The campaniform sensilla in the haltere base of the fleshfly, Boettcherisca peregrina, have been examined with the electron microscope. The sensillum attached to the dome-shaped cuticle is composed of three types of cells: a sensory cell, a neurilemma cell, and an attachment cell. The distal process of the sensory cell becomes abruptly narrow in neck-shape at the point close to the inner surface of the cuticular dome, where numerous dense cords and nine pairs of fibrils occur. Distal to this neck region numerous microtubules run within the swollen process of the sensory cell, and proximally an axial filament runs with a few branches within the elongated process of the sensory cell. At the distal end of the sensory cell each of the microtubules is inserted into a pore of the meshwork structure within the sensory cell process. A centriole is located between the neck region and the distal end of the axial filament of the sensory cell. The portion of the sensory element immediately distal to the neck region is surrounded by a scolopale consisting of several microtubules and a dense, amorphous substance, whereas the terminal portion of it is invested with another sheath of the cuticle composed of dense, amorphous material. The dome-shaped cuticle consists of an inner and an outer layer. The outer layer of the cuticle is joined loosely to the inner at the base of the dome. The terminal part of the process of the sensory cell covered with cuticular sheath invades the space between the two layers of the dome cuticle, and terminates there, in close attachment to the outer layer of the dome. These morphological findings support the idea that the campaniform sensilla are receptors which are sensitive to the deformation of the dome cuticle.
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Uga et al. (1967) studied this question.