286 THE BIOLOGY OF THE SEASONS 



real need for setting out, and before the wintry conditions 

 have begun to be appreciably felt ; the departure of young 

 birds apparently unguided, and similar phenomena, recall 

 the wonders of untutored instinct among insects ; and a 

 few observations on the restlessness of comfortably caged 

 birds at the proper season point in the same direction. 

 Matthew Arnold has a fine reference to the restlessness of 

 the captive stork when the time comes to travel south, 

 though in his picture the bird is supposed to see its fellows 

 passing overhead. 



" And as a stork which idle boys have trapp'd, 

 And tied him in a yard, in Autumn sees 

 Flocks of his kind pass flying o'er his head 

 To warmer lands, and coasts that keep the sun; 

 He strains to join their flight, and from his shed 

 Follows them with a loud complaining cry" 



Another of the arguments that may be used in support 

 of the conclusion that the migrational effort has an in- 

 stinctive basis, is that we find somewhat similar periodic 

 movements, from and to a breeding-place, in widely 

 separated divisions of the animal kingdom. We find 

 migrations of mammals, of sea-turtles, of fishes, such as 

 the salmon, of land-crabs, and of other types. But it is 

 uecessary to be careful in distinguishing from true migra- 

 tions part of the essence of which is a return of adults 

 to their birthplace certain other mass-movements which 

 are merely outpourings of superabundant population, or 

 enforced pursuits of a nomadic food-supply. 



It is a migration when the land-crabs make their quick 

 march, sometimes of several miles, to the sandy coast to 

 have their eggs hatched in the old home, but it is not a 

 migration when the irresistible aerial army of locusts 

 spreads over the land. It is a migration when the salmon 

 and the sturgeon return to breed in their native fresh 

 waters, but it is not a migration when the mackerel shoals 



