1. Some aspects of the orientation and stability of flying locusts have been studied in free flight and with animals mounted so that they were free about the rolling axis only. Free flights were observed in white or infra-red light, with or without the wind-sensitive head hairs covered. Rolling behaviour was studied in light or darkness in front of a wind tunnel fitted with a movable simulated horizon while electrical recordings were made from flight control muscles. Flight muscles or single wings were removed in some experiments.

2. In the absence of visual feedback many intact animals roll consistently in one direction, and there is asymmetry in the motor output pattern. Removal of a wing causes a changed rolling torque in the absence of exteroceptive feedback.

3. In free flight, or in the presence of the illuminated simulated horizon, the centrally inherent or surgically induced asymmetrical behaviour is corrected by compensatory changes in the motor pattern.

4. Even though the locust flight control system contains a central motor score it exhibits the sort of adaptability called Plasticität in the case of insect walking. In locust flight the compensations depend mainly upon exteroceptive feedbacks.

A portion of this work was performed at the Department of Molecular Biology, University of California, Berkeley.