PREFACE. vii 



elected to clothe my facts more heavily with 

 incident, or to confirm my views and opinions 

 more emphatically with many additional instances. 

 I trust, however, that the elaborateness and length 

 at which the various points have been treated will 

 at least be sufficient to create interest, to stimu- 

 late research, and to illustrate the Phenomenon of 

 Migration sufficiently well. I am deeply indebted 

 to a great number of illustrious workers at the sub- 

 ject, not only for material which they have furnished 

 in their published records, but in various other 

 ways, and all of which I trust has been fully acknow- 

 ledged. To several valued and distinguished direct 

 correspondents my thanks are also due. In the 

 course of my study of Migration many bye-paths 

 of research have been suggested, which it has only 

 been possible to indicate and not to follow. One 

 thing, how^ever, has impressed me profoundly 

 during my years of investigation. In my opinion 

 the study of Migration foreshadows great discoveries 

 relating to the Origin of Species, and the present 

 and past distribution of Life over the earth's surface. 

 The whole subject of Migration is so vast, so 

 wide-reaching, and so complicated, that it would be 

 absurd to regard it as exhausted, and the present 



