THE MECHANICS OF FLIGHT MOVEMENTS IN DIPTERA

Abstract

1. The mechanics of insect flight are usually studied by squeezing the thorax so as to imitate the action of the indirect flight muscles. In flies certain elements of the articulation are not properly set in such experiments, so the interpretations made are not accurate. That CCl4 sets the articulations of flies as in normal flight is shown by the dramatic wing movements easily produced in these insects. This report is based on the study of CCl4-treated flies and outlines the main features of the mechanics of wing movement. Much additional physiological evidence for the interpretations given here has been accumulated and will be reported separately. The abstracts referred to state some of the experimental results. 2. The secret of the peripheral control of wing rate certainly lies in the indirect flight muscles. These muscles are the power plants of the wings, operating in essentially an all-or-none fashion. It is shown here that they play little part in steering or in amplitude changes. They operate between definite mechanical limits and so do not halt each other's movement as in a conventional antagonistic system. 3. The anterior notum is shown to have a spring action which unloads the muscle at a critical point and so plays a basic physiological role. If the recoil of the notum alone is capable of completing the movement, the indirect flight muscles would not be required to exert any tension at their resting or shorter lengths. The energy would be put into the mechanism almost isometrically and it would not be necessary to assume high tension in a rapidly shortening muscle. 4. By a combination of the mechanical properties of the thorax and the physiological properties of the fibrillar muscle the peripheral control of wing rate is achieved.