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The organization of the tympanic nerve within the thoracic ganglia of Heliothis zea (Boddie) was investigated. Cobalt chloride infiltration of cut axons was used to investigate the central terminations of the tympanic nerves. The axonal terminals of the A2 acoustic cell were confined to the meso-metathoracic ganglia, whereas the Al acoustic and the nonacoustic B cell were found in the thoracic ganglia. The relevance of this organization for neural circuitry of evasive flight behavior to acoustic stimulation is discussed.