194 FIRST LESSONS IN ZOOLOGY. 



tory of Selborne," relates that one was kept in a village till 

 it was supposed to be one hundred years old. 



When we see how few turtles are devoured by other ani- 

 mals because of their thick shell, and also take into account 

 their vitality and the length of time it requires for them to 

 arrive at maturity, the cause of their great longevity is ex- 

 plained. 



The Crocodiles. In the crocodile, gavial, and alligator, 

 we return again to a lizard-like form. They present a de- 

 cided step in advance of other reptiles, the heart approach- 

 ing that of birds, in having the ventricle completely di- 

 vided by a partition into two chambers; the venous and ar- 

 terial blood mingling outside of the heart, not in it, as in the 

 foregoing orders. The brain is also more like that of birds. 



FIG. 200. Head of the Florida Crocodile. 



The nostrils are capable of closing, so that crocodiles and 

 alligators draw their prey under the water and hold it 

 there unti. 1 it is drowned; but they are obliged to drag 

 it ashore in order to devour it. 'The skin is covered 

 with large bony, epidermal scales. The conical teeth are 

 lodged in sockets in the jaws. The feet are partly webbed. 

 The crocodiles and ga vials lay from twenty to thirty cylin- 

 drical eggs in the sand on river-banks. The crocodiles are 

 distributed throughout the tropics, even Australia; the ga- 

 vials are mostly confined to India and Malaysia, and also 

 Australia. 



It is among certain fossil reptiles that we find links con- 

 necting the reptiles and birds, and thus the highest, best- 

 developed reptiles are not those now in existence, but those 



