The ommatidium is from the first segregate and consists of few cells.
The cells of tl ommatidium are a good deal larger than the neighbouring common cells of the epidermis.
The surface of a compound eye is seen to be covered with a large number of hexagonal corneal facets, each of which overlies an ommatidium or series of cell elements (fig.
The ommataeum, as already stated, tends to segregate into retinulae which correspond potentially each to an ommatidium of the compound eye.
The ommatidium (soft structure beneath the lens-unit of a compound eye) is very simple in both Scorpio and Limulus.