116 ANIMAL COLORATION. 



possibility of snow falling from a cloudless sky, the darkness 

 of the flakes seen against the bright sky would be more 

 marked still. This difficulty in the way of accounting for the 

 above-mentioned facts was suggested to me by Prof. Weldon. 

 There are several species of white birds which, not being 

 inhabitants of the polar regions, can get no advantage from 



Fig. 7. — Aptenodyles patagonica (from Brelim). 



their coloration. Some of them, like the pelican, are strong 

 birds, which can defend themselves without the help of any such 

 adventitious aids ; but others are distinctively not so. Mr. W. 

 H. Hudson has called attention to the way in which the White 

 Egret of South America is singled out from a flock by pre- 

 daceous birds, and wonders how it can be so common in the 

 face of this obvious persecution. Here again we may emphasise 



