用戶:Koala0090/昆蟲形態學

昆蟲形態學
昆蟲的身體構造 A：頭節；B：胸節；C：腹節

1. 觸角
2. 單眼 （下）
3. 單眼（上）
4. 複眼
5. 腦（頭神經節）
6. 前胸
7. 背血管
8. 氣管（軀幹上有氣門）
9. 中胸
10. 後胸
11. 前翅
12. 後翅
13. 中腸 （胃）
14. 背管 （心臟）
15. 卵巢
16. 後腸 （小腸、直腸、肛門）
17. 肛門
18. 產卵管
19. 神經節
20. 馬氏管
21. 跗節墊
22. 爪
23. 跗節
24. 脛節
25. 股節
26. 轉節
27. 前腸
28. 胸神經節
29. 基節
30. 唾腺
31. 食道下神經節
32. 口器

昆蟲形態學是研究及描述昆蟲身體形態的學科。由於昆蟲與其他節肢動物在演化上相關，兩者的術語會相當類似。昆蟲具有三個能與其他節肢動物鑑別的主要特徵：昆蟲的身體分成三個部分（頭節、胸節和腹節）；擁有三對足；口器位於頭殼（head capsule）之外。口器的位置將昆蟲和他們同是六足亞門但非昆蟲的近親區分開，包含原尾目、雙尾目和彈尾目等。

昆蟲各類群間的解剖學差異可能極大。有身長 0.3 mm 的纓小蜂（fairflies），也有展翅寬可達 30 cm 的強喙夜蛾（great owlet moth）；有些物種有很多眼睛，有些卻一個都沒有；有些物種具有發達的翅膀，有些卻連翅膀都沒有；有些物種則演化出擅長奔跑、跳躍、游泳，甚至挖掘的足；這些特化構造，使昆蟲幾乎佔據了地球上除深海和南極洲之外的所有的生態棲位。本篇將介紹昆蟲的基本結構，以及身體各部分的一些重要變異，並介紹一些形容昆蟲解剖構造的術語及其定義。

解剖學概述

昆蟲就如同其他節肢動物一樣，僅有外骨骼而沒有內骨骼。外骨骼是一種通常由幾丁質組成的堅硬外殼，可以保護並支撐身體。昆蟲身體可區分為三個體段：頭、胸節和腹節。頭部專門感知外界和攝取食物；胸節具有足和翅（有些昆蟲無翅）的基部，專門進行運動；腹節則負責消化、呼吸、排泄，以及繁殖。雖然所有昆蟲身體三體段的功能相似，基本結構上卻有巨大的差別，不同群體的翅、腿、觸角和口器能明顯的被做出區別。

外部型態

外骨骼

主條目：表皮 (昆蟲)

昆蟲的外骨骼又稱表皮層（cuticle），表皮層又可分為兩層；外層稱作上表皮（epicuticle），薄、覆蓋蠟、防水且不含幾丁質。在其底下為由幾丁質組成的原表皮（procuticle），且厚於上表皮。原表皮可分為2層，外層是外表皮（exocuticle），內層是內表皮（endocuticle）。內表皮是由無數層纖維性幾丁質和蛋白質所構成，質地堅韌且具彈性，如同三明治般層層交疊而成；外表皮骨質化，質地較為堅硬。許多身體較軟昆蟲的外表皮非常薄，特別是幼蟲階段（如毛蟲）。就化學性質而言，幾丁質是N-乙酰葡糖胺的長鏈聚合物，一種葡萄糖的衍生物。在未經化學修飾前，幾丁質易彎曲、半透明、具彈性且堅韌。但就節肢動物而言，幾丁質往往以經過修飾的形式出現，嵌入在硬化的蛋白質網格中，形成大部分的外骨骼。純幾丁質材質類似皮革，但當外面裹着碳酸鈣時，他的硬度會大幅提升。修飾與未修飾的差別可以透過比較毛蟲（未修飾）和甲蟲（已修飾）的體壁的得知。

外表皮及其底部的內基底膜，源自於胚胎期間的單層柱狀或立方上皮細胞。內表皮則儲備了昆蟲大部分的構成原料。表皮提供肌肉支持軀體和保護昆蟲。然而，因為表皮無法增長，外部骨化的部分會週期性的脫落，也就是蛻皮（ecdysis）。當快要蛻皮時，外表皮的大部分物質會被吸收。在蛻皮時，舊的表皮和上皮分離（此程序稱為離解作用（apolysis）），催化蛻皮的液體酶被釋放至舊表皮和上皮之間，同時透過消化內表皮（endocuticle）使外表皮（exocuticle）脫離，並將消化後的物質回收做為新表皮的原料。當新的表皮完全形成後，舊的上表皮和外表皮即會脫落。

昆蟲身體的四個主要部分是：背板（tergum）、胸板（Sternum），和兩個側板（pleura）。外骨骼上硬化扁平構造叫做骨片（sclerites），骨片可以再細分為背片（tergites）、腹片（sternites）和側片（pleurites）。

頭節

蝗蟲的頭部：a：觸角，b：單眼，c：頭頂；d：複眼，e：後頭區 f:gena; g:pleurostoma; h:mandible; i:labial palp; j:maxillary palps; k:maxilla; l:labrum; m:clypeus; n:frons

天牛科的甲蟲幼蟲，圖中可以看到幼蟲的頭部骨化，身體的骨化程度較低，維持柔軟的狀態。

Larva of Syrphid fly, member of Cyclorrhapha, without epicranium, almost without sclerotisation apart from its jaws.

大部分昆蟲的頭皆包覆在堅硬且骨化的外骨骼頭殼（head capsule）或上頭殼（epicranium）之中，除了那些幼蟲期沒有完全骨化的物種，大部分是內生翅群；但就連無骨化或是稍微骨化的幼蟲都傾向擁有完全骨化的上頭殼，例如鞘翅目和膜翅目的幼蟲，而環裂群（Cyclorrhapha）的幼蟲則幾乎沒有頭殼。

上頭殼具有大部分的主要感覺器官，包括觸角（antennae）、單眼（ocelli）和複眼（compound eyes）。口器也位於上頭殼上。成蟲的頭殼不分節，但其實在胚胎期間頭殼是由6個分節癒合而成，每節都擁有一對附肢，包括口器。但現代的昆蟲不是每節都有可見的附肢。

在昆蟲眾多的目之中，直翅目表現出最多的頭部多樣性，包括癒合處（sutures）和骨片（sclerites）。頭頂（vertex）位於下口式（hypognathous）或是後口式（opisthognathous）之頭型物種的複眼之間。在前口式（prognathous）的昆蟲中，頭頂不存在於複眼之間，而是常常在單眼附近。這是由於頭部的主軸旋轉了90°，才得以與身體的主軸平行。在某些物種中，這個部位有特殊的專有名詞描述。

The ecdysial suture is made of the coronal, frontal, and epicranial sutures plus the ecdysial and cleavage lines, which vary among different species of insects. The ecdysial suture is longitudinally placed on the vertex and separates the epicranial halves of the head to the left and right sides. Depending on the insect, the suture may come in different shapes: like either a Y, U, or V. Those diverging lines that make up the ecdysial suture are called the frontal or frontogenal sutures. Not all species of insects have frontal sutures, but in those that do, the sutures split open during ecdysis, which helps provide an opening for the new instar to emerge from the integument.

蛻皮縫（ecdysial suture）是由上面（coronal）縫、前面（frontal）縫、頭上縫（epicranial suture）加上蛻皮線（ecdysial "line", 異於前述之ecdysial "suture"）和裂線（cleavage line）組成，此縫在昆蟲物種中呈現極大的相異性。蛻皮縫由頂部（vertex）往下縱向延伸並將上頭殼（epicranial）分割成左右兩半。不同的昆蟲的蛻皮縫呈現不同形狀，如Y形、U形或V形。這些組成蛻皮縫的切割線稱為額縫（frontal suture）或是額頰縫（frontogenal suture）。並非所有的昆蟲都擁有額縫，但是在那些具額縫的昆蟲中，這些縫會在蛻皮時分裂剝離，提供一個開口幫助新一齡的昆蟲從舊體壁中鑽出。

The frons is that part of the head capsule that lies ventrad or anteriad of the vertex. The frons varies in size relative to the insect, and in many species the definition of its borders is arbitrary, even in some insect taxa that have well-defined head capsules. In most species, though, the frons is bordered at its anterior by the frontoclypeal or epistomal sulcus above the clypeus. Laterally it is limited by the fronto-genal sulcus, if present, and the boundary with the vertex, by the ecdysial cleavage line, if it is visible. If there is a median ocellus, it generally is on the frons, though in some insects such as many Hymenoptera, all three ocelli appear on the vertex. A more formal definition is that it is the sclerite from which the pharyngeal dilator muscles arise, but in many contexts that too, is not helpful. In the anatomy of some taxa, such as many Cicadomorpha, the front of the head is fairly clearly distinguished and tends to be broad and sub-vertical; that median area commonly is taken to be the frons.

額部（frons）是頭殼的一部分，位於頂部的前面（anteriad）和腹面（ventrad）。額部的大小根據不同的昆蟲物種而異，在許多物種中額部邊界的定義並不明確，甚至是那些具有明確定義頭殼的昆蟲類群。在大部分的物種中，額部的邊界在頭楯（clypeus）上的額楯溝（frontoclypeal sulcus）或是口上溝（epistomal sulcus）；而側面的邊界則是位於前額與頰之間的溝（fronto-genal sulcus）；有些物種上部還有一條邊界位於頭頂（vertex）的蛻皮線（ecdysial cleavage line）。如果某物種具有中央單眼（median ocellus），通常位於額部上，然而，在某些物種上，如大多數的膜翅目，三顆單眼都位於頭頂。比較正式的定義是 : 從咽擴張肌（pharyngeal dilator muscles）一路往上骨化，然而此定義在大部分情況沒有太大的幫助。在某些類群的解剖學中，如蟬下目（Cicadomorpha），頭部的前面觀構造可以清楚的分辨，而且傾向於近垂直的構造；於是中間的部分通常被視為額部。

thumbs

The clypeus is a sclerite between the face and labrum, which is dorsally separated from the frons by the frontoclypeal suture in primitive insects. The clypeogenal suture laterally demarcates the clypeus, with the clypeus ventrally separated from the labrum by the clypeolabral suture. The clypeus differs in shape and size, such as species of Lepidoptera with a large clypeus with elongated mouthparts. The cheek or gena forms the sclerotized area on each side of the head below the compound eyes extending to the gular suture. Like many of the other parts making up the insect's head, the gena varies among species, with its boundaries difficult to establish. For example, in dragonflies and damselflies, it is between the compound eyes, clypeus, and mouthparts. The postgena is the area immediately posteriad, or posterior or lower on the gena of pterygote insects, and forms the lateral and ventral parts of the occipital arch. The occipital arch is a narrow band forming the posterior edge of the head capsule arching dorsally over the foramen. The subgenal area is usually narrow, located above the mouthparts; this area also includes the hypostoma and pleurostoma. The vertex extends anteriorly above the bases of the antennae as a prominent, pointed, concave rostrum. The posterior wall of the head capsule is penetrated by a large aperture, the foramen. Through it pass the organ systems, such as nerve cord, esophagus, salivary ducts, and musculature, connecting the head with the thorax.

