pupil


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pupil:

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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.

Pupil

 

the opening in the iris through which light rays enter the eye.

The dimensions of the pupil change according to the amount of light present: the pupil dilates in darkness, under emotional excitement and painful sensations, or with the injection of atropine or adrenalin into the body; it contracts in bright light. Change in the dimensions of the pupil is regulated by fibers of the autonomic nervous system and is accomplished by means of two smooth muscles located in the iris—the sphincter, which contracts the pupil, and the dilator, which expands it. In higher vertebrates, changes in the dimensions of the pupil are produced reflexively by the effect of light on the retina of the eye; in lower vertebrates, these changes are produced by the direct action of light on contrac-tile formations in the pupil. The pupil is usually round or slitlike; in some fish (for example, in a number of sharks, rays, and flounder) and mammals (for example, in sperm whales and dolphins) a projection of the iris, suspended from the superior edge of the pupil, can cover the pupil completely in the presence of intense illumination. In man the pupil is round; its diameter may change from 1.1 mm to 8 mm. Changes in the shape, dimensions, and speed of reaction of the pupil (so-called pupillary reflexes) are of diagnostic significance in eye diseases.

O. G. STROEVA

pupil

[′pyü·pəl]
(anatomy)
The contractile opening in the iris of the vertebrate eye.

pupil

1
1. a student who is taught by a teacher, esp a young student
2. Civil and Scots law a boy under 14 or a girl under 12 who is in the care of a guardian

pupil

2
the dark circular aperture at the centre of the iris of the eye, through which light enters
References in classic literature ?
Master and pupil understood each other, and Ginevra no longer feared to ask:--
The baffled pupil returned for the bag, expressing surprise at her carelessness; but this act of Servin's was to her fresh proof of the existence of a mystery, the importance of which was evident.
His pupil was a little surprised by this striking in with so sudden and decided and emotional an objection, but took it as a proof of the master's interest in himself.
The school at which young Charley Hexam had first learned from a book--the streets being, for pupils of his degree, the great Preparatory Establishment in which very much that is never unlearned is learned without and before book--was a miserable loft in an unsavoury yard.
After his death, Miss Ladd had taken Netherwoods (as the place was called), finding her own house insufficient for the accommodation of the increasing number of her pupils.
There were rooms unoccupied, even when the limit assigned to the number of pupils had been reached.
Only when her pupils quitted the establishment, or when they were about to be married, and once, when poor Miss Birch died of the scarlet fever, was Miss Pinkerton known to write personally to the parents of her pupils; and it was Jemima's opinion that if anything could console Mrs.
I descended to the schoolroom with no remarkable eagerness to join my pupils, though not without some feeling of curiosity respecting what a further acquaintance would reveal.
After this she looked in upon me once or twice, during the absence of my pupils, to enlighten me concerning my duties towards them.
When your pupil was a little innocent child, did she ever amuse herself by building a house of cards?
Perhaps you would prefer talking to me about these two pupils of yours?
I had thought I should have been allowed at least 3 days to prepare; but it is a bad omen to commence any career by hesitation, so I just stepped to the professor's desk near which we stood, and faced the circle of my pupils.