CHAPTER XVIII 



THE REPTILES 



THE class Reptilia includes the Snakes and Lizards, the curious 

 New Zealand Tuatara, the Turtles, Tortoises, Alligators, and Croco- 

 diles. They are the only cold-blooded vertebrates, and the ven- 

 tricles of the heart are not completely separated. They have a 

 single occipital condyle to the back of the head, have a scaly or 

 bony-plated skin, breathe by lungs, and lay eggs or produce living 

 young. The Reptilia take up a very central position in the evolu- 

 tion of the main classes of the vertebrates, for on the one hand 

 they have undoubtedly evolved from some branch of amphibian 

 ancestors, and on the other hand have given rise to the mammals 

 and birds. The existing Reptiles may be divided into four orders, 

 namely, the Chelonians, or Tortoises and Turtles ; the Crocodilia, 

 or Crocodiles and Alligators ; the Saurians, or Lizards ; and the 

 Ophidia, or Snakes. 



Tortoises and Turtles are familiar to most people in appear- 

 ance. They are cold-blooded, four-footed reptiles, protected by 

 a buckler or " shell," and possessing no teeth in their jaws ; char- 

 acteristics which distinguish them from all other animals. They 

 frequent land, fresh water, and the sea, and have a very wide 

 geographical distribution. While all lay eggs, and, with the ex- 

 ception of the marine forms, pass some part of the year in hiberna- 

 tion, some are carnivorous, some prefer a mixed diet, and others 

 are strictly vegetarian. The buckler is a deeply seated, bony 

 framework, that part which covers the back of the animal being 

 called the carapace, while that which is below the body is known 

 as the plastron. The carapace is a modification of the bones of 

 the vertebral column and ribs, and also consists of bony plates 

 which, growing in the skin, unite all together. The under part 

 of the buckler, the plastron, is formed exclusively of skin or dermal 

 bones, and usually consists of nine pieces or plates, more or less 



248 