頭楯（clypeus）是臉部和上唇（labrum）之間的一個骨片（sclerite）。原始昆蟲的頭楯背面被額部上的額楯縫線（frontoclypeal suture）分割，而側面的界線則是頰楯縫線（clypeogenal），腹面界線則是上唇的上唇楯縫線（clypeolabral suture）。不同的物種頭楯大小形狀相異，如鱗翅目具有較大的頭楯和加長的口器。頰部（gena）在複眼下方頭部兩側形成骨化的區塊直至外咽片縫（gular suture）。如同其他組成昆蟲頭部的區塊一般，頰部的外形因物種不同而異，而相異的情況族繁不及備載。

舉例來說，蜻蛉目的頰部位於複眼（compound eyes）、頭楯（clypeus）及口器（mouthparts）之間。在有翅亞綱的昆蟲中，頰部後方或下方的區域稱為後頰（postgena），且形成頭弓（occipital arch）的側邊及腹邊。頭弓是一個狹帶，形成頭殼的後緣，且在背側拱起蓋過後頭孔（foramen）。頰部之下的區域通常狹窄，位於口器之上。頰下區通常包含口下區（hypostoma）及口側區（pleurostoma）。頭頂向前延伸至觸角基部上方，形成一個突出的尖端，有凹面的突。頭殼的後方穿過一個孔洞，也就是後頭孔。從後頭孔之間穿過的是器官系統，如神經節、食道（esophagus）、唾液管（salivary ducts）及連接頭部與胸節的肌肉。

On the posterior aspect of the head are the occiput, postgena, occipital foramen, posterior tentorial pit, gula, postgenal bridge, hypostomal suture and bridge, and the mandibles, labium, and maxilla. The occipital suture is well founded in species of Orthoptera, but not so much in other orders. Where found, the occipital suture is the arched, horseshoe-shaped groove on the back of the head, ending at the posterior of each mandible. The postoccipital suture is a landmark on the posterior surface of the head, and is typically near the occipital foremen. In pterygotes, the postocciput forms the extreme posterior, often U-shaped, which forms the rim of the head extending to the postoccipital suture. In pterygotes, such as those of Orthoptera, the occipital foramen and the mouth are not separated. The three types of occipital closures, or points under the occipital foramen that separate the two lower halves of the postgena, are: the hypostomal bridge, the postgenal bridge, and the gula. The hypostomal bridge is usually found in insects with hypognathous orientation. The postgenal bridge is found in the adults of species of higher Diptera and aculeate Hymenoptera, while the gula is found on some Coleoptera, Neuroptera, and Isoptera, which typically display prognathous-oriented mouthparts.

頭部的後方為後頭區（occiput）、後頰、後頭孔、後幕狀骨孔（posterior tentorial pit）、口下縫（hypostomal suture）、口下接區（bridge）、大顎、下唇及小顎。直翅目的頭縫線能被明顯的觀察到，其他目則非。頭縫為頭後方拱狀、馬蹄形的溝槽，收於大顎的後方。後頭後縫（postoccipital suture）是區分頭部後方的標線，通常位於後頭孔附近。在有翅亞綱中，後頭（postocciput）位於極後方，通常為Ｕ字形，通常形成頭部延伸至後頭後縫的邊緣。在有翅亞綱中，例如直翅目，後頭孔和口器相連。頭部的閉合處有三種，也就是位於後頭孔下方，將後頰區分為兩個半區的點，分別為：口下帶（hypostomal bridge）、後頰帶（postgenal bridge）、外咽片（gula）。口下帶通常可在下口式（hypognathous orientation）昆蟲中發現，後頰帶可以在大型雙翅目成蟲及膜翅目中的針尾下目（aculeate）成蟲中發現，外咽片則可在鞘翅目、脈翅目、等翅下目（白蟻）等通常為前口式的昆蟲中發現。

複眼及單眼

Most insects have one pair of large, prominent compound eyes composed of units called ommatidia （ommatidium, singular）, possibly up to 30,000 in a single compound eye. This type of eye gives less resolution than eyes found in vertebrates, but it gives acute perception of movement. There can also be an additional two or three ocelli, which help detect low light or small changes in light intensity. The image perceived is a combination of inputs from the numerous ommatidia, located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess very large view angles, and can detect fast movement and, in some cases, the polarization of light.

大部分的昆蟲都有一對主要的複眼（compound eye），複眼由小眼（ommatidia, 單數型：ommatidum）組成，一個複眼有可能由多達30000個小眼組成。這種形式的眼睛提供的解像度相較於脊椎動物的眼睛來的低，但複眼能精準的感知移動的物種。同時，亦有可能生有2或3個單眼（ocelli），單眼能偵測低光源和微小的光密度變化。複眼感知到的影像是由無數個位於凸面上的小眼所輸入的影像組成，因此昆蟲能感知多個方向的影像。相較於單眼（simple eye），複眼的視線角度極大，且能感知快速的移動，甚至有些昆蟲還能感知光的偏振（polarization）。

Ocellus cross-section

Compound eye cross-section

Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained （assuming they do not function as phased arrays）. This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require compound eyes that would each reach the size of their heads. Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image. Compound eyes grow at their margins by the addition of new ommatidia.

由於單一晶狀體很小，繞射（diffraction）的作用限制了解像度（假設它們作用方式與相位陣列（phased arrays）不同）。這個問題只能透過提升晶狀體的大小和數量解決。如果要獲得和人眼一樣的解像度，人類必須要生有和頭顱同樣大小的複眼。複眼能細分為兩種，並置眼（apposition eyes）能輸出複數個倒像，疊加眼（superposition eyes）能輸出單個正像。複眼透過增加小眼數目來成長增大。

觸角

主條目：Antenna (Biology) § Insects

Closeup of a fire ant, showing fine sensory hairs on antennae

Antennae, sometimes called "feelers", are flexible appendages located on the insect's head which are used for sensing the environment. Insects are able to feel with their antennae because of the fine hairs （setae） that cover them. However, touch is not the only thing that antennae can detect; numerous tiny sensory structures on the antennae allow insects to sense smells, temperature, humidity, pressure, and even potentially sense themselves in space. Some insects, including bees and some groups of flies can also detect sound with their antennae.

觸角（antennae），有時也稱為感覺器（feeler），為位於昆蟲頭部上具彈性的附肢，用以感知環境。昆蟲之所以能利用觸角感知環境是因為觸角上面覆蓋着細毛（剛毛, setae）。然而，感知觸覺不是觸角的唯一功能；觸角上所佈滿的無數受器使昆蟲能夠感知氣味、溫度、濕度、壓力，甚至有可能感知他們本身的狀態（本體感覺, 自我知覺）。有些昆蟲，如蜜蜂和某些蒼蠅，能夠透過觸角感知聲音。

The number of segments in an antenna varies considerably amongst insects, with higher flies having only 3-6 segments, while adult cockroaches can have over 140. The general shape of the antennae is also quite variable, but the first segment （the one attached to the head） is always called the scape, and the second segment is called the pedicel. The remaining antennal segments or flagellomeres are called the flagellum.

觸角部位的節數因蟲而異，如Higher flies只有3-6節，蟑螂成蟲卻有超過140節。觸角的形狀也非常歧異，但第一節（連結頭部那節）永遠都叫做柄節，第二節叫做梗節。剩下的部分或是鞭小節稱為鞭節。

General insect antenna types are shown below:

常見的昆蟲觸角樣式如下：

昆蟲觸角分類

Aristate	Capitate	Clavate	Filiform	Flabellate	Geniculate	Setaceous
Lamellate	Moniliform	Pectinate	Plumose	Serrate	Stylate

口器

主條目：口器 (昆蟲)

The insect mouthparts consist of the maxilla, labium, and in some species, the mandibles. The labrum is a simple, fused sclerite, often called the upper lip, and moves longitudinally, which is hinged to the clypeus. The mandibles （jaws） are a highly sclerotized pair of structures that move at right angles to the body, used for biting, chewing, and severing food. The maxillae are paired structures that can also move at right angles to the body and possess segmented palps. The labium （lower lip） is the fused structure that moves longitudinally and possesses a pair of segmented palps.

昆蟲的口器包括小顎（maxilla）、下唇（labium），在有些物種中也包含大顎（mandible）。上唇（labrum）是一片簡單且癒合的骨片，可由頭楯部 （clypeus）縱向拉動。大顎是一對高度骨化的結構，移動方向與身體垂直，用以啃咬、咀嚼和進食。小顎一對，移動方向也和身體垂直，並生有分節的附肢。下唇，是一個癒合的結構，縱向移動，並生有一對分節的附肢。

The development of insect mouthparts from the primitive chewing mouthparts of a grasshopper in the centre （A）, to the lapping type （B） of a bee, the siphoning type （C） of a butterfly and the sucking type （D） of a female mosquito.
Legend: a - antennae
c - compound eye
lb - labium
lr - labrum
md - mandibles
mx - maxillae

The mouthparts, along with the rest of the head, can be articulated in at least three different positions: prognathous, opisthognathous, and hypognathous. In species with prognathous articulation, the head is positioned vertically aligned with the body, such as species of Formicidae; while in a hypognathous type, the head is aligned horizontally adjacent to the body. An opisthognathous head is positioned diagonally, such as species of Blattodea and some Coleoptera. The mouthparts vary greatly between insects of different orders, but the two main functional groups are mandibulate and haustellate. Haustellate mouthparts are used for sucking liquids and can be further classified by the presence of stylets, which include piercing-sucking, sponging, and siphoning. The stylets are needle-like projections used to penetrate plant and animal tissues. The stylets and the feeding tube form the modified mandibles, maxilla, and hypopharynx.

