VI. 



THE MIGRATION OF ANIMALS. 



THE peculiar instincts which lead certain kinds of animals, and most 

 notably certain groups of birds, to leave one country or region and 

 to pass to another on the arrival of certain seasons, has long formed 

 one of the best known facts of the natural history knowledge of 

 ordinary life. The migratory habits of animals, indeed, could hardly 

 escape the notice of even the most casual observer of the phenomena 

 of life at large ; and it is not surprising to find the accuracy of 

 ancient zoologists and philosophers well exemplified in the chronicles 

 they have left us regarding the seasons of migration of the birds with 

 which they were best acquainted. The " appointed times " of birds 

 were a subject of remark with observers even before the era of the 

 classic naturalists ; and on the regularity with which certain species 

 appeared and disappeared, a very natural argument respecting the 

 wisdom which presides over and regulates natural phenomena was 

 founded. As our knowledge of other groups of animals advanced, 

 the habit of migration was seen to be represented in fishes, in insects, 

 and in other classes of lower animals, and amongst mammals or 

 quadrupeds as well. The habits of birds, however, naturally at- 

 tracted the largest share of attention, because of their conspicuous 

 nature ; and, indeed, the explanation of migration and its causes is 

 chiefly drawn from what has been observed regarding migrating birds 

 and " the time of their coming." The interest attaching to this subject 

 has, moreover, largely increased within recent years, from the relation- 

 ship it possesses to the alteration of the physical universe around 

 us. Cases of migration and instances of the alteration of land sur- 

 faces become mutually explanatory, as we shall endeavour presently 

 to show ; and a study in natural history may thus be shown to relate 

 itself in a very important fashion to matters of the deepest interest to 

 all who recognise in the history of our universe and its living beings 

 a legitimate and absorbing theme for thought. 



Some of the more prominent cases of migration in animals may 

 be first glanced at, by way of preliminary to the discussion of the 

 nature and causes of the instincts which prompt this curious habit. 

 There appears to be little doubt that the habit is possessed by certain 

 kinds of insects, although, obviously, the exact nature of the journey- 

 ings of these animals is more difficult of determination than that of 



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