Fig. 7. CO₂ emission during steady flight in a male Manduca sexta (mass 1.5g, 9 days old). The results are from a split-specimen chamber (see insets at the top of the figure). In A, only air from the anterior chamber (connected to the anterior spiracles) was conveyed to the CO₂ analyser directly, while air from the posterior chamber first passed through a vessel containing NaOH to absorb CO₂. No CO₂ emission was detected from the anterior spiracles (spiracles I), although the air presssure in the anterior chamber was slightly lower than in the posterior chamber. In B, only the air flow from the posterior chamber (including the posterior thoracic, spiracles II, and all abdominal spiracles) was conveyed to the CO₂ analyser without first passing through the NaOH vessel. All CO₂ is expired from these posterior spiracles. Sampling rate was 400Hz.