74 COMPARISONS OF STRUCTURE IN ANIMALS. 



when seen deep beneath a boat in clear water, 

 it reminds the spectator of a bird, Avinging its 

 way with easy^ strokes through the air. 



Many other reptiles afford ns singular and 

 very interesting examples of a modification of 

 the feet, in order to meet certain exigencies ; 

 and in every case, according to the law of 

 creation, the structure of the whole framework 

 is in harmonious accordance. We have thrown 

 out a hint that the pterodactyles may have 

 been arboreal reptiles with parachutes, as are 

 the little dragons, excepting that the limbs of 

 the latter do not stretch the membrane; which 

 they do in certain mammalia, namely, the 

 flying squirrels and opossums, and that singular 

 flying or sweeping lemur, the colugo, {galeo- 

 pithecus,) all arboreal in their habits. There 

 are, however, as we have seen, many arboreal 

 quadrupeds destitute of these aids in taking 

 long leaps, being provided in a different 

 manner for the branches of the trees, as for 

 example, the monkey and the sloth — and so 

 among reptiles the same diversity prevails. 



If we turn to the chameHon, an arboreal 

 reptile which to a great degree seems in its 

 class what the sloth is among quadrupeds, we 

 shall find a curious modification of its limbs 



