ADAPTATIONS 



145 



have their hind legs greatly enlarged and elon- 

 gated, and provided with strong muscles, so as 

 to make of them "leaping legs." The grubs 



\ 



FIG. 82. Head of rainbow trout (Salmo irideus) with gill cover bent back to show 

 gills, the breathing organs. 



or larvae of beetles which live as " borers " in tree-trunks 

 have mere rudiments of legs, or none at all (Fig. 86). 

 They have great, strong, biting jaws for cutting away 

 the hard wood. They move simply by wriggling along 

 in their burrows or tunnels. 



Insects that live 

 in water either come 

 up to the surface to 

 breathe or take down 

 air underneath their 



FIG. 83. Tree-toad (Hyla regttla). 



wings, or m some 

 other way, or have 

 gills for breathing the 

 air which is mixed 

 with the water. These 

 gills are special adap- 

 tive structures which present a great variety of form and 

 appearance. In the young of the May-flies they are deli- 

 cate plate-like flaps projecting from the sides of the body. 

 They are kept in constant motion, gently waving back and 

 11 



