1 6 The Field Naturalist's Quarterly Feb. 



continue in the descendants who were removed to milder 

 climates. The case of the Raven, it may be observed, is 

 hardly so strong an example of the exception proving the 

 rule as has been thought. The Raven is not a purely arctic 

 bird : that it occurs in the most northerly climes is a fact ; 

 but it is a wanderer to those polar regions from the south, 

 and it does not change in hue, a fact which is at least as 

 much in harmony with the view that continued dwelling in 

 icy conditions is itself in some cases responsible for the 

 white coat of winter or of the whole year. Very significant, 

 too, is the case of the Virginian Eagle Owl ; and Mr Keeler, 

 to whom reference has already been made, comments upon 

 the large amount of white in the North American birds 

 generally. In fact, there is something to be said in favour of 

 looking upon this seasonal change, exemplified in so many 

 of the inhabitants of polar regions, as an extreme develop- 

 ment of the paleness of hue, a partial blanching, which is 

 characteristic of many species which are inhabitants of dry, 

 not necessarily cold, though frequently also at least tem- 

 perate, regions. This fits in well with the capriciousness of 

 the change in species and in individuals : one species or 

 some individuals are more sensitive than others. If this be 

 the vera causa of the winter change, the possibility of the 

 same change being in itself useful is not thereby excluded. 

 But that is a very different matter from attributing the 

 change to selection. And in any case, as it appears to me, 

 utility has yet to be proved ; nor will it be proved by 

 ingenious reflections, suggestions, and assertions emanating 

 from occupants of study-chairs. What is to be desired is 

 more study of the actual pigmentary changes, and experi- 

 mentation as to the effects of heat and cold upon these 

 pigments, and upon the complex physiological questions 

 involved. 



