_Description._--The muskrat is a large aquatic rodent. Head and body measure about 14 inches; the tail about 10 inches. The body is plump and the head small. Eyes and ears are relatively small. The forefeet are small and handlike with furred wrists. The hind feet are large with webbed toes and naked wrists. The tail is narrow, constricted at the base and flattened vertically. It is scaled and possesses scattered, stiff hairs. The underfur is dense and soft. The guard hair is stiff and shiny. The upper parts are rich, dark brown. The underparts are gray washed with cinnamon. [Illustration: FIG. 119. Muskrat (_Ondatra zibethicus osoyoosensis_), male, Lake Washington, Seattle, October 13, 1939; weight 906 grams on November 4, 1939. (Fish and Wildlife Service photo by Victor B. Scheffer, No. 736.)] Muskrats are found in Canada and the United States. They are lowland animals, rarely ranging into the Canadian Life-zone. Their aquatic habitat makes them relatively independent of temperature, and consequently they occur in both the Transition and Upper Sonoran life-zones. The muskrat is well adapted to aquatic life. The toes of the large hind feet are webbed at the base, the hind feet are turned slightly outward, a fringe of stiff bristles at the rear edge of each foot furnishes additional aid in swimming, and the laterally compressed tail makes it an efficient rudder. In the water the surface of the fur flattens down to entrap air in the dense underfur, keeping the body dry. The typical habitat of the muskrat is slow-moving water or still water, such as in lakes, ponds, marshes and sluggish rivers and streams. Muskrats occur commonly, though not in large numbers, in more swiftly moving streams. In Puget Sound and the San Juan Islands they occupy a marine habitat. In the extensive marshes along Lake Washington, King County, muskrats are abundant. They occupy sluggish water, often water polluted by garbage and sewage. In these marshes, banks suitable for the construction of burrows are absent and houses are made of cattail stalks and leaves. The food of these marsh-living muskrats consists principally of cattail and other marsh vegetation. In contrast to the marsh-occupying muskrats, muskrats along the open, marsh-free shores of the lake live in deep clear water where waves lap the shore. These muskrats live exclusively in burrows dug in the banks and feed upon fresh-water mussels. In still greater contrast were muskrats living 20 miles away, near Cottage Lake, King County. Here we found them in small clear streams, 4 to 10 feet wide. Depth of the water varied from a few inches to three feet. The streams flowed through meadows, pastures and junglelike, deciduous woods. Muskrats were slightly more common along wooded stretches than in open areas. Some were trapped where the streams flowed at high velocity over shallow, gravel bottoms. The animals lived in burrows and fed upon fresh-water mussels and a variety of plants.