口器和頭部剩下的部位，能夠被歸類為至少三種型式：前口式（prognathous）、後口式（opisthognathous）與下口式（hypognathous）。下口式的物種頭部和身體垂直，如蟻科（formicidae）；前口式物種頭部和身體平行排列；後口式物種頭部和身體呈斜線，如蜚蠊目（Blattodea）和某些鞘翅目（Coleoptera）。口器的種類因昆蟲目的不同而異，但主要的兩種為具顎式（mandibulate）和吸吮式（haustellate）。吸吮式口器用來吸取液體，並能以刺器（stylets）的有無進一步分類，分別為刺吸式（piercing-sucking）、汲取式（sponging）與虹吸式（siphoning）。刺器是一種針狀的突起物，用以穿刺植物或是動物組織。刺器和取食管為特化的大顎、小顎與下咽（hypopharynx）。

• Mandibulate mouthparts, among the most common in insects, are used for biting and grinding solid foods.
• Piercing-sucking mouthparts have stylets, and are used to penetrate solid tissue and then suck up liquid food.
• Sponging mouthparts are used to sponge and suck liquids, and lack stylets （e.g. most Diptera）.
• Siphoning mouthparts lack stylets and are used to suck liquids, and are commonly found among species of Lepidoptera.
• 具顎式口器，用以啃咬與磨碎固體食物，大部分的昆蟲皆為此類。 刺吸式口器，具刺器，以刺器刺穿固體組織後吸食液體食物。 汲取式口器，用以汲取與吸食液體，缺乏刺器，如大部分的雙翅目（Diptera） 虹吸式口器，缺乏刺器，用以吸食液體，在大部分的鱗翅目（Lepidoptera）物種中被發現。

Mandibular mouthparts are found in species of Odonata, adult Neuroptera, Coleoptera, Hymenoptera, Blattodea, Orthoptera, and Lepidoptera. However, most adult Lepidoptera have siphoning mouthparts, while their larvae （commonly called caterpillars） have mandibles.

具顎式口器能在以下昆蟲中被發現：蜻蛉目（Odonata）、脈翅目（Neuroptera）成蟲、鞘翅目（Coleoptera）、膜翅目（Hymenoptera）、蜚蠊目（Blattodea）、直翅目（Orthoptera）、鱗翅目（Lepidoptera）。然而，鱗翅目成蟲為虹吸式口器，牠們的幼蟲（通常被稱為毛蟲（caterpillar））為具顎式口器。

Mandibulate

參見：Mandible (insect mouthpart)

The labrum is a broad lobe forming the roof of the preoral cavity, suspended from the clypeus in front of the mouth and forming the upper lip. On its inner side, it is membranous and may be produced into a median lobe, the epipharynx, bearing some sensilla. The labrum is raised away from the mandibles by two muscles arising in the head and inserted medially into the anterior margin of the labrum. It is closed against the mandibles in part by two muscles arising in the head and inserted on the posterior lateral margins on two small sclerites, the tormae, and, at least in some insects, by a resilin spring in the cuticle at the junction of the labrum with the clypeus. Until recently, the labrum generally was considered to be associated with first head segment. However, recent studies of the embryology, gene expression, and nerve supply to the labrum show it is innervated by the tritocerebrum of the brain, which is the fused ganglia of the third head segment. This is formed from fusion of parts of a pair of ancestral appendages found on the third head segment, showing their relationship. Its ventral, or inner, surface is usually membranous and forms the lobe-like epipharynx, which bears mechanosensilla and chemosensilla.

具顎式

上唇（labrum）是一覆蓋於口前腔（preoral cavity）之上的寬葉，上接頭楯（clypeus），並形成上唇（upper lip）。上唇裏邊為膜質，且有可能形成一個中葉，也就是咽（epipharynx），生有一些感覺器。將上唇提起離開大顎的肌肉，為兩條從頭殼中生出，並插入上唇外緣中間的肌肉。而將上唇拉近大顎的肌肉，為兩條從頭殼生出，插入內緣側邊的兩個小骨片上，也就是tormae，且，至少在某些昆蟲中，被彈性蛋白（resilin）拉在上唇和頭楯的關節處表皮上。直到最近，上唇普遍被認為和第一頭節有關。然而，根據最近的胚胎學、基因表現及上唇神經的研究，上唇由大腦的第三大腦（tritocerebrum）支配，第三大腦為第三頭節的癒合神經結，且上唇為第三頭節上古老附肢癒合的產物，此點也揭露了第三大腦和上唇的關聯。上唇的腹側，也就是內側，表面通常為膜質，且形成一個半葉狀的咽（epipharynx），上頭生有機械受器（mechanosensilla）及化學受器（chemosensilla）。

Chewing insects have two mandibles, one on each side of the head. The mandibles are positioned between the labrum and maxillae. The mandibles cut and crush food, and may be used for defense; generally, they have an apical cutting edge, and the more basal molar area grinds the food. They can be extremely hard （around 3 on Mohs, or an indentation hardness of about 30 kg/mm²）; thus, many termites and beetles have no physical difficulty in boring through foils made from such common metals as copper, lead, tin, and zinc. The cutting edges are typically strengthened by the addition of zinc, manganese, or rarely, iron, in amounts up to about 4% of the dry weight. They are typically the largest mouthparts of chewing insects, being used to masticate （cut, tear, crush, chew） food items. They open outwards （to the sides of the head） and come together medially. In carnivorous, chewing insects, the mandibles can be modified to be more knife-like, whereas in herbivorous chewing insects, they are more typically broad and flat on their opposing faces （e.g., caterpillars）. In male stag beetles, the mandibles are modified to such an extent as to not serve any feeding function, but are instead are used to defend mating sites from other males. In ants, the mandibles also serve a defensive function （particularly in soldier castes）. In bull ants, the mandibles are elongated and toothed, used as hunting （and defensive） appendages.

咀嚼式的昆蟲擁有一對大顎，頭部兩側各一。大顎位於上唇及小顎之間。大顎用以切割及磨碎食物，亦可用於防禦；普遍來說，大顎有一個切面（cutting edge），與佔大部分面積的磨麵（molar area）用以磨碎食物。大顎的硬度可以極高（大約3摩氏硬度，或是30 kg/mm2的壓痕硬度）；因此，白蟻和甲蟲在常見金屬組成的土壤，如銅、鉛、錫或鋅，挖掘不會遭受物理上的困難。切面通常被金屬附加物強化，如鋅與鎂，較少見的還有鐵，金屬附加物占的比重大約是乾重的4%。大顎通常是咀嚼式昆蟲口器中最大的部分，用以咀嚼（切、撕、粉碎、嚼）食物。大顎向外張開並向內靠攏。在肉食性的咀嚼式昆蟲中，大顎可以被特化成刀狀，然而在植食性昆蟲中，大顎內側通常寬扁（如毛蟲）。在鍬形蟲雄蟲中，大顎被特化且失去了取食功能，但能用來與其它雄蟲爭取配偶。在螞蟻中，大顎也可用作防禦用途（特別是兵蟻階級）。在鬥牛犬蟻中，大顎被延長且生有齒，用作獵食（和防禦）。

Situated beneath the mandibles, paired maxillae manipulate food during mastication. Maxillae can have hairs and "teeth" along their inner margins. At the outer margin, the galea is a cupped or scoop-like structure, which sits over the outer edge of the labium. They also have palps, which are used to sense the characteristics of potential foods. The maxillae occupy a lateral position, one on each side of the head behind the mandibles. The proximal part of the maxilla consists of a basal cardo, which has a single articulation with the head, and a flat plate, the stipes, hinged to the cardo. Both cardo and stipes are loosely joined to the head by membrane so they are capable of movement. Distally on the stipes are two lobes, an inner lacinea and an outer galea, one or both of which may be absent. More laterally on the stipes is a jointed, leglike palp made up of a number of segments; in Orthoptera there are five. Anterior and posterior rotator muscles are inserted on the cardo, and ventral adductor muscles arising on the tentorium are inserted on both cardo and stipes. Arising in the stipes are flexor muscles of lacinea and galea and another lacineal flexor arises in the cranium, but neither the lacinea nor the galea has an extensor muscle. The palp has levator and depressor muscles arising in the stipes, and each segment of the palp has a single muscle causing flexion of the next segment.

在大顎下方，成對的小顎在咀嚼時負責抓住食物。小顎內側可能生有毛或是齒。在外側，生有外葉（galea），外葉為杯狀或湯匙狀的結構，用以感受食物的存在。小顎也生有鬚，用來感受食物的存在。小顎位於側面，大顎後方頭部兩側各一。小顎靠近頭部的一端基部生有軸節（cardo），軸節與頭部以單關節相連，一個扁平板，也就是蝶絞節（stipes），生在軸節之上。軸節和蝶絞節都鬆弛的以膜質的結構連結頭部，因此他們能夠自由移動。在離頭部的遠端，蝶絞節之上生有兩瓣，內側為內葉（lacinea），外側為外葉（galea），其中一者或是兩者有可能消失。蝶絞節的外側端生有具關節，足狀的鬚，由數分節組成；直翅目為5節。前後側的肌肉插入軸節中，而腹側生於幕狀骨（tentorium）上的收縮肌插入軸節和蝶絞節中。蝶絞節上生有外葉及內葉的屈肌，外葉的另一條屈肌著生於頭殼，外葉及內葉皆不具有伸肌。小顎鬚有生於蝶絞節之上的提肌與升肌，且每一小顎鬚節皆具有一條肌肉，使下一節彎曲。

In mandibulate mouthparts, the labium is a quadrupedal structure, although it is formed from two fused secondary maxillae. It can be described as the floor of the mouth. With the maxillae, it assists with manipulation of food during mastication or chewing or, in the unusual case of the dragonfly nymph, extends out to snatch prey back to the head, where the mandibles can eat it. The labium is similar in structure to the maxilla, but with the appendages of the two sides fused by the midline, so they come to form a median plate. The basal part of the labium, equivalent to the maxillary cardines and possibly including a part of the sternum of the labial segment, is called the postmentum. This may be subdivided into a proximal submentum and a distal mentum. Distal to the postmentum, and equivalent to the fused maxillary stipites, is the prementum. The prementum closes the preoral cavity from behind. Terminally, it bears four lobes, two inner glossae, and two outer paraglossae, which are collectively known as the ligula. One or both pairs of lobes may be absent or they may be fused to form a single median process. A palp arises from each side of the prementum, often being three-segmented.

