compound eye

n. The eye of most insects and some crustaceans, which is composed of many light-sensitive elements, each having its own refractive system and each forming a portion of an image.

compound eye

n (Zoology) the convex eye of insects and some crustaceans, consisting of numerous separate light-sensitive units (ommatidia). See also ocellus

com′pound eye′

n. an eye, typical of insects, composed of many individual light-sensitive units that form a mosaic of images on the retina.

compound eye

An eye, as of an insect or crustacean, consisting of hundreds or thousands of tiny light-sensitive parts, with each part creating a portion of an image.Did You Know? The eyes have it—the important ability to see, that is. But not all eyes are created equal. Insects and other arthropods (which include lobsters and other crustaceans) have compound eyes, which are quite different from ours. The compound eye, greatly magnified, looks like a fencer's mask. It consists of many repeating units, called ommatidia, each of which is a separate light receptor. Some species' eyes have many ommatidia while others have only a few—the more ommatidia an eye has, the better it can resolve images. But even with many ommatidia, the typical compound eye is poor compared with ours at creating a sharp image. A honeybee, for example, sees only one-sixtieth as clearly as we do. However, the compound eye has other special talents. It is excellent at detecting motion, as the moving object passes from one ommatidium to the next. And some insects see ultraviolet light, which is invisible to us.

Thesaurus

Noun

compound eye - in insects and some crustaceans: composed of many light-sensitive elements each forming a portion of an imageeye, oculus, optic - the organ of sightommatidium - any of the numerous small cone-shaped eyes that make up the compound eyes of some arthropods

compound eye

compound eye:

see eyeeye,
organ of vision and light perception. In humans the eye is of the camera type, with an iris diaphragm and variable focusing, or accommodation. Other types of eye are the simple eye, found in many invertebrates, and the compound eye, found in insects and many other
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Compound Eye

(also faceted eye), the principal paired organ of vision in insects, crustaceans, and some other invertebrates. Compound eyes are made up of special structural units, ommatidia, whose corneal lenses are in the shape of convex hexahedrons. In insects they are immobile and located at the sides of the head, often occupying almost the entire surface, for example, in dragonflies, flies, and bees. In crustaceans they sometimes are set on movable stalks. The compound eyes most thoroughly studied are those of insects and larvae of species with incomplete metamorphosis; the eyes of such insects are composed of hundreds or even thousands of ommatidia.

Depending on the anatomical characteristics and optical properties of the ommatidia, three types of compound eyes are distinguished: apposition, superposition, and neurosuperposition. In apposition compound eyes, which are usually characteristic of diurnal insects, adjacent ommatidia are isolated from one another by an opaque pigment, and the receptors perceive only perpendicular light rays falling along the axis of a given ommatidium.

In superposition compound eyes, which are characteristic of nocturnal and crepuscular insects and many crustaceans, the ommatidia may be isolated as a result of the pigment’s ability to shift. When there is insufficient light, the rays that fall at an oblique angle are superposed and pass through several facets. Thus the sensitivity of the eye increases with weak illumination.

Neurosuperposition compound eyes accumulate signals from sense cells in various ommatidia, which receive light from the same point in space. In some insects, such as praying mantises and mayflies, one part of the eye may be of the apposition type, while the other is of the superposition type.

In all types of compound eyes the rhabdomeres of the sense cells, which contain a photopigment similar to rhodopsin, serve as the photosensitive element. The absorption of quanta of light by the photopigment is the first link in the chain of processes that results in the generation of a nerve signal by the sense cell.

Because of the projection of the retina on the optic ganglia of the brain and, in part, the characteristics of compound-eye optics, the ommatidium’s raster plays a more important role in the perception of the environment than individual sense cells. Because the optical axes of the ommatidia diverge at extremely acute angles (l°–6°), the compound eye is unable to distinguish minute details. However, its high adaptability and high contrast sensitivity (1–5 percent) permit some insects to distinguish the flashing of light at frequencies as high as 250–300 hertz (Hz) (the human limit is approximately 50 Hz). Compound eyes enable many invertebrates to distinguish color, perceive ultraviolet rays, and determine the direction of the plane of linearly polarized light.

REFERENCES

Mazokhin-Porshniakov, G. A. Zrenie nasekomykh. Moscow, 1965.
Prosser, L., and F. Brown. Sravnitel’naia fiziologiia zhivotnykh. Moscow, 1967. Chapter 12. (Translated from English.)

G. A. MAZOKHIN-PORSHNIAKOV

compound eye

[′käm‚pau̇nd ′ī] (invertebrate zoology) An eye typical of crustaceans, insects, centipedes, and horseshoe crabs, constructed of many functionally independent photoreceptor units (ommatidia) separated by pigment cells.

compound eye

compound eye

compound eye

com′pound eye′

compound eye

compound eye

compound eye:

Compound Eye

REFERENCES

compound eye

compound eye

com·pound eye

compound eye

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Words related to compound eye

noun in insects and some crustaceans: composed of many light-sensitive elements each forming a portion of an image

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