190 COLIN CLOUT'S CALENDAR. 



in the wider continents where it dwells. Iii Britain, 

 though so recently separated from the mainland, as Mr. 

 Wallace points out, this tendency has already produced a 

 fe\v very marked effects- An immense number ,of our 

 hative plantis appear in slightly different varieties from 

 tniofce of the mainland ; and in our outlying islands, such 

 as Mali} Wight > Lundy, Arran, and the Hebrides, such 

 Variation is exceptionally common. Among insects we 

 have several British species ; among fish we have six or 

 seven kinds of trout ; and among birds we have the 

 grouse, which is quite unknown in any other part of the 

 world. Its nearest Continental representative is the 

 willow-grouse of Scandinavia, which ranges all round the 

 northern hemisphere even up to the Pole. But the willow- 

 grouse changes its coat to white in winter, like the ptar- 

 migan, whereas the Scotch red grouse keeps its summer 

 dress the whole year round : and many minor points of 

 difference have caused our own bird to be universally 

 ranked by naturalists as a good species. Ought we really 

 to regard it as the primitive type from which the Conti- 

 nental bird is derived, or ought we rather to consider it 

 as a special insular descendant of the willow-grouse, or 

 ought we finally to look upon both as divergent lateral 

 branches from a single original common stock ? Prob- 

 ably the last, and for these reasons. 



The bird which came northward at the close of the 

 glacial period, to inhabit the now thawed plains of north- 

 ern Europe, much as the American partridge might take 

 possession of Greenland if all its glaciers were to clear 

 away in a more genial era, was doubtless a more or less 

 southern and temperate type of grouse-kind. Coming 

 into Britain, it would soon be entirely isolated from all 

 its allies elsewhere ; for it is of course a poor flyer for 

 distance, and it inhabits only the northerly or westerly 



