Migration-routes 345 



migration of birds, and hasty conclusions or summaries are 

 to be deprecated. Nor must it be supposed that all migra- 

 tion is in a direct course from north to south, or from south 

 to north, for even in Great Britain, as Mr. Eagle Clarke 

 has observed, a great stream of migration sets in from 

 east to west, in the autumn, across the narrowest portion 

 of the North Sea, and further records of the passage of birds 

 on the opposite shores of the Channel may explain much 

 which at present it is difficult to understand. Even in the 

 Arctic regions the migration of Ross's Gull (Rhodostethia 

 rosea) appears to be more from east to west than from north 

 to south, just as the journeys of the Black Redstart 

 {Ruticilla titys) to our own shores seem to be in a similar 

 direction. The same phenomenon is witnessed in the 

 Mediterranean, where an east and west migration crosses 

 the lines of the flight from north to south, just as it does in 

 our higher latitudes, and will doubtless be found to do in 

 other parts of the world, when the facts concerning the 

 movements of species are more fully accumulated. 



It must also be remembered that migration exists among 

 species which inhabit the countries in the Southern Hemi- 

 sphere. Thus in South America and in South Africa many 

 species are known to breed in certain districts and to 

 vanish in the cold season northward. In Australia the 

 same fact has been noticed, but the migrations are appar- 

 ently restricted to the confines of that great continent 

 itself. 



Partial migration exists in all probability everywhere, 

 and though many species may not leave a country, they 

 often shift their ground in winter-time, while it is certain 

 that of our common species, like the Song-Thrush, the 

 Robin, and the Pied Wagtail, a large number of individuals 

 are strictly migratory and leave the country altogether. 



The routes taken by some species would seem to sug- 

 gest that they follow the course taken by their ancestors 



