CHAP. JV.] EVOLUTION THE KEY TO DISTKIBUTION. 



^5 



species, E. passerina, which ranges eastwards to the Lena river, 

 and in winter as far south as Amoy in China ; but in Japan 

 the original species appears again, receiving a new name [E. 

 pyrrJiulina), but Mr. Seebohm assures us that it is quite 

 indistinguishable from the European bird.^ Although the 

 distance between these two portions of the species is not so 

 great as in the last example, being about 2,000 miles, in other 

 respects the case is a most satisfactory one, because the forms 

 which occupy the intervening space are recognised by Mr. 

 Seebohm himself as undoubted species. 



The European and Japanese Jays. — Another case somewhat 

 resembling that of the marsh tit is afforded by the European 

 and Japanese jays (G-arrulus glandarius and G. japoniciis). Our 

 common jay inhabits the whole of Europe except the extreme 

 north, but is not known to extend anywhere into Asia, where 

 it is represented by several quite distinct species. (See Map, 

 Frontispiece.) But the great central island of Japan is in- 

 habited by a jay {G. japonicus) which is very like ours, and was 

 formerly classed as a sub-species only, in which case our jay 

 would be considered to have a discontinuous distribution. But 

 the specific distinctness of the Japanese bird is now universally 

 admitted, and it is certainly a very remarkable fact that among 

 the twelve species of jays which together range over all temperate 

 Europe and Asia, one which is so closely allied to our English 

 bird should be found at the remotest possible point from it. 

 Looking at the map exhibiting the distribution of the several 

 species, we can hardly avoid the conclusion that a bird very like 

 our jay once occupied the whole area of the genus, that in 

 various parts of Asia it became gradually modified into a variety 

 of distinct species in the manner already explained, a remnant 

 of the original type being preserved almost imchanged in 

 Japan, owing probably to favourable conditions of climate and 

 protection from competing forms. 



Supposed Examples of Discontinuity among North American 

 Bio'ds. — In North America the eastern and western provinces 

 are so different in climate and vegetation, and are besides 

 separated by such remarkable physical barriers — the arid 

 1 Ills, 1879, p. 40. 



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