Fine structure of the dorsal organ of the house fly larva, Musca domestica L.

Abstract

The dorsal organs of the cephalic lobes of the house fly larva, Musca domestica L. were studied by light, scanning and transmission electron microscopy. Five types of receptors were found in the distal part of the dorsal organ: (1) The dome, whose ultrastructure is similar to that of thin-walled pegs, is assumed to be an olfactory receptor. (2) A lateral pore receptor, with the distal tips of two dendrites exposed to the exterior through a pore, is presumed to be a contact chemoreceptor. (3) A scolopidium-like receptor, with an ultrastructure characteristic of a scolopidium receptor except that the dendrite might be exposed to the exterior through an opening, is assumed to be both a mechanoreceptor and contact chemoreceptor. (4) Two receptors, each with one of its two dendrites exposed to the exterior, are probably contact chemoreceptors. (5) Two unclassified receptors, each with one dendritic tip exposed to the exterior and the other dendrite with a tubular body ending near the pore, may serve as both contact chemoreceptors and mechanoreceptors. The last four types are located in the invagination between the dome and the cylindrical portion of the dorsal organ. The seven basal pores of the dome are apparently points of origin of the scolopales and have no sensory function. The dorsal organ is supplied by 35–41 bipolar neurons, indicating the possibility of additional undescribed receptors.