ANIMAL LOCOMOTION 195 



to stick on to a smooth surface such as a sheet of 

 glass. These pads owe their clinging power to 

 strong muscular pressure combined with a sticky 

 secretion which exudes from the skin. In some 

 of the former creatures the under part of the body 

 is also of an adhesive nature and clings tightly 

 when pressed against the object upon which the 

 animal is reposing. 



Quite a large number of creatures possess the 

 power to fly, and amongst the mammals thus gifted 

 are the bats, the flying-squirrels, the flying-phal- 

 angers, and the cobego, although, strictly speaking, 

 only the former are capable of true flight and of 

 sustaining themselves in the air for any length of 

 time. The remaining animals, however, can glide 

 through the air for a short distance, supporting 

 then* weight by stretching taut the membrane- 

 like flap of skin that lies along either side of the 

 body, and is attached to the hind and fore limbs. 



In a like manner some of the lizards are able 

 to skim through the air ; while, moreover, certain 

 frogs can also indulge in aerial excursions by means 

 of their enormous webbed feet which offer a resisting 

 surface to the atmosphere much in the manner of 

 the planes of an aeroplane. 



With the exception of the bats, which propel 

 and lift their bodies by moving their large and 

 membranous wings up and down, the motive power 

 of the foregoing creatures is derived from the impetus 

 gained when they hurl themselves into the air, and 

 supplemented by the force of gravity as they glide 

 towards the earth. As they can only progress in 



