REPRESENTATIVE SPECIES. 83 



of colour and even of size which characterize many 

 of these races are primarily due to the influences 

 of climate. It is absolutely impossible to explain 

 or account for them by natural selection. The 

 influence of climate on the resident birds of the 

 Palaearctic region alone is perfectly astonishing. 

 In this vast area, which stretches longitudinally 

 from the British Islands to Japan, and latitudinally 

 . from the Sahara, Persia, the Himalayas, and China, 

 to the Arctic regions, almost every modification 

 of climate may be found temperate, arctic, and 

 tropical ; pluvial and dry. Where each description 

 of climate reaches its maximum, there we find the 

 most pronounced climatal races, and this quite 

 irrespective of latitude. Thus we find in many 

 cases the most pronounced Arctic forms in Kamt- 

 schatka, a country within the same parallels of 

 latitude as the British Islands, but from various 

 physical causes one of the coldest regions in the 

 world. Birds from Siberia, where the climate is 

 uniformly dry, are paler than birds from Western 

 Europe, where the temperature is more humid ; 

 individuals from the north of Africa vary consider- 

 ably from those that inhabit the wet areas of the 

 Himalayas. Thus in the Marsh Titmouse (Parus 

 palustris], and its various forms, we find that in 



