CROCODILIA 253 



the margin being conspicuously marked with red. The plastron is yellow, 

 blotched with brown. There are markings of yellow and red upon the 

 sides, neck, limbs, and tail, a pair of bright yellow patches behind the eyes, 

 and a smaller pair on the back of the head. The toes are strong and broadly 

 webbed. They are especially fond of insects and worms. They are very 

 shy and active. Chrysemys marginata is a western form. 



The common box-turtle (Cistu'do), a terrestrial member of this group, is 

 built for life on land. Its carapace is high and it can withdraw its head, 

 legs, and tail within it. Across the center of the plastron is a double 

 hinge, so that when disturbed it completely shuts itself in the box, and 

 nothing short of injuring the shell can harm it. One was once subjected 

 to a strong dose of chloroform in our tight-covered " killing jar " for two 

 hours with little or no effect, so tightly was it shut up in its box. It is surely 

 a good illustration of special adaptation to environment. Since it cannot 

 run, like the rabbit, nor swim, like its relatives of the streams, it closes up 

 its house and remains motionless. It is found from New York to Missouri 

 and southward. 



The musk terrapin (Aromoch'elys odora'tus), a representative of the family 

 Kinosternidce, is a small fresh-water specimen which has a strong, musky 

 characteristic odor. Its food consists of aquatic insects, small fishes, and 

 worms. 



The Land Tortoises (Testudin'idce). The giant tortoise, which inhabits 

 the Galapagos Islands and two islands of the Indian Ocean, is the only sur- 

 vivor of a race of giant tortoises of the Reptilian Age. A specimen once 

 in the New York Zoological Garden weighed 310 pounds, and was estimated 

 to be four hundred years old. 



Almost every island of the Galapagos group has had or has 

 its own peculiar form of tortoise. How they got to these islands 

 or where they came from it is impossible to say definitely. 

 They could not have migrated, since land tortoises are easily 

 drowned, and anyway, " there are now none of their kind on the 

 continents of Asia, Africa, or South America." 1 So it is as- 

 sumed that they are descendants of tortoises once populating 

 the land which, except these islands, now lies below the Indian 

 Ocean. 



Our native species of this family is the Gopher tortoise, found 

 in the pine barrens of the Southern States. 



ORDER V. CROCODILIA 



Crocodiles and alligators are the largest of living reptiles, 

 some of the largest crocodiles attaining a length of 30 feet. 

 They are covered with horny plates or scales. 



The head is remarkable for its powerful jaws, whose enor- 

 mous gape enables the animal to seize and crush its prey. 



1 Gadow. 



