'CLASS REPTILIA 399 



small neighboring islands and is threatened with extinction. It is 

 lizard-like (Fig. 289), about two feet in length, hves in burrows, is 

 nocturnal in its habits, and feeds on any other animal it can secure. 

 Among other structural features which it possesses is a more highly 

 developed 'pineal eye than is possessed by any other animal. This is an 

 eye developed from a median dorsal outgrowth of the diencephalon ; 

 it is rudimentary in all living vertebrates, being most highly developed 

 in Hzards, and is often called the pineal gland or pineal body. It is 



Fig. 289. — Tuatara, Sphenodon punctatum (Gray), of New Zealand, an example of the 

 Rhynchocephalia. X about Je- Compiled from several sources. 



believed to have functioned as an eye in types now extinct and in living 

 forms it has been looked upon as a gland of internal secretion. Although 

 this animal has some characteristics which belong to fossil reptiles and 

 has long been looked upon as the most primitive of existing reptiles, 

 it now seems probable that it is not an ancestral form from which other 

 Hzards have sprung but rather a highly modified type which has persisted 

 from earlier times. 



Fig. 290. — North American alligator, Alligator mississippiensis (Daudin), an example of 

 the Crocodilia. X about He- From several sources. 



421. Crocodilia. — This order contains some of the largest hving 

 reptiles, the gavials of southern Asia and the caymans of South and 

 Central America reaching a length of 20 feet or more and a Philippine 

 crocodile having been captured measuring 29 feet in length. A crocodile 

 and an alligator (Fig. 290) are found in southern United States. Cro- 

 codiHa are hzard-hke in form but the scales do not overlap, being set 

 into the thick, leathery skin, broadened, and sometimes raised to form 

 ridges. The snout is long and the nostrils are at its tip. Since the eyes 



