254 



MAMMALS OF AMERICA 



northwestern coast region of Oregon and the 

 southwestern part of Washington. 



In general structure and in the character of 

 the teeth, the Musk-rat is simply a great Mouse ; 

 but in shape and habits it is a small edition of 

 the Beaver. In fact, Linnaeus put it into the 

 same family genus with the latter. However, 

 it is much smaller than the Beaver, and the tail 

 is entirely different, that of the Beaver being 

 very broad and flattened laterally, while that of 

 the Musk-rat is narrow and flattened vertically. 

 This flattening enables the Musk-rat to use it 



in a place where the water is about two feet 

 deep. When the pile is sufficiently large, the 

 Musk-rat makes a tunnel from the bottom up- 

 ward, and hollows out a chamber just below the 

 upper surface of the dome, or through it in some 

 cases, so that only a few plant stalks stick out 

 above. More mud and stalks are placed on top 

 of the chamber, as the roof sinks, until the whole 

 house is firm. The single main room may be a 

 foot or more in diameter and sufificiently high 

 to enable the owners to move about freely. 

 .Sometimes there are two main chambers, each 



Photograph by William Brewster (U. S. Biological Survey) 



MUSK-RAT HOUSE 



These resemble Beaver houses, but are smaller. An elaborate system of 



tunnels is within 



both as rudder and propeller. The hind feet are 

 slightly webbed and assist in swimming. 



Anyone who has visited marshy ponds and 

 sluggish shallow streams has noticed the conical 

 piles of mud and vegetable matter which extend 

 from a foot to three feet above the surface of 

 the water. These are Musk-rat houses, similar 

 to, but smaller than, Beaver houses. The method 

 of building these is rather unusual. A pile of 

 mud mixed with plant stalks is brought together 



with its own entrance, but they are probably 

 occupied by different families. These houses are 

 chiefly used in winter. Work of repairing old 

 houses and erecting new ones begins in early 

 summer, in order that they may be sntig and 

 shipshape when ice begins to form. 



In summer an elaborate system of tunnels and 

 chambers is used for refuge and for breeding. 

 The mouths of these tunnels start well under the 

 surface of the water and lead upward gradu- 



