344 



EVOLUTION AND ANIMAL LIFE 



FIG. 205. Tree toad, Hyla regilla. 



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

 retain the primitive lunglike 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 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 

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

 the toes swollen, forming little pads by 

 which they cling to the bark of trees. 



Among other adaptations relating to 

 special surroundings or conditions of life 

 are the great cheek pouches of the pocket 

 gophers, which carry off the soil dug up 

 by the large shovellike feet 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, Gri/llotalpa, 

 with fore legs modi- 

 fied for digging. 



