CHAPTER Xn 

 ANIMAL LOCOMOTION 



THE many and varied creatures which populate 

 the earth show as great a diversity in their 

 manner of progression as they do in their 

 structure and habits. Some of them, for instance, 

 are experts at swimming, others are endowed with 

 the power to fly, others are proficient at leaping, 

 while certain kinds can only get about by crawling 

 along. 



Although most animals move in a forward direc- 

 tion under normal conditions, yet some individuals 

 progress backwards, while, moreover, in the worm- 

 like and limbless lizard known as the amphisbsena 

 we have an example of a creature that can get 

 about equally well in either direction. 



Reviewing first the mammals as being the highest 

 class of animals, we find that the greater number 

 of them possess four limbs of almost equal length. 

 But in some species the hinder pair are developed 

 to a much greater extent than the foremost pair ; 

 in others just the reverse is the case, while many 

 of the aquatic and semi-aquatic types have theii 

 fore-limbs modified into paddle-like structures, 



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