3<d8 systematic zoology 



CLASS IV. REPTILIA 



The Reptilia (Lat. rcpar, to crawl) are cold-blooded animals 

 like the fishes and amphibians ; from the former they may be 

 distinguished by the absence of gills, and from the latter by the 

 outer covering of the body, which is never soft, but has a hard, 

 horny surface, often scaly; there are frequently bony plates 

 the deeper part of the integument as well, and no glands for the 

 most part. Although many reptiles live a good part of the time 

 in water, they are as a group essentially land animals and breathe 

 exclusively by means of lungs. Each individual is provided with 

 a pair of lungs, but in the greatly elongated species the left lung 

 becomes rudimentary and may almost disappear. In the serpents 

 and some lizards there are no appendages, but most lizards, as 

 well as the turtles and crocodiles, possess two pairs, well adapted 

 to walking and with claws on the ends of the digits ; the append- 

 ages are also well developed in fossil reptiles. 



The eyes arc provided with lids, except in the serpents and 

 some lizards, where they are covered by the skin, which there 

 becomes thin and transparent ; this skin represents the fused 

 eyelids. In many lizards a sort of third eye is present, median 

 in position on the dorsal side of the head; it is connected by 

 a stalk with the brain and is covered with a transparent scale. 

 This third eye is called the parietal or pineal eve, and a similar 

 structure occurs in the brains of all the other classes of verte- 

 brates, but in no case is it so highly developed as here. The 

 organs of smell and hearing are usually well developed. 



Teeth are present in all reptiles except turtles, and are sharply 

 pointed and often recurved ; they merely serve for holding the 

 prey and not for mastication. In the poisonous serpents one 

 pair of teeth in the upper jaw is deeply grooved or even tubular 

 and serves to convey the poison to the victim. In most reptiles 

 there are glands in the mouth, called salivary glands, and some 

 of these are modified in certain serpents into poison glands. The 

 tongue is slender, bifid, and protrusible in the serpents and most 

 lizards; in other reptiles it is flat and immovable, attached to 

 the floor of the mouth. The alimentary canal terminates in a 

 cloaca, which also receives che ureters or ducts from the kid- 

 neys, and also the ducts from the reproductive organs. In the 





