Ocellus
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An ocellus (plural: ocelli) is a type of photoreceptor organ in animals. Also called "simple eyes", ocelli are miniature eyes capable of sensing light but not distinguishing its direction. See also stemmata, which are structurally similar.
Ocelli are found in many invertebrates. Insects in particular have two types of ocelli, dorsal ocelli and lateral ocelli.
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[edit] Dorsal Ocelli
Dorsal ocelli are light-sensitive organs on the dorsal surface or on the top of the head. There are generally three, forming a triangle.
They consist of a few tens of rod cells covered with a corneal lens. Insects with dorsal ocelli also have compound eyes, but lateral ocelli are the only eyes of the larvae of several orders of insects (fleas, springtails, silverfish, and Strepsiptera). Some species dorsal ocelli may contain several hundreds of retinula cells, such as locusts.
[edit] Lateral Ocelli
Lateral ocelli have a mixture of rod cells and cone cells and are found on the sides of the head, one to six on each side.
[edit] Function
In insects, ocelli are involved (along with compound eyes) in the horizon-detecting response, decreasing the latency between horizon changes and the insect's response.
The term ocellus is also applied to eye-like markings. In many species, such markings provide protection by appearing threatening or by diverting attention away from vital body parts (See automimicry).
[edit] External links
- John R. Meyer, Photoreceptors
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