PROGRESSIVE MOTION OF INSECTS. 303 



principally concerned in this action are those of 

 the thigh and tibia, as they furnish 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 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. 

 AVhile 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 accu- 

 mulated impulse, to a considerable height in the 

 air. The leaps of insects being generally forwards, 

 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, necessarily swell that division of the limb 

 to an unusual thickness ; and in order to procure 

 sufficient velocity of action, both the femur and 

 tibia are much elongated. Thus the locust, which 

 is so constructed, leaps with ease to a distance two 

 hundred times the length of its own body. We may 

 generally, indeed, infer the particular kind of pro- 

 gressive motion for which the insect is intended by 

 observing the comparative length of the different 

 pairs of legs. When they are of equal size, the 



