ADAPTATION 



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Adhesive organs are found in insects and in such vertebrates as 

 the tree frogs. Adhesion may be accomphshed by the secretion 

 of fluids or by the vacuum-cup principle, and is especially effective 

 for climbing on smooth surfaces. The ability of a fly to walk up a 

 window pane or across the ceiling is due to such organs. 



Some animals use other organs than the limbs for climbing. 

 The true chameleon of Africa and some monkeys have prehensile 



Fig. 131. — The two-toed sloth, Choloepus didadylus. (From Parker and Has- 



well, after Vogt and Specht.) 



tails which are used to grasp branches, and parrots use their power- 

 ful beaks for the same purpose. 



Adaptations to Light. In addition to adaptations of the appen- 

 dages terrestrial animals are adapted to conditions of light and 

 moisture, although to a lesser degree than the green plants. Since 

 sunlight plays so large a part in the metabolism of the latter organ- 

 isms, they are nicely adjusted to it. Shade-loving species are of 

 more delicate texture, for various reasons, and have broader 

 leaves than those which live in the open. Violets afford a familiar 

 illustration; most species have entire leaves, but in those which 

 are found on the dry, brightly lighted prairies the leaves are finely 



