i66 MIGRATION IN ENGLAND 



touches on the glacial epochs and inherited memory, 

 and concludes with the following suggestions: 



If we conclude that we are dealing with more or less expUcable 

 tropisms, the most diUgent and skilful observer among naturahsts 

 would acknowledge that those learned in biology, physiology 

 and physiography might be of service in solving the problem. 

 He might even go further and, considering that the earUest 

 mass movements of birds must have originated soon after they 

 were differentiated from reptiles and acquired powers of flight, 

 would acknowledge that the geologist, palaeontologist and astro- 

 nomer, all of whom are conversant with earth variations over 

 great periods of time, could be of assistance. Furthermore, as 

 tropistic movements must in the end be considered as questions 

 of energetics, it would not be absurd to ask a physicist to sit 

 at the round table of inquiry. 



These may be valuable suggestions, and I will 

 only add that, as those who sit at round tables are 

 not as a rule all equally open-minded or tolerant 

 of other persons' opinions, it would be well to remove 

 any chunks of old red sandstone which may be 

 lying about in the conference chamber before the 

 members meet. 



The fact is, all these theories are equally satis- 

 factory so long as the difficulties, all the facts, are 

 not taken into account. 



When I consider migration as it appears to me 

 in this northern island, I think that if I had been 

 born and bred here, seeing it in no other aspect, the 

 problem would have appeared to me, as to so many 

 others, an insoluble one. Year by year I have watched 

 it so far as I was able. In March, April and May, 

 one becomes aware of the arrival of the migrants, 

 the summer visitors; they are here all about us after 



