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  • 1
    ISSN: 1432-0878
    Keywords: Fine structure ; Cornea ; Retina ; Compound eye ; Hymenopteran insects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Structurally specialized ommatidia at the dorsal rim of the compound eyes of honey bees have been shown to be indispensable for polarized skylight navigation. In this study numerous other hymenopteran genera belonging to various superfamilies are shown to exhibit similar specializations in this part of the eye: (1) The cornea is penetrated by pore canals, which affect the optics of the ommatidia by scattering the light falling into the eye. In Andrena and Ammophila the cornea contains extensive cavities. (2) Each retinula contains 9 long receptor cells as opposed to 8 long ones in the adjacent dorsal area, and the rhabdom area is increased by a factor of up to 2. In all ant species examined there are no corneal but only retinal specializations at the dorsal rim of the eye. They include a specially shaped rhabdom as in Cataglyphis, in which polarization vision has also been demonstrated.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0878
    Keywords: Compound eye ; Cornea ; Photoreceptor cells ; Polarized light detection ; Melolontha melolontha (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The superposition eye of the cockchafer, Melolontha melolontha, exhibits the typical features of many nocturnal and crepuscular scarabaeid beetles: the dioptric apparatus of each ommatidium consists of a thick corneal lens with a strong inner convexity attached to a crystalline cone, that is surrounded by two primary and 9–11 secondary pigment cells. The clear zone contains the unpigmented extensions of the secondary pigment cells, which surround the cell bodies of seven retinula (receptor) cells per ommatidium and a retinular tract formed by them. The seven-lobed fused rhabdoms are composed by the rhabdomeres of the receptor cells 1–7. The rhabdoms are optically separated from each other by a tracheal sheath around the retinulae. The orientation of the microvilli diverges in a fan-like fashion within each rhabdomere. The proximally situated retinula cell 8 does not form a rhabdomere. This standard form of ommatidium stands in contrast to another type of ommatidium found in the dorsal rim area of the eye. The dorsal rim ommatidia are characterized by the following anatomical specializations: (1) The corneal lenses are not clear but contain light-scattering, bubble-like inclusions. (2) The rhabdom length is increased approximately by a factor of two. (3) The rhabdoms have unlobed shapes. (4) Within each rhabdomere the microvilli are parallel to each other. The microvilli of receptor 1 are oriented 90° to those of receptors 2–7. (5) The tracheal sheaths around the retinulae are missing. These findings indicate that the photoreceptors of the dorsal rim area are strongly polarization sensitive and have large visual fields. In the dorsal rim ommatidia of other insects, functionally similar anatomical specializations have been found. In these species, the dorsal rim area of the eye was demonstrated to be the eye region that is responsible for the detection of polarized light. We suggest that the dorsal rim area of the cockchafer eye subserves the same function and that the beetles use the polarization pattern of the sky for orientation during their migrations.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 287 (1996), S. 211-221 
    ISSN: 1432-0878
    Keywords: Key words: Immunocytochemistry ; Photoreceptor cells ; Neurotransmitters ; Insect brain ; Fluorescent dyes ; Gryllus campestris (Insecta) ; Apis mellifera (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The distribution of histamine-like immunoreactivity has been analyzed in the visual system and brain of the cricket Gryllus campestris and of the bee Apis mellifera by using an antiserum against histamine. Specific immunolabeling of the photoreceptors has been found in the compound eyes and ocelli of both examined species. Intense immunostaining can be also detected in the midbrain of these species. The axons of immunoreactive cells innervate almost every area in the protocerebrum. Most of the reactive neurons are typically wide-field neurons with bilateral ramifications that form dense arborizations. Numerous small buttons on the arborizations probably represent pre- and postsynaptic sites. The histamine-like immunoreactive neurons are apparently connected to many postsynaptic neurons. In both bees and crickets, some regions of the nervous system such as the first two optic neuropils and the central body show the same labeling pattern, whereas the mushroom bodies exhibit no immunoreactivity. Nevertheless, several differences in the staining pattern can be seen: the glomeruli of the antennal lobe are invaded by histamine-like immunoreactive fibers in the bee but not in the cricket. Furthermore, an interneuron connects the second and third optic neuropil in the cricket, whereas no histamine-like immunoreactive interneuron is found in the second optic neuropil in the bee. In accord with the work of other authors on the distribution histamine in the insect nervous system, we suggest that histamine is not only a transmitter within the visual system, but also a transmitter or co-transmitter in the insect midbrain.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 216 (1981), S. 491-501 
    ISSN: 1432-0878
    Keywords: Ultrastructure ; Cornea ; Compound eye ; Honey bee (Apis mellifera)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The fine structure of the cornea in an anatomically and functionally specialized part of the honey bee's compound eye (dorsal rim area) was examined by light microscopy, transmission electron and scanning electron microscopy. Under incident illumination the cornea appears grey and cloudy, leaving only the centers of the corneal lenses clear. This is due to numerous pore canals that penetrate the cornea from the inside, ending a few μm below the outer surface. They consist of (1) a small cylindrical cellular evagination of a pigment cell (proximal), and (2) a rugged-walled, pinetree-shaped extracellular part (distal). The functional significance of these pore canals is discussed. It is concluded that their light scattering properties cause the wide visual fields of the photoreceptor cells measured electrophysiologically in the dorsal rim area, and that this is related to the way this eye region detects polarization in skylight.
    Type of Medium: Electronic Resource
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