MECHANICS OF WALKING 



105 



of the normal insect leg, i.e. the trochanter (Figs. 116, 117, r), as grown together 

 with the third lever, i.e. the femur, as the movement of both parts mostly takes 

 place uniformly. 



The pulling of the small trochanter muscle 

 works against the weight of the body when 

 this is carried over on to the trochanter by 

 means of the coxa, as seen at the arrow e in 

 Fig. 115. It may be designated as the femo- 

 ral lever. 



The plane of direction in which the femur, 

 as seen by the rotation just mentioned, is 

 moved, exactly coincides in insects with that 

 of the tibia and the foot, while all can be 

 simultaneously raised or dropped, or, as the 

 case may be, stretched out or retracted. 

 Therein, therefore, lies an essential difference 

 from the fully developed extremities of verte- 

 brates among which, even on the lever arms 

 which are stationary at the end, an extensive 

 turning is possible. 



The muscles which move the tibia, and 

 indirectly the femur, also consist of an ex- 

 tensor muscle which is situated in the upper 

 side of the femur (Fig. 116, s, Fig. 115, /), 

 and of a flexor (Fig. 116, b, Fig. 115, 0), 

 which lies under the former. 



The stilt-like spines on the point (Figs. 

 115 and 118, L z n) on which this segment is 

 directly supported are important parts of the 

 tibia. (Graber.) 



Considering the respective positions 

 of the individual levers of the leg and 



FIG. 116 Section of the fore leg of a 

 stag-beetle, showing the muscles: S, ex- 

 tensor, B, flexor, of the leg ; s, exten- 

 sor, b, flexor, of the femur ; o. femur ; 

 v, tibia ; ./', tarsus ; k, claw ; 109, s, ex- 

 tensor, b, flexor, of the femoro-tibial 

 joint, both enlarged. After Graber. 



FIG. 



the nature of the materials of which they 

 are made, the legs of insects may be likened, 

 as Graber states, to elastic bows, which,when 

 pressed down together from above, their 

 own indwelling elasticity is able to raise 

 again and thus keep the body upright. 



This is very plainly shown in certain 

 stilt-legged bark-beetles, in which, as in a 

 rubber dull, as soon as the body is pressed 

 down on the ground, the organs of motion 

 extend again without the intervention of 

 muscles ; indeed this experiment succeeds 

 even with dead, but not yet wholly stiff, 

 insects. 



Graber then turns to the analysis of the 



117. Left fore leg of a 



cid beetle: h, coxa; r, 



trochanter; o, femur; u, tibia; 



/, tarsus ;,claw. After Graber. movements of illSCCt legs when ill motion, 



