Fig. 11. Details of the posterior thoracic spiracle after descaling the cuticle around the wing hinge. (A,B) Light scanning micrographs. (A) Subalar intersegmental cleft with stretched intersegmental membrane (ISM) in extreme wing-up position showing the orifice (O) of the posterior spiracle with wide open external lip (L). (B) Intersegmental cleft constricted in the wing-down position enclosing the posterior spiracle. The metathorax is adducted to the mesothorax by contraction of the dorsal longitudinal muscles along the direction of the arrow. BP, basalar pad; FW, base of forewing; Pl II, pleuron of mesothorax; Pl III, pleuron of metathorax. (C,D) Scanning electron micrographs. (C) External valve lip (L) with marginal spines and spinose perispiracular cuticle (arrowheads). (D) Detail of cuticle at the transition between smooth tracheal intima and spinose perispiracular cuticle (see arrowheads in C).