ORIGIN OF THE SPECIFIC TYPE 335 



moving one like a snail, the intermingling from neighbouring sporadic 

 colonies will be much slower than in the case of a resident bird such 

 as a woodpecker. Many interesting results would undoubtedly be 

 gained if the numerous careful investigations into the geographical 

 distributions of species and their local races were studied with 

 special reference to this point, and much light would undoubtedly 

 be thrown upon the evolution of the specific type. But it would 

 be absolutely necessary to study carefully all the biological relations 

 of the animals concerned, to trace back the history of the species 

 as far as possible, and to decide the period of immigration, the mode 

 and direction of distribution, and so on. 



Nothing shows more plainly the enormous duration of the period 

 of constancy in species than the wide distribution of the same specific 

 type on scattered areas or even over different areas absolutely isolated 

 from one another. If, as we saw, the same diurnal buttex-flies live 

 in the Alps and the far Xorth, they must have remained unvaried 

 since the Glacial period, for it was the close of that period that brought 

 them to their present habitats, and while other diurnal butterflies 

 now living on the Alps differ from their relatives in the Arctic zone 

 (Lapland, Siberia, and Labrador) in some unimportant spot or line, 

 and must therefore have diverged from one another in the course 

 of the long period since the Glacial epoch, they have done so only 

 to a minimal degree, and in characters which possibly depend solely 

 upon germinal selection and can hardly be regarded as adaptations. 



I should like, however, to cite one of the few cases knoAvn to me 

 in which a slight deviation from the specific type undoubtedly 

 depending upon adaptation has occurred on an isolated region. The 

 nut-jay {Caryocatactes nucifraga) lives not only upon our Alps and in 

 the Black Forest, but also in the forests of Siljeria, and the birds 

 there differ from those with us in small peculiarities of the bill, which 

 is longer and thinner in them, shorter and more powerful in ours. 

 Ornithologists associate this difference with the fact that in this 

 country the birds feed chiefly on hard hazel nuts,, which they break 

 open with their bill, and on acorns, beechmast, and, in the Alps, on 

 eembra-cones, while in Siberia, where there are no hazel nuts, 

 they feed chiefly upon the seeds of the Siberian cedar, which are 

 concealed deep down in the cones. Thus we find that in Siberia 

 the bill is slender, and that the upper jaw protrudes awl-like 

 beyond the lower, for about 2-5 mm., and probably serves chiefly 

 to pick out the cedar nuts from behind the cone-scales. In the 

 Alps the birds (var. jMchyrhynchus) break up the whole cone of 

 the cembra-pine with their thick, hard biU, and in the Upper 



Digitized by Microsoft® 



