ARCTIC COLOURING 



179 



deception rules there as in the sea. The white colour- 

 ing of the polar bear, Arctic fox, of the gulls and terns, 

 seems at first sight an admirable case of sympathy 

 between scenic and animal colouring. But, strictly 

 speaking, white is not a colour so much as the sum 



FlG. 30 Female Orange-tip Butterfly (Anthocaris cardamines) on the 



wing (a) and at rest (b), to show the sympathetic colouring of the 

 under-surface. - -(Copyright, C. D. Head, Dublin.) 



of colours ; it is due not to a pigment, but to the 

 covering of the body with a coating of air-bubbles — 

 a froth in the pelage or plumage — that reflects the light 

 and confers additional warmth by acting as a non- 

 conductor. The resemblance, therefore, of many Arctic 



