The Origin of Sensory Neurones in an Insect, Rhodnius prolixus (Hemiptera)

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Abstract
Throughout post-embryonic growth in Rhodnius new sensory neurones are differentiated from among the ordinary epidermal cells. The four cells forming the sensillum, the trichogen, tormogen, sense cell, and neurilemma cell probably arise from the division of a single epidermal cell. These four cells are at first alike. At an early stage in their differentiation, one of them, the sense cell, gives off an axon process which grows inwards, joins the first nerve or axon which it meets, and accompanies this to the central nervous system. If established sensory nerves are interrupted by burning, the axons grow out from the peripheral end and eventually join up with an existing nerve. Sometimes they grow round and meet the nerve from which they were derived. They may then become trapped outside the basement membrane and grow in loops and circles until a stout nerve is produced which has no connexion with the central nervous system. At the imaginal moult most of the sensory hairs on the dorsum of the abdomen with their trichogen and tormogen cells disappear, but the sense cells, neurilemma cells, and axons may persist, the distal process of the sense cell ending blindly in the cuticle. Dermal glands also arise from four cells which at the earliest stage of their development are indistinguishable from the four cells of the sensilla. If the adult is induced to moult the dermal glands may develop non-articulated outgrowths resembling illformed hairs.