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Spiders do not have compound eyes, but instead have several pairs of simple eyes with each pair adapted for a specific task or tasks. The principal and secondary eyes in spiders are arranged in four, or occasionally fewer, pairs. Only the principal eyes have moveable retinas. The secondary eyes have a reflector at the back of the eyes.
Most other living chelicerates have lost their lateral compound eyes, evolving simple eyes in their place that vary in number. [24] Up to five pairs of lateral eyes occur in scorpions, whereas three pairs of lateral eyes are typical for Tetrapulmonata (e.g., spiders; Amblypygi). [25]
Compound eye of Antarctic krill as imaged by an electron microscope. A compound eye is a visual organ found in arthropods such as insects and crustaceans.It may consist of thousands of ommatidia, [1] which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which distinguish brightness and color.
The eyes can be categorised by their location and are divided into the anterior median eyes (AME), anterior lateral eyes (ALE), posterior median eyes (PME), and posterior lateral eyes (PLE). The exact arrangement of the eyes varies significantly by family, and to a lesser degree genus, so is often used as a diagnostic feature to identify or ...
In vertebrate eyes, the nerve fibers route before the retina, blocking some light and creating a blind spot where the fibers pass through the retina. In cephalopod eyes, the nerve fibers route behind the retina, and do not block light or disrupt the retina. 1 is the retina and 2 the nerve fibers. 3 is the optic nerve. 4 is the vertebrate blind ...
The human eye, showing the iris and pupil. In 1802, philosopher William Paley called it a miracle of "design."In 1859, Charles Darwin himself wrote in his Origin of Species, that the evolution of the eye by natural selection seemed at first glance "absurd in the highest possible degree". [3]
Image credits: historycoolkids The History Cool Kids Instagram account has amassed an impressive 1.5 million followers since its creation in 2016. But the page’s success will come as no surprise ...
A lobster is heavily cephalized, with eyes, antennae, multiple mouthparts, and the brain (inside the armoured exoskeleton), all concentrated at the animal's head end. Cephalization is an evolutionary trend in animals that, over many generations, the special sense organs and nerve ganglia become concentrated towards the front of the body where ...