Few persons of the many who delight to drift along our sea-shores are unfamiliar with the Toad-fish. So closely does he in shape and color resemble a moss-covered stone that his enemies are deceived. Intrenched among the weeds and gravel, which the mother-fish carelessly throws aside, after the fashion of some of the gulls, the young are reared, their yolk-sacs enabling them to cling to the rocks of the nest soon after birth. There, under the watchful eye of the parent, they remain until old enough to swim away. But the most vigilant of all nest-builders is the Four-spined Stickleback--_Apeltes quadracus_. In some neighboring stream, that sooner or later finds its way to the ocean, he may be found. There are different species of these fish, but their architectural ideas are pretty much the same. They vary mainly in the locations they select for nesting. Some place the nests upon the bottom, concealed among the sea-weed found there, while others hang theirs from some projecting ledge, or swing it in the tide from the sunken bough of some overhanging tree. As is unusual, the work of nidification is solely performed by the male Stickleback, the female taking no part in the labor. The spawning season having arrived, he, assuming a bright nuptial lustre, shows remarkable activity in selecting a site for an edifice, and transporting the building material thither. Fragments of all kinds of plants, gathered often at a distance, are brought home in his mouth. These are arranged as a sort of a carpet, but as there is danger of the light materials being carried away by the current, they are weighted down by sand to keep them in their places. Having entwined them with his mouth to his complete satisfaction, he then glides gently over them on his belly, and glues them with the mucus that exudes from his pores. More solid materials, sometimes bits of wood, sometimes bits of straw, which he seizes with his mouth, are adjusted to the sides of the floor to constitute the walls. He is now very particular. If the piece cannot be properly adjusted to his building, and he does not lose patience in his efforts to fit it in, he carries it to some distance from the nest and leaves it. After the side walls are erected, a roof of the same materials with the floor is laid over the chamber. Firmness is given to the whole structure by passing over it with his body, the light and useless particles being fanned away by the action of his fins and the vibratory movements of his tail. In carrying on his building operations care is taken to preserve a circular opening into the chamber, his head and a great part of his body being thrust therein, thus widening and consolidating it, and rendering it a fit receptacle for the female. When choosing material, the fish has been seen testing its specific gravity by letting it sink once or twice in the water, and if the descent was not rapid enough finally abandoning it.