The eye of the firefly Photuris

Abstract

1. The pseudocone eye of Photuris has long corneal cones that are laminated in a series of concentric paraboloids which have the effect of bending rays towards the optical axis within the cone. 2. Between the proximal end of each cone and the receptor layer is a crystalline thread which conducts light by internal reflexion to the receptors. Not all light travels by this path in the dark-adapted eye. 3. The receptor layer has proximal and distal rhabdomeres in a pattern unlike that of any other known eye. The enormously developed rhabdoms form two superimposed continuous sheets across the eye. 4. The eighth retinula fibre in each bundle at the basement membrane comes from the basal retinula cell. 5. Off-axis light which escapes the route down the crystalline thread in the dark-adapted eye is refracted by the curved end of the cone in such a direction that it tends towards a receptor in the ommatidium which points towards the origin of the light. There is no functional superposition image at the level of the receptors.