CHAP. VIII. MIGRATION OF MICE. 249 



bers at particular seasons. Dr. Richardson remarks 

 of the Caribou, or Barren Ground reindeer (./?#. 70.), 

 (c that it travels in herds,, varying in number from eight 

 or ten to two or three hundred." * And captain Lyon 

 adds, that they regularly visit the polar regions at the 

 latter end of May, or the early part of June, and re- 

 main until late in September. The woodland reindeer 

 (Rangifer sylvestris Sw.) cross the Nelson and Severn 

 rivers in immense herds in the month of May, pass 

 the summer on the marshy shores of James's Bay, and 

 return to the northward in September, t These in- 

 stances, taken almost at random from among the true 

 ruminants, sufficiently establishes the frequency, in this 

 order of quadrupeds, of regular migration. 



(26'5.) Among the Glires, or gnawing animals, these 

 movements, although conducted on a scale equally large, 

 generally occur at uncertain periods ; and they there- 

 fore, in all probability, originate in other causes than a 

 search after food. The history of the economic field 

 mouse, as given by Pallas, affords a striking instance of 

 this : their migrations take place in uncertain years, 

 but chiefly in the spring, at which season they assemble 

 in surprising numbers : this mighty host proceeds in a 

 direct course westward, occasionally swimming with 

 the utmost intrepidity over rivers, lakes, and even arms 

 of the sea. During these perilous adventures, some 

 are drowned, or fall a prey to fish or other enemies; 

 those which escape, rest awhile to bask, dry their fur, 

 and refresh themselves, and then again set out on 

 their migration. On these occasions the flocks are so 

 numerous, that an observer has waited two hours to see 

 them all pass. 



(266.) The migratory habits of the lemming, ob- 

 serves major Smith, almost exceed credibility, were 

 they not authenticated on very respectable authority. 

 The natural or general residence of this animal is in 

 the mountains of Lapland and Norway, from which 

 tracts, .at particular but uncertain periods, it descends 

 * North. Zool. vol. i. p. 45. \ f Id. ibid. p. 250, 



