OF THE INTELLIGENCE AND OF INSTINCT. 165 



and display all their architectural industry. Here they select 

 a stream of sufficient depth as not to freeze throughout 

 during the winter. They begin by forming with branches of 

 trees, interlaced, the intervals being filled up with stones and 

 mud, a sloping dyke, with the convexity towards the stream ; 

 this dyke they crisp entirely with a thick and solid covering. 

 The dyke is generally eleven or twelve feet at the base. It is 

 strengthened annually by new works, and ultimately becomes 

 covered with a thick vegetation. Thus is provided a pool of 

 stagnant waters, or at least waters but little disturbed, in 

 proximity with their dwellings. 



When the dyke is finished, or when the waters are smooth, 

 such a preliminary work is not required. The beavers 

 separate into a certain number of families, and commence 

 constructing their huts, or repairing those already built. 

 These cabins are raised against the dyke or on the edge 

 of the waters, and are of an oval form ; they are constructed 

 in the same way as the dyke itself, of branches of trees, 

 strongly cemented together by a kind of puddle work. For 

 this purpose they use the earth dug from under the wall 

 or the banks, and work it with their feet ; it does not appear 

 that the tail is employed for this purpose. The branches 

 of the trees, no matter what be their size, are readily cut 

 through with their sharp rodent teeth; and when a larger 

 trunk is required so as to intercept the stream, they, work- 

 ing in groups, divide it so that it shall fall in the most 

 favourable manner to be floated to its destined resting-place. 

 Their cabins have two floors, one under water, the other above ; 

 the entrance and exit are by the chamber which is under 

 water. Finally, all these works are carried on at night, and 

 with extreme rapidity. When the proximity of man hinders 

 the beaver from uniting in numbers sufficient to carry on those 

 works requiring the association of many, they no longer 

 build huts ; but the instinct of construction remains even in 

 captivity, as has been seen in beavers confined in the Garden 

 of Plants, in Paris, as shown by their collecting bits of wood 

 fora work which was not to be carried through. 



Perfect societies, like the one just described, are rare amongst 

 birds ; yet we have in the Loxia soda, a kind of sparrow of 

 the Cape of Good Hope, a specimen of the sociable instinct. 

 These birds construct their nests under a roof-work common 

 to the whole colony (Fig. 111). 



The nests of wasps surprise us by the regularity and per- 



