MOVEMENT OF JOINT ANGLES IN THE LEGS OF A WALKING INSECT, CARAUSIUS-MOROSUS

This paper provides a quantitative description of the leg movement of a stick insect walking in three different situations, namely walking tethered on a treadwheel, on a slippery glass plate and walking free on a horizontal plane. These descriptions concern the trajectories of the end of the tibia and the changes of the femur-tibia joint (gamma), the coxa-trochanter joint (beta) and the movement of the thoracic-coral joint of all three pairs of legs. As the latter joint comprises a ball and socket joint, the changes of the position of the rotational axis of this joint have been measured. No simple rule could be found which allowed the control of more than one joint of a leg by a common control parameter. Co-ordination of the joints of one leg seems to be simpler during the swine than during the stance movement. Measurements of the forces at the end of the swing movement indicate that there is no information transfer between legs with respect to an expected height of the ground at the end of the swing movement, nor is there an internal ''expectation'' which may have led to a decrease of force before probable ground contact.