Functional development of the auditory system of the cricket,Teleogryllus commodus

Abstract

1. InTeleogryllus commodus andT. oceanicus, vibration of the tibia of the prothoracic leg at audio-frequencies stimulates auditory receptors in the tympanal organ, despite immobilization of the large tympanum by vaseline. 2. Responses of characteristic auditory interneurons in the adult cervical connective are similar whether stimulation is by sound or by vibration of the tibia (Figs. 3–5). 3. Interneurons in second-last (A-2) and last (A-1) immature instars are stimulated by sound and by vibration of the tibia and we conclude that these interneurons are the same as those recorded in adults (Figs. 6, 7). Peripheral receptors and some interneurons in the immature auditory system are, therefore, physiologically competent. 4. At the imaginai moult, auditory threshold at the optimum frequency decreases dramatically (Fig. 8 A). This increase in sensitivity to sound is attributed mainly to the appearance of the auditory tympanum in the adult. There is a much smaller increase in sensitivity to vibration of the tibia at audio frequencies between last instar nymphs and adults (Fig. 8 B). 5. From the A-2 to adult stages ofT. commodus, auditory receptors stimulated by sound show a peak sensitivity at 3.8 to 4.0 kHz (Fig. 8 A). Such tuning must be independent of vibration characteristics of the tympanum and of acoustic resonance characteristics depending on the dimensions of the leg trachea.