The fine structure of haltere sensilla in the blowfly Calliphora erythrocephala (Meig.), with scanning electron microscopic observations on the haltere surface.

The dipteran haltere incorporates large numbers of regularly disposed mechanoreceptors providing the sensory input enabling the vibrating haltere to function as a gyroscopic organ of equilibrium. Campaniform sensilla of the basal and scapal regions have been investigated by light and transmission electron microscopy, and these observations are augmented by scanning electron studies of the cuticle overlying the groups of sensilla. Each sensillum possesses a specialized fan-shaped terminal containing a complex and ordered association of microtubules and filaments. The transmission of stress to this region via the cuticle, and its possible role in transduction is considered. The fine structure of apical and basal sections of the distal sensory process and associated sheath cells is described; the functional significance of the distribution of mitochondria and other components is discussed. The organization of haltere chordotonal sensilla is described briefly, and compared with other mechanoreceptors with particular reference to microtubules and scolopale structures.