136 PHILOSOPHY OF ZOOLOGY. 



mptiun resembling the action of feet. Where the organs of 

 :ulhebion are double, one at each extremity, as in the leech, 

 the mouth adheres to one part of the surface, while the tail 

 is brought up towards it, and is then fixed, the body being at 

 this time like an arch. The head then quits its hold, the body 

 extends itself, and, when at full length, the head is again 

 attached, and the tail brought up. By these alternate move- 

 ments, the leech, at every step, advances nearly the length 

 of its own body. In some of the intestinal worms, the ad- 

 hesion of the head takes place by means of reversed spines 

 or hooks, as in the Echihorinchus. 



3. Leaping. In the action of leaping, the whole body 

 rises from the ground ; and, for a short period, is suspend- 

 ed in th6 air. It is produced by the sudden extension of 

 the limbs, after they have undergone an unusual degree of 

 ilcxion. The extent of the leap depends on the form and 

 size of the body, the length and the strength of the limbs. 

 The myrmpoda are not observed to leap. Many of the spi- 

 ders and insects leap with ease, both forwards, backwards, 

 and laterally. In those which are remarkable for this fa- 

 culty, the thighs of the hind-legs are in general of uncom- 

 mon size and strength. Among reptiles, the leaping frog 

 is well known, in opposition to the crawling toad. Among 

 quadrupeds, those are observed to leap best, which have 

 the hind legs longer and thicker than the fore legs, as the 

 kangaroo and the hare. These walk with difficulty, but 

 leap with ease. 



The motion of leaping is not confined to animals furnish- 

 ed with legs ; nor, even among these, is the action confined 

 to the legs. Serpents are said to leap, by folding their bo- 

 dies into several undulations, which they unbend all at once, 

 according as they wish to give more or less velocity to their 

 motion. The jumping maggot, found in cheese, erects it- 

 self upon its anus, then forms its body into a circle, by 



