The cercal sensilla of the blowfly Lucilia cuprina. II. Structure of the enveloping cells and the basal regions of the sensory dendrites

The gustatory, olfactory, touch and stress receptors on the cerci of Lucilia cuprina Wied. (Diptera: Calliphoridae) have either two or three enveloping cells. The gustatory and olfactory sensilla have three enveloping cells: a tormogen, trichogen and thecogen cell. The tormogen and trichogen cells contribute to a sub-cuticular sensillar lumen which divides into two lobes basally. The thecogen cell forms a lumen around the dendrites. Distally the dendrites lie in the contents of the thecogen lumen within the dendritic sheath. Proximally the dendrites embed in the thecogen cell which has an expanded, microlamellate lumen basally. The sensillar lumen of the mechanosensory (trichoid mechanoreceptors and campaniform) sensilla is formed by a single enveloping cell: the presumptive tormogen cell. In trichoid mechanoreceptors the thecogen lumen is restricted to the region of the transitional region of the dendrite whereas the thecogen lumen of campaniform sensilla extends proximally although it is not as well-developed as that of the chemoreceptive sensilla. The dendrites of all sensillum types on the cerci have a granular body in the transitional region: a situation which has not been previously reported in chemoreceptive sensilla although common in the mechanoreceptors of Calliphoridae and Sarcophagidae.