在具顎式口器中，下唇為一個四腳的結構，雖然他是從兩個癒合的次要小顎（secondary maxillae）而來。可以用口器的地板來形容下唇，下唇用以在咀嚼的過程中把握住食物，但在一個不尋常的例子中，蜻蜓雉蟲，能夠向外延展以攫住獵物並拉向頭部，再透過大顎進食。下唇的結構相似於小顎，但兩邊的鬚於中央癒合，因此形成一個中央平板。下唇的基部相當於小顎的軸節，且可能包含一部分的下唇節腹骨片，也就是下唇後基節（postmentum），有時可進一步細分為近端的下唇亞基節（submentum）及遠端的下唇基節（mentum）。下唇亞基節的外端，是下唇前基節（prementum），相當於小顎的蝶絞節。下唇前基節蓋住後方的口前腔（preoral cavity）。末端生有4個葉狀體，一對內側的中舌（glossa），及一對外側的側舌（paraglossa），合在一起稱作唇舌（ligula）。一或二對葉狀體可能消失或癒合形成一個中央突起。一個鬚著生於下唇前基節的兩側，通常為三節。

The hypopharynx is a median lobe immediately behind the mouth, projecting forwards from the back of the preoral cavity; it is a lobe of uncertain origin, but perhaps associated with the mandibular segment; in apterygotes, earwigs, and nymphal mayflies, the hypopharynx bears a pair of lateral lobes, the superlinguae （singular: superlingua）. It divides the cavity into a dorsal food pouch, or cibarium, and a ventral salivarium into which the salivary duct opens. It is commonly found fused to the libium. Most of the hypopharynx is membranous, but the adoral face is sclerotized distally, and proximally contains a pair of suspensory sclerites extending upwards to end in the lateral wall of the stomodeum. Muscles arising on the frons are inserted into these sclerites, which distally are hinged to a pair of lingual sclerites. These, in turn, have inserted into them antagonistic pairs of muscles arising on the tentorium and labium. The various muscles serve to swing the hypopharynx forwards and back, and in the cockroach, two more muscles run across the hypopharynx and dilate the salivary orifice and expand the salivarium.

下咽（hypopharynx）為一個緊接在口後方的中央葉狀體，從前口腔（preoral cavity）的後方往前突；此葉的起源目前未知，但推測與顎的小節有關；在無翅亞綱、蠼螋及蜉蝣雉蟲中，下咽側面生有一對葉狀體，也就是舌上葉（superlinguae，單數形superlingua）。舌上葉將下咽劃分為上下兩腔，背側的是食料腔（cibarium），腹側則是連結到唾液管開口的唾液腔（salivarium）。舌上葉經常被發現和下唇癒合。下咽大部分為膜質，但接近口的那面末端骨化，且具有一對支撐用的骨片往上延伸連結至原口腔（stomodeum）側壁的末端。從額部生出的肌肉也沒入這些骨片中，同時末端連結一對舌骨片（lingual sclerites）。這些形成了多對在幕狀骨和下唇拮抗的肌肉。這些多樣的肌肉負責將下咽前後擺盪，且在蟑螂中，多了兩條橫跨下咽的肌肉，用以放大唾液口和擴大唾液腔。

Examples of mandibles

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Piercing-sucking

Mouthparts can have multiple functions. Some insects combine piercing parts along with sponging ones which are then used to pierce through tissues of plants and animals. Female mosquitoes feed on blood （hemophagous） making them disease vectors. The mosquito mouthparts consist of the proboscis, paired mandibles and maxillae. The maxillae form needle-like structures, called stylets, which are enclosed by the labium. When mosquito bites, maxillae penetrate the skin and anchor the mouthparts, thus allowing other parts to be inserted. The sheath-like labium slides back, and the remaining mouthparts pass through its tip and into the tissue. Then, through the hypopharynx, the mosquito injects saliva, which contains anticoagulants to stop the blood from clotting. And finally, the labrum （upper lip） is used to suck up the blood. Species of the genus Anopheles are characterized by their long palpi （two parts with widening end）, almost reaching the end of labrum.

刺吸式

口器功能變化多端。有些昆蟲結合了刺的部分和虹吸，用以穿刺植物或動物的組織。雌蚊的吸血性（hemophagous）使之成為病媒。蚊子的口器包含了食管（proboscis）、成對的大顎及小顎。小顎形成針狀結構，稱之為口針（stylets），收於下唇之內。當蚊子吸血時，小顎刺穿皮膚並固定口器，使其他部分得以植入。鞘狀的下唇後縮，剩餘的口器通過它的尖端並進入組織。接着，透過下咽，蚊子注入包含抗凝劑（anticoagulants）的唾液來阻止血液凝固，最後，透過上唇吸取血液。Anopheles 屬的物種特化的小顎鬚（兩末端寬大的部分）極長，幾乎和上唇一樣長。

Examples of piercing mouthparts

• Aedes aegypti
  Aedes aegypti
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  Mosquito
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  Cimex lectularius
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  Flea
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  Horsefly (female)
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  Tick (Ixodes ricinus), which is not an insect, but an arachnid, given for comparison

Siphoning

The proboscis is formed from maxillary galeae and is adaption found in some insects for sucking. The muscles of the cibarium or pharynx are strongly developed and form the pump. In Hemiptera and many Diptera, which feed on fluids within plants or animals, some components of the mouthparts are modified for piercing, and the elongated structures are called stylets. The combined tubular structures are referred to as the proboscis, although specialized terminology is used in some groups.

食管由小顎外葉形成，且在某些昆蟲中特化用以吸食用。食料腔或咽的肌肉極度發達並形成泵。在取食植物或動物的液體的半翅目及許多雙翅目中，口器的某些部分特化用以穿刺用，此延長的結構稱為口針。此複合的管狀結構稱為食管，但在某些特定族群中有更特定的用詞。

In species of Lepidoptera, it consists of two tubes held together by hooks and separable for cleaning. Each tube is inwardly concave, thus forming a central tube through which moisture is sucked. Suction is effected through the contraction and expansion of a sac in the head. The proboscis is coiled under the head when the insect is at rest, and is extended only when feeding. The maxillary palpi are reduced or even vestigial. They are conspicuous and five-segmented in some of the more basal families, and are often folded. The shape and dimensions of the proboscis have evolved to give different species wider and therefore more advantageous diets. There is an allometric scaling relationship between body mass of Lepidoptera and length of proboscis from which an interesting adaptive departure is the unusually long-tongued hawk moth Xanthopan morganii praedicta. Charles Darwin predicted the existence and proboscis length of this moth before its discovery based on his knowledge of the long-spurred Madagascan star orchid Angraecum sesquipedale.

在鱗翅目中，食管由兩個由鈎連接的管組成，且可分離彼此以便清潔。管巢內的部分生有溝渠，因此形成一個中央管道，液體從之經過。吸取的過程與液體濃度及頭部中一個囊的舒張有關。在休息時，食管捲起收於頭部下方，並只在取食時張開。小顎鬚退化甚至只剩下痕跡。在某些基群中，小顎鬚明顯且分為五節，且通常捲起。食管的形狀及尺寸因不同的物種而異，因此對各自的食性有益。鱗翅目身體重量和食管長度為具縮放關係的異速成長，特別是一個適應性偏差的案例：Xanthopan morganii praedicta，長喙天蛾。查爾斯‧達爾文（Charles Darwin）根據他對長花萼的馬達加斯加樹蘭 Angraecum sesquipedale的研究，預測了此種天蛾的存在與其食管的長度。

Examples of siphoning mouthparts

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Sponging

The mouthparts of insects that feed on fluids are modified in various ways to form a tube through which liquid can be drawn into the mouth and usually another through which saliva passes. The muscles of the cibarium or pharynx are strongly developed to form a pump. In nonbiting flies, the mandibles are absent and other structures are reduced; the labial palps have become modified to form the labellum, and the maxillary palps are present, although sometimes short. In Brachycera, the labellum is especially prominent and used for sponging liquid or semiliquid food. The labella are a complex structure consisting of many grooves, called pseudotrachea, which sops up liquids. Salivary secretions from the labella assist in dissolving and collecting food particles so they can be more easily taken up by the pseudotracheae; this is thought to occur by capillary action. The liquid food is then drawn up from the pseudotracheae through the food channel into the esophagus.

汲取式

取食液體的昆蟲口器變化多端，形成一個管道讓流質食物通過，且通常有另一個管道讓唾液通過。食料腔或咽的肌肉極度發達形成一個泵。在不咬人的蒼蠅中，大顎消失且其他結構退化；下唇鬚特化形成唇瓣（labellum），且小顎鬚存在，雖然有時候可能很短。在短角亞目（Brachycera）中，唇特別重要，用以汲取液體或半液體食物。唇瓣（labella）為一包含數個溝渠的複雜結構，此溝渠稱為假器管（pseudotrachea），也就是吸取液體的部位。從唇瓣分泌的唾液可以幫助溶解並收集食物顆粒，使得他們能更容易被假器管吸取；此行為被認為由毛細作用所驅動。液體食物被假器管吸入後通過食料腔進入食道（esophagus）。

The mouthparts of bees are of a chewing and lapping-sucking type. Lapping is a mode of feeding in which liquid or semiliquid food adhering to a protrusible organ, or "tongue", is transferred from substrate to mouth. In the honey bee （Hymenoptera: Apidae: Apis mellifera）, the elongated and fused labial glossae form a hairy tongue, which is surrounded by the maxillary galeae and the labial palps to form a tubular proboscis containing a food canal. In feeding, the tongue is dipped into the nectar or honey, which adheres to the hairs, and then is retracted so the adhering liquid is carried into the space between the galeae and labial palps. This back-and-forth glossal movement occurs repeatedly. Movement of liquid to the mouth apparently results from the action of the cibarial pump, facilitated by each retraction of the tongue pushing liquid up the food canal.

蜜蜂的口器為咀吸式。吸為一種取食液體或半液體食物的方式，將食物吸附在一個可伸縮的器官上，也就是舌（tongue），最後送入口中。在西方蜂（Hymenoptera: Apidae: Apis mellifera）中，延長且癒合的中舌（glossae ）形成一根毛茸茸的舌，外層被小顎外葉及小顎鬚包覆，形成一個管狀的食管，內含一個食物通道。取食時，舌浸入花粉或蜂蜜中，以毛吸附之，然後縮回舌讓吸附的液體進入到外葉與小顎鬚之間的空間中。中舌會持續前後來回，形成一個抽取食物的泵，每次舌的收回都可以幫助將食物推入食料腔中。

Examples of sponging mouthparts

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Thorax

主條目：Thorax (insect anatomy)

The insect thorax has three segments: the prothorax, mesothorax, and metathorax. The anterior segment, closest to the head, is the prothorax; its major features are the first pair of legs and the pronotum. The middle segment is the mesothorax; its major features are the second pair of legs and the anterior wings, if any. The third, the posterior, thoracic segment, abutting the abdomen, is the metathorax, which bears the third pair of legs and the posterior wings. Each segment is dilineated by an intersegmental suture. Each segment has four basic regions. The dorsal surface is called the tergum （or notum） to distinguish it from the abdominal terga. The two lateral regions are called the pleura （singular: pleuron）, and the ventral aspect is called the sternum. In turn, the notum of the prothorax is called the pronotum, the notum for the mesothorax is called the mesonotum and the notum for the metathorax is called the metanotum. Continuing with this logic, there is also the mesopleura and metapleura, as well as the mesosternum and metasternum.

