Fig. 5. Recordings of CO₂ and O₂ exchange of Circellium bacchus (mass 5.790 g) from the posterior and anterior spiracles when a gas mixture containing 30 % O₂ was drawn over the elytral cavity (A). O₂-enriched air entered through these spiracles because it could be seen to exit via the anterior mesothoracic pair of spiracles. When the 30 % O₂-enriched air mixture was drawn over the anterior mesothoracic spiracles (B), no high-O₂-content air was seen to leave via the posterior spiracles opening into the subelytral cavity. Comparison of Figs 3 and 5 reveals no change in the breathing pattern due to the elevated O₂ concentration in the gas mixture.