DIFFERENTIATION, MIGRATION, AND MIMICRY. 373 



Cape to Nova Zembla. (2) The Baltic line with bifurcation, one 

 proceeding by the Gulf of Bothnia, and the other by the Gulf of 

 Finland, which is afterwards again subdivided. (3) A Black Sea 

 line, reaching nearly as far north as the valley of the Petchora. 

 (4) The Caspian line, passing up the Volga, and reaching as far 

 east as the valley of the Obi by other anastomosing streams. 



Palmen has endeavoured to trace the lines of migration on 



the return autumnal journey in the eastern hemisphere, and has 



arranged them in nine routes : (1) From Nova Zembla, round the 



West of Norway, to the British Isles. (2) From Spitzbergen, by 



Norway, to Britain, France, Portugal, and West Africa. (3) From 



North Russia, by the Gulf of Finland, Holstein, and Holland, 



and then bifurcating to the west coast of France on the one side, 



and on the other up the Rhine to Italy and North Africa. 



(4 a) Down the Volga by the Sea of Azof, Asia Minor, and Egypt, 



while the other portion (4 6), trending east, passes by the Caspian 



and Tigris to the Persian Gulf. (5) By the Yenesei to Lake 



Baikal and Mongolia. (6) By the Lena on to the Amoor and 



Japan. (7) From East Siberia to the Corea and Japan. 



8) Kamschatka to Japan and the Chinese coast. (9) From 



Greenland, Iceland, and the Faroes, to Britain, where it joins 



line 2. 



All courses of rivers of importance form minor routes, and 

 consideration of these lines of migration might serve to explain 

 the fact of North American stragglers, the waifs and strays which 

 have fallen in with great flights of the regular migrants, having 

 been more frequently shot on the east coast of England than on 

 the west coast, or in Ireland. They have not crossed the Atlantic, 

 but have come from the far north, where a very slight deflection 

 east or west might alter their whole course, and in that case they 

 would naturally strike either Iceland or the west coast of Norway, 

 and in either case would reach the east coast of Britain. But, 

 if by storms, and the prevailing winds of the North Atlantic 

 coming from the west, they had been driven out of their usual 

 course, they would strike the coast of Norway, and so find their 

 way hither in the company of their congeners. 



As to the elevation at which migratory flights are carried on, 

 Herr Gatke, as well as many American observers, holds that it is 

 generally far above our ken, at least in normal conditions of the 

 atmosphere, and that the opportunities of observation, apart from 



