389 



the Kangaroos and Gerboas, which are content to use an 

 ordinary walking pace when undisturbed, but when alarmed 

 can make tremendous leaps, and outstrip almost any pursuer. 



Even in Man, the Horse, the Dog, &c., which are most essen- 

 tially leaping animals, the same principle is employed, the legs 

 being used as muscular springs acted upon by the will of 

 the owner. 



