168 ZOOLOGY. 



of cold and enemies. This is the case with the marmot 

 exhibited in the streets by Savoyard boys. 



325. A third class of instinctive faculties, which, like 

 the preceding, have a reference to the preservation of the 

 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 happens, 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 New World change their habitat irregu- 

 larly ; 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 I^amtschatka for the 

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

 when they reach the banks of the Ocholsk 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 



