356 



GENERAL ZOOLOGY 



captor, while the creature hurries away to safety. Fig. 183 

 shows a Mexican species of iguana which had thus responded 

 to the efforts of the photographer to take its picture. The 

 same animal before mutilation is shown in Fig. 182. The 

 tail is usually reproduced, at least so far as the flesh and 



skin are concerned ; 

 new vertebrae are not 

 developed. The pat- 

 tern of the scales on 

 the newer portion of 

 the tail is usually sim- 

 pler, sometimes ap- 

 parently reverting to 

 an ancestral type. 



The chameleons of 

 the Old World are 

 noted for their color 

 changes, but this 

 power is possessed to 

 a greater or less extent 

 by nearly all lizards. 

 It is accomplished by 

 the shifting of pig- 

 ment granules in cells 

 in the deeper layers of 

 the skin, toward or away from the colorless outer skin. The 

 movement of the granules, though affected by external con- 

 ditions, such as color and temperature of surrounding ob- 

 jects, is said to be largely under the control of the animal. 

 On the islands off the Malay coast lizards close to twenty 

 feet long have recently been discovered. 



Only one genus of lizard found in North America is pois- 

 onous. These are the Gila monsters (Heloder'ma) which live 

 in the deserts of our southwestern states. 



Fig. 182. Photograph of a Mexican iguana 



