Fig. 1. Split-specimen chamber used for measuring CO2 emission from specified spiracles of hawkmoths. The device allows the air pressure in both chambers to be measured and adjusted. In A, the anterior chamber with the air flow from the anterior spiracles is connected to the CO2 analyser directly, and the posterior chamber with the air flow from all other spiracles is connected to the CO2-absorbing vessel. In B, the air flow passing through the posterior chamber is conveyed directly to the CO2 analyser, while the air flow from the anterior chamber passes via the CO2-absorbing vessel. The wingbeat is recorded by projecting the shadow of the wings onto a silicon photocell installed on the bottom of the transparent experimental chamber. SpI, mesothoracic spiracle; SpII, metathoracic spiracle; Spabd, abdominal spiracles.