S Though ten is the prevailing number of retinula cells and rhabdomeres in the lateral eye of Limulus, Watase states that they may be as few as nine and as many as eighteen.
- Section through a portion of the lateral eye of Limulus, showing three ommatidia - A, B and C. hyp, The epidermic cell-layer (so-called hypodermis), the cells of which increase in volume below each lens, 1, and become nerve-end cells or retinula-cells, rt; in A, the letters rh point to a rhabdomere secreted by the cell rt; c, the peculiar central spherical cell; n, nerve fibres; mes, mesoblastic skeletal tissue; ch, chitinous cuticle.
Ret, Retinula cells.
Rhabdom of a retinula of the scorpion's central eye, showing its five constituent rhabdomeres as rays of a star.
D, Transverse section of a retinula of the lateral eye of Limulus, showing ten retinula cells (ret), each bearing a rhabdomere (rhab).
A, Diagram of a retinula of the central eye of a scorpion consisting of five retina-cells (ret), with adherent branched pigment cells (pig).
23, article Arachnida) a single retinula or group of nerve-end-cells is grouped beneath each associated lens.
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.
The black represents the cuticular product of the epidermal cells of the ocular area, taking the form either of))...,r,, f lens, cl, of crystalline body, cry, or of rhabdom, rhab; hy, hypodermis or epidermal cells; corn', laterallyplaced cells in the simpler stage, A, which like the nerve-end cells, vit' and ret', are corneagens or lens-producing; corn, specialized corneagen or lens-producing cells; vie, potential vitrella cells with cry', potential crystalline body now indistinguishable from retinula cells and rhabdomeres; vit, vitrella cell with cry, its contained cuticular product, the crystalline cone or body; ret', rhab', retinula cells and rhabdom of scorpion undifferentiated from adjacent cells, vit'; ret, retinula cell; rhab, rhabdom; nf, optic nerve-fibres.