THE MIGRATION OF ANIMALS. 123 



directs its way in the air, and passes unerringly to its destination 

 through the illimitable azure. 



Allusion has been already made to the exactitude with which 

 migratory birds may arrive and depart from any given region, and 

 this punctuality has been cited in support of the exact regulation, 

 through instinct and habit, of the life of the birds. A bird almanac 

 might, indeed, be constructed through the observation of the " ap- 

 pointed times " of certain species, on the principle of constructing a 

 " floral clock " by watching the times of the opening and closing of 

 flowers. The vast majority of the migratory sea-birds and water- 

 fowl arrive punctually to a day on our coasts from the far north. 

 Amongst such birds none appear with greater exactitude than the 

 puffins ; and despite contrary winds and delaying storms, many 

 allied species of sea-birds arrive at their particular stations with 

 almost clockwork regularity. So also the periods of return to their 

 foreign quarters, or of departure from our shores, appear to be fixed 

 and adhered to with an undeviating punctuality which bespeaks a 

 regulation by unconscious instinct and automatic will. That the 

 periods of departure from our shores are in particular regulated by 

 the influence of such unconscious habit and inherited instinct is 

 clearly proved by two very notable circumstances, calculated to 

 attract the notice alike of the reflecting naturalist and of the un- 

 skilled observer of birds and their history. The first of these cir- 

 cumstances has already been referred to in the case of the swallows, 

 the migratory instinct in which is so strong, that the unfledged young 

 contained in the nest when the day of departure arrives have been 

 left to die by the retreat of their parents. In such a case a more 

 powerful incentive that of inherited and obdurate instinct has 

 triumphed over parental affection itself. Then, also, a curious and 

 perhaps more notable feature of bird life than the preceding circum- 

 stance is found in the fact that the caged young of migratory birds 

 exhibit a decided restlessness at the period of migration when their 

 free neighbours are leaving our shores. Such confined migrants, 

 which themselves have never migrated, will beat their wings against 

 the bars of their cages, and will show by every symptom and indica- 

 tion that they participate, by nature and instinct, in the movement of 

 migration, of which they have had no previous experience of any 

 kind. This latter fact is in itself a powerful argument in favour of 

 the idea that true migration is in itself instinctive and acquired by 

 heredity ; and the fact tells also in favour of the acquirement and 

 perpetuation of the migratory habit under circumstances to be 

 presently detailed. 



The manner in which migration is performed varies with the 

 group of birds which exemplifies the habit. The best example of a 

 bird which leaves Britain en masse is the swallow, whilst the cranes, 



