National Geographic magazine's February issue features a close-up look at the eyes of various species. Inside the Eye: Nature's Most Exquisite Creation, an article by Ed Yong, discusses the anatomy and evolution of eyes, looking at how a creature's environment contributes to the function, form and appearance of its eyes.

animals eyes
The eye of a western lowland gorilla (Gorilla gorilla gorilla)David Liittschwager/National Geographic
animals eyes
The eye of a white rhinoceros (Ceratotherium simum)David Liittschwager/National Geographic
animals eyes
The eye of a southern ground-hornbill (Bucorvus leadbeateri)David Liittschwager/National Geographic
animals eyes
The eye of a domestic dog (Canis lupus familiaris)David Liittschwager/National Geographic
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The eye of a red-eyed tree frog (Agalychnis callidryas)David Liittschwager/National Geographic
animals eyes
The eye of a gargoyle gecko (Rhacodactylus auriculatus)David Liittschwager/National Geographic
animals eyes
The eye of a scarlet macaw (Ara macao)David Liittschwager/National Geographic
animals eyes
The eye of a Cuban rock iguana (Cyclura nubile nubila)David Liittschwager/National Geographic
animals eyes
The eye of a common ostrich (Struthio camelus)David Liittschwager/National Geographic
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The eye of a blue-eyed black lemur (Eulemur flavifrons)David Liittschwager/National Geographic
animals' eyes
National Geographic

Yong says there is an almost endless variation of eyes in the animal kingdom. Some see only in black and white, while others perceive the full rainbow and beyond, to wavelengths invisible to human. Some can't even gauge the direction of incoming light; others can spot running prey miles away. The smallest animal eyes, on the heads of fairy wasps, are barely bigger than an amoeba; the biggest are the size of dinner plates, and belong to gigantic squid species.

"To understand how eyes evolved," writes Yong, "Scientists need to do more than examine their structures. They need to ... understand how animals use their eyes."

Read the full article in National Geographic's February 2016 issue.