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PRACTICAL ZOOLOGY 



The glass " snake " (Fig. 201) is a lizard without limbs and 

 with a very brittle tail. It may easily be confused with the 

 true snakes, but is distinguished from them by the presence of 

 ear openings and movable eyelids. 



Fig. 200. — Gila monster. (Photo, of living animal. From Metcalf.) 



Snakes 



The snakes are degenerate reptiles entirely without legs except 

 in a few examples like the python, on which spearlike remnants 

 occur. The exoskeleton of scales is shed several times a year and 

 a fresh, clean covering acquired. Snakes require a rough surf ace 

 for locomotion on land. They press the scales on the ventral 

 surface against the ground, and by sidewise undulations draw the 

 body forward. Snakes that normally live in the water are able 

 to swim rapidly by similar undulations, and most of the terrestrial 

 species can also swim. 



The eyelids of the snake are not movable as are the lizard's, 



