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TEXT-BOOK OF ENTOMOLOGY 



quickly, the distances of the steps, measured by the length as well as by the 

 cross-direction, hardly differ a hair's breadth from one another, and this is also 

 the case when the tarsi are cut off and the insects are obliged to run on the 

 points of their heels (tibiae). 



" Thence, inasmuch as the trunk of insects is carried by two legs and by one 

 on each side alternately, it may surely be concluded a priori that when walking 

 it is inclined now to the right and now to the left, and that the track, too, which 

 is left behind by a precise point of the leg, can in no wise be a straight line ; and 

 in reality this is not the case. 



"A plainly marked regular curve, which approaches a sinuous line, as seen 

 in Fig. 125, is often obtained by painting many insects, for example Trichodes, 

 Meloe, etc., which, when running, either bring the end of their hind body near 

 to the ground or into contact with it. 



"The locomotive machine of insects may be called, to a certain extent, a 

 double set of three feet each, as most insects, and particularly those provided 



2' J 



o 



/ 



o 



/ 



with a broad trunk, are able to balance themselves with 

 one of these two sets of feet, and indeed when walking, 

 as well as when standing still, can move about even better 

 with one set of these feet than with four legs. In the latter 



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 V 



v 



'30 



a i 



V 



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FIG. 125. FIG. 1'2'j. 



FIG. 125. Tracks of Trichodes; the middle sinuous line is made by the tip of the abdomen. 

 Natural size. 



FIG. 126. Tracks of another insect which, in running, can only use three legs (r lt I t , r a ) which 

 become indicated differently from normal conditions. Natural size. 



FIG. 127. The same of an insect crossing over a surface inclined 30 from the horizon, whereby 

 the placing of the feet becomes changed. Natural size. This and Figs. 120-126 after Graber. 



case, that is, if one cuts off a pair of legs from an insect, the trunk can balance 

 itself only with extreme difficulty, and there is therefore little prospect that 

 insects will ever become four-footed. 



" But if one compels insects to run on three legs, he will thus make the inter- 

 esting discovery that to make up the deficiency they place the remaining feet 

 and bring them to the ground somewhat differently than when the second set 

 of feet is active. Figs. 124 and 126 may be compared for this purpose. The 

 former shows the footprints of a burying beetle running with all six legs, the 

 latter the track of the same insect, which, however, has at its disposal only the 

 right fore leg, the left middle leg, and the right hind leg. One may plainly see 

 here that the track of the hind leg on the right side (r 3 ) approaches the track of 

 the middle leg on the left side, and then further, that the right fore leg (r\) steps 

 out more to the right to make up for the deficiency of the middle leg. 



