344 



EVOLUTION AND ANIMAL LIFE 



•A 



Fig. 205. — Tree toad, Hyla regilla. 



short excursions from the water. Still others (mud fishes) 



retain the primitive lunghke 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 con- 

 cerned with the places 

 - chosen by animals for 

 their homes. The fishes 

 that live in the water 

 have special organs for 

 breathing under water 

 (Fig. 204). Many of 



the South American monkeys have the tip of the tail adapted 



for cHnging to hmbs 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 



or tree toads (Fig. 205) have the tips of 



the toes swollen, forming Httle pads by 



which they cling to the bark of trees. 



Among other adaptations relating to 



special surroundings or conditions of hfe 



are the great cheek pouches of the pocket 



gophers, which carry food, as grass-roots 



and the like, when the gopher excavates its 



burrow. 



Those insects which live underground, 



making burrows or tunnels in the soil, 



have their legs or other parts adapted for 



digging and burrowing. The mole cricket 



(Figs. 206 and 207) has its legs stout and 



short, with broad, shovellike feet. Some 



water beetles and water bugs have one 



or more of the pairs of legs flattened and 



broad to serve as oars or paddles for swim- 

 ming. The grasshoppers or locusts, which leap, have their 



hind legs greatly enlarged and elongated, and provided with 



strong muscles so as to make of them "leaping legs.'" The 



Fig. 206. — The mole 

 cricket, Gryllotalpa, 

 with fore legs modi- 

 fied for digging. 



