Fig. 1. Timeline depicting the morphological, physiological and behavioral changes preceding ecdysis to the second larval instar in Drosophila. (A) All time points are relative to the double vertical plates (dVP) stage as shown. Broken bars (e.g. A-P) indicate periodically repeated contractions in each stage. Bars depicting a gradient of color indicate gradual changes in morphology. (B) Shedding of the mouthparts and old tracheal tubes (red) during ecdysis. Left: the forward thrust (FT) phase of ecdysis results in deposition of the old mouth hooks and vertical plates onto the substrate (forward blue arrow) and removal of the old tracheal tubes, which are pulled out through spiracular pits, functional only during ecdysis. Right: during the backward thrust (BT) phase of ecdysis, the old spiracles are detached and slide forward (curved red arrow) a maneuver that also extracts the old tracheal trunks (red).
