APPARENT EXCEPTIONS. 187 



prevails. Jet black, side by side with pure white, 

 and the most brilliant crimsons, are common in 

 the plumage of the Woodpeckers. No birds are 

 more conspicuous in colouring, yet none are more 

 seldom seen. The Green Woodpecker itself, with 

 its yellow tints and crimson hood, contrasts strongly 

 with the bark on which it climbs. The purpose of 

 concealment being effected by other means, gives 

 way to the purpose of beauty or of adornment in 

 the disposition of colours. And in general the 

 same rule applies to all birds whose life is led 

 among woods and forests. Comparatively inacces- 

 sible to birds of prey, they exhibit every variety 

 of tint, and the principle of invisibility from assi- 

 milated colouring is almost unknown. 



It must always be remembered, that ani- 

 mals of prey are as much intended to capture 

 their food, as their victims are intended to have 

 some chances and facilities of escape. The pur- 

 pose here is a double purpose — a purpose not in 

 all cases to preserve life, but to maintain its bal- 

 ance and due proportion. In order to effect this 

 purpose, the means of aggression, and of defence, 

 or of escape, must bear a definite relation to each 



