PINE-LIZARD AND ITS ALLIES: REPTILIA 353 



Many lizards possess the power, when seized suddenly, of 

 snapping off the tail, which may be left in possession of the 

 captor, while the creature hurries away to safety. Fig. 179 

 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, 178. The .tail is 

 usually reproduced, at least so far as the flesh and skin are 



FIG. 179. Photograph of Mexican Iguana with Broken Tail 



concerned ; new vertebrae are not developed. The pattern 

 of the scales on the newer portion is usually simpler, some- 

 times apparently reverting to an ancestral type. 



The chameleons (Chame'leo) of the Old World are famous 

 for their color changes, but the power is possessed to a greater 

 or less extent by nearly all lizards. It is accomplished by the 

 shifting of pigment 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 objects, 

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



Snakes. The snakes, which belong to the class Ophid'ia 

 (Gr. ophis, a serpent), are usually very easily distinguished 



