46 THE WONDER OF LIFE 



power of adaptive colour-change. They have the secret of 

 the Gyges ring, and putting on the garment of invisibility 

 is for them as easy as winking. ' Wherever its home ', says 

 the monographer, ' the horned lizard resembles the colour 

 of the substratum so closely that it is practically invisible 

 except when in motion. Specimens from the white sand 

 of the desert are very light in colour, those from the 

 black lava belt are almost black, whereas those from the 

 vari- coloured mountain districts show red and even 

 bluish markings. How quickly a change of environment 

 would bring about a change in colour is not definitely 

 known, although Coues states that the change takes place 

 in from twenty-four to forty-eight hours '. 



Given horns and scales and the mantle of invisibility, 

 the horned lizards are safe, and we are not surprised to learn 

 that most of the species are represented by large numbers 

 of individuals. We can understand now why they have 

 such a wide geographical range from Canada to southern 

 Mexico, and from the Mississippi to the Pacific coast ; 

 why they rarely bite ; why they can afford to take things 

 easily, basking in the sun and moving with leisurely deliber- 

 ation. When an enemy comes they ' play 'possum ' ; 

 when they are thoroughly scared they seek refuge in a bush 

 or burrow in the sand. 



Even in their burrowing they are unlike most other 

 creatures, for they work their way beneath the ground 

 head-foremost. As Mr. Bryant says, ' The chisel-shaped 

 head is the principal tool, the legs being used almost 

 solely for forcing the head forward. A wriggling motion 

 of the head and body serves to drive the head beneath the 

 sand and soon covers the body completely with earth. 

 A little shake of the tail flings the dirt over that appendage, 



