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 paracnute, 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 tilled with 



PIG. 126. Diagrammatic section of Star-fish: a, month; 6, stomach; c, hepatic c- 

 cum ; d, dorsal or aboral surface ; e, ambulacral plates ; /, ovary ; g, tubular feet ; 

 A, internal sacs for distending 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 

 has 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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