THE INSURGENCE OF LIFE 175 



inquire where we should rank migration on the inchned 

 plane of animal activities, but no secure answer can be 

 given in the present state of science. It seems to partake 

 very largely of the nature of instinct, that is to say, birds 

 have a specific hereditary preparedness or disposition for 

 their migratory movements, which enables them to go 

 through with them without education or experience. But 

 this does not exclude the view that birds have their wits 

 about them as they fly, for many instinctive activities 

 show a spice of intelligence. Nor does it exclude the view 

 that birds migrate more successfully as they grow older, 

 for instinctive routine may be intelligently perfected by 

 practice. That the migratory activity has an instinctive 

 basis is suggested by its regularity and orderhness, without 

 much individuahty and with little hint of caprice ; by the 

 preparations made before there is any real need; more- 

 over it must be remembered that none of our summer 

 visitors have any personal experience of wintry conditions, 

 hteraUy knowing no winter in their year ; by the success 

 with which many young birds carry it through, apparently 

 unguided and untutored ; by a few observations of the 

 restlessness shown at the proper time by comfortably caged 

 migrants ; and by the sporadic occurrence of other true 

 migrations in widely separated divisions of the animal 

 kingdom. 



Periodic movements occur in many other creatures besides 

 birds — ^in landcrabs, in fishes like sahnon and eel, herring 

 and mackerel, in turtles, in lemmings and field mice, in 

 some deer, in eared seals and in most cetaceans, such as 

 the bottle-nose whale, the right whale, and the white- 

 beaked dolphin. The term migration should not be used, 

 hpvever, without quahfication, unless the movement is really 