胸節

昆蟲的胸節分三節：前胸（prothorax）、中胸（mesothorax）及後胸（metathorax），前側最靠近頭部的分節為前胸；前胸的特徵為第一對足及前胸背板（pronotum）。中央的分節為中胸；特徵為第二對足及前翅（如果具翅）。位於後側的第三節為後胸，生有第三對足及後翅。各節之間可被縫線區隔。每節又可分為四個基本區域，背側稱作背板（tergum 或notum），腹節的背板則稱作腹背板（terga）。兩側邊區域則稱作側板（pleura，單數形為pleuron ），腹側區域則稱作腹板（sternum）。依此類推，前胸的背板稱作前胸背板，中胸，中胸背板，後胸則是後胸背板。照此規則，中胸側板、後胸側板、中胸腹板、後胸腹板。

The tergal plates of the thorax are simple structures in apterygotes and in many immature insects, but are variously modified in winged adults. The pterothoracic nota each have two main divisions: the anterior, wing-bearing alinotum and the posterior, phragma-bearing postnotum. Phragmata （singular: phragma） are plate-like apodemes that extend inwards below the antecostal sutures, marking the primary intersegmental folds between segments; phragmata provide attachment for the longitudinal flight muscles. Each alinotum （sometimes confusingly referred to as a "notum"） may be traversed by sutures that mark the position of internal strengthening ridges, and commonly divides the plate into three areas: the anterior prescutum, the scutum, and the smaller posterior scutellum. The lateral pleural sclerites are believed to be derived from the subcoxal segment of the ancestral insect leg. These sclerites may be separate, as in silverfish, or fused into an almost continuous sclerotic area, as in most winged insects.

胸背板在無翅亞綱和許多非成蟲中結構簡易，但在有翅成蟲中則多樣的特化。生翅胸（pterothoracic ）的背板則區分為兩區，前方為生有翅的翅背板（alinotum ），後方則為生有懸骨（phragma）的後背板（postnotum）。懸骨（Phragmata ，單數形為phragma）為脊前縫線（antecostal suture）下內伸的板狀游離骨（apodemes），懸骨區分節與節；懸骨提供縱走飛翔肌（longitudinal flight muscle）附着的部位。翅背板（alinotum 有時會與背板，notum，混淆），有幾條橫走縫線，這些縫線代表內部的強化稜脊所在的位置，且常將翅背板分為三區，前側為前楯片（prescutum），中間為楯片（scutum），最小位於後側的為小楯片（scutellum）。側面的側骨片被認為是從古老昆蟲足的亞基節衍生而來。三骨片可能分離，如衣魚；亦可能癒合為一連續的骨片區，如大部分的有翅昆蟲。

Prothorax

主條目：prothorax

The prothorax on this conehead is shielded by a large pronotum that extends from over the cervix （neck） on the anterior side to cover the mesothorax and most of the metathorax on the posterior side, as well as covering the pleura on the prothorax. The pronotum of the prothorax may be simple in structure and small in comparison with the other nota, but in beetles, mantids, many bugs, and some Orthoptera, the pronotum is expanded, and in cockroaches, it forms a shield that covers part of the head and mesothorax.

前胸

參見：前胸 (昆蟲)

前胸被大面積的前胸背板蓋住，由頸部（cervix ）延伸蓋住中胸及大部分的後胸，也蓋住了前胸的側板。前胸背板相較於其他的胸節背板可能小且結構簡單，但在甲蟲、螳螂、許多臭蟲及某些直翅目中，前胸背板延展，且在蟑螂中，前胸背板形成一個蓋住部分頭部和中胸的構造。

Pterothorax

Because the mesothorax and metathorax hold the wings, they have a combined name called the pterothorax （pteron = wing）. The forewing, which goes by different names in different orders （e.g., the tegmina in Orthoptera and elytra in Coleoptera）, arises between the mesonotum and the mesopleura, and the hindwing articulates between the metanotum and metapleura. The legs arise from the mesopleura and metapleura. The mesothorax and metathorax each have a pleural suture （mesopleural and metapleural sutures） that runs from the wing base to the coxa of the leg. The sclerite anterior to the pleural suture is called the episternum （serially, the mesepisternum and metepisternum）. The sclerite posterior to the suture is called the epimiron （serially, the mesepimiron and metepimiron）. Spiracles, the external organs of the respiratory system, are found on the pterothorax, usually one between the pro- and mesopleoron, as well as one between the meso- and metapleuron.

生翅胸

由於翅膀生於中胸及後胸上，因此也可稱作為生翅胸（pterothorax，pteron=wing）。前翅（forewing）在不同的目中有不同的名字（直翅目：翅覆，鞘翅目：翅鞘），著生於中胸背板及中胸側板之間，而後翅的關節則著生於後胸背板及後胸側板之間。足著生於中胸側板及後胸背板之間。中胸和後胸各有一從翅膀基部延伸至足基節的側板縫線（pleural suture，中胸側板縫線及後胸側板縫線）。位於側板縫線前側的骨片稱作前側片（episternum ）（中胸前側片mesepisternum 、後胸前側片metepisternum），位於側板縫線後方的骨片稱作後側片（epimiron ）（中胸後側片mesepimiron 、後胸後側片metepimiron）。氣孔，呼吸系統的外部器官，能在生翅胸上發現，通常在前－中側板及中－後側板之間各一。

The ventral view or sternum follows the same convention, with the prosternum under the prothorax, the mesosternum under the mesothorax and the metasternum under the metathorax. The notum, pleura, and sternum of each segment have a variety of different sclerites and sutures, varying greatly from order to order, and they will not be discussed in detail in this section.

腹側，也就是腹板也遵循同樣規律，前胸腹板、中胸腹板及後胸腹板。每個體節的背板、側板及腹板各有多樣的骨片及縫線，依目的不同而變化多端，在本節中將不詳細討論。

Wings

主條目：Wing (insect)

Most phylogenetically advanced insects have two pairs of wings located on the second and third thoracic segments. Insects are the only invertebrates to have developed flight capability, and this has played an important part in their success. Insect flight is not very well understood, relying heavily on turbulent aerodynamic effects. The primitive insect groups use muscles that act directly on the wing structure. The more advanced groups making up the Neoptera have foldable wings, and their muscles act on the thorax wall and power the wings indirectly. These muscles are able to contract multiple times for each single nerve impulse, allowing the wings to beat faster than would ordinarily be possible.

Insect flight can be extremely fast, maneuverable, and versatile, possibly due to the changing shape, extraordinary control, and variable motion of the insect wing. Insect orders use different flight mechanisms; for example, the flight of a butterfly can be explained using steady-state, nontransitory aerodynamics, and thin airfoil theory.

翅膀

大多數在系統發生學上先進的昆蟲都具有兩對翅膀，方別位於中胸及後胸。昆蟲是唯一發展出飛行能力的無脊椎動物，這點為昆蟲的成功貢獻了極大的部分。關於昆蟲的飛行尚未完全了解，只知道其極度依賴紊流空氣效應（ turbulent aerodynamic effects）。原始的昆蟲類群用肌肉直接驅動翅膀。較為後期的類群，新翅類群（Neoptera）具有可折疊的翅膀，且他們的肌肉施力於胸壁上，間接驅動翅膀。這些肌肉能夠在一次的神經衝動內收縮好幾次，使翅膀能夠揮動的比正常預期得更快。昆蟲飛行可以極為快速、機動及多種功能，可能是因為持續變化的形狀、超常的控制及多樣的動作方式。不同的目擁有不同的飛行機制；例如，蝴蝶的飛行可以藉由穩定態、非暫態性的空氣動力學及薄翼理論來解釋。

Internal

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 and the cuticle may be thicker and more heavily sclerotized. Within each of the major veins is a nerve and a trachea, and, since the cavities of the veins are connected with the hemocoel, hemolymph can flow into the wings. Also, the wing lumen, being an extension of the hemocoel, contains the tracheae, nerves, and hemolymph. As the wing develops, the dorsal and ventral integumental layers 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. Hairs of two types 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.

內部

翅膀由以翅脈作骨架的薄膜構成。薄膜由兩層極接近的外皮堆疊而成，而翅脈存在於兩外皮之間的空間，翅脈位置的表皮可能較厚且高度骨化。主要的脈之中具有神經及氣管（trachea），且由於翅脈中的空間與循環系統相連，血淋巴能夠流入翅膀中。翅腔（wing lumen）為循環系統的一部分，內含氣管、神經及血淋巴。隨着翅膀的發育，腹側及背側的外皮大部分的面積會慢慢靠近彼此，形成翅膜。其他的區域則形成管道，也就是未來的翅脈，同時也是氣管及神經生長之處。翅脈周遭的表皮加厚且高度骨化，提供翅膀力量及剛度。翅膀上可能生有兩種毛髮：微毛（microtrichia），小且不規則分散，大毛（macrotrichia），大且著生於槽中，可能只生長於脈上。鱗翅目及毛翅目的鱗片為高度特化的大毛。

Veins

Venation of insect wings, based on the Comstock-Needham system

In some very small insects, the venation may be greatly reduced. In chalcid wasps, for 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 wings of Odonata （dragonflies and damselflies） and at the base of the forewings of Tettigonioidea and Acridoidea （katydids and grasshoppers, respectively）.

翅脈

翅脈是根據Comstock-Needham系統來命名。在一些極小的昆蟲中，翅脈有可能極度縮減，例如，在小蜂總科中（chalcid wasps），只有亞前緣脈（subcosta ，Sc）及部分的徑脈（raidus，R）存在。相反地，翅脈有可能增加，可能透過原有翅脈的分支以形成副脈（accessory veins），或是透過新翅脈的增生，形成介於原有翅脈之間的插脈（intercalary veins），例如直翅目的翅膀。大量的橫脈存在於一些昆蟲中，並分別於蜻蛉目的翅及螽斯科（Tettigonioidea）與蝗蟲總科（Acridoidea）的前翅基部形成網狀結構（reticulum）。

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 evolved from a common ancestor, the archediction represents the "template" that has been modified （and streamlined） by natural selection for 200 million years. According to current dogma, the archedictyon contained six to eight longitudinal veins. These veins （and their branches） are named according to a system devised by John Comstock and George Needham—the Comstock-Needham system:

理想翅脈（archedictyon ）係指假想的，第一隻有翅昆蟲的翅脈。基於推測及化石資料而成。由於普遍相信所有的有翅昆蟲都是由一共同祖先演化而來，因此理想翅脈扮演的是一個模板，代表着經過2億年天擇後特化（和優化）的翅的雛形。根據現時公認的理想翅脈，共包含6至8條縱走脈。這些脈（及他們的分支）以John Comstock及George Needham所設立的系統所命名，Comstock-Needham system系統：

• Costa （C） - the leading edge of the wing
• Subcosta （Sc） - second longitudinal vein （behind the costa）, typically unbranched
• Radius （R） - third longitudinal vein, one to five branches reach the wing margin
• Media （M） - fourth longitudinal vein, one to four branches reach the wing margin
• Cubitus （Cu） - fifth longitudinal vein, one to three branches reach the wing margin
• Anal veins （A1, A2, A3） - unbranched veins behind the cubitus
• 前緣脈（Costa (C)） - 翅的上緣 亞前緣脈（Subcosta (Sc)） - 第二條縱走脈（前緣脈之後），通常不分支 徑脈（Radius (R)） - 第三條縱走脈，1到5條延伸至翅末端的分支 中脈（Media (M)） - 第四條縱走脈，1到4條延伸至翅末端的分支 肘脈（Cubitus (Cu)） - 第五條縱走脈，1到3條延伸至翅末端的分支 臀脈（Anal veins (A1, A2, A3)） - 肘脈後一條不分支的脈

The costa （C） is the leading marginal vein on most insects, although a small vein, the precosta, is sometimes found above the costa. In almost all extant insects, the precosta is fused with the costa; the costa rarely ever branches because it is at the leading edge, which is associated at its base with the humeral plate. The trachea of the costal vein is perhaps a branch of the subcostal trachea. Located after the costa is the third vein, the subcosta, which branches into two separate veins: the anterior and posterior. The base of the subcosta is associated with the distal end of the neck of the first axillary. The fourth vein is the radius, which is branched into five separate veins. The radius is generally the strongest vein of the wing. Toward the middle of the wing, it forks into a first undivided branch （R1） and a second branch, called the radial sector （Ra）, which subdivides dichotomously into four distal branches （R2, R3, R4, R5）. Basally, the radius is flexibly united with the anterior end of the second axillary （2Ax）.

