“Let us first pursue the tracks of the Blaps, for example (Fig. 123). Let the insect begin its motion. The left fore leg stands at _a_, the right middle leg at β, and the left hind leg at _c_. The corresponding number of the other set of three feet at α, _b_, γ. At the first step the three feet first mentioned advance to _a′_β′_c′_, the second set on the other hand to α′_b′_γ′. Thereby the tracks made by the successive steps fall quite, or almost quite, on each other, as appear also in the tracks of a burying beetle (Fig. 124). “As the fore legs are directed forward and the hind legs backward, while the middle legs are placed obliquely, the reason of the more marked impressions of the latter is evident. “The highest testimony to the precise exactitude and accuracy of the walking mechanism of insects is furnished by the fact that in most insects, and particularly in those most fleet of foot, which, whether they are running away or chasing their prey, must be able to rely entirely upon their means of locomotion;—the fact, we say, that whether they desire to move slowly or more 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 (tibiæ). “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, Meloë, etc., which, when running, either bring the end of their hind body near to the ground or into contact with it. [Illustration: FIG. 125.—Tracks of Trichodes; the middle sinuous line is made by the tip of the abdomen. Natural size. ] [Illustration: FIG. 126.—Tracks of another insect which, in running, can only use three legs (_r_{1}_, _l_{4}_, _r_{3}_) which become indicated differently from normal conditions. Natural size. ] [Illustration: 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. ]