Figure 7
Comparison of median eye visual systems in (A) Onychophora ( Euperipatoides rowelli ), (B) Pycnogonida ( Achelia spp. , Endeis spinosa ), (C) Xiphosura ( Limulus polyphemus ), (D) Scorpiones ( Euscorpius spp. , Androctonus australis ), and (E) Araneae ( Cupiennius salei ). A, visual pathways from eyes with optic neuropils indicated. After Strausfeld et al. [23]. B, retinula cells terminate in first and second visual neuropils. Second visual neuropil in close vicinity to an unpaired midline neuropil, possibly an arcuate body. After Lehmann et al. [21]. C, left: terminals of median rudimentary eye have some branches in first median eye neuropil, then continue and terminate near arcuate body; right: median eye photoreceptor cells terminate in first median eye neuropil, arhabdomeric cells in second median eye neuropil, which partly overlaps with second lateral eye neuropil. After Calman et al. [14] and Chamberlain and Barlow [13], second median eye neuropil added (see text). D, photoreceptor cells terminate in first median eye neuropil, arhabdomeric cells in second median eye neuropil, which partly overlaps with second lateral eye neuropil. Connection between median eyes to region near arcuate body omitted. According to Heinrichs and Fleissner [35] these fibres belong to neurosecretory cells with origin in the tritocerebrum, hence are cells of the brain rather than retinula cells. E, retinula cells terminate in first median eye neuropil. After Strausfeld et al. [18] and Strausfeld and Barth [19]. LON, lateral eye optic nerve; L1, first lateral eye visual neuropil; L2, second lateral eye visual neuropil; MON, median eye optic nerve; M1, first median eye visual neuropil; M2, second median eye visual neuropil; M/L2, region were M1 and L1 overlap; ON, optic nerve; OT, optic tract; VN, visual neuropil.