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Topic: Ommatidia

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	Encyclopedia: Ommatidia (Site not responding. Last check: 2007-10-08)
		Ommatidia were seen in which the R3 and R4 fates are correctly specified and rotation occurs in either the correct or incorrect direction, with respect to the R3 and R4 fates.
		In ommatidia that adopted the correct polarity for their position in the eye, R3 and R4 were derived from the equatorial and polar precursor cells, respectively, while in reversed polarity ommatidia, the R3 was derived from the polar precursor cell and R4 from the equatorial cell.
		In contrast, ommatidia in the equatorial region of the clone are phenotypically wild-type, suggesting that wild-type ommatidia outside the equatorial boundary of the clone rescue genetically mutant ommatidia within the equatorial region of the clone.
	www.nationmaster.com /encyclopedia/Ommatidia (788 words)

	Insect Senses
		The ommatidia is the visual sensing element of the compound eye.
		What is seen by the insect is a mosaic of "pictures" from each of the ommatidia.
		Ommatidia - light gathering and sensing function, hexagonal or circular in shape.
	www.ndsu.nodak.edu /instruct/brewer/senses.htm (262 words)

	IPO Structure and Function in Insects (Site not responding. Last check: 2007-10-08)
		In each compound eye, each ommatidia consists basically of a system of lenses that collect and focus the luminance rays; and a sensorial portion that transforms the luminance energy into an electric signal.
		In the eyes of apposition, each ommatidia is optically isolated from its neighbors, meaning that each rhabdom receives only the rays that enter through its own focus system, while the rays that enter through the neighboring facets are absorbed by the pigments of the secondary pigmenting cells.
		This is possible because these eyes have a "clear zone," free of pigmentation, between the crystalline cone and the rhabdom; and because the rhabdom is restrained from the proximal portion of the retinular cells.
	faculty.ucr.edu /~insects/teresita/english9.html (601 words)

	J. A. Serra - Cytophysiological Theory
		Bar larvae shall have their ommatidia limited to an area along the greater axis of the ellipsoid surface of the normal eye, but the final number ommatidia is fixed during the subsequent course of development, according to the rest of the genotype and a series of ambiental factors.
		This latter type of action seems to be excluded by the fact that the ommatidia of the Bar eye are practically of the same size as those of the wild fly.
		It seems that the action of the Bar mutant consists in depriving the differentiating cells of the ocular disc of a substance, or a condition, necessary for the differentiation of the ommatidia, except in a small area along the long axis of the eye.
	www.geocities.com /fadjar_z/Serra/serra2.htm (5507 words)

	MSN Encarta - Multimedia - Compound Eye
		The eyes of insects and many other arthropods are compound, each composed of up to several thousand individual visual organs called ommatidia.
		Light entering the ommatidium is focused by these lenses down a central structure called the rhabdom, where an inverted image forms on light-sensitive retinular cells.
		Optic nerve fibers transmit information from each rhabdom separately to the brain, where it is combined to form a single image of the outside world.
	encarta.msn.com /media_461517934/Compound_Eye.html (100 words)

	Red Skimmer Eyes Crocothemis chinensis
		Compound eyes are comprised of individual facets called ommatidia each containing a lens capable of resolving a unique signal to the optic nerve.
		Size of the individual ommatidia vary with the location on the compound eye which is believed to offer varying sensitivity and resolution.
		Because dragonflies rely on their keen vision to catch prey in mid flight, their huge compound eyes are comprised of up to 30,000 individual ommatidia which translates into highly resolved vision with a wide field of view.
	www.insects.org /entophiles/odonata/odon_007.html (136 words)

	Interactive Fly, Drosophila (Site not responding. Last check: 2007-10-08)
		The eye is composed of dorsal and ventral fields of photoreceptor clusters called ommatidia.
		Ommatidia in the dorsal half of the eye are the mirror image of those in the ventral half.
		Recent work has demonstrated that the degree of ommatidial rotation is controlled by several genes, including nemo and roulette, and has suggested that tissue polarity genes such as spinylegs, prickly-spinylegs, frizzled, and dishevelled are necessary for regulating DV polarity in the eye (McNeill, 1997 and references).
	www.flybase.net /allied-data/lk/interactive-fly/newgene/mirror1.htm (3382 words)

