Fig. 8. Spectral reflectivities for the perpendicular and parallel planes of polarisation of the mantle ‘red’ stripe at a position halfway along the length of the mantle at angles of incidence of (A) 15°; (B) 45° and (C) 55° for Alloteuthis subulata (thick lines) and Loligo vulgaris (thin lines). The diagrams at the side of each figure show a squid mantle in dorso-ventral section. They indicate the direction in which the light is reflected, i.e. the angle of incidence at which the measurements were made.