Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A small simple eye, found in many invertebrates, usually consisting of a few sensory cells and a single lens.
  • n. A marking that resembles an eye, as on the tail feathers of a male peacock; an eyespot.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A simple eye consisting of a single lens and a small number of sensory cells
  • n. An eyelike marking in the form of a spot or ring of colour, as on the wing of a butterfly or the tail of a peacock

from the GNU version of the Collaborative International Dictionary of English

  • n. A little eye; a minute simple eye found in many invertebrates.
  • n. An eyelike spot of color, as those on the tail of the peacock.

from The Century Dictionary and Cyclopedia

  • n. A little eye; an eye-spot; a stemma; one of the minute simple eyes of insects and various other animals.
  • n. One of the simple elements or facets of a compound eye. See cut of compound eye, under eye.
  • n. In Hydromedusæ, a pigment-spot at the base of the tentacles, or combined with other marginal bodies, in some cases provided with refractive structures which recall the crystalline cones of some other low invertebrates. Also called ocellicyst.
  • n. One of the round spots of varied color, consisting of a central part (the pupil) framed in a peripheral part, such as characterize the tail of a peacock or the wing of an argus-pheasant.
  • n. See the adjectives.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. an eyelike marking (as on the wings of some butterflies); usually a spot of color inside a ring of another color
  • n. an eye having a single lens

Etymologies

Latin, diminutive of oculus, eye.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Latin ocellus ("little eye"), from oculus ("eye") (Wiktionary)

Examples

  • In dinoflagellates, four types of eye-spots are known: type A, an independent structure that is not membrane-bound; type B, an independent membrane-bound structure; type C, structure as part of a chloroplast; and type D, an elaborate eye-like structure called ocellus

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  • All have compound eyes and may or may not have a single ocellus over each eye.

    Insecta (Aquatic)

  • Aquila In nubibus Imperator literatorum, columen literarum, abyssus eruditionis, ocellus Europae, Scaliger.

    Anatomy of Melancholy

  • The Ciona βγ-crystallin is only expressed in the palps and in the otolith, the pigmented sister cell of the light-sensing ocellus.

    Insight Into Eye Evolution Deals Blow To Intelligent Design - The Panda's Thumb

  • There is genetic variation among individuals for genes that affect ocellus number, but the developmental effects of that variation are prevented by the system of buffering (Waddington 1953, 1957).

    The Genotype/Phenotype Distinction

  • If a sufficiently large perturbation is introduced, the developmental buffering capacity is overcome and the genetic variation for ocellus number is revealed.

    The Genotype/Phenotype Distinction

  • The head oblong, slightly narrowed posteriorly and emarginate behind, longitudinally striated, the striæ diverging from the centre at the anterior ocellus; at half the distance between the posterior ocelli and the margin of the vertex the striæ are transverse.

    Journal of the Proceedings of the Linnean Society - Vol. 3 Zoology

  • Black; the head and thorax strongly punctured; the mandibles, clypeus, a line above extending to the anterior ocellus, the emargination of the eyes, a spot at their vertex and a line at their outer orbits, yellow; the antennæ reddish-yellow, with the scape pale yellow in front and a narrow fuscous line above; the yellow marking more or less stained orange.

    Journal of the Proceedings of the Linnean Society - Vol. 3 Zoology

  • Black; the face above the clypeus, as high as the anterior ocellus, reddish-yellow; the extreme edge of the clypeus, the labrum and base of the mandibles ferruginous; the antennæ reddish-yellow.

    Journal of the Proceedings of the Linnean Society - Vol. 3 Zoology

  • Frontal lobes: in Psyllidae, two lobes or swellings more or less completely divided by a suture in which an ocellus is situated.

    Explanation of Terms Used in Entomology

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