388 



THE TRANSITION TO LAND 



a heavy tail that acts as a food reservoir to tide it over periods of food 

 scarcity. It is found primarily in Arizona and is especially abundant 

 along the Gila River. It moves awkwardly but, when molested, is capa- 

 ble of quick movements of the head accompanied with a snapping of the 

 jaws which may easily fasten onto a hand held too near. Gila monsters 

 have grooved teeth with poison glands at their base and once they have 

 fastened their grip they hold on for a time, chewing a little to work the 

 poison down into the wound. The bite makes a person quite ill, but the 

 poison does not seem to be injected in sufficient quantities to cause death. 

 The horned lizard of Texas and other southwestern states has an ap- 

 pearance that would make it look like some prehistoric monster if it were 

 much larger. It has a broad flattened body resembling that of a toad 





mmmm 





R. Martin Perkins, Chicago Park District 



Fig. 26.11. The glass snake or the jointed snake. This reptile is not a snake at all, 

 but a legless lizard. Like many lizards it will throw off portions of its tail when 



excited. 



and is often called a horned toad. When disturbed it may shoot a fine 

 stream of blood out of its eyes for a distance of several feet. This does 

 not seem to accomplish any particular purpose except that it might startle 

 an attacker and give the lizard a chance to escape. 



The American chameleon {Anolis carolinensis) is very common in the 

 southeastern United States. It is another one of those animals that can 

 alter their color. It has a basal pigment of green in the skin, but over 

 this there are chromatophores of brown which are capable of expansion 

 and contraction. When they are expanded they mask the green and the 

 animal is brown, but the green shows when these bodies are contracted. 

 The color changes come about in response to a hormone from the inter- 

 mediate lobe of the pituitary gland. When this gland is removed the 

 chameleons remain green — the hormone is necessary for the expansion 

 of the brown chromatophores. It is commonly believed that these ani- 



