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The term "ocellus" (plural ocelli) is derived from the Latin oculus (eye), and literally means "little eye". In insects, two distinct ocellus types exist: [9] dorsal (top-most) ocelli, and lateral ocelli (often referred to as ocelli and stemmata, respectively), most insects have dorsal ocelli while stemmata are found in the larvae of some ...
Ocelli (the plural of ocellus) are a type of simple eye, or eyespot. They are photoreceptive, but very simple; differing from complex eyes with compound lenses, ocelli cannot morph the sensation of light into a complete image, and are utilized to sense movement and the absence and presence of light.
[11] [21] The ocelli are not homologous to the simple eyes of caterpillars which are differently named as stemmata. [5] The ocelli of Lepidoptera are reduced externally in some families; where present, they are unfocussed, unlike stemmata of larvae which are fully focussed. The utility of ocelli is not understood at present. [5]
Some reptiles, such as the sand lizard of Europe, have eyespots; in the sand lizard's case, there is a row of spots along the back, and a row on each side. [12]Many species of cat, including Geoffroy's cats, jungle cats, pampas cats, and servals, have white markings, whether spots or bars, on the backs of their ears; it is possible that these signal "follow me" to the young of the species.
Neuropterans are soft-bodied insects with relatively few specialized features. They have large lateral compound eyes, and may or may not also have ocelli.Their mouthparts have strong mandibles suitable for chewing, and lack the various adaptations found in most other holometabolan insect groups.
Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain.
Chalcidoid wasps are small wasps (most within the range 0.5–5 mm). However the group does include the smallest known insect (Dicopomorpha echmepterygis males have a body length of 0.14–0.24 mm); the largest chalcidoids include Leucospis gigas with a body length of up to 21 mm [2] and Doddifoenus wallacei with a body length of up to 19.6 mm. [3]
A micrograph of a single ocelloid; scale bar = 5 μm. [1] A negative staining transmission electron micrograph of an ocelloid (white box), indicating the hyalosome (H) and retinal body (R), as well as a portion of the piston (Ps).