist on creations of this kind which are independent of the animal’s will and reflection. Near these facts must be placed those in which animals, still using a natural secretion, yet endeavor to obtain ingenious advantages from it unknown by related species. There is, for example, the Macropus viridiauratus, or paradise-fish, which blows air bubbles in the mucus produced from its mouth. This mucus becomes fairly resistant, and all the bubbles imprisoned and sticking side by side at last form a floor. It is beneath this floating shelter that the fish suspends its eggs for its little ones to undergo their early development.