	Drosophila: eye genetics (Site not responding. Last check: 2007-10-08)
		Differentiation occurs in posterior to anterior sequence: the first ommatidia to differentiate do so at the posterior pole of the eye disc, the last at the anterior pole.
		The morphogenetic furrow marks the boundary between dividing, non-differentiating cells and differentiating ommatidia.
		The further posterior ommatidia are from the furrow the closer they are to having all cell types (R1-R8 cone cells and pigment cells) differentiated.
	www.ucl.ac.uk /~ucbhhks/FlyI.htm (1093 words)

	CHAPTER TWENTY SIX (Site not responding. Last check: 2007-10-08)
		The basic unit of compound eyes is the ommatidium (singular of ommatidia).
		At one extreme, dragonflies have thousands of ommatidia in each compound eye; many insects have far fewer, and at the other extreme, the workers of the ant species Pomera punctatissima have only one ommatidium in each eye.
		Ommatidia are functionally isolated because the retinula cells are surrounded by the secondary pigment cells.
	entomology.unl.edu /ent801/vision.html (1738 words)

	Interactive Fly, Drosophila
		Extra machrochaetes (sensory bristles) are occasionally seen in the head, notum and scutellum, and some mutants show variable but conspicous wing phenotypes such as a notched blade and the loss of a cross vein.
		In the eye, clones of mutant photoreceptor cells are devoid of any ommatidia, while small mutant patches have reduced numbers of photoreceptors.
		Fused ommatidia have been reported to occur in scabrous mutants; sca mutants are also accompanied by bristle abnormalities.
	www.sdbonline.org /fly/dbzhnsky/canoe1.htm (1448 words)

	Scabrous (Site not responding. Last check: 2007-10-08)
		The targets of Scabrous are R8 cells, the first of the eight cells comprising the ommatidia.
		Scabrous is probably a second ligand for Notch, preparing the way for the primary ligand Delta to fulfill its role in lateral inhibition, a process restricting the number of ommatidia in the developing eye.
		In the wing disc, scabrous expression is coextensive with the anlagen for anterior wing margin bristles and machrochaetae, and is controlled by genes of the achaete-scute complex (Mlodzik M., 1990).
	www.iephb.nw.ru /labs/lab38/spirov/hox_pro/sca.htm (395 words)

	The Compound Eye (Site not responding. Last check: 2007-10-08)
		There may be thousands of ommatidia in a compound eye with their facets spread over most of the surface of a hemisphere.
		Even so, the resolving ability of the honeybee eye is poor in comparison with that of most vertebrate eyes and only 1/60 as good as that of the human eye; that is, two objects that we could distinguish between at 60 feet could only be discriminated by the bee at a distance of one foot.
		Arthropods that are apt to be active in dim light (e.g., crayfish, praying mantis) concentrate the screening pigments of their ommatidia into the lower ends of the pigment cells.
	users.rcn.com /jkimball.ma.ultranet/BiologyPages/C/CompoundEye.html (747 words)

	Drosophila Gp150 is required for early ommatidial development through modulation of Notch signaling (Site not responding. Last check: 2007-10-08)
		To examine how ommatidia assembly can be affected by gp150 mutations, a neural-specific nuclear marker, Elav (Robinow and White, 1991), was used to highlight all R cells.
		In the wild type, developing ommatidia are evenly patterned with precursor cells sequentially recruited into ommatidia clusters (Figure 4G).
		To address whether accumulation of oversized ommatidia close to the MF is due to defects in furrow progression, expression of decapentaplegic (dpp) and a bHLH gene hairy (h) was examined, since both of them are involved in regulating furrow progression (Brown et al., 1995; for review see Treisman and Heberlein, 1998).
	www.nature.com /emboj/journal/v21/n5/full/7594325a.html (7544 words)

	Reflections on colourful ommatidia of butterfly eyes -- Stavenga 205 (8): 1077 -- Journal of Experimental Biology
		The eye shine patterns in the eyes of the satyrine Bicyclus anynana (A), the heliconian Heliconius melpomene (B) and the small white Pieris rapae (B) observed with the large-aperture optical apparatus depicted in Fig.
		The red reflection is absent from a large dorsal area of the eye of Bicyclus anynana and from a small dorsal area of the eye of Pieris rapae; in Heliconius melpomene, both reflection types co-exist throughout the eye.
		The frontal and ventral parts of the eye contain a mixture of red- and yellow-green-reflecting ommatidia, but dorsally the reflection colours are a mixture of blue and green; red reflection is absent from the dorsal region.
	jeb.biologists.org /cgi/content/full/205/8/1077 (5028 words)