前緣脈為大多數昆蟲的上緣，雖然有一條小脈，先前緣脈（precosta），有時候位置高於前緣脈。在大多數現生的昆蟲中，先前緣脈是和前緣脈癒合的；由於基部在肩板（humeral plate）的位置，前緣脈位於上緣，因此通常不分支。前緣脈的氣管可能是亞前緣脈氣管的分支。位於前緣脈之後的是第三條脈，也就是亞前緣脈，又分支成2條獨立的脈：前亞前緣脈（anterior）及後亞前緣脈（posterior）。亞前緣脈的基部與第一翅腱骨的遠端頸部有關。第四條脈是徑脈，又分支成5條獨立的脈。徑脈通常是最強壯的翅脈。往翅的中央延伸，分成一條不可細分的分支（R1）及一條徑區脈（radial sector，Ra），又可兩兩細分成4條位於遠端的脈（R2, R3, R4, R5）。徑脈的基部彈性的生於第二翅腱骨（2Ax）前側的末端。

The fifth vein of the wing is the media. In the archetype pattern （A）, the media forks into two main branches, a media anterior （MA）, which divides into two distal branches （MA1, MA2）, and a median sector, or media posterior （MP）, which has four terminal branches （M1, M2, M3, M4）. In most modern insects, the media anterior has been lost, and the usual "media" is the four-branched media posterior with the common basal stem. In the Ephemerida, according to present interpretations of the wing venation, both branches of the media are retained, while in Odonata, the persisting media is the primitive anterior branch. The stem of the media is often united with the radius, but when it occurs as a distinct vein, its base is associated with the distal median plate （m'） or is continuously sclerotized with the latter. The cubitus, the sixth vein of the wing, is primarily two-branched. The primary forking takes place near the base of the wing, forming the two principal branches （Cu1, Cu2）. The anterior branch may break up into a number of secondary branches, but commonly it forks into two distal branches. The second branch of the cubitus （Cu2） in Hymenoptera, Trichoptera, and Lepidoptera, was mistaken by Comstock and Needham for the first anal. Proximally, the main stem of the cubitus is associated with the distal median plate （m'） of the wing base.

第五條脈是中脈。在理想翅脈圖中，中脈分支成二個主要的分支，前中脈（MA），又可細分成二末端的脈（MA1, MA2），另一主分支為中區脈，也就是後中脈（MP），又可細分成4個末端的脈（M1, M2, M3, M4）。在大多數現代昆蟲中，前中脈都已經丟失，而通常所謂＂中脈＂是基於一共同基脈且分四叉的後中脈。在蜉蝣目中，根據現生翅脈的分析，中脈的兩條分支都還存在，然而在蜻蛉目中，還存在的中脈是原始前中脈的分支。中脈的幹常常和徑脈癒合，但當它是一條獨立的脈時，中脈的基部位於中板（median plate）的遠端，且兩者以骨化連接。

The postcubitus （Pcu） is the first anal of the Comstock and Needham system. The postcubitus, however, has the status of an independent wing vein and should be recognized as such. In nymphal wings, its trachea arises between the cubital trachea and the group of vannal tracheae. In the mature wings of more generalized insects, the postcubitus is always associated proximally with the cubitus, and is never intimately connected with the flexor sclerite （3Ax） of the wing base. In Neuroptera, Mecoptera, and Trichoptera, the postcubitus may be more closely associated with the vannal veins, but its base is always free from the latter. The postcubitus is usually unbranched; primitively, it is two-branched. The vannal veins （lV to nV） are the anal veins immediately associated with the third axillary, and which are directly affected by the movement of this sclerite that brings about the flexion of the wings. In number, the vannal veins vary from one to 12, according to the expansion of the vannal area of the wing. The vannal tracheae usually arise from a common tracheal stem in nymphal insects, and the veins are regarded as branches of a single anal vein. Distally, the vannal veins are either simple or branched. The jugal vein （J） of the jugal lobe of the wing is often occupied by a network of irregular veins, or it may be entirely membranous; sometimes it contains one or two distinct, small veins, the first jugal vein, or vena arcuata, and the second jugal vein, or vena cardinalis （2J）.

第六條脈，肘脈，在原始的情況分兩支。原始的分支位於翅膀基部附近，形成2條主要的分支（Cu1, Cu2）。前分支可能進一步分成大量的次級分支，但通常只分支成二遠端的分支。第二條主要的分支（Cu2）在膜翅目、毛翅目及鱗翅目中，被Comstock和Needham錯當成第一臀脈。肘脈的主幹大約連結於中板的遠端。後肘脈在Comstock - Needham系統中是第一臀脈。然而，後肘脈具有獨立一條脈的地位，也應被當作獨立的一條脈。在若蟲的翅膀中，氣管生於肘脈氣管與扇氣管群之間。在比較普遍的昆蟲的成熟翅膀中，後肘脈永遠著生於肘脈之上，不和第三翅腱骨連接。在脈翅目、廣翅目、毛翅目中，後肘脈可能更靠近扇脈，但基部永遠不與扇脈相連。後肘脈通常不分支；但在原始的情況中，後肘脈分二支。扇脈（lV to nV），為最後的脈，著生於第三翅腱骨上，第三翅腱骨的移動直接影響扇脈，並造成翅膀的彎曲。扇脈的數量分佈由1至12，依扇區的面積而異。扇氣管通常由若蟲的氣管主幹衍生，且扇脈群被認為是單一臀脈的分支。扇脈群的遠端，可能簡單或複雜分支。垂脈（J）可能被不規則脈的網絡覆蓋，亦可能完全膜質；有時候包含一或二條明顯的小脈，也就是第一垂脈，或稱為弓狀脈（vena arcuata），第二垂脈，也稱為韌脈（vena cardinalis）。

• C-Sc cross-veins - run between the costa and subcosta
• R cross-veins - run between adjacent branches of the radius
• R-M cross-veins - run between the radius and media
• M-Cu cross-veins - run between the media and cubitus
• C-Sc橫脈 - 跨過前緣脈及亞前緣脈 R橫脈 - 跨過徑脈分支群 R-M橫脈 - 跨過徑脈及中脈 M-Cu橫脈 - 跨過中脈及肘脈

All the veins of the wing are subject to secondary forking and to union by cross-veins. In some orders of insects, the cross-veins are so numerous, the whole venational pattern becomes a close network of branching veins and cross-veins. Ordinarily, however, a definite number of cross-veins having specific locations occurs. The more constant cross-veins are the humeral cross-vein （h） between the costa and subcosta, the radial cross-vein （r） between R and the first fork of Rs, the sectorial cross-vein （s） between the two forks of R8, the median cross-vein （m-m） between M2 and M3, and the mediocubital cross-vein （m-cu） between the media and the cubitus.

所有的翅脈皆為次級分叉且被橫脈串聯。在某些目的昆蟲中，橫脈非常大量，整個脈相變成一個由分脈及橫脈交織成的網絡。然而通常而言，橫脈發生的數量和位置有關。較密集的橫脈是位於前緣脈及亞前緣脈之間的肩橫脈（h），徑橫脈（r）位於R脈及Rs脈的第一條分支之間，有關該區域的橫脈位於R8脈的二分支之間，中橫脈（m-m）位於M2及M3之間，中肘橫脈（m-cu）位於中脈及肘脈之間。

The veins of insect wings are characterized by a convex-concave placement, such as those seen in mayflies （i.e., concave is "down" and convex is "up"）, which alternate regularly and by their branching; whenever a vein forks there is always an interpolated vein of the opposite position between the two branches. The concave vein will fork into two concave veins （with the interpolated vein being convex） and the regular alteration of the veins is preserved. The veins of the wing appear to fall into an undulating pattern according to whether they have a tendency to fold up or down when the wing is relaxed. The basal shafts of the veins are convex, but each vein forks distally into an anterior convex branch and a posterior concave branch. Thus, the costa and subcosta are regarded as convex and concave branches of a primary first vein, Rs is the concave branch of the radius, posterior media the concave branch of the media, Cu1 and Cu2 are respectively convex and concave, while the primitive postcubitus and the first vannal have each an anterior convex branch and a posterior concave branch. The convex or concave nature of the veins has been used as evidence in determining the identities of the persisting distal branches of the veins of modern insects, but it has not been demonstrated to be consistent for all wings.

昆蟲翅脈成凹凸狀，如同在蜉蝣目中所見一般，規律的連同分支一起凹凸分佈；每當一個脈分叉成二時永遠會有一個逆位的脈插入兩分支間。一下凹的脈會分叉成二下凹的脈（之間插入一上凸的脈），規律的凹凸交替也存在。無論休息時翅膀是立起或平放的，翅脈都成波浪狀的樣式。翅脈的基軸是上凸的，但每條脈往遠端分叉，形成一上凸的前分支及一下凹的後分支。因此，前緣脈及亞前緣脈被認為是原始第一翅脈的上凸及下凹分支，Rs是徑脈的下凹分支，後中脈是中脈的下凹分支，Cu1及Cu2分別為上凸及下凹，然而原始的後肘脈及第一扇脈各擁有一前上凸分支及一後下凹分支。上凸及下凹的性質被用作證據，以辨別現生昆蟲翅脈遠端的分支，但並不是所有的翅膀都遵循本規律。

Fields

Wing areas are delimited and subdivided by fold lines, along which the wings can fold, and flexion lines, which flex during flight. Between the flexion and the fold lines, the fundamental distinction is often blurred, as fold lines may permit some flexibility or vice versa. Two constants, found in nearly all insect wings, are the claval （a flexion line） and jugal folds （or fold line）, forming variable and unsatisfactory boundaries. Wing foldings can very complicated, with transverse folding occurring in the hindwings of Dermaptera and Coleoptera, and in some insects, the anal area can be folded like a fan. The four different fields found on insect wings are:

• Remigium
• Anal area （vannus）
• Jugal area
• Axillary area
• Alula

Most veins and cross-veins occur in the anterior area of the remigium, which is responsible for most of the flight, powered by the thoracic muscles. The posterior portion of the remigium is sometimes called the clavus; the two other posterior fields are the anal and jugal areas. When the vannal fold has the usual position anterior to the group of anal veins, the remigium contains the costal, subcostal, radial, medial, cubital, and postcubital veins. In the flexed wing, the remigium turns posteriorly on the flexible basal connection of the radius with the second axillary, and the base of the mediocubital field is folded medially on the axillary region along the plica basalis （bf） between the median plates （m, m'） of the wing base.

