- Single Ommatidium of Cockroach's Eye (after Grenacher).
Each such unit is termed an "ommatidium."
The lateral eyes of Scorpio consist of groups of separate small lenses each with its ommatidium, but they do not form a continuous compound eye as in Limulus.
The ommatidium (soft structure beneath the lens-unit of a compound eye) is very simple in both Scorpio and Limulus.
The cells of tl ommatidium are a good deal larger than the neighbouring common cells of the epidermis.