HOW ANIMALS MOVE. 
161 
of flight, as Bats, by means of long-webbed fingers; Fly¬ 
ing Fishes, by large pectoral fins. Flying Reptiles, Flying 
Squirrels, and the like, have a membrane stretched on the 
long ribs, or connecting the fore and hind limbs, which they 
use as a parachute, enabling them to take very long leaps. 
(3) Locomotion on Solids. — This requires less muscular 
effort than swimming or flying. The more unyielding 
the basis of support, the greater the amount of force left 
to move the animal along. The simplest method is the 
suctorial, the animal attaching itself to some fixed object, 
and then, by contraction, dragging the body onward. But 
the higher and more common method is by the use of 
bones, or other hard parts, as levers. 
The Star-fish creeps by the working of hundreds of 
tubular suckers, which are extended by being filled with 
Fig. 126.—Diagrammatic section of Star-fish: a, mouth; b, stomach; e, hepatic cse- 
cum; d , dorsal or aboral surface; e, ambulacral plates; /, ovary; g , tubular feet; 
h , internal sacs for extending the feet 
fluid forced into them by little sacs. The Clam moves 
by fixing and contracting a muscular appendage, called 
a “foot.” The Snail has innumerable short muscles on 
the under side of its body, which, by successive contrac¬ 
tions, resembling minute undulations, enable the animal 
to glide forward apparently without effort. The Leech 
lias a sucker at each end: fixing itself by the one on its 
tail, and then stretching the body, by contracting the mus¬ 
cular fibres which run around it, the creature fastens its 
mouth by suction, and draws forward the hinder parts by 
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