Fig. 1
From: Trilobite compound eyes with crystalline cones and rhabdoms show mandibulate affinities
The two major compound eye types of Recent euarthropods. a, b Simplified schemes of the dioptric apparatus of a single unit (ommatidium) of a Recent xiphosuran eye (a) and a Recent mandibulate eye (b). Pigment cells are omitted. Light green: cuticular lens, turquoise: crystalline cone, white: vitreous cells, dark magenta: rhabdom, light magenta: retinula cell bodies gray: cell nuclei. a The cuticular lens forms a cone-like extension. The light is guided via a small transparent vitreous region of about a hundred cells to the rhabdom, i.e. the light-perceiving microvilli of the circularly arranged retinula cells. b A relatively flat cuticular lens is combined with a cellular transparent crystalline cone. The position of the nuclei of the crystalline cones and the retinula cells differ among the mandibulate taxa. c Micrograph of the internal view of a compound eye of the horseshoe crab Limulus polyphemus with numerous cuticular cone-like projections (arrow). d cross-section through the eye of the centipede Scutigera coleoptrata showing biconvex cuticular lenses (le) and the cellular crystalline cones (cc). Scale bars: 200 μm (c), 50 μm (d)
