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  • 1
    Electronic Resource
    Electronic Resource
    The fine structure of a nauplius eye (1964)
    Springer
    Cell & tissue research 62 (1964), S. 182-197 
    Details
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The nauplius eye of the cyclopoid copepod Macrocyclops albidus has been studied by means of the electron microscope. It is composed of 1 ventral and 2 dorsal ocelli. Each dorsal ocellus consists of a large, pigmented cell, 2 tapetal cells which form a hemispherical cup and are tightly packed with crystals, 9 retinula cells and 5 conjunctival cells. The retinula cells have large masses of endoplasmic reticulum, which can be found in two distinct distributional states, also numerous bodies composed of variously coiled membranes, large amounts of glycogen, mitochondria and scattered neurotubules. The light-sensitive brush borders of these cells are closely coapted and form the irregularly shaped rhabdome. Each of the 9 retinula cells sends an axon by one of three routes to the protocerebrum. In addition, a dendrite emerges from the protocerebrum, enters the ocellus and ends blindly in immediate vicinity to the rhabdome. The observations concerning the structure of the eye made in the present study have been compared to those of light microscopical investigations. Comparison of structure and probable function of the nauplius eye and other arthropod eyes has led to consideration of the probable mode of synaptic transmission between primary and secondary sensory neurons in the ocellus, i.e. between retinula cells and eccentric cell dendrite, and various morphological features that might be of importance in this connection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00332499
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  • 2
    Electronic Resource
    Electronic Resource
    The micromorphology of some simple photoreceptors (1965)
    Springer
    Cell & tissue research 66 (1965), S. 233-254 
    Details
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The median eye of Balanus cariosus consists of 7 photoreceptor cells contained in a ganglionic enlargement of the optic nerve. Each cell has multiple distal dendritic branches capped by microvilli and a large axon running to the supraesophageal ganglion. These primary neurons are surrounded by wrappings of glial cells. The glial cells are interconnected by desmosomes and tight junctions over most of the region of mutual contact, and contain an abundance of microtubules. The periphery of the nerve and ganglion is covered by fibroblasts, connective tissue fibrils, an incomplete endothelial covering and varying numbers of amoebocytes. Each lateral eye of Balanus amphitrite contains three sensory cells, backed by a tapetum and pigmented layer. The axons of these cells course in a haemocoelic space to the brain. They have a covering of glial cells and connective tissue, but no endothelium. Certain physiological data available in the literature concerning these photoreceptors have been correlated with the morphological findings. In particular, propagation of the light-induced depolarization occurs by electronic spread; it is, therefore, directly aided by such morphological features as the increased axonal diameter and the greatly reduced extracellular space lacking or absent between glial cells and between the neuron and its glial investment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00344338
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  • 3
    Electronic Resource
    Electronic Resource
    The morphology of the eyes of Limulus (1968)
    Springer
    Cell & tissue research 93 (1968), S. 451-483 
    Details
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The Limulus ommatidium consists of 4 to 20 retinula cells surrounding the dendrite of the eccentric cell. Adjoining membranes are differentiated into the microvillous rhabdome in the central area of the ommatidium. Three types of pigment cells envelop the sensory cells. The distal pigment cells cover the periphery of the distal half of the ommatidium; proximal pigment cells (beneath the base of the ommatidium) and intraommatidial pigment cells provide glial wrapping for the sensory cells, the partitions between them, and the peripheral loose framework. Processes of the overlying cone cells penetrate into the ommatidium and lie at the edges of the rhabdomal fins. Numerous neurosecretory axons terminate at all levels of the ommatidium on pigment cells, conveyed there either by enveloping pigment cells or by separate neuroglial cells. Tight junctions in the ommatidium are confined to the contacts between rhabdomal miorovilli. The periphery of the rhabdome is surrounded by continuous adhering junctions except at the tip and exit of the eccentric cell dendrite. The discussion centers on possible correlations between known neurophysiological characteristics of ommatidial cells and significant morphological aspects of the ommatidium, such as distribution of supporting cells, extracellular space, and junctional specializations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338531
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  • 4
    Electronic Resource
    Electronic Resource
    The morphology of the eyes of Limulus (1968)
    Springer
    Cell & tissue research 87 (1968), S. 278-291 
    Details
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The dioptric apparatus of the Limulus compound eye is composed of the corneal cuticle with its internally projecting cuticular cones and the specialized underlying epidermis. The latter is composed of three distinct cell types. The guanophores, located between cuticular cones, contain guanine as a reflecting pigment. The distal pigment cells, which clothe the sides of the cuticular cones and form a sheath around the underlying ommatidium, contain massive bundles of microtubules, abundant pigment droplets and a large Golgi system. The cone cells are positioned between the flattened tip of the cuticular cone and the apex of the ommatidium. They serve to anchor the retinula cells to the cuticle and, by virtue of long processes along the periphery of the rhabdome, perform a glial function with respect to the interaction of adjacent retinula cells. The geometry and fine structure of the dioptric apparatus provide supporting evidence for the wide angle of acceptance and lack of polarized light perception by the ommatidia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00319725
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  • 5
    Electronic Resource
    Electronic Resource
    Fine structure of endocrine hindgut cells of a lepidopteran, Ostrinia nubilalis (Hübn.) (1969)
    Springer
    Cell & tissue research 94 (1969), S. 337-345 
    Details