	THE INTERACTIVE FLY (Site not responding. Last check: 2007-10-08)
		The arrangement and spacing of the developing ommatidia are completely normal, even in very large clones induced in a minute background; some examples cover more than half of the eye disc.
		Therefore, the central patterning event in establishing the overall arrangement of the ommatidia is the transformation of uniform Atonal expression into modulated expression, as controlled by a combination of Scabrous and the Egfr-dependent inhibitory signal (Baonza, 2001).
		A rosette-like ring of wedge-shaped cells surrounds the bristle precursor; it is reminiscent of the cell preclusters that precede segregation of the R8 photoreceptor during development of ommatidia.
	flybase.bio.indiana.edu /allied-data/lk/interactive-fly/neural/scabrous.htm (15787 words)

	oe magazine - life lessons (Site not responding. Last check: 2007-10-08)
		The dragonfly has approximately 28,000 ommatidia and is one of the supreme examples of biological micro-optics.
		Under high illumination conditions, a light shield or baffle extends between the ommatidia (photoreceptors) to restrict light collection to a single detector.
		The disadvantage is the decreased spatial resolution when light from several ommatidia are integrated on one photoreceptor.
	www.oemagazine.com /fromTheMagazine/feb02/lifelessons.html (1674 words)

	Wingless eliminates ommatidia from the edge of the developing eye through activation of apoptosis -- Lin et al. 131 ...
		Wingless eliminates ommatidia from the edge of the developing eye through activation of apoptosis -- Lin et al.
		The kinetics of apoptosis are slower in hid
		The onset of apoptosis in the ommatidia at the edge is delayed, as indicated by the presence of many cells positive for Elav, TUNEL and Wg, which is not seen in wild type (compare with Fig.
	dev.biologists.org /cgi/content/full/131/10/2409/DC1 (250 words)

	math lessons - Compound eye
		The compound eye consists of between 12 and 1,000 ommatidia, little dark/bright sensors.
		The image perceived by the arthropod is "recalculated" from the numerous ommatidia which point in slightly different directions.
		Strepsiptera have a different kind of eye, in which each lens does form an image, and the images are combined in the brain.
	www.mathdaily.com /lessons/Compound_eyes (309 words)

	Otd/Crx, a dual regulator for the specification of ommatidia subtypes in the Drosophila retina. (Site not responding. Last check: 2007-10-08)
		Otd/Crx, a dual regulator for the specification of ommatidia subtypes in the Drosophila retina.In Drosophila, this is achieved in each ommatidium by the inner photoreceptors R7 and R8.
		Two classes of ommatidia are distributed stochastically in the retina: 30% contain UV-Rh3 in R7 and blue-Rh5 in R8, while the remaining 70% contain UV-Rh4 in R7 and green-Rh6 in R8.
		Therefore, Otd is a key player in the terminal differentiation of subtypes of photoreceptors by regulating rhodopsin expression, a function reminiscent of the role of one of its mammalian homologs, Crx, in eye development.
	www.pdg.cnb.uam.es /UniPub/iHOP/gp/9997888.html (182 words)

	Ectopic scute induces Drosophila ommatidia development without R8 founder photoreceptors -- Sun et al. 97 (12): 6815 -- ... (Site not responding. Last check: 2007-10-08)
		To form ommatidia (4, 17, 18), as in the formation of other sensory organs (1, 2, 6, 7), early expression
		Ommatidia rescued by ato or scute exhibit different structure and developmental processes.
		Ommatidia Development Initiated by Ectopic scute Without Inducing R8 Photoreceptors.
	www.pnas.org /cgi/content/full/97/12/6815 (3378 words)

	Wingless eliminates ommatidia from the edge of the developing eye through activation of apoptosis -- Lin et al. 131 ...
		that Wg expression in the peripheral ommatidia preceded PCD.
		This induction of Wg expression in the perimeter ommatidia was
		By 36 hours APF, Wg expression in the ommatidia is fading and the expression of the pro-apoptotic genes hid, grim and rpr are triggering apoptosis, causing the elimination of these ommatidia.
	dev.biologists.org /cgi/content/full/131/10/2409 (6703 words)

