THE ORIGIN OF MAN 55 



more or less quantity of food (yolk) and these 

 eggs are fertilized internally by the males before 

 they are laid by the females upon the land where 

 they hatch by the warmth of the sun. This is 

 the most fundamental difference between the 

 lower vertebrates, the fishes and amphibians, and 

 the higher vertebrates, the reptiles, birds and 

 mammals. 



The word reptile means crawling or creeping 

 and has reference to an animal that goes on its 

 belly like the snake, or moves with difficulty on 

 short sprawling legs like the alligator. All liv- 

 ing reptiles are cold-blooded like the fishes and 

 amphibians, and their skin is never soft, but al- 

 ways more or less hardened by horny or bony 

 material that occurs more often as scales than as 

 armor plate. Each animal has a pair of lungs 

 and the legs are either wholly absent or are mere 

 vestiges buried in the flesh and in such animals 

 locomotion is attained by wriggling movements 

 either over the ground or through the water. 



