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. l.Apt<.,wdiilc& jiatctgoiufa (from Brehm). 



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 



