370 



COMPARATIVE ZOOLOGY 



arid their power, in proportion to the weight of the bird, 

 is very great. Yet the insect is even superior in vigor 

 and velocity of flight. 137 In ascending, the bird slightly 

 rotates the wing, striking downward and a little back- 

 ward ; while the tail acts as a rudder. A short, rounded, 

 concave wing, as in the common fowl, is not so well 

 fitted for high and prolonged flight as the long, broad, 

 pointed, and flat wing of the eagle. The wing is folded 

 by means of an elastic skin and muscle connecting the 

 shoulder and wrist. Besides insects and birds, a few 

 other animals have the power of flight, as bats, by 

 means of long webbed fingers ; flying 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 power 

 left to move the animal along. The simplest method is 



FIG. 323. Diagrammatic Section of the Disk and one Ray of Starfish: a, mouth; b, 

 stomach; c, hepatic caecum; d, dorsal or aboral surface; e, ambulacral plates; f> 

 ovary; g t tubular feet; k, internal sacs for distending the feet. 



the suctorial, the animal attaching itself to some fixed 

 object, and then, by contraction, dragging the body on- 

 ward. But the higher and more common method is by 

 the use of bones, or other hard parts, as levers. 



