OF THE INTELLIGENCE AND OF INSTINCT. 173 



the uncultivated plains near Harden sburgh, he saw these wild 

 pigeons in considerable numbers, flying from north-west to 

 south-east ; as he journeyed on to Louisville the flock of birds 

 became more and more numerous, until the light of midday 

 was obscured as in an eclipse ; the droppings fell like snow ; 

 before sunset he arrived at Louisville, a distance of fifty-five 

 miles, but the flight of the migratory pigeons still went on ; 

 this phenomenon continued for three days ; the droppings 

 from the birds formed a distinct layer on the soil ; forests 

 were stripped of their leaves, and sometimes destroyed, and 

 the traces of their passage will remain for years. 



Fishes and insects are also gregarious, the herring for 

 example, and locust ; the former assembling in vast shoals, 

 and the latter in such numbers as to devastate a country. 



330. The Psittacus infucatus is described by Levaillant 

 as assembing in numbers towards evening to bathe and sport 

 in some limpid stream, returning to the woods so soon as the 

 evening pastime is finished. It is this instinct of sociability 

 which brings together the warren rabbit and the prairie 

 dog of America, a small rodent, with habits resembling gene- 

 rally this class of animals. But it is chiefly in the beaver, the 

 wasp, bee, the ant, that this sociable instinct shows itself in 

 its utmost development ; that is, instinct directing all towards 

 some common labour. 



331. The Canadian beaver is of all animals the most 

 remarkable for its sociability and instinctive industry. During 

 summer it leads a solitary life in burrows dug by the banks 

 of some lake or river ; but, when winter approaches, it quits 

 its burrow to assemble with its fellows to construct in common 

 with them its winter dwelling. In a spot remarkable for its 

 solitude, a group of two or three hundred assemble, and dis- 

 play 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, 



