OF THE INTELLIGENCE AND OF INSTINCT. 159 



individual, but which at other times seem combined with the 

 faculty of" securing to the young conditions favourable to their 

 existence, is exhibited by those animals which undertake distant 

 journeys : sometimes even to change their climate periodically; 

 occasionally they merely leave the district when they have 

 exhausted the provisions it furnishes to them; sometimes it 

 is the cold of winter which urges them towards the south, or 

 the heats of summer which drive them to the north. But 

 these journeys are always undertaken before any atmospheric 

 change appreciable by us has happened to warn them of a 

 necessity for such a change ; or, in other words, their instinct 

 leads them to perceive the coming event, and directs them at 

 once to the object sought, the region they aim at, without 

 the least hesitation or error. They unite in bands, and thus 

 proceed on their journey. 



The apes of the Xew \Vorld change their habitat irregularly; 

 they exhaust the resources of a district, and proceed in search 

 of another with loud cries, carrying their young on their backs. 



The lemmings also undertake distant journeys, seemingly 

 in an irregular manner, and for reasons which man cannot 

 discover. They inhabit the shores of the Icy Sea, and descend 

 occasionally from the mountains in innumerable bands. These 

 migrations, fortunately for the inhabitants of Sweden and 

 Norway, happen only about once in ten years ; for the lem- 

 mings travelling in straight lines, and thus, crossing rivers, 

 rocks, and mountains, destroy all vegetation, even to the 

 roots and grains. Nothing diverts them from their course 

 but smooth walls, which they cannot cling to. 



In general such journeys are periodic. A small rodent, 

 resembling the lemming, annually leaves Kamtschatka for the 

 west ; they march in straight lines, and are so numerous, that 

 when they reach the banks of the Octrolsk and of the Jou- 

 doma, after having traversed 25 degrees of longitude, a single 

 column will occupy two hours in defiling. In October 

 they return to Kamtschatka, and their return is a jour 

 defete for the inhabitants, for the number of the carnivora 

 which follow them is so great as to furnish an abundance of 

 valuable furs. At the Cape of Good Hope and in North 

 America are also met with, in spring time and autumn, vast 

 herds of antelopes and deer, migrating to great distances.* 

 But it is chiefly in the class Birds that the more remarkable 

 instances of this migratory habit are found. A great number 



* These migrations of the Antelope in Southern Africa appeared to me to 

 be chiefly regulated by the condition of the pasture. B. K. 



