i8o THE WONDER OF LIFE 



by geological and climatic changes gradually diverged from 

 each other, we can easily understand how the habit of 

 incipient and partial migration at the proper seasons would 

 at last become hereditary, and so fixed as to be what we 

 term an instinct. It will probably be found that every 

 gradation still exists in various parts of the world, from a 

 complete coincidence to a complete separation of the breed- 

 ing and subsistence areas ; and when the natural history of 

 a sufficient number of species in all parts of the world is 

 thoroughly worked out, we may find every link between 

 species which never leave a restricted area in which they 

 breed and live the whole year round, and those other cases 

 in which the two areas are absolutely separated ' (Nature, 

 October 8, 1874, p. 459). 



Way -Finding. The most fascinating question in 

 regard to migration is the one whose solution is probably 

 most remote, How do the birds -find their way ? It is in 

 agreement with scientific method that instead of giving too 

 much time to speculation on this theme, we should devote 

 years of patient investigation to the much humbler question, 

 What way do they find ? After years of devotion to the less 

 ambitious question, we shall probably be able to ask the 

 more fascinating question in some more hopeful form. 



No doubt the wonder is great that birds return from the 

 south to their birthplace in the north ; that inexperienced 

 young birds make a long journey, often over-sea, to suit- 

 able winter-quarters, with success in a large proportion 

 of cases ; that they keep their direction in the dark and at 

 great heights, and while flying over the pathless sea. It 

 is true that there are many failures, a crop of tragedies 

 every year, a never-ceasing process of discriminate and 

 indiscriminate elimination, but the marvel is the relative 



