Oc', Central monomeniscous eyes.
Monomeniscous eyes with a double (really triple) cell-layer formed by invagination, as in the Eu-arachnida, are present.
Median eyes are present, which are monomeniscous, with distinct retinal and corneagenous cell-layers, and placed centrally on the prosoma.
Two distinct forms of the Arthropod eye are observed - the monomeniscous (simple) and the polymeniscous (compound).
They show in the monomeniscous eye (see article Arachnida, fig.
The monomeniscous eye is rarely provided with a single layer of cells beneath its lens; when it is so, it is called monostichous (simple lateral eye of Scorpion, fig.
Each such complex of cells underlying the lenticle of a compound eye is called an " ommatidium "; the entire mass of cells underlying a monomeniscous eye is an " ommataeum."
- Diagram to show the derivation of the unit or "ommatidium " of the compound eye of Crustacea and Hexapoda, C, from a simple monomeniscous monostichous eye resembling the lateral eye of a scorpion, A, or the unit of the compound lateral eye of Limulus (see article Arachnida, figs.
A pair of central monomeniscous diplostichous eyes is often present on the head.
Monomeniscous eyes are rarely present,and when present,single,minute,and central in position.
Simple monomeniscous eyes are also present in many Hexapods.