THE REPTILES l8l 



true crocodile found in southern Florida. They spend 

 most of the time in the water where they lie in wait for 

 prey with the nostrils exposed at the surface. They often 

 come out upon the banks to bask in the sunshine but 

 they are comparatively awkward upon the land. Their 

 eggs are laid in the sand and hatch out by the heat of the 

 sun. Crocodiles occur in the Nile and other rivers of 

 Africa and a related form, the gavial, inhabits the Ganges. 

 Both alligators and crocodiles live mainly on fish, but they 

 sometimes overcome fairly large animals which come to 

 the water to drink. The American species have a whole- 

 some fear of man and rightly so, since thousands of them 

 are killed every year for their hides. 



The most highly modified of existing reptiles are the 

 Chelonians. The body of most turtles is enclosed in an 

 armor of plates joined to the ribs and the backbone. The 

 dorsal piece, or carapace, is composed in part of bony plates 

 and in part of large horny scales overlying the plates, 

 but not corresponding to them in position. The ventral 

 piece, or plastron, is firmly joined to the carapace at the 

 sides. The head and legs may be more or less completely 

 withdrawn into the shell, and in the box turtles the plas- 

 tron is formed of two movable plates united by a hinge 

 joint which permits the two parts to be drawn up against 

 the carapace so as to completely enclose the animal. 

 The jaws of chelonians are entirely devoid of teeth, but 

 they are furnished with a sharp, horny rim, by which 

 they can retain hold of prey as well as inflict a severe 

 bite. Most species are carnivorous, but there are several 

 that feed upon vegetation. Among these are several spe- 

 cies of land-tortoises which live entirely upon the land. 

 One species occurs in the desert regions of Arizona and 

 California and another in Texas and New Mexico. The 

 gopher tortoise of the southern states is related to the pre- 



