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"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, l, and become nerve-end cells or retinula-cells, rl; in A, the letters rh point to a rhabdomere secreted by the cell rl; c, the peculiar central spherical cell; n, nerve fibers; mes, mesoblastic skeletal tissue; ch, chitinous cuticle." — The Encyclopedia Britannica, 1910

Limulus

"Section through a portion of the lateral eye of Limulus, showing three ommatidia—A, B and C.…