Testing steering functions of the frontal zone in the locomotion of Amoeba proteus.

Light and chemical stimuli were asymmetrically applied to the advancing front of amoeba without affecting any body region behind the frontal zone. Stimulation limited to the front alone was sufficient to control the frontal expansion and, as a further consequence, the locomotion and shape of the whole cell. Contracting factors applied locally to the front inhibited it, whereas the relaxing agents activated its expansion.