Larval and adult eye of the western rock lobster (Panulirus longipes).

A number of differences exists between the compound eyes of larval and adult rock lobsters, Panulirus longipes. The larval eye more closely resembles the apposition type of compound eye, in which retinula cells and rhabdom lie immediately below the cone cells. The adult eye, on the other hand, is a typical clear-zone photoreceptor in which cones and retinula cell layers are separated by a wide transparent region. The rhabdom of the larval eye, if cut longitudinally, exhibits a "banded" structure over its entire length; in the adult the banded part is confined to the distal end, and the rhabdom is tiered. Both eyes have in common an eighth, distally-located retinula cell, which possesses orthogonally-oriented microvilli, and a peculiar lens-shaped "crystal", which appears to focus light onto the narrow column of the distal rhabdom. Migration of screening pigment on dark-light adaptation is accompanied by changes in sensitivity and resolution of the eye. Retinula cells belonging to one ommatidium do not arrange into one single bundle of axons, but interweave with axons of four neighbouring facets in an extraordinarily regular fashion.