ommatidium


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Related to ommatidium: Rhabdomere

ommatidium

(ŏm′ə-tĭd′ē-əm)
n. pl. ommatid·ia (-ē-ə)
One of the optical units, consisting of photoreceptors and usually one or more lenses, that make up a compound eye of an insect or a crustacean.

om′ma·tid′i·al (-ē-əl) adj.

ommatidium

(pl. ommatidia) any of the numerous facets which make up the compound eye of insects and other arthropods. Each ommatidium has its own lens and is composed of a group of retinal cells surrounded by pigment cells. The light-sensitive part of the ommatidium is the RHABDOM, and on its receiving a stimulus a photochemical reaction takes place which results in impulses being sent to the optic nerve.

ommatidium 

One of the visual elements of the compound eye of arthropods. It is hexagonal in shape and about ten times longer than its diameter. It consists of a corneal facet below which is a crystalline cone which collects light and a sensory area called the rhabdom, all of it being enclosed in a dark pigment.
References in periodicals archive ?
Bactrocera dorsalis had a smaller eye width and a smaller individual square ommatidium area than the other 2 species, and the largest number of ommatrichia.
saltator, like some other amphipods, possesses an undifferentiated cornea, a fused-type rhabdom attached to the crystalline cone, and five retinula cells in each ommatidium (Ball, 1977; Meyer-Rochow, 1978; Hallberg et al., 1980; Mayrat, 1981), including one small cell producing a rhabdomere and four other larger retinula cells (Ercolini, 1964).
exotica grew, the visual angles, representing optical catchment per ommatidium, also remained basically the same (i.e., 30[degrees]) for different body lengths (Fig.
With the high magnification of a stereomicroscope, we identified the ommatidium whose optic axis was aligned with that of the microscope.
Normally, all photoreceptors in a single ommatidium view an identical receptive field, which may be imaged onto several photoreceptor types for spectral or polarizational analysis.
After isolating the response of a single optic nerve fiber, we align the animal so that the optic axis of the recorded ommatidium views the center of the pattern.
The video frames were taken 6 s after the beginning of the response records (arrows), when the grey-black edge of the cylinder began to enter the field of view of the recorded ommatidium from the right.
Figure 1A shows the intensity response functions for a single dark-adapted ommatidium during the day and at night.
The final step was to optically isolate the ommatidium of the single active nerve fiber by aligning a fiber optic light pipe (70 [[micro]meter] diameter) along the axis of the ommatidium and in contact with the cornea (4).
Because photon catch is proportional to the cross-sectional area of ommatidial corneal facets, a single Limulus ommatidium (0.029 m[[Mu].sup.2]) should catch [approximately]1.8 times more photons than a Tachypleus ommatidium (0.016 m[[Mu].sup.2]).
A glass microelectrode filled with 3 M KCl (25 M[Omega]) was connected to a DC bridge amplifier (Electronics Shop, Rockefeller University) and advanced into an ommatidium using a Burleigh Inchworm (Burleigh Instruments, Fishers, NY) attached to a manipulator.
Biometrical data of the constituent parts of one representative central ommatidium of the compound eye of the two crustaceans are given in Table I.