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 
m& 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- 
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. 
dles for swimming. The grasshoppers or locusts, who leap, 
‘Fia, $1.—Insect galls on leaf. 
