MAMMALS 329 



is covered with a thick coat of soft fur beneath a layer of 

 longer coarse hair. The hind feet are webbed for swimming, 

 but the fore feet are fitted for digging. 



Moreover, the beaver is one of the greatest gnawers of 

 the whole group. It 'lives in colonies and is very indus- 

 trious ; but most of its work is done at night. The houses, 

 or " lodges," of the beaver are built on the edge of the water, 

 are dome-shaped, and some four or five feet high. They 

 are built of stones, sticks, and mud, and are finally plastered 

 over in the autumn with mud, which freezes, thus forming a 

 hard impenetrable shell. The opening into the lodge is 

 beneath the water. The living apartment is at the top, 

 above the water line; but near by are stored branches of 

 trees, the bark of which serves for the winter food. In 

 order to maintain the water at the desired height about 

 their lodges, the beavers build dams of considerable length 

 (perhaps the longest ever noted being three hundred yards) 

 across streams, with the convex side upstream, to with- 

 stand the pressure. The dam is built of sticks, stones, and , 

 mud, not in regular fashion, yet forming a water-tight and 

 very firm barrier. 



Insect-eating Mammals (Insedivora) 



The order, Insedivora, contains only very small mammals 

 with a thick, furry (sometimes spiny), covering. The muzzle 

 is short and soft and the molars are fitted for crushing the 

 bodies of insects. They live mostly on insects and the order 

 includes the shrew, moles, hedgehogs, and some other little- 

 known mammals. 



Shrews. — These are the smallest of mammals. One 

 species known as the least shrew, which measures only a 