	Parallel Processing and Image Analysis in the Eyes of Mantis Shrimps -- Cronin and Marshall 200 (2): 177 -- The ... (Site not responding. Last check: 2007-10-08)
		The visual regions of the compound eyes, revealed here by the densely packed facets (each of which represents the cornea of a single ommatidium), lie at the ends of stalks that pivot at their proximal ends.
		Ommatidia like those of Figure 2 are also typical of crabs and
		The main rhabdom (R1–7) exists in a single tier in Type I ommatidia (left), but is divided into two tiers by separating R1, 4, and 5 from R2, 3, 6, and 7 in Types II (center) and III (right).
	www.biolbull.org /cgi/content/full/200/2/177 (3575 words)

	Ommatidia from LiveJournal (Site not responding. Last check: 2007-10-08)
		A fly eye, a human eye; a grid of ommatidia, a ball with an iris and lens and retina and cornea.
		Some scientists have theorized that the compound eye of a moth, with its peripheral ommatidia (light receptor cells), causes the moth to perceive a very dark area around a very bright point of light.
		Worker honey bees have a ring of iron oxide ("magnetite") in their abdomens that may be used to detect magnetic fields.
	www.ljseek.com /search/Ommatidia (358 words)

	Photoreceptors (Site not responding. Last check: 2007-10-08)
		A pair of compound eyes are the principle visual organs of most insects; they are found in nearly all adults and in many immatures of ametabolous and hemimetabolous orders.
		The number of ommatidia varies considerably from species to species: some worker ants have fewer than six while some dragonflies may have more than 25,000.
		Their ommatidia are stimulated by light from larger fields of view.
	www.cals.ncsu.edu:8050 /course/ent425/tutorial/photo.html (751 words)

	The Rockefeller University - Understanding blood clots
		By manipulating the timing of gene expression, Rockefeller researchers led by assistant professor Bertrand Mollereau, in the Strang Laboratory of Cancer Research, were able to change the development and function of cells in the fly eye —; in one instance even causing the flies to become colorblind.
		But two studies, done at Rockefeller, show that for the ommatidia to develop correctly, spalt must be present in several of the photoreceptor cells.
		Beyond detecting motion, the R3 and R4 cells also help arrange the ommatidia into their final design: a spoked, circular pattern similar to a daisy flower.
	www.rockefeller.edu /pubinfo/news_notes/rus_082605_e.php (630 words)

	Interactive Fly, Drosophila (Site not responding. Last check: 2007-10-08)
		Roughest is also involved in terminal stages of the development of the regular pattern of ommatidia in the eye.
		The final step of pattern formation in the developing retina is the elimination of excess cells between the ommatidia and the differentiation of the remaining cells into secondary and tertiary pigment cells.
		This suggests that the accumulation of Rst protein at the border of primary pigment and interommatidial cells is responsible for the proper sorting of cell contacts, and that this accumulation can be influenced by the presence of Rst in cone cells.
	flybase.bio.indiana.edu /allied-data/lk/interactive-fly/hjmuller/roughst1.htm (2596 words)

	Postembryonic Eye Growth in the Seashore Isopod Ligia exotica (Crustacea, Isopoda) -- Keskinen et al. 202 (3): 223 -- ... (Site not responding. Last check: 2007-10-08)
		Ommatidial diameter was defined as the corner-to-corner distance (g), while debris on the cornea (white arrows) served as landmarks, assisting in identifying specific places on the eye.
		in ommatidia with age was neither strictly linear, as in the
		The structure of the ommatidia of the Malacostraca (Crustacea)—a phylogenetic approach.
	www.biolbull.org /cgi/content/full/202/3/223 (4508 words)

	New Camera Technology: Eyes from Eyes
		Thus, rays coming from other parts of the wall are prevented by the walls of the tube and the backing of the dome from hitting the back of the tube where the photocells are (Figure).
		The lenses of all ommatidia conspire to form a single image on a shared retina which is put together from the light-sensitive cells of all the ommatidia.
		In this case, the ommatidia are isolated tubes just as in the case of the apposition eye, but they achieve a superposition-like effect by ingenious wiring of nerve cells behind the ommatidia.
	www.cfar.umd.edu /~larson/dialogue/newCameraTech.html (1883 words)

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