Homozygotes cannot fly. Myofibrils in the indirect flight muscle are narrower than normal and show a range of defects ultrastructurally. In some cases the H-zone wanders from the middle of sarcomere and the M-line is broken up into electron-dense aggregates. In more severe cases, the H-zones are shifted further from the middle of the sarcomere. The bare zones of the thick filaments are in the displaced H-zone and thin filaments are longer in one half sarcomere than the other. Thin filaments sometimes extend into the H-zone.