Fig. 14. Diagram to illustrate the meaning of the symbols used in Ratio 1, showing a squid mantle in dorso-ventral section (d and v represent dorsal and ventral regions) and an observer looking at a reflective area on the surface of the squid. Dotted line, vertical line; dashed line, light (L) incident to the iridophore at an angle ₁ with the vertical; dashed double-dotted line, normal incidence to the iridophore; solid line, reflected (R) and transmitted (T) light at an angle of incidence to the normal of the iridophore; the group of four arrows indicates the background light field at an angle ₂ with the vertical.