MIGRATION. 287 



being the exceptional characteristic it used formerly to be 

 thought, may really be almost universal."* 



I have neither the occasion nor the space to discuss the 

 large question of migration in general ; and having now 

 indicated the animals in which the instinct is most pro- 

 nounced, I shall pass on to consider the theory of its forma- 

 tion. First I may allude to Mr. Darwin's remarks on 

 Migration at the beginning of the Appendix. It will be 

 seen from them that among others he establishes the follow- 

 ing points : — 



1. There is " in different breeds of birds a perfect series 

 from those which occasionally or regularly shift their quarters 

 ^vithin the same country, to those which periodically pass to 

 far distant countries." 



2. " The same species often migrates in one country and 

 is stationary in another ; or different individuals of the same 

 species in the same country are migratory or stationary." 



3. " The migratory instinct is laade up of two very distinct 

 factors — viz., an impulse to travel periodically, and a faculty 

 of knowing the direction in which to travel." 



4. " Savage man shows a sense of direction which may be 

 analogous to that shown by migratory animals." 



5. " Certain cases are on record of breeds of domesticated 

 animals having truly migratory instincts." 



Such being the data, the problem is to account for the ' 

 origin of the instinct. Mr. Darwin's theory is that the 

 ancestors of migratory animals were annually driven, by cold 

 or want of food, slowly to travel southwards ; " and in time ■ ^ 

 we may well believe that this compulsory travelling would 

 become an instinctive passion," as is the case with domesti- 

 cated sheep in Spain. In the case of birds, the wings would 

 be used, and if in the course of many successive generations 

 the land over which they flew in their annual journeys were 

 to become slowly submerged, the line of flight would remain 

 unaltered, and thus we should have the state of things which 

 we now perceive — viz., migratory birds flying over wide 

 stretches of ocean. 



Before I proceed to consider this theory, I should like to ( 

 call prominent attention to the fact that it has been inde- 



* Professor NeAvton, F.R.S., Art. Birds, where see for a good rh ume oi 

 tlie main facts of migration as regards bii'ds. 



