268 CROCODILES AND SNAKES 



equally true of every member of the group. But there are, neverthe- 

 less, certain rules with regard to these animals to which there is no 

 exception, 'iliey are all, for instance, what we call "cold-blooded;" 

 that is, their blood is not so thoroughly mingled with air in its passage 

 through the lungs as is that of the mammals and the birds. Much of it, 

 indeed, passes through the body more than once without entering the 

 lungs at all, the heart sending only a part to be purified, and allowing 

 the remainder to circulate as before without being freshened by contact 

 with the air. And as the heat of the body depends almost entirel}- Ujjon 

 the manner in wdiich the blood is purified, the faster it travels through 

 the body, and the more often it passes through the lungs, the greater 

 becomes the bodily w'armth. 



The heart and other blood vessels of the reptiles are formed in a 

 different manner from our own, and the blood flows through them 

 quite slowly, so that it never becomes very warm, and causes the body 

 to feel quite cold to the touch. And, in consequence, nearly all reptiles 

 are dull and sluggish in their movements, unless they are aroused l)y 

 passion. 



No reptile of any kind is provided with either fur or feathers; 

 and the reason of this is evident enough, for, as its blood is cold, 

 there is no need for the body to be clothed in the warm garments 

 w^iich are so necessary to mammals and birds. Some i)rotection, liow- 

 ever, the body Diust have, and so it is covered with either ])lates or 

 scales, according to the character of the life which it is intended to lead. 



The now existing reptiles are divided into four orders. These are 

 the crocodiles, the tortoises or turtles, the lizards and the snakes. To 

 these wt have here, for the sake of convenience, added the frogs, 

 although these are now properly considered as a family by themselves, 

 differing from the reptiles in several important w^ays. 



The crocodiles and alligators are the very lions and tigers 

 of the reptile world. The animals pass much of their time in the 

 water, and are never found very far from the rivers in which they 

 dwell. Upon dry land they are slow, awkward, and even clumsv 

 creatures, for their short limbs are scarcely strong enough to su]:)port 

 their bodies, and they waddle along in consequence, very nnich as do 

 the over-fed lap-dogs w^hich we sometimes see in the streets. But in 



