Fig. 3. Structure of the caudal fin of Enallagma cyathigerum larva. (A) Dorsal view of the end of the abdomen bearing the three tracheal plates. Each plate receives two trunks from the abdominal tracheal network. The inset shows a cross section of the abdominal tip. Note that the base of the median plate has a quadrangular section, that of the two lateral plates a triangular section, with thickening along the ridges. (B) Lateral view of the left lateral tracheal plate. The arrows point to the flexion line separating the stiffened basal segment from the apical segment. The inset shows that the serrated appearance of the stiffening ribs is due to the presence of a single row of stout setae. (C) Configuration of the tracheal plates during swimming. Throughout the cycle, the height (h) of the apex of the fin varies from approximately 2 plate widths (configuration 1) to 3 plate widths (configuration 2). The dashed line in the side view of the tail plates represents the location of the vertical section on the right.
