Fig. 2. Occurrence of rhythmic tracheal compression in different regions of the body of Pterostichus stygicus. (A) Tracheal system, showing tracheae in resting (inflated) posture. Image is a compilation of multiple x-ray images of a freshly killed specimen. Posterior abdomen not shown. (B–E) Movie stills showing inflated (left image) and compressed (right image) tracheae, depicting compression in the prothorax (B), mesothorax (C), metathorax (D) and posterior abdomen (E). Asterisks mark tracheal tubes that are compressed in the corresponding image. Compressions also occurred in the head and legs (not shown). Scale bars: 1 mm (A), 200 µm (B–E).