Fig. 4. Angles of the knee joint, femur retraction, femur rotation and femur depression versus time (as a percentage of stride cycle) for a single stride for C. calyptratus (A) and D. dorsalis (B) moving on a level treadmill. The arrows indicate the end of stance, and footfall occurs at time 0%. The speeds for C. calyptratus and D. dorsalis were approximately 17 cm s^-1 and 50 cm s^-1, respectively.