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Those nearest to the lens are the corneagen cells of this more elaborated eye, and those between the original retinula cells and the corneagen cells become firm and transparent.

B represents an intermediate hypothetical form in which the cells beneath the lens are beginning to be superimposed as corneagen, vitrella and retinula, instead of standing side by side in horizontal series.

C, Transverse section of the rhabdom of a retinula of the scorpion’s central eye, showing its five constituent rhabdomeres as rays of a star.

Retinula -ae: the retina of a single ocellus: the nerve fibres or cells between pigment cells and retina of the compound eye.

Rhabdom: the rod lying in the axis of the retinula, below the crystalline cone of an eye.