Torn at the Genes Case Study - amazonia.fiocruz.br

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Insect wings are adult outgrowths of the insect exoskeleton that enable insects to fly. They are found on the second and third thoracic segments the mesothorax and metathoraxand the two pairs are often referred to as the forewings and hindwingsrespectively, though a few insects lack hindwings, even rudiments. The wings are strengthened by a number of longitudinal veins, which often have cross-connections that form closed "cells" in the membrane extreme examples include the dragonflies and lacewings.

The patterns resulting from the Cxse and cross-connection of the wing veins are often diagnostic for different evolutionary lineages and can be used Totn identification to the family or even genus level in many orders of insects. Physically, some insects move their flight muscles directly, others indirectly. In insects with direct flight, the wing muscles directly attach to the wing base, so that a small downward movement Torn at the Genes Case Study the wing base lifts the wing itself upward.

Those insects with indirect flight have muscles that attach to and deform the thorax, causing the wings to move as well. The wings are present in only one sex often the male in some groups such as velvet ants and Strepsipteraor are selectively lost in "workers" of social insects such as ants and termites. Rarely, the female is winged but the male not, as in fig wasps. In some cases, wings are produced only at particular times in the life cycle, such as in the dispersal phase of aphids.

Wing structure and colouration often vary with morphssuch as in the aphidsmigratory phases of locusts and polymorphic butterflies. At rest, the wings may be held Torn at the Genes Case Study, or folded a number of times along specific patterns; most typically, it is the hindwings which are folded, but in a few groups such as the vespid waspsit is the forewings. How and why insect wings evolved is not well understood and there has been a long-standing debate about their origins.

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During the 19th century, the question of insect wing evolution originally rested on two main positions. One position postulated insect wings evolved from pre-existing structures, while the second proposed insect wings were entirely novel formations. Among these include: gills, respiratory appendages of legs, and lateral paranotal and posterolateral projections of the thorax to name a few. Today, there are three main theories on the origins of insect flight.

These theories are referred to as the paranotal lobe theory, the gill theory and the dual theory of insect wing evolution.

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These theories postulate that wings either developed from paranotal lobes, source of the thoracic terga ; [5] that they are modifications of movable abdominal gills as found on aquatic naiads of mayflies ; [5] or that insect wings arose from the fusion of pre-existing endite and exite structures each with pre-existing articulation and tracheation. Each of the wings consists of a thin membrane supported by a system of veins. The membrane is formed by two layers of integument closely apposed, while the veins are formed where the two layers remain separate; sometimes the lower cuticle is thicker and more heavily sclerotized under a vein.

Within each of the major veins there is a nerve and a tracheaand, since the cavities of the veins are connected with the go herehemolymph can flow into the wings. As the wing develops, the dorsal and ventral integumental Torn at the Genes Case Study become closely apposed over most of their area forming the wing membrane.

The remaining areas form channels, the future veins, in which the nerves and tracheae may occur. The cuticle surrounding the veins becomes thickened and more heavily sclerotized to provide strength and rigidity to the wing.

Two types of hair may occur on the wings: microtrichia, which are small and irregularly scattered, and macrotrichia, which are larger, socketed, and may be restricted to veins. The scales of Lepidoptera and Trichoptera are highly modified macrotrichia. In some very small insects, the https://amazonia.fiocruz.br/scdp/blog/culture-and-selfaeesteem/the-conflict-of-the-american-civil-rights.php may be greatly reduced. In Chalcidoidea Chalcid waspsfor instance, only the subcosta and part of the radius are present. Conversely, an increase in venation may occur by the branching of existing veins to produce accessory veins or by the development of additional, intercalary veins between the original ones, as in the wings of Orthoptera grasshoppers and crickets.

Large numbers of cross-veins are present in some insects, and they may form a reticulum as in the qt of Odonata dragonflies and damselflies and at the base of the forewings of Tettigonioidea and Acridoidea katydids and grasshoppers respectively.

The archedictyon is the name given to a hypothetical scheme of wing venation proposed for the very first winged insect. It is based on a combination of speculation and fossil data. Since all winged insects are believed to have teh from a common ancestor, the archedictyon represents the Torn at the Genes Case Study that has been modified and streamlined by natural selection for million years.]