IN THE GRIP OF AN ICE AGE 49 



animals which lived in one of the regions that were 

 being gradually drained would become simply land 

 animals. As long as they have both elements, land 

 and water, they use both. But even in nature to-day 

 we have frogs that live in trees or in almost waterless 

 regions. We will suppose then that, as the waters 

 are drained, these large primitive salamanders, as 

 described in the last chapter, take m.ore and more to 

 the land. They will lose their gills. Their legs will 

 grow stronger, and their feet firmer. In short, the 

 salamander will become a reptile with a short, stump}'' 

 tail. 



This new branch of the tree of life appeared before 

 the end of the coal forest period. The reptile was the 

 new m^onarch of the earth. He was very different 

 from the snakes and lizards, crocodiles and turtles, 

 of to-day. He had a thick, squat body, several feet 

 long, a very short tail, and a head more like that of 

 a frog. He was the patriarch of the reptile family, 

 and the descendant of the salamander and the lung- 

 fish. But he appeared for the same reason as they 

 did : the land was gaining on the water. 



At first the reptile also had a golden age. He can 

 live in water, like a crocodile, or in a waterless desert, 

 like some of the Australian lizards. What he chiefly 

 wants is warmth. He is a cold-blooded animal. That 

 is to say, his heart has only three chambers, so that 

 the blood purified in the lungs is not kept completely 

 separate from the unpurified blood, and it does not 



