Anatomy and physiology of trochanteral campaniform sensilla in the stick insect, Cuniculina impigra

. Four groups of campaniform sensilla are found on the trochanter of Cuniculina impigra Tedtenbacher (Phasmidae). One of these groups can be divided into two sub‐groups. The sensilla are approximately parallel within each group or sub‐group. As sensilla with parallel orientation will respond to the same direction of shear force, each group or sub‐group of campaniform sensilla should act as one unit. When the coxa is fixed, activity in the nerve supplying the campaniform sensilla can be released by bending the femur forwards and backwards. The sensilla are sensitive to movement only in one direction. The investigated sensilla react to the stimulus with phasic‐tonic discharge patterns. The dependence of the phasic component upon the velocity of the stimulus can be described by a power function. The tonic component depends on the amplitude of the stimulus. By mechanical stimulation of individual groups of sensilla it can be shown that at least two groups of campaniform sensilla contain units which respond to bending the femur backwards. The activity of some motor neurones can be influenced by slightly bending the leg in the horizontal plane. The levator trochanteris muscle is activated when the femur is bent forwards, and the frequency of the slow extensor tibiae motor neurone is increased when the femur is bent backwards. The reaction of both muscles is phasic. There is no detectable reaction in the protractor or the retractor of the coxa or the depressor trochanteris.