MIGRATION COMPREHENSIVE 277 



and we have seen that this conclusion is in 

 accord with the facts of observation — that is the 

 general result of our inquiry into the functioning 

 of the two powerful impulses, the impulse 

 associated with the disposition to secure a 

 territory and the gregarious impulse. 



The phenomenon of migration embraces a 

 number of separate problems, each one of which 

 presents features of great interest and of still 

 greater difficulty. On some of these problems 

 I do not intend to touch ; I seek only to 

 ascertain whether the impulses that are con- 

 cerned in the securing of a territory, and in the 

 search for society, bear any relation to the 

 problem as a whole. I hold that the origin of 

 migration is not to be found merely in conditions 

 peculiar to a remote past, but that the conditions 

 inhere in the organic complex of the bird, 

 and are thus handed down from generation to 

 generation. Starting with this assumption I 

 examined the behaviour which normally accom- 

 panies the seasonal life-history of the individual, 

 and found, in that behaviour, manifestations of 

 cyclical change leading to definite biological 

 consequences. I now propose to inquire whether 

 those consequences are such as might, in the 

 course of time, give rise to the seasonal change 

 of abode. 



We are apt to think of migration in terms of 

 the Warbler that enlivens our hedgerows in the 

 spring after travelling hundreds of miles from 

 the south, or of the Redwing that comes from 



