156 THE STORY OF REPTILE LIFE. 



by the Mata-mata Tortoise (p. 42), the Croco- 

 diles and Alligators (p. 59), who, by their 

 resemblance to logs, are enabled to creep up to, 

 or be approached by, their prey without creating 

 suspicion. The Grass-snake and the Viper of 

 the British Islands, and the green tree-snakes, 

 and the sand-coloured desert forms are all in- 

 stances of aggressive resemblance. The giant 

 arboreal Boas and Anacondas have also to be 

 regarded under this head. Their enormous 

 bodies, if uniformly coloured, would be too con- 

 spicuous, consequently the surface is broken up, 

 in the case of the Boas (e.g. Python molurus) by a 

 net-work of black and yellow, and by the Ana- 

 condas by blotches of the same tints. Thus 

 the effect of strong light and shade, as of sun- 

 light breaking through a dense mass of leaves, 

 is produced. Instances of reptiles which resort 

 to what are known as adventitious colours for 

 protective or aggressive purposes are rare. The 

 Mata-mata, and a few other fresh- water Tortoises, 

 are cases in point. 



Protective coloration, however, is sometimes 

 assumed for its own sake, and not for aggressive 

 purposes, as in the case of those snakes which 

 frequent rocky or desert places. But for their 

 harmony with their surroundings, they would be 

 in constant danger of being pounced upon by 

 snake-eating hawks and other enemies with a 

 liking for snake-flesh. 



Certain lizards, and some snakes, have adopted 

 a system of what is known as "warning colora- 

 tion," whereby the creature, by exhibiting certain 

 conspicuously coloured areas, endeavours to make 



