INTERNAL MIGRATIONS. 143 



with orbital eccentricity. The ineA'itable deduction 

 from these clearly demonstrable facts is, that which- 

 ever Pole is passing through a period of mild 

 climatal conditions and freedom from glaciation, 

 the region round that Pole will be the great breed- 

 ing area of birds whose migrations are latitudinal. 

 Hence at the present time we have few birds under- 

 taking a latitudinal migration during summer in 

 the Southern Hemisphere, and possibly only one 

 or two breeding sufficiently high in South Polar 

 latitudes to bring them into the Northern Hemi- 

 sphere to winter during our summer, as by the law 

 that the further north a bird goes to breed the 

 further south it goes to winter, and inversely, by 

 inference, the further south a bird goes to breed, 

 the further north it goes to winter, they un- 

 doubtedly would do. The reason for this is, that 

 the now glaciated condition of the Southern Pole 

 has destroyed the once fair Antarctic paradise, the 

 Mecca of migratory birds during the ages the 

 Northern Pole was labouring under its desolate 

 burden of glaciation. At the present day con- 

 ditions are exactly reversed. The Arctic and 

 north temperate regions are free from glaciation, 

 and furnish suitable breeding-grounds for these 

 migrants, and as a natural consequence we find 

 the progress of migration reversed, and birds come 

 north to breed and go south to winter, as we during 

 historic time have only known them to do, and as 

 appears to us therefore the only normal procedure. 

 Migration then in the Southern Hemisphere, as we 



