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TEXT-BOOK OF ENTOMOLOGY 



walking function, which brings the body a bit forward ; the thinner, on the other 

 hand, or we might say the hair line (6c), which, however, is but rarely made 

 quite clearly, is produced by the ineffectual backward movement, by which the 

 insect again approaches its working posture (c). It is at first placed at some 

 distance from the body, in order that (like c also) it may draw near to the body 

 again ; but in such a way, naturally, that it coincides with the starting-point of 

 the following active curve (cd). It is evident that even the passive curve is not 

 the imprint of the movement accomplished exclusively by the leg, for this latter, 

 while struggling to reach its resting-place, is really involuntarily carried forward 

 with the rest of the body. 



"The scroll-like lines drawn by the swimming beetle (Dyticus), with the 

 large, sharp points of its hind tibia, are also very instructive (Fig. 119, A). 



"The diversions and modifications in the course of the active step, as fur- 

 nished by the moving factor of the remaining legs, are already clearly illustrated 

 by the curves shown by the joints of the hind tibia of a May-beetle (Fig. 120) 



S 



.a 



FIG. 119. 



FIG. 120. 



FIG. 121. 



FIG. 119. A, trail curves described by the tibial spines of the right and left hind limb of 

 Dyticus. B, the same made bv the right hind leg (r a ) alone. Natural size. After Graber. 



FIG. 120. The same by the two hind legs of Melolontha : a, the active and thickened section of 

 the curve. Natural size. 



FIG. 121. A, track curves of two of the tibial spines of the left, middle legs of a stag-beetle. 

 Natural size. S, the same enlarged ; fg, the longitudinal axis of the trunk ; al and <tl>, the active 

 curve passing inward, be and t/e, the passive going outward. (', two curves described by the left 

 hind legs ; in this case, the curves are not inwards or backwards, but partly directly inward (/>), 

 and in part obliquely forwards (a). 



and a stag-beetle (Fig. 121, c). The actual faint line in this case does not run 

 from the front toward the back, as would correspond to the active leg-motion, 

 but either directly inward (Fig. 121, ch), or even somewhat to the front. In 

 the May-beetles, and even more in the running garden-beetle, the curves of the 

 hind legs present themselves as screw-like lines (Fig. 122, / 3 ), while the scrawl- 

 ing of the remaining members (/ t , 7 2 ) is much simpler. 



" Inasmuch as we now have a cursory knowledge of the movements made by 

 each individual leg for itself, movements, however, which plainly occur very 

 differently according to the structure of these appendages, the question now is 

 of the combined play, the total effect of all the legs taken together, and there- 

 fore of the walk and measure of the united work of the foot. 



"In opposition to the caterpillars and many other crawling animals which 

 extend their legs in pairs and really swing them by the worm-like mode of con- 

 traction of the- dermomuscular tube, the legs of fully grown insects are moved 

 in the contrary direction and in no sense in pairs, but alternately or, more 

 strictly speaking, in a diagonal direction. 



