Figure 2. Structure of the os¹ hinge and adult musculature.

Scanning electron micrographs of the adult dorsal (A–D) and ventral (E–F) wing hinge regions of wild type (A, E) and os¹ (B–D and F) individuals. The relative expressivity of the os¹ allele phenotypes is indicated by ‘weak’ ‘moderate’ and ‘strong’ labels. Note how increasing phenotypic strength is associated with the progressive loss of the AS1, AS2 and PNWP. Wing hinge structures are named in [25]. Unnamed plate (UP), first, second and third auxiliary sclerites (AS1, AS2 and AS3), anterior notal wing process (ANWP) and posterior notal wing process (PNWP) are present in the dorsal hinge. In the ventral hinge, auxillary pouch (AP) and proximal ventral radius (PVR) are shown. (G–J) Longitudinal sections through adult males of the indicated genotypes show the structure of the primary flight muscles.