CHAPTER XVIII. 

 The Reptiles. 



' I HE next class or division in the tree of animal life Is that 

 of the reptiles. To a casual observer it may seem that 

 the reptiles having the general shape of body and to a cer- 

 tain extent a similar internal plan are not materially differ- 

 ent from that of the amphibians. But notwithstanding 

 external resemblance, they present to those concerned with 

 Evolution's facts a distinct line of demarcation. They were 

 the first true air-breathing land animals and they dominated 

 the earth for millions of years. They developed the first 

 egg with a shell and hatched their young on land without 

 returning to the sea. They pass through the fish-like stages 

 of ancestral development within the shell but they breathe 

 by lungs only after they are hatched. In these the circula- 

 tory system was undergoing great changes to meet the 

 changed conditions on land and the heart had developed 

 into four chambers. The size of the brain had increased 

 and nervous sensation had become more highly developed. 



During the period of more than thirty million years 

 covering the Age of Reptiles, hundreds of bird-like, fish-like, 

 animal-like forms were developed. They became, through 

 adaptation, crawlers, climbers, runners, flyers and swim- 

 mers. They were both carnivorous and herbivorous. They 

 developed Into the most gigantic forms the world has ever 



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