A Story Outline of Evolution 



these adaptations have developed about ten thousand kinds 

 of bony fishes. These are divided into approximately two 

 hundred different families and these may be grouped into 

 eighteen or twenty orders. These adaptations and changes 

 in forms are found in a proportionate degree in all the other 

 classes of the vertebrate group. But fishes are those verte- 

 brate creatures which spend the whole of their life in water 

 and which do not develop legs, fingers or toes. There was 

 a call from the sea to the land but fins and gills were use- 

 less on the land because they are adapted for use in the 

 water. To prepare for the environment on land, it was 

 necessary for the fishes that desired to change their environ- 

 ment from sea to land, to develop lungs with which to 

 breathe the air, limbs and toes with which to crawl, walk 

 and climb. One group of fish began to develop lungs, 

 whether from desire or necessity we do not know, but some 

 of their lineal descendants are still found in the rivers of 

 Australia, Africa and South America. They breathe like 

 other fishes during the wet seasons and then breathe with 

 their lungs when the rivers dry up. They are the ances- 

 tors of the next general class of vertebrates — the Amphibia. 

 But since fins are useless as a means of locomotion on land, 

 they then began to develop legs. Nature aids the efforts of 

 her creatures if these efforts are directed in the right direc- 

 tion. When gills were of no further use, she developed a 

 spongy lung capable of extracting oxygen from the air. 

 Where fins could be no longer used, she developed legs as 

 a means of locomotion. As the fish were flopping about in 

 the shallow water, the fins became less useful and the neces- 

 sity for legs increased. If we wear a tight fitting shoe 



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