The vannus is bordered by the vannal fold, which typically occurs between the postcubitus and the first vannal vein. In Orthoptera, it usually has this position. In the forewing of Blattidae, however, the only fold in this part of the wing lies immediately before the postcubitus. In Plecoptera, the vannal fold is posterior to the postcubitus, but proximally it crosses the base of the first vannal vein. In the cicada, the vannal fold lies immediately behind the first vannal vein （lV）. These small variations in the actual position of the vannal fold, however, do not affect the unity of action of the vannal veins, controlled by the flexor sclerite （3Ax）, in the flexion of the wing. In the hindwings of most Orthoptera, a secondary vena dividens forms a rib in the vannal fold. The vannus is usually triangular in shape, and its veins typically spread out from the third axillary like the ribs of a fan. Some of the vannal veins may be branched, and secondary veins may alternate with the primary veins. The vannal region is usually best developed in the hindwing, in which it may be enlarged to form a sustaining surface, as in Plecoptera and Orthoptera. The great fan-like expansions of the hindwings of Acrididae are clearly the vannal regions, since their veins are all supported on the third axillary sclerites on the wing bases, though Martynov （1925） ascribes most of the fan areas in Acrididae to the jugal regions of the wings. The true jugum of the acridid wing is represented only by the small membrane （Ju） mesad of the last vannal vein. The jugum is more highly developed in some other Orthoptera, as in the Mantidae. In most of the higher insects with narrow wings, the vannus becomes reduced, and the vannal fold is lost, but even in such cases, the flexed wing may bend along a line between the postcubitus and the first vannal vein.

The jugal region, or neala, is a region of the wing that is usually a small membranous area proximal to the base of the vannus strengthened by a few small, irregular vein-like thickenings; but when well developed, it is a distinct section of the wing and may contain one or two jugal veins. When the jugal area of the forewing is developed as a free lobe, it projects beneath the humeral angle of the hindwing and thus serves to yoke the two wings together. In the Jugatae group of Lepidoptera, it bears a long finger-like lobe. The jugal region was termed the neala （"new wing"） because it is evidently a secondary and recently developed part of the wing.

The auxiliary region containing the axillary sclerites has, in general, the form of a scalene triangle. The base of the triangle （a-b） is the hinge of the wing with the body; the apex （c） is the distal end of the third axillary sclerite; the longer side is anterior to the apex. The point d on the anterior side of the triangle marks the articulation of the radial vein with the second axillary sclerite. The line between d and c is the plica basalis （bf）, or fold of the wing at the base of the mediocubital field.

At the posterior angle of the wing base in some Diptera there is a pair of membranous lobes （squamae, or calypteres） known as the alula. The alula is well developed in the house fly. The outer squama （c） arises from the wing base behind the third axillary sclerite （3Ax） and evidently represents the jugal lobe of other insects （A, D）; the larger inner squama （d） arises from the posterior scutellar margin of the tergum of the wing-bearing segment and forms a protective, hood-like canopy over the halter. In the flexed wing, the outer squama of the alula is turned upside down above the inner squama, the latter not being affected by the movement of the wing. In many Diptera, a deep incision of the anal area of the wing membrane behind the single vannal vein sets off a proximal alar lobe distal to the outer squama of the alula.

Joints

The various movements of the wings, especially in insects that flex their wings horizontally over their backs when at rest, demand a more complicated articular structure at the wing base than a mere hinge of the wing with the body. Each wing is attached to the body by a membranous basal area, but the articular membrane contains a number of small articular sclerites, collectively known as the pteralia. The pteralia include an anterior humeral plate at the base of the costal vein, a group of axillaries （Ax） associated with the subcostal, radial, and vannal veins, and two less definite median plates （m, m'） at the base of the mediocubital area. The axillaries are specifically developed only in the wing-flexing insects, where they constitute the flexor mechanism of the wing operated by the flexor muscle arising on the pleuron. Characteristic of the wing base is also a small lobe on the anterior margin of the articular area proximal to the humeral plate, which, in the forewing of some insects, is developed into a large, flat, scale-like flap, the tegula, overlapping the base of the wing. Posteriorly, the articular membrane often forms an ample lobe between the wing and the body, and its margin is generally thickened and corrugated, giving the appearance of a ligament, the so-called axillary cord, continuous mesally with the posterior marginal scutellar fold of the tergal plate bearing the wing.

The articular sclerites, or pteralia, of the wing base of the wing-flexing insects and their relations to the body and the wing veins, shown diagrammatically, are as follows:

• Humeral plates
• First Axillary
• Second Axillary
• Third Axillary
• Fourth Axillary
• Median plates （m, m'）

The humeral plate is usually a small sclerite on the anterior margin of the wing base, movable and articulated with the base of the costal vein. Odonata have their humeral plates greatly enlargened, with two muscles arising from the episternum inserted into the humeral plates and two from the edge of the epimeron inserted into the axillary plate.

The first axillary sclerite （lAx） is the anterior hinge plate of the wing base. Its anterior part is supported on the anterior notal wing process of the tergum （ANP）; its posterior part articulates with the tergal margin. The anterior end of the sclerite is generally produced as a slender arm, the apex of which （e） is always associated with the base of the subcostal vein （Sc）, though it is not united with the latter. The body of the sclerite articulates laterally with the second axillary. The second axillary sclerite （2Ax） is more variable in form than the first axillary, but its mechanical relations are no less definite. It is obliquely hinged to the outer margin of the body of the first axillary, and the radial vein （R） is always flexibly attached to its anterior end （d）. The second axillary presents both a dorsal and a ventral sclerotization in the wing base; its ventral surface rests upon the fulcral wing process of the pleuron. The second axillary, therefore, is the pivotal sclerite of the wing base, and it specifically manipulates the radial vein.

The third axillary sclerite （3Ax） lies in the posterior part of the articular region of the wing. Its form is highly variable and often irregular, but the third axillary is the sclerite on which is inserted the flexor muscle of the wing （D）. Mesally, it articulates anteriorly （f） with the posterior end of the second axillary, and posteriorly （b） with the posterior wing process of the tergum （PNP）, or with a small fourth axillary when the latter is present. Distally, the third axillary is prolonged in a process always associated with the bases of the group of veins in the anal region of the wing, here termed the vannal veins （V）. The third axillary, therefore, is usually the posterior hinge plate of the wing base and is the active sclerite of the flexor mechanism, which directly manipulates the vannal veins. The contraction of the flexor muscle （D） revolves the third axillary on its mesal articulations （b, f）, and thereby lifts its distal arm; this movement produces the flexion of the wing. The fourth axillary sclerite is not a constant element of the wing base. When present, it is usually a small plate intervening between the third axillary and the posterior notal wing process, and is probably a detached piece of the latter.

The median plates （m, m'） are also sclerites that are not so definitely differentiated as specific plates as are the three principal axillaries, but they are important elements of the flexor apparatus. They lie in the median area of the wing base distal to the second and third axillaries, and are separated from each other by an oblique line （bf）, which forms a prominent convex fold during flexion of the wing. The proximal plate （m） is usually attached to the distal arm of the third axillary and perhaps should be regarded as a part of the latter. The distal plate （m'） is less constantly present as a distinct sclerite, and may be represented by a general sclerotization of the base of the mediocubital field of the wing. When the veins of this region are distinct at their bases, they are associated with the outer median plate.

Coupling, folding, and other features

In many insect species, the forewing and hindwing are coupled together, which improves the aerodynamic efficiency of flight. The most common coupling mechanism （e.g., Hymenoptera and Trichoptera） is a row of small hooks on the forward margin of the hindwing, or "hamuli", which lock onto the forewing, keeping them held together （hamulate coupling）. In some other insect species （e.g., Mecoptera, Lepidoptera, and some Trichoptera） the jugal lobe of the forewing covers a portion of the hindwing （jugal coupling）, or the margins of the forewing and hindwing overlap broadly （amplexiform coupling）, or the hindwing bristles, or frenulum, hook under the retaining structure or retinalucum on the forewing.

When at rest, the wings are held over the back in most insects, which may involve longitudinal folding of the wing membrane and sometimes also transverse folding. Folding may sometimes occur along the flexion lines. Though fold lines may be transverse, as in the hindwings of beetles and earwigs, they are normally radial to the base of the wing, allowing adjacent sections of a wing to be folded over or under each other. The commonest fold line is the jugal fold, situated just behind the third anal vein, although, most Neoptera have a jugal fold just behind vein 3A on the forewings. It is sometimes also present on the hindwings. Where the anal area of the hindwing is large, as in Orthoptera and Blattodea, the whole of this part may be folded under the anterior part of the wing along a vannal fold a little posterior to the claval furrow. In addition, in Orthoptera and Blattodea, the anal area is folded like a fan along the veins, the anal veins being convex, at the crests of the folds, and the accessory veins concave. Whereas the claval furrow and jugal fold are probably homologous in different species, the vannal fold varies in position in different taxa. Folding is produced by a muscle arising on the pleuron and inserted into the third axillary sclerite in such a waythat, when it contracts, the sclerite pivots about its points of articulation with the posterior notal process and the second axillary sclerite.

As a result, the distal arm of the third axillary sclerite rotates upwards and inwards, so that finally its position is completely reversed. The anal veins are articulated with this sclerite in such a way that when it moves they are carried with it and become flexed over the back of the insect. Activity of the same muscle in flight affects the power output of the wing and so it is also important in flight control. In orthopteroid insects, the elasticity of the cuticle causes the vannal area of the wing to fold along the veins. Consequently, energy is expended in unfolding this region when the wings are moved to the flight position. In general, wing extension probably results from the contraction of muscles attached to the basalar sclerite or, in some insects, to the subalar sclerite.

