Fig. 16. Cross section through the mantle of a squid (from Fig.5B) showing how squid may maximise camouflage to observers from below. A large fraction of the incident light available at point O will pass through the spaces between the iridophores, through the mantle muscle (m) and through the internal organs (IO) to point P. Only a small fraction of the light is reflected by the iridophores (e.g. the ‘red’ stripe, at point R), allowing a large fraction to be transmitted into the mantle cavity. The ventral iridophores (V₁) reflect weakly at angles around normal incidence, allowing a large part of the light to be transmitted. At oblique angles of incidence (V₂), the ventral iridophores have high reflectivity and low transmission, channelling the incident light downwards.