CLASS REPTILIA 



389 



In the reptiles the organs of sight and hearing are generally well 

 developed, as are also to a lesser degree those of taste and smell, while the 

 skin over various parts of the body is very sensitive to touch. There 

 is usually a middle ear, with a tympanic membrane, a eustachian tube, 

 and a columella. In the chameleons and snakes the tympanic membrane 

 is absent; in the turtles it is on the surface of the body; and in the Hzards 

 and crocodiles it is at the bottom of a pit, which may be considered the 

 beginning of an outer ear. 



415. Squamata. — This order is characterized by a typical scaly 

 covering which is shed periodically. In the case of snakes it is cast off 



Fig. 275. 



-Common chameleon of southern Europe, Chamaeleo vulgaris Daudin. 



(Based 

 upon figure in Brehm, " Thierleben.") 



complete and at one time, but in the lizards it is stripped off in shreds 

 during a period of several days. Three groups of Squamata are usually 

 recognized — chameleons, lizards, and snakes. 



416. Chameleons. — Some lizards are erroneously called chameleons 

 because of the ease with which they change color. This term, properly 

 speaking, should be restricted to certain Old World reptiles which possess 

 several pronounced characteristics (Fig. 275). Among such character- 

 istics connected with arboreal life may be mentioned a lateral com- 

 pression of the body; the possession of a long prehensile tail which is not 

 easily broken and which if lost cannot be regenerated; and the existence 

 of long, slender limbs with digits so arranged that two are opposable 

 to the three others, making the foot effective in grasping. In each group 

 of digits, they are united nearly to their tips. The eyelids are united, 

 except for a small central opening. The eyes are capable of being moved 



