328 



THE RISE OF ANIMAL LIFE 



Fig. 13-47. These two reptiles inhabit the Southwestern United States. The horned toad (Phrynosoma) is not a toad 

 at all (top). The gila monster {Heloderma suspectum) is the only poisonous lizard in the United States (bottom). 



such as the cobra are deadly. There is httle 

 reason for man to wreak his vengeance on 

 every helpless snake that crosses his patli 

 and yet he does so with unrelenting fury. 

 Once he has made the kill, he often proudly 

 displays the mutilated body of a creature 

 that could never do him any harm but, if 

 allowed to live, could do him considerable 

 good by its constant pursuit of insects and 

 small rodents which are its diet. In the 



United States, all snakes except four are 

 helpful rather than harmful. 



With the exception of pythons and boas, 

 snakes are without limbs. They move in an 

 undulating fashion much the same as fish 

 swim. The posterior edge of tlie ventral 

 scales is loose, thus allowing these scales to 

 make a firm contact with the ground, which, 

 in turn, permits the animal to move forward 

 but not backward. Their eyes are large and 



