CHAPTER XXIV. 

 CHORDATA (CONTINUED): CLASS REPTILIA. 



314. General Statement. We have now for the first time 

 a group of vertebrates that do not breathe by gills at any 

 stage of life. They may live in the water, but they are air- 

 breathing from the time they are hatched. In this 

 respect they are like the birds and mammals. All of 

 these higher classes, however, show their kinship with 

 the fishes and amphibians in having rudimentary signs 

 of gills in the early embryonic stage, before hatching or 

 birth. These are never used and all external signs of 

 them soon fade away. All the reptiles are cold-blooded 

 and in this they agree with the lower classes rather 

 than with the higher. 



When the term reptile is used, most people think of the 

 snakes; but the snakes are the least typical of the reptiles. 

 The lizards and the alligators are more nearly like the 

 main stock of reptiles. The turtles also belong to the 

 group but they, like the snakes, are in some degree degener- 

 ate animals. At least they have become so specialized 

 as to cease to be fairly representative. 



The class of reptiles was at its height in the Mesozoic 

 age of the earth, or the "age of reptiles" as it is called. 

 At this time there were great land reptiles, as is shown by 

 the fossils, 60 or 70 feet in length, and 20 feet high 

 Others equally huge lived in and ruled the seas. Still 

 others, much smaller, had membranous wings like those 

 of the bats, and were the first vertebrates to learn to fly 

 306 



