Ultra-structure of the Insect Ear

LIGHT microscope studies1–4 have long established that the sensory unit (chordotonal sensillum or stiftführendes Organ) of the insect ear consists of three cells, namely, the bipolar neuron, the axon of which runs directly to the central nervous system, the sheath cell, which surrounds the dendrite of the neuron, and the attachment cell, which appears to anchor the whole assembly to the ear-drum. The approximate topographical arrangement of these cells and their inclusions are shown in Fig. 1. Examination of fresh material with the phase-contrast microscope by one of us (E. G. G.) has demonstrated that, though the vacuole (v) is a fixation artefact, the scolopale and the axial fibre are distinguishable in vivo. It is with the fine structure of the latter that this communication is principally concerned. All material has been taken from the auditory ganglia of adult female locusts (Locusta migratoria migratorioides) and fixed with 1 per cent osmium tetroxide buffered at plEL 7.4 with veronal acetate. Each ganglion contains about eighty sensory units of the type described.