Fig. 12. Schematic lateral view of the thorax of Manduca sexta showing the deformation (arrows in upper diagrams) of the thorax during the downstroke (A) and upstroke (B) of the wings and its coupling with the adduction and retraction (arrowheads) of the metathorax enclosing and exposing the posterior thoracic spiracle (SpII) in the subalar cleft. The increase in volume of the thoracic air sacs and closure of SpII during the downstroke produce a retrogradely directed air stream, with inspiration through the anterior spiracles (SpI) and expiration through the posterior thoracic spiracles (broken arrows). I, prothorax; II, mesothorax; III, metathorax.