Fig. 6. Natural and peptide-induced ecdysis behavioural sequences in intact and ligated pharate larvae. (A) Natural pre-ecdysis was initiated by weak pre-ecdysis I contractions (stippled lines), which developed into strong pre-ecdysis I and II. Animals switched to ecdysis movements 1 h later, which resulted in cuticle shedding within 10-12 min. Injection of epitracheal-gland extract or ecdysis-triggering hormone (ETH) induced both pre-ecdysis I and pre-ecdysis II behaviours for 30-40 min, followed by ecdysis movements for 10-30 min. (B) Injection of pre-ecdysis-triggering hormone (PETH) 20-24 h prior to ecdysis elicited only pre-ecdysis I, but subsequent ETH injection induced pre-ecdysis II and ecdysis behaviours. Injection of PETH 10-15 h prior to ecdysis elicited the entire behavioural sequence, and subsequent ETH injection caused only weak pre-ecdysis II and ecdysis (stippled lines). (C) Isolated abdomens initiated natural pre-ecdysis and ecdysis behaviours at the expected time. ETH injection also induced the entire behavioural sequence, but latency to the onset of ecdysis behaviour was much shorter. (D) Shaded areas and arrows depict asynchronous dorso-ventral and leg contractions in thorax and abdomen during PETH-induced pre-ecdysis I. (E) The subsequent ETH injection induced asynchronous ventral, posterio-lateral and proleg contractions (pre-ecdysis II; shaded areas and arrows). (F) Ecdysis movements were characterized by subsequent dorso-ventral contractions and proleg retractions (shaded areas and arrows, arrowheads) during which each segment was moved anteriorly (arrowhead). See text for details.