102 THE COLOURS OF ANIMALS 



land, occasionally in the Midlands, and Mr. Couch 

 has seen two white stoats in Cornwall. 1 It would be 

 extremely interesting to take a number of Scotch 

 stoats to Cornwall and an equal number of Cornish 

 stoats to Scotland, in order to test whether the 

 southern individuals are less susceptible to change 

 than the northern. It is likely that the great differ- 

 ence is not wholly to be explained by the relation of 

 northern to southern temperature, but at any rate 

 partially by the fact that the change is disadvantageous 

 in most parts of England ; for it would render the 

 animal conspicuous against the prevalent tints of a 

 midland or southern winter. Of course, any such 

 disadvantage implies that natural selection would 

 gradually blunt the susceptibility of the apparatus by 

 which the change is produced. The rare cases of 

 a change of colour in Cornwall are probably examples 

 of a formerly beneficial susceptibility, as yet unaltered 

 by natural selection. 



Loss pf susceptibility to stimulus of cold in animals 

 which remain white all the year 



Such a nervous mechanism as that to which I have 

 alluded, would be of the highest intricacy and com- 

 plexity, and would speedily lose its efficiency unless 

 constantly preserved by natural selection. Thus 

 certain Arctic animals which remain on the snow 



1 Boll : British Quadrupeds, second edition, pp. 196-201. 



