The femoral chordotonal organ of the stick insect Cuniculina impigra Redtenbacher (Phasmida) can be stimulated precisely by moving the receptor apodeme. Single sensory units in the sensory nerve are recorded using glass microelectrodes. The units are classified according to their sensitivity to (a) position, (b) position and velocity and (c) velocity. Nearly all transitional forms exist between the position and velocity receptors. Both elongation- and relaxation-sensitive receptors exist, and also units which are bi-directionally sensitive. Many position receptors have their maximum frequency at one of the extreme joint positions, but others have their maximum frequency near the middle position of the joint. Some velocity-sensitive units respond with equal sensitivity over the whole operating range of the joint, whereas other velocity receptors respond only in a part of the operating range, thus providing further evidence of rangefractionation.

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