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Notes: Summary Eyes of the Coleoptera previously examined possess fused rhabdoms in all but a few species that have open rhabdoms consisting of 2 central and 6 peripheral rhabdomeres. Recent investigation of more than 70 species from about 20 families (with a total of 150,000 species) led to the conclusion that nearly one-half of all Coleoptera species possess the open-rhabdom type of eye. All of these species belong to the Cucujiformia (composed of the 5 superfamilies Cleroidea, Lymexyloidea, Cucujoidea, Chrysomeloidea and Curculionoidea, sensu Crowson, 1967), and — until now — no species of this group has been found to have fused rhabdom eyes. The open rhabdomic eye is therefore considered a synapomorphous feature (sensu Hennig, 1966) of the Cucujiformia, and this taxon is regarded as a monophyletic. From electronmicroscopic examinations of 41 Chrysomelidae species from 9 subfamilies and of 18 Cerambycidae of 3 subfamilies, the position of the central rhabdomeres (R 7, 8) relative to the peripheral rhabdomeres (R 1–6) and the direction of microvilli in the central rhabdomeres were chosen for comparison. The central rhabdomeres were found to be fused, laterally, to R 1 and R 4 in all of the species from the subfamily Chrysomelinae, but no such fusion was found in any species of the other 8 subfamilies of the Chrysomelidae, nor in any of the Cerambycidae or Bruchidae examined. Microvilli of R 7 and R 8 are parallel in Donaciinae, Criocerinae, Eumolpinae, and many Chrysomelinae, and in Lepturinae, Cerambycinae and Lamiinae (Cerambycidae) and in Bruchidae. Microvilli of both rhabdomeres are aligned in several directions in the Galerucinae, Hispinae, Clytrinae, but only inPhytodecta of the Chrysomelinae, and characteristic differences in the arrangement of microvilli were recognized among these Chrysomelidae. Microvilli were parallel in one of the central rhabdomeres, but aligned in two or more directions in the other, in species of Megalopodinae, Orsodacninae, but only inTimarcha among Chrysomelinae, and again the arrangement of microvilli was characteristic of the subfamilies of these Chrysomelidae (exception: Chrysomelinae). The central rhabdomere systems possessing microvilli of only one direction, but not fused at any level of the ommatidia with peripheral rhabdomeres, are considered symplesiomorphous for this superfamily. This simple arrangement of microvilli in many diverse groups of Chrysomelidae, Cerambycidae and Bruchidae may be regarded as the basic pattern from which the different arrangements in other subfamilies were derived. Similarities in arrangement of the microvilli (among taxa of different families) are considered to be convergences. — The results are also discussed with a view to functional properties of the rhabdomeres.