PROGRESSIVE MOTION OF INSECTS. 339 



sudden extension of all the joints of the limb, 

 which are previously folded as close as possible. 

 The joints principally concerned in this action, 

 are those of the thigh and tibia, as they furnish 

 the longest and most powerful levers. Prepara- 

 tory 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 posi- 

 tion with most advantage, we find in many of 

 the Coleoptera, 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 violently exerted, and by producing a sudden 

 unbending of this apparatus of folded springs, 

 they project the whole body, by the accumu- 

 lated impulse, to a considerable height in the 

 air. The leaps of insects being generally for- 

 wards, all the legs do not participate equally in 

 the effect ; for the fore legs contribute much 

 less to it than the hind legs, and are more useful 

 in modifying the direction of the leap, than in 

 adding to its force. The power of leaping is 

 derived principally from the great size and 

 strength of the extensor muscles of the legs, 

 which, being contained within the femur, neces- 

 sarily swell that division of the limb to an 



