Figure 1. Experimental setup.

(A) The recording configuration. A cockroach was glued to a flexible tether and walked in place on a plate of oiled glass. One camera was slightly to the front of the animal and the other viewed its ventral surface through a mirror. (B) Ventral view of a cockroach, Blaberus discoidalis, with the body colored black for contrast. The colored dots on the legs indicate the points which were marked and then tracked by our software. The black arrows at right indicate the coordinate system used in this analysis, with the z-axis extending into the page (shaded cube added to indicate depth). The x and y vectors shown would be approximately 1 cm in length. (C) Details of digitized points and definitions of joint angles. (D) Reduction of the trochanter-femur (TrF) joint results in lowering the foot toward the substrate. (E) The thorax-coxa (ThC) joint has three rotational degrees of freedom in the front leg; in the middle and hind legs, only the first two degrees of freedom are actuated.