OKKilN OK MIGRATION. 01 



vital a part in the iiiii^ration of birds, I liave no explana- 

 tion t(^ olTer. We know, however, that it exists not only 

 in hiivls Itut in iniiny other animals. It is this instinct, 

 aided hy the ''heredity of habit," which iz;uides a bird 

 to its nestini^ ground. The Carrier Pigeon is taught its 

 lines of flight by gradually extending its journeys; a 

 species establishes its routes of migration by gradually 

 extending its range. 



