Fig. 1. (A) Scanning electron micrograph of the metathoracic tymbal of Bertholdia femida. Scale bar, 100 µm. (B) Oscillogram of one complete modulation cycle of B. femida with both tymbals intact. The active modulation half-cycle is produced as muscles buckle the structure inward. After a brief intra-cycle silent interval the structure returns to its resting state producing the passive modulation half-cycle.