Muskrats are peculiar to North America, where they exist in great numbers. Aquatic in habits, they have a wide distribution along streams of all sizes and among marshes, ponds, and lakes from the Atlantic to the Pacific, and from a little beyond the limit of trees on the Arctic barrens south throughout most of the United States. They reach our southern border at the delta of the Mississippi and the delta of the Colorado, at the head of the Gulf of California. Within this vast area they have been modified by their environment into several species and geographic races, none of which differ much in appearance from the well-known animal of the Eastern States. The nearest kin of the muskrats are the short-tailed field mice, so numerous in our damp meadows. Like the latter, the muskrat has several litters of young each season. The young are born blind, naked, and helpless, and number from three to thirteen to a litter. This great fecundity has enabled the muskrats to hold their own through years of persistent trapping. They still occupy practically all their original range and yield a steady toll of valuable fur each season. In 1914 more than 10,000,000 of their skins were sold in London, and other millions were handled in America. The aggregate returns on muskrat skins are so great as to constitute it our most valuable fur-bearer. The furriers make its skins up in its natural color or dress and dye it and give it the trade names of “Hudson seal,” “river mink,” or “ondatra mink.” In suitable marshes, as on the eastern shore of Maryland, muskrats become extremely abundant and render such areas valuable as natural “fur farms.” One Maryland marsh containing 1,300 acres has yielded from $2,000 to $7,000 worth of skins a year. Not only are the skins of value, but the flesh is palatable, and is sold readily under the trade name of “marsh rabbit” in the markets of Baltimore, Philadelphia, and elsewhere. There is little doubt that owners of favorably situated marshes could derive from them a steady revenue by keeping them stocked with proper food plants and protecting the muskrats from their enemies. The value of these fur-bearers is becoming more and more appreciated and many States have laws restricting the trapping season to a period in fall and winter when the fur is prime. In marshes about shallow lakes or bordering sluggish rivers muskrats build roughly conical lodges or “houses,” three to four feet high, with bases, usually in shallow water, several feet broader. These houses are made of roots and stems of plants with a mixture of mud. An oval chamber is left in the interior, well above the water level, to which entrance is gained by one or more passageways opening under water. These shelters are mainly for winter use, but the young are sometimes born in them as well as in large grass nests among dense marsh vegetation.