l86 THE REIGN OF LAW. 



ciently endowed with other more effective means 

 of escape. 



This is the higher Law of Purpose which governs 

 the lesser law, whatever it may be, by which assi- 

 milative colouring is produced. Now, no man 

 who had observed this higher law could ever fall 

 into the error of supposing that the colour of the 

 Green Woodpecker was given to it as a means of 

 concealment. Few birds are so invisible as Wood- 

 peckers, because their structure and habits give 

 them other methods of escaping observation which 

 are most curious and effective. They have few 

 natural enemies but Man, and when in danger of 

 being seen by him, they slip and glide round the 

 bole of the tree or bough on which they may be 

 climbing with a swift, silent, and cunning motion, 

 and from behind that shelter, with nothing visible 

 but their head, they keep a close watch upon the 

 movements of the enemy. With such sleight of 

 feet there is no need of lazier methods of con- 

 cealment. 



Accordingly in this family of birds the law of 

 assimilation is withheld from application, and the 

 most violent and strongly contrasted colouring 



