The fine structure of rhabdomeric photoreceptors of Cirrifera aculeuta, Monocelis fusca and Nematoplana coelogynoporoides is described. The existence of one receptor cell and one pigmented or unpigmented mantle cell is thought to be a basic feature of the Neoophora at least. The existence of a pigment shield formed by many cells is derived, in addition to one receptor and one unpigmented mantle cell, in the eyes of Monocelis fuscu.