Fenestrate membrane: of the compound eye is at the base of the ommatidia, at their junction with the optic nerve; see retina.
The retinal portion is composed of a corresponding number of ocular units or ommatidia.
It shows in Scorpio and Limulus a tendency to segregate into minor groups or “ommatidia.”
These are in some genera like the single elements (ommatidia) of a compound insect eye, in others like simple ocelli.
The compound eye of the king-crab (Limulus) is the only recognized instance of ommatidia in their simplest state.
One of the tiny light-sensitive parts of the compound eye of insects and other arthropods. An ommatidium resembles a single simplified eye. See more at compound eye.