A Story Outline of Evolution 



Nature's way, again changing their body forms to meet their 

 new environment. They shed and cast away their teeth. 

 Their long and heavy tails disappeared. Their bodies devel- 

 oped a shape that would offer the least resistance to the air 

 and their bones became thinner, lighter and stronger. Their 

 plate-like armor was cast off because their swiftness of 

 motion enabled them to escape their enemies and this protec- 

 tive armor was no longer needed. Their wings were bat- 

 like and in some, had a wing spread of twenty feet. The 

 change from land to air was no quick and sudden change 

 but on the other hand, it was a change covering millions of 

 years. It is generally conceded that like the flying squirrel, 

 it was at first a crawler or climber to the palm and fern 

 tops after its favorite food and as necessity arosie, folds of 

 skin were flattened out to resist the air and, perhaps, lessen 

 the fall. Then the hind legs were reduced and the fore legs 

 developed into wings. Nature was laying the foundation 

 preparing the way for a new order of flying creatures — 

 the birds. 



We have seen that the heart of the fishes was two-cham- 

 bered, the amphibians three-chambered, while that of the 

 reptiles was four-chambered. But the circulatory system 

 was not yet perfected to a point where the body temperature 

 could be controlled and the blood purified as in the next 

 class — the mammals. The reptiles were still cold-blooded. 

 Many of these reptiles, after living for millions of years on 

 land and adapting themselves to its uses, forsook the land 

 and returned again to the sea. Nature began all over again 

 to adapt their bodies to the environment of the sea. Here 

 their legs were developed into flappers and they became the 



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