FIGURE 4. Iridiscence in Papilo palinurus.

a, SEM of an iridescent scale showing its array of concavities, each with a section that exhibits the curved multilayering shown by transmission electron micrography in b. This structure produces two simultaneous structural colours c, yellow and blue . d, The blue annulus is created by a double reflection from opposite and perpendicular concavity sides. d also schematically illustrates the way in which incident linearly polarized blue light has its e-vector (dotted lines) rotated by this double reflection. Bars, a, 15 m; b, 1 m; c, 6 m.