腿

The typical and usual segments of the insect leg are divided into the coxa, one trochanter, the femur, the tibia, the tarsus, and the pretarsus. The coxa in its more symmetrical form, has the shape of a short cylinder or truncate cone, though commonly it is ovate and may be almost spherical. The proximal end of the coxa is girdled by a submarginal basicostal suture that forms internally a ridge, or basicosta, and sets off a marginal flange, the coxomarginale, or basicoxite. The basicosta strengthens the base of the coxa and is commonly enlarged on the outer wall to give insertion to muscles; on the mesal half of the coxa, however, it is usually weak and often confluent with the coxal margin. The trochanteral muscles that take their origin in the coxa are always attached distal to the basicosta. The coxa is attached to the body by an articular membrane, the coxal corium, which surrounds its base. These two articulations are perhaps the primary dorsal and ventral articular points of the subcoxo-coxal hinge. In addition, the insect coxa has often an anterior articulation with the anterior, ventral end of the trochantin, but the trochantinal articulation does not coexist with a sternal articulation. The pleural articular surface of the coxa is borne on a mesal inflection of the coxal wall. If the coxa is movable on the pleural articulation alone, the coxal articular surface is usually inflected to a sufficient depth to give a leverage to the abductor muscles inserted on the outer rim of the coxal base. Distally the coxa bears an anterior and a posterior articulation with the trochanter. The outer wall of the coxa is often marked by a suture extending from the base to the anterior trochanteral articulation. In some insects the coxal suture falls in line with the pleural suture, and in such cases the coxa appears to be divided into two parts corresponding to the episternum and epimeron of the pleuron. The coxal suture is absent in many insects.

The inflection of the coxal wall bearing the pleural articular surface divides the lateral wall of the basicoxite into a prearticular part and a postarticular part, and the two areas often appear as two marginal lobes on the base of the coxa. The posterior lobe is usually the larger and is termed the meron. The meron may be greatly enlarged by an extension distally in the posterior wall of the coxa; in the Neuroptera, Mecoptera, Trichoptera, and Lepidoptera, the meron is so large that the coxa appears to be divided into an anterior piece, the so-called "coxa genuina," and the meron, but the meron never includes the region of the posterior trochanteral articulation, and the groove delimiting it is always a part of the basicostal suture. A coxa with an enlarged meron has an appearance similar to one divided by a coxal suture falling in line with the pleural suture, but the two conditions are fundamentally quite different and should not be confused. The meron reaches the extreme of its departure from the usual condition in the Diptera. In some of the more generalized flies, as in the Tipulidae, the meron of the middle leg appears as a large lobe of the coxa projecting upward and posteriorly from the coxal base; in higher members of the order it becomes completely separated from the coxa and forms a plate of the lateral wall of the mesothorax.

The trochanter is the basal segment of the telopodite; it is always a small segment in the insect leg, freely movable by a horizontal hinge on the coxa, but more or less fixed to the base of the femur. When movable on the femur the trochantero femoral hinge is usually vertical or oblique in a vertical plane, giving a slight movement of production and reduction at the joint, though only a reductor muscle is present. In the Odonata, both nymphs and adults, there are two trochanteral segments, but they are not movable on each other; the second contains the reductor muscle of the femur. The usual single trochanteral segment of insects, therefore, probably represents the two trochanters of other arthropods fused into one apparent segment, since it is not likely that the primary coxotrochanteral hinge has been lost from the leg. In some of the Hymenoptera a basal subdivision of the femur simulates a second trochanter, but the insertion of the reductor muscle on its base attests that it belongs to the femoral segment, since as shown in the odonate leg, the reductor has its origin in the true second trochanter.

The femur is the third segment of the insect leg, is usually the longest and strongest part of the limb, but it varies in size from the huge hind femur of leaping Orthoptera to a very small segment such as is present in many larval forms. The volume of the femur is generally correlated with the size of the tibial muscles contained within it, but it is sometimes enlarged and modified in shape for other purposes than that of accommodating the tibial muscles. The tibia is characteristically a slender segment in adult insects, only a little shorter than the femur or the combined femur and trochanter. Its proximal end forms a more or less distinct head bent toward the femur, a device allowing the tibia to be flexed close against the under surface of the femur.

The terms profemur, mesofemur and metafemur refer to the femora of the front, middle and hind legs of an insect, respectively. Similarly protibia, mesotibia and metatibia refer to the tibiae of the front, middle and hind legs.

The tarsus of insects corresponds to the penultimate segment of a generalized arthropod limb, which is the segment called the propodite in Crustacea. adult insects it is commonly subdivided into from two to five subsegments, or tarsomeres, but in the Protura, some Collembola, and most holometabolous insect larvae it preserves the primitive form of a simple segment. The subsegments of the adult insect tarsus are usually freely movable on one another by inflected connecting membranes, but the tarsus never has intrinsic muscles. The tarsus of adult pterygote insects having fewer than five subsegments is probably specialized by the loss of one or more subsegments or by a fusion of adjoining subsegments. In the tarsi of Acrididae the long basal piece is evidently composed of three united tarsomeres, leaving the fourth and the fifth. The basal tarsomere is sometimes conspicuously enlarged and is distinguished as the basitarsus. On the under surfaces of the tarsal subsegments in certain Orthoptera there are small pads, the tarsal pulvilli, or euplantulae. The tarsus is occasionally fused with the tibia in larval insects, forming a tibiotarsal segment; in some cases it appears to be eliminated or reduced to a rudiment between the tibia and the pretarsus.

For the most part the femur and tibia are the longest leg segments but variations in the lengths and robustness of each segment relate to their functions. For example, gressorial and cursorial, or walking and running type insects respectively, usually have well-developed femora and tibiae on all legs, whereas jumping （saltatorial） insects such as grasshoppers have disproportionately developed metafemora and metatibiae. In aquatic beetles （Coleoptera） and bugs （Hemiptera）, the tibiae and/or tarsi of one or more pairs of legs usually are modified for swimming （natatorial） with fringes of long, slender hairs. Many ground-dwelling insects, such as mole crickets （Orthoptera: Gryllotalpidae）, nymphal cicadas （Hemiptera: Cicadidae）, and scarab beetles （Scarabaeidae）, have the tibiae of the forelegs （protibiae） enlarged and modified for digging （fossorial）, whereas the forelegs of some predatory insects, such as mantispid lacewings （Neuroptera） and mantids （Mantodea）, are specialized for seizing prey, or raptorial. The tibia and basal tarsomere of each hindleg of honey bees are modified for the collection and carriage of pollen.

腹節

The ground plan of the abdomen of an adult insect typically consists of 11–12 segments and is less strongly sclerotized than the head or thorax. Each segment of the abdomen is represented by a sclerotized tergum, sternum, and perhaps a pleurite. Terga are separated from each other and from the adjacent sterna or pleura by a membrane. Spiracles are located in the pleural area. Variation of this ground plan includes the fusion of terga or terga and sterna to form continuous dorsal or ventral shields or a conical tube. Some insects bear a sclerite in the pleural area called a laterotergite. Ventral sclerites are sometimes called laterosternites. During the embryonic stage of many insects and the postembryonic stage of primitive insects, 11 abdominal segments are present. In modern insects there is a tendency toward reduction in the number of the abdominal segments, but the primitive number of 11 is maintained during embryogenesis.Variation in abdominal segment number is considerable. If the Apterygota are considered to be indicative of the ground plan for pterygotes, confusion reigns: adult Protura have 12 segments, Collembola have 6. The orthopteran family Acrididae has 11 segments, and a fossil specimen of Zoraptera has a 10-segmented abdomen.

Generally, the first seven abdominal segments of adults （the pregenital segments） are similar in structure and lack appendages. However, apterygotes （bristletails and silverfish） and many immature aquatic insects have abdominal appendages. Apterygotes possess a pair of styles; rudimentary appendages that are serially homologous with the distal part of the thoracic legs. And, mesally, one or two pairs of protrusible （or exsertile） vesicles on at least some abdominal segments. These vesicles are derived from the coxal and trochanteral endites （inner annulated lobes） of the ancestral abdominal appendages. Aquatic larvae and nymphs may have gills laterally on some to most abdominal segments. Of the rest of the abdominal segments consist of the reproductive and anal parts.

The anal-genital part of the abdomen, known as the terminalia, consists generally of segments 8 or 9 to the abdominal apex. Segments 8 and 9 bear the genitalia; segment 10 is visible as a complete segment in many "lower" insects but always lacks appendages; and the small segment 11 is represented by a dorsal epiproct and pair of ventral paraprocts derived from the sternum. A pair of appendages, the cerci, articulates laterally on segment 11; typically these are annulated and filamentous but have been modified （e.g. the forceps of earwigs） or reduced in different insect orders. An annulated caudal filament, the median appendix dorsalis, arises from the tip of the epiproct in apterygotes, most mayflies （Ephemeroptera）, and a few fossil insects. A similar structure in nymphal stoneflies （Plecoptera） is of uncertain homology. These terminal abdominal segments have excretory and sensory functions in all insects, but in adults there is an additional reproductive function.

外生殖器

主條目：Insect reproductive system

參見：Lepidoptera genitalia

The abdominal terminus of male scorpionflies is enlarged into a "genital bulb", as seen in Panorpa communis

The organs concerned specifically with mating and the deposition of eggs are known collectively as the external genitalia, although they may be largely internal. The components of the external genitalia of insects are very diverse in form and often have considerable taxonomic value, particularly among species that appear structurally similar in other respects. The male external genitalia have been used widely to aid in distinguishing species, whereas the female external genitalia may be simpler and less varied.

The terminalia of adult female insects include internal structures for receiving the male copulatory organ and his spermatozoa and external structures used for oviposition （egg-laying; section 5.8）. Most female insects have an egg-laying tube, or ovipositor; it is absent in termites, parasitic lice, many Plecoptera, and most Ephemeroptera. Ovipositors take two forms:

1. true, or appendicular, formed from appendages of abdominal segments 8 and 9;

1. substitutional, composed of extensible posterior abdominal segments.

內部形態

神經系統

The nervous system of an insect can be divided into a brain and a ventral nerve cord. The head capsule is made up of six fused segments, each with a pair of ganglia, or a cluster of nerve cells outside of the brain. The first three pairs of ganglia are fused into the brain, while the three following pairs are fused into a structure of three pairs of ganglia under the insect's esophagus, called the subesophageal ganglion.

The thoracic segments have one ganglion on each side, which are connected into a pair, one pair per segment. This arrangement is also seen in the abdomen but only in the first eight segments. Many species of insects have reduced numbers of ganglia due to fusion or reduction. Some cockroaches have just six ganglia in the abdomen, whereas the wasp Vespa crabro has only two in the thorax and three in the abdomen. Some insects, like the house fly Musca domestica, have all the body ganglia fused into a single large thoracic ganglion.

At least a few insects have nociceptors, cