FIELD-MICE OF KAMTSCHATKA. 



Although great numbers perish during the voyage, they never- 

 theless do immense damage to the districts over which they pass, 

 destroying all the vegetation which lies in their way, and even 

 turning up the ground, and consuming the fresh sown seed. 

 Happily for the Lapland and Norwegian farmers, the visits of 

 these animals are rare, seldom occurring more than once in ten 

 years. 



37. Such migrations, however, are much more frequently 

 periodical, being determined, as already stated, by the change of 

 seasons. Thus, it is found that in spring, immense legions of a 

 little field-mouse, which inhabits Kamtschatka, depart from that 

 country and direct their course towards the west. These animals, 

 like the lemmings, proceeding constantly in one direction, 

 travel for hundreds of leagues, and are so numerous that even 

 after a journey of twenty-five degrees of longitude, in which a 

 considerable proportion of their entire number must be lost, a 

 single column often takes more than two hours to pass a given 

 point. In the month of October they return to Kamtschatka, 

 where their arrival constitutes a fete among the hunters, as they 

 never fail to bring in their train a vast number of carnivorous 

 animals, which supply furs in abundance to the inhabitants of 

 these regions. 



38. Nature seems even more sedulous for the preservation of 

 the species than for that of the individual, and we find accord- 

 ingly the instincts which are directed to the former purpose 

 more strongly developed even than those of self-preservation. 

 The animal world presents innumerable examples of this in the 

 measures which nearly all species adopt with a view to the care 

 of their young. The bird continues often for weeks to sacrifice 

 all her own pleasures, and sits upon her eggs almost immovably. 

 Before these eggs are laid she constructs with infinite labour and 

 art a place in which she may with safety deposit them, and 

 where the young which are destined to issue from them may be 

 sheltered, protected, and fed by her until they have attained the 

 growth and strength necessary to enable them to provide food and 

 shelter for themselves. 



39. The same instinct is manifested in a still more striking 

 manner by insects. Many of these die immediately after they 

 have laid their eggs, and consequently do not survive to see their 

 young, of whose condition and wants therefore they can have no 

 knowledge whatever by observation or experience. Their bene- 

 ficent Maker has, however, taught them to provide as effectually 

 for the security and well-being of their posthumous offspring, as 

 if they had the most complete knowledge of their condition and 

 wants. The effects of this instinct are so much the more remark- 

 is 2 131 



