Reference Terms
from Wikipedia, the free encyclopedia
Pupil
In the eye, the pupil is the opening in the middle of the iris. It appears black because most of the light entering it is absorbed by the tissues inside the eye. In humans and many animals (but few fish), the size of the pupil is controlled by involuntary contraction and dilation of the iris, in order to regulate the intensity of light entering the eye. This is known as the pupillary reflex. In bright light, the human pupil has a diameter of about 1.5 millimeters, in dim light the diameter is enlarged to about 8 millimeters. The shape of the pupil varies between species. Common shapes are circular or slit-shaped, although more convoluted shapes can be found in aquatic species. The reasons for the variation in shapes are complex; the shape is closely related to the optical characteristics of the lens, the shape and sensitivity of the retina, and the visual requirements of the species.
Related Stories
1
2
Plants & Animals News
October 27, 2025
Oct. 27, 2025 — Extinction rates are not spiraling upward as many believe, according to a large-scale study analyzing 500 years of data. Researchers found that species losses peaked about a century ago and have decreased since, with different drivers shaping past ...
Oct. 27, 2025 — A team of researchers has developed a floral-scented fungus that tricks mosquitoes into approaching and dying. The fungus emits longifolene, a natural scent that irresistibly draws them in. It’s harmless to humans, inexpensive to produce, and ...
Oct. 26, 2025 — Dinosaurs weren’t dying out before the asteroid hit—they were thriving in vibrant, diverse habitats across North America. Fossil evidence from New Mexico shows that distinct “bioprovinces” of dinosaurs existed until the very end. Their ...
Oct. 26, 2025 — New research shows that hippos lived in central Europe tens of thousands of years longer than previously thought. Ancient DNA and radiocarbon dating confirm they survived in Germany’s Upper Rhine Graben during a milder Ice Age phase. Closely ...
Oct. 25, 2025 — Reptiles don’t just pee, they crystallize their waste. Researchers found that snakes and other reptiles form tiny uric acid spheres, a water-saving evolutionary trick. This discovery could illuminate how to prevent gout and kidney stones in ...
Oct. 23, 2025 — In the mist-shrouded mountains of New Guinea, a Czech researcher has achieved a world-first — capturing photos, video, and data of the elusive Subalpine Woolly Rat, Mallomys istapantap. Once known only from museum specimens, this giant, shaggy ...
Oct. 22, 2025 — Common dolphins in the North Atlantic are living significantly shorter lives, with female longevity dropping seven years since the 1990s. Researchers found this decline by analyzing stranded dolphins, revealing a 2.4% drop in population growth ...
Oct. 20, 2025 — Naked mole-rats seem to have found nature’s cheat code for longevity. Scientists discovered that small tweaks in one of their proteins make it better at fixing DNA damage, helping the animals resist aging. Even fruit flies with the same changes ...
Oct. 19, 2025 — Researchers have developed a light-emitting sugar probe that exposes how marine microbes break down complex carbohydrates. The innovative fluorescent tool allows scientists to visualize when and where sugars are degraded in the ocean. This ...
Oct. 18, 2025 — EMBL researchers created SDR-seq, a next-generation tool that decodes both DNA and RNA from the same cell. It finally opens access to non-coding regions, where most disease-associated genetic variants lie. By revealing how these variants affect gene ...
Oct. 11, 2025 — Researchers have unearthed South America’s first amber deposits containing ancient insects in an Ecuadorian quarry, offering a rare 112-million-year-old glimpse into life on the supercontinent ...
Oct. 10, 2025 — Coccolithophores, tiny planktonic architects of Earth’s climate, capture carbon, produce oxygen, and leave behind geological records that chronicle our planet’s history. European scientists are uniting to honor them with International ...
Latest Headlines
updated 12:56 pm ET
Oct. 26, 2025 — Life’s origin story just became even more mysterious. Using mathematics and information theory, Robert G. Endres of Imperial College London found that the spontaneous emergence of life from ...
Oct. 26, 2025 — Scientists have found that mushrooms can act as organic memory devices, mimicking neural activity while consuming minimal power. The Ohio State team grew and trained shiitake fungi to perform like ...
Oct. 25, 2025 — In a groundbreaking discovery, scientists at Trinity College Dublin have identified a "universal thermal performance curve" that governs how all living organisms respond to temperature. This finding ...
Oct. 24, 2025 — Scientists have unveiled Khankhuuluu, a new Mongolian dinosaur species that predates and closely resembles early Tyrannosaurs. With its long snout, small horns, and lean build, it represents a ...
Oct. 24, 2025 — MIT researchers discovered that the genome’s 3D structure doesn’t vanish during cell division as previously thought. Instead, tiny loops called microcompartments remain (and even strengthen) ...
Oct. 22, 2025 — Under the sea, green algae have evolved a clever way to handle too much sunlight. Scientists found that a special pigment called siphonein acts like a natural sun shield, protecting the algae’s ...
Oct. 19, 2025 — Mars’ north polar vortex locks its atmosphere in extreme cold and darkness, freezing out water vapor and triggering a dramatic rise in ozone. Scientists found that the lack of sunlight and moisture ...
Oct. 19, 2025 — Researchers discovered the gene that gives a rare wheat variety its unusual “triple-grain” trait. When switched on, the gene helps wheat flowers produce extra grain-bearing parts. The finding ...
Oct. 16, 2025 — Scientists discovered true teeth growing on the head of the spotted ratfish, a distant shark relative. The toothed structure, called a tenaculum, helps males hold onto females during mating. Genetic ...
Oct. 15, 2025 — A parasitic worm uses static electricity to launch itself onto flying insects, a mechanism uncovered by physicists and biologists at Emory and Berkeley. By generating opposite charges, the worm and ...