Form optical activity in crustacean cuticle

Some decalcified crustacean cuticle reflects left and transmits right circularly polarized light. The form optical rotatory dispersion is negative at lower and positive at higher wavelengths than that giving the interference colour for the system. The helicoidal structure deduced from the optics is supported by parabolic patterning in electron micrographs of oblique sections. The cuticle helicoid is anti-clockwise so that the right circularly polarized light transmitted through it rotates in the same sense as the helicoid from which it is produced.