PROGRESSIVE MOTION OF INSECTS. 039 



and they act, indeed, in the same manner, and on the same 

 prineii:)les. 



§ 8. Progressive Motion of Insects on Land, 



The actions of the limbs of insects in walking are quite 

 different from what they are in swimming, and are very 

 similar to those of the caterpillar, in which we have seen 

 that the motions of the anterior and posterior legs on one 

 side are combined with that of the middle one on the other 

 side; and the two sets of legs arc moved alternately. In 

 consequence of their relative positions with the trunk, the 

 anterior legs are advanced by the extension, and the poste- 

 rior legs by the flexion of the corresponding joints. When 

 the feet have fixed themselves on the ground, the contra- 

 ry actions take place, and the body is brought forwards. 

 During this period the legs which compose the other set arc^ 

 called into play, and are advanced; and the same succession 

 of actions takes place with these as with the former. This 

 can easily be seen when the insect walks very leisurely; but 

 in a more quickened pace, the succession of actions is too 

 rapid to be followed by the eye. 



The action of leaping is performed by the sudden exten- 

 sion of all the joints of the limb, which are prcviouslv 

 folded as close as possible. The joints principally concerned 

 in this action, are those of the tliigli and tibia, as they fur- 

 nish the longest and most powerful levers. Preparatory 

 to the effort, the tibia is brought down as close as possible 

 to the ground, by bending it over the tarsus; and the thigh 

 also is bent upon the tibia, so as to form with it a very acute 

 angle. In order to enable it to take this position with most 

 advantage, we find In many of the Coleoptcra, that the thigh 

 has a longitudinal groove for the reception of the tibia, with 

 a row of spines on each side of the groove. While the 

 limb is in this bent position, the extensor muscles are vio- 

 lently exerted, and by producing a sudden unbending of this 

 apparatus of folded springs, they project tlie whole body, 



