CHAPTEK XIII 



bution, migration, play, battle, enemies, dis- 

 ease, age, and size of reptiles 



Means of Motion 



KowHERE has Mature been more liberal in modes 

 of motion than in the Reptiles. Here she has run 

 the whole scale. Many swim ; some wriggle only ; 

 others burrow ; most walk on four feet, a few on 

 two ; one glides or sails on the air like a flying 

 squirrel ; while another ancient form doubtless had 

 well-sustained flight, like that of a bat. As varia- 

 tions of these methods some have lea]3ed on two legs 

 as a kangaroo, and others have waded in a sort of 

 upright, half -floating way in deep water. This record 

 can not be excelled in any class of creatures. Be- 

 sides mere wriggling, the snakes (having lost their 

 limbs by indulging too largely in that) seem to have 

 needed some means of slow, gradual motion ; where- 

 upon Mature loosed the hold of the ribs from 

 the breast-bone, caused the bone to absorb, brought 

 the tips of the ribs to the lowest surface, connected 

 them with the scales below, and strung to each a 

 separate active muscle. Along the back-bone she 



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