144 ANIMAL LIFE 



of water above their gills, by means of which they can 

 breathe during short excursions from the water. Still 

 others (mud-fishes) retain the primitive lung-like structure 

 of the swim-bladder, and are able to breathe air when, in the 

 dry season, the water of the pools is reduced to mud. 



Another series of adaptations is concerned with the 

 places chosen by animals for their homes. The fishes that 

 live in water have special organs for 

 breathing under water (Fig. 82). 

 Many of the South American mon- 

 keys have the tip of the tail adapted 

 for clinging to limbs of trees or to 

 the bodies of other monkeys of its 

 own kind. The hooked claws of the 

 bat hold on to rocks, the bricks of 

 chimneys, or to the surface of hollow 

 trees where the bat sleeps through 

 the day. The tree-frogs (Fig. 83) or 

 tree-toads have the tips of the toes 

 swollen, forming little pads by which 

 they cling to the bark of trees. 



Among other adaptations relat- 

 ing to special surroundings or con- 

 ditions of life are the great cheek 

 pouches of the pocket gophers, 

 which carry off the soil dug up by 

 the large shovel-like feet when the 

 gopher excavates its burrow. 



Those insects which live under- 



FIQ. 81. Insect galls on leaf. 



ground, making burrows or tunnels 



in the soil, have their legs or other parts adapted for dig- 

 ging and burrowing. The mole cricket (Fig. 84) has its 

 legs stout and short, with broad, shovel-like feet. Some 

 water-beetles (Fig. 85) and water-bugs have one or more of 

 the pairs of legs flattened and broad to serve as oars or pad. 

 dies for swimming. The grasshoppers or locusts, who leap, 



