The muskrats of Canada live in colonies on the banks of streams or deep lakes, and construct dwellings which are very well arranged. In their methods we find combined the woven shelter with the house of built earth. Their cabins are established over the highest level of the water and look like little domes. In building them the animals begin by placing reeds in the earth; these they interlace and weave so as to form a sort of vertical mat. They plaster it externally with a layer of mud, which is mixed by means of the paws and smoothed by the tail. At the upper part of the hut the reeds are not pressed together or covered with earth, so that the air may be renewed in the interior. A dwelling of this kind, intended to house six or eight individuals who have combined to build it, may measure up to sixty-five centimetres in diameter. There is no door directly opening on to the ground. A subterranean gallery starts from the floor and opens out beneath the water. It presents secondary branches, some horizontal, through which the animal goes in search of roots for food, while others descend vertically to pits specially reserved for the disposal of ordure. [Illustration: Fairy Flies (magnified 30 diameters) 1, Caraphractus Cinctus, Male; 2, 3, same, Female; 4, 5, Mymar Pulchellus, Male and Female; 6, 7, Prestwichia Aquatica, Female and Male; 8, Cosmocomo Fumipennis, Female] But it is, above all, the beaver (Castor fibre) who exhibits the highest qualities as an engineer and mason. This industrious and sagacious rodent is well adapted to inconvenience the partisans of instinct as an entity, apart from intelligence, which renders animals similar to machines and impels them to effect associated acts, without themselves being able to understand them, and with a fatality and determination from which they can under no circumstance escape. The civilization of the beaver has perished in the presence of man’s civilization, or rather of his persecution. In regions where it is tracked and disturbed by man the beaver lives in couples, and is content to hollow out a burrow like the otter’s, instead of showing its consummate art. It merely vegetates, fleeing from enemies who are too strong for it, and depriving itself of a dangerous comfort. But when the security of solitude permits these animals to unite in societies, and to possess, without too much fear, a pond or a stream, they then exhibit all their industry.