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Cells of the hindgut of the European corn borer, Ostrinia nubilalis, have two functions, namely, ion transport and secretion of a hormone called proctodone. In this species, proctodone is an essential requisite to the prepupal molt in conjunction with brain hormone synthesis. Apical infoldings and their associated mitochondria form mitochondrial pumps for ion transport from the gut lumen to the hemocoel. The endocrine function of the cells is evidenced by rhythmical formation and discharge of inclusion bodies every 8 hours. These measure from 800 Å to 3 μ. in diameter and vary in composition from bodies with whorled, myeloid content to inclusions with densely granular matrix. During the discharge phase, granular material appears in the basal infoldings and accumulates in large quantities underneath the basal lamina and in the hemocoelic clefts adjacent to the active cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00319181
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  • 6
    Electronic Resource
    Electronic Resource
    The morphology of the Limulus visual system (1970)
    Springer
    Cell & tissue research 105 (1970), S. 303-316 
    Details
    ISSN: 1432-0878
    Keywords: Eye ; Arthropods ; Neurosecretion ; Microscopy, Electron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The lateral rudimentary eye of Limulus polyphemus, the horseshoe crab, is located beneath the posterior border of the compound eye. It consists of a bipartite mass of guanophores and about 100 associated photoreceptor cells. These neurons, up to 150 μ in diameter, have standard attributes of arthropod retinula cells and send large, uninterrupted axons to the brain. Their cytoplasm contains conspicuous clumps of residual bodies and variable, but usually extensive, masses of glycogen and glycoprotein. Hence, these neurons are not neurosecretory in the strict sense, notwithstanding axonal transport of glycogen masses toward the brain. Efferent axons to the rudimentary eye terminate in synaptoid fashion on the axon hillock of sensory cells. Since the rudimentary eye does not transmit impulses to the brain, but is photosensitive, its function may reside in a metabolic responsiveness to long-term changes in illumination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335458
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  • 7
    Electronic Resource
    Electronic Resource
    The morphology of the Limulus visual system (1971)
    Springer
    Cell & tissue research 114 (1971), S. 532-545 
    Details
    ISSN: 1432-0878
    Keywords: Arthropods ; Eye ; Optic Nerve ; Axons ; Denervation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The lateral optic nerve of Limulus polyphemus, the horseshoe crab, contains 4 types of axons, which originate from eccentric cells, retinula cells, rudimentary eye cells, and from unidentified cells in the brain that give rise to the efferent fibers. Though small in diameter in a young animal, the eccentric cell axons in the adult grow to the same size as the rudimentary eye axons, which are originally the largest fibers in the nerve of the small Limulus. Cytoplasmic content, particularly the orderly distribution of microtubules, is identical in the three types of visual fibers. The segregation of rudimentary eye axons into a separate grouping within the optic nerve in small animals gives way to a homogeneous distribution in the adult. Interrupting the optic nerve leads to a proximal pile-up of secretory granules in a few fibers. The identity of these granules with those in the synaptoid terminations of photoreceptors establishes these fibers as efferent. The same operation leads to a conspicuous hypertrophy of subsurface cisternae within retinula cell axons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00325638
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  • 8
    Electronic Resource
    Electronic Resource
    The morphology of the horseshoe crab (Limulus polyphemus) visual system (1981)
    Springer
    Cell & tissue research 216 (1981), S. 655-659 
    Details
    ISSN: 1432-0878
    Keywords: Eye ; Neuroeffector junction ; Octopamine ; Circadian rhythm ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Efferent fibers to the compound eye of the horseshoe crab, Limulus polyphemus, not only innervate the various pigment cells, but also invade the eccentric cell dendrite and the retinula cells. This finding provides a structural basis for the coupling of circadian rhythm between the efferents and the receptor cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238660
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  • 9
    Electronic Resource
    Electronic Resource
    The morphology of the Limulus visual system (1973)
    Springer
    Cell & tissue research 144 (1973), S. 153-166 
    Details
    ISSN: 1432-0878
    Keywords: Arthropods Limulus ; Eye ; Neurosecretion ; Neuroeffector junction ; Nerve degeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the protocerebrum of Limulus polyphemus, the horseshoe crab, neurosecretory cells are grouped within the curvature of the central body, an association area for inputs from lateral, median, and ventral eyes. Scattered neurohemal terminals face circulatory sinusoids within the brain. Efferent fibers, originating from unspecified, presumably neurosecretory cells in the central nervous system, course through the optic nerves and terminate on pigment and receptor cells of the eyes. Their terminals have a synaptoid structure and their granules have the characteristic density and crystalline substructure of neurosecretory granules. Transection of the lateral optic nerve leads to degranulation and gradual disappearance of terminals and to accumulation of granules at the proximal ends of cut fibers. The Limulus ocular innervation presents a striking example of directed delivery of neurosecretion to pigmentary effector cells, whose adaption is usually controlled by circulating neurohormones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00307299
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  • 10
    Electronic Resource
    Electronic Resource
    The morphology of the Limulus visual system (1975)
    Springer
    Cell & tissue research 159 (1975), S. 39-47 
    Details
    ISSN: 1432-0878
    Keywords: Limulus ; Ocellus ; Connectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary An ocellus of the horseshoe crab, Limulus polyphemus, has been serially sectioned for light and electron microscopy, its sensory cells have been indexed, and the interconnections of a third of these traced. The ocellus contains 155 retinula cells and 26 arhabdomeric cells, which are secondary sensory neurons. Of these, 55 retinula cells constitute 7 quasi-ommatidial assemblages, each innervated by at least one and a total of 9 arhabdomeric cells. When known electrotonic coupling patterns are compared with gap-junctional connections, retinula cells sensitive to visible or ultraviolet light can be tentatively identified. Retinula cell axons contribute collaterals to a synaptic plexus, in which the arhabdomeric cells apparently do not participate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231993
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