BIRDS 1 1 I 



often change in regard to the four quarters. A mag- 

 netic sense would be expected to guide its possessor 

 in the straightest possible line. 



The migration - lines of the birds show, on the 

 contrary, that the travellers know the way to their old 

 home, and that they travel along the same paths as 

 their ancestors did. It is clear that the animals, in 

 their extension northward, only sought localities that 

 promised them sufficient maintenance. A sea - bird, 

 though its nesting-places are spread far and wide over 

 the shore, will not fly over the land, but along the sea, 

 where alone its food is to be had. Now we find that 

 the migration-paths of the sea-birds always run along the 

 shore and never cross any extensive land, although their 

 goal, the winter quarters, could be reached much more 

 quickly by land. These circuitous routes are very 

 striking in many species. The Richard's pipit, for 

 instance, nests in East Siberia, and migrates from 

 Heligoland to West Africa, instead of straight to 

 China.^ How can we understand such an aimless 

 direction, unless we admit that the paths of birds follow 

 the ancient line of advance, the recollection of which 

 has been transmitted from generation to generation ? 

 The animals spread gradually further and further north, 

 and each time some of the descendants nested in a 

 higher latitude than their ancestors. Hence the further 

 north a species of migratory birds nests to-day, the more 

 nesting-places of their progenitors must they fly over 

 during the migration. And as these nesting - places 



^ Some of these birds, however, must fly to China and Ceylon. We 

 must suppose that this variety has spread from the south of Asia. 



