OF DENISON UNIVERSITY. 17 



of the rat are sealed for four or five months and he is forced to con- 

 struct a building suited to the seemingly infelicitous and conflicting 

 conditions. The house must extend above water to admit air; it 

 must be deeply buried from the cold ; it must connect with the water ; 

 it must contain food ; the food should be growing or fresh ; the house 

 should afford protection from enemies and escape when attacked. 



The solution of these problems might tax the ingenuity of the 

 ablest mind, yet nature, by the use of the simplest materials under the 

 guidance of natural selection, has solved every one. Let us watch 

 the process and, I doubt not, learn a lesson of skill and patience. The 

 situation is a shallow pool which is destined to freeze nearly solid. It 

 is grown up with rushes and Nuphar or spatter dock, two plants 

 which play an important part in the domestic economy of this animal, 

 supplying him at once with food and building materials. 



In the placid days of early autumn a pair of muskrats may be 

 seen diving to the bottom and tugging and biting at the roots of the 

 rush. After tearing them off, the rat collects four or five of the rushes, 

 say four feet long, and swims with them to a spot selected over the 

 deepest part of the pool. Here they are arranged in parallel order 

 and carefully straightened. Then another mouthful is brought and 

 placed across the first at right angles. The angles are bisected by 

 other clusters until a circular raft is formed sufficiently strong to sup- 

 port the weight of the animal. Now the colony of rats sets at work in 

 earnest. And all day long one or more rats may be seen on the plat- 

 form apparently eating rushes. Closer inspection shows that they are 

 biting rushes into short lengths to form the "filling" of the structure. 

 The accummulation increases and its weight causes the raft to sink 

 and a new series of long rushes is added. Thus repeatedly until suf- 

 ficient material has been accummulated to rest on the bottom of the 

 pond. All the previous weeks the rats seemed to make little progress, 

 as the material sank as fast as lifted much above the surface. During 

 the early stages a strong wind may ruin the work of weeks but the 

 rats are never discouraged. 



So far only vegetable matter has entered into the composition of 

 the hut. but as soon as it begins to rise permanently above the water 

 there is a change of method and the whole space about the lodge is 

 cleared of vegetation. The rats dive to the bottom and pull up the 

 rushes and water-lillies by the roots and build them into the structure 

 with large masses of earth adhering. The bottom is deepened and 



