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In humans, the pupil is circular, but its shape varies between species; some cats, reptiles, and foxes have vertical slit pupils, goats and sheep have horizontally oriented pupils, and some catfish have annular types. [3] In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop.
[47] [49] The ears are rounded and the eyes have a round pupil. [47] The snout ends in a triangular, pink tip with small black dots, the number of which increase with age. [50] The tiger's skull is robust, with a constricted front region, proportionally small, elliptical orbits, long nasal bones and a lengthened cranium with a large sagittal crest.
Its appearance is similar to the western, and eastern tiger swallowtails, but has narrower black stripes and usually two tails on each hindwing (rather than only one). Most two-tails have a black "slit pupil" in the orange eyespot on each hindwing, never present in western tiger.
The smalltooth sand tiger has a bulky body with a long, bulbous, slightly flattened snout. The eyes are medium-sized, with large, round pupils (as opposed to slit-like in the grey nurse shark), and lack nictitating membranes. The mouth is large and filled with projecting teeth.
Several species of Felidae (cats) and snakes have vertically elongated (slit) pupils, advantageous for nocturnal ambush predators as it helps them to estimate the distance to prey in dim light; diurnal and pursuit predators in contrast have round pupils. [30]
Some aquatic animals have a second eyelid in each eye which refracts the light and helps them see clearly both above and below water. Most creatures will automatically react to a threat to its eyes (such as an object moving straight at the eye, or a bright light) by covering the eyes, and/or by turning the eyes away from the threat.
Few people have spent time gazing into a sheep’s eyes, but if you have, you may have noticed something very strange about their pupils. Instead of being round, as is the case with humans, they ...
However, this is not always the case and many albino animals do not have pink pupils. [9] The common belief that all albinos have pink pupils results in many albinos being incorrectly labeled as 'leucistic'. The neural crest disorders that cause leucism do not result in pink pupils and therefore most leucistic animals have normally colored eyes.