THE ANIMAL KINGDOM 451 



frequently have vocal sacs. There is usually a marked 

 metamorphosis. 



Examples: Rana pipiens, the grass or leopard frog; Rana 

 catesbeiana, the bullfrog; Bufo americanus, a common toad. 



CLASS V. REPTILIA. Reptiles. The skeleton of reptiles is 

 well ossified ; the body is covered by epidermal scales or ossified 

 dermal plates ; there are claws on the digits ; breathing by lungs ; 

 no gill respiration at any time in the life history; the heart has 

 two incompletely separated ventricles and two atria. Most 

 reptiles are oviparous, though viviparous forms also occur. 

 The egg in either case is large, resembling a bird's egg, and in the 

 oviparous forms the egg is laid on the ground. There is no 

 metamorphosis in development. 



Order 1. Crocodilia. Alligators and crocodiles. The 

 teeth are set in sockets (thecodont); there are bony plates in the 

 skin; two pairs of legs, and a laterally flattened tail. A 

 tympanum is present. All are oviparous. 



Examples: Alligator mississippiensis, the common American 

 alligator has a broad head, blunt snout and its length may 

 reach 15 ft. Crocodylus acutus, the American crocodile, has a 

 long head, pointed snout and reaches a length of 20 ft. Both 

 occur in Southeastern United States and tropical America. 



Order 2. Lacertilia. Lizards. The body is elongate and is 

 covered with scales, which are periodically shed and renewed. 

 The teeth are either attached to the edge of the jaws (acrodont) 

 or laterally to the walls of a groove (pleurodont) in the jaw. 

 The tongue is usually well developed and is protractile. Most 

 lizards are oviparous. 



Examples: Sceloporus undulatus, the common fence lizard; 

 Phrynosoma cornutum, the horned toad; Sphenodon punctatum, 

 a New Zealand lizard remarkable for the presence of a well- 

 developed pineal eye: Rhineura fioridana, the legless lizard 

 of Florida, about 8 or 9 in. in length. 



Order 3. Serpentes. Snakes. The elongate body is limbless 

 and covered with scales, which are periodically shed and 

 renewed. The teeth are acrodont and the jaws are loosely 

 articulated to the skull. The tongue is long and forked. 

 There is no middle ear. The eyelids are not movable. Loco- 

 motion is brought about by the lateral bending of the body and 



