362 ELEMENTARY BIOLOGY 



and other animals. Several other plants are capable of moving 

 their leaves when disturbed, as the sensitive plant (Fig. 179). 



407. Color changes. To be able to elude the vision of the 

 enemy must be of real advantage to any animal. It is therefore 

 reasonable to assume that the color changes of the chameleon 



FIG. 1 80. The true chameleon 



African monitor (Varanus niloticus). (From photograph by American Museum of 

 Natural History) 



must be of protective value to him, and that they are brought 

 about by the color of the surroundings. The true chameleon, 

 a native of Africa (Fig. 180), and the American chameleon 

 (Fig. 181), or green lizard, quickly change their color through a 

 wide range of shades, from bright green to rather dull brown. 

 These changes are brought about by the contraction or expan- 

 sion of various parts of the skin, containing different pigments. 



Careful experiments show that the color changes are produced 

 by a response to temperature changes or by the intensity of the 

 illumination rather than by the color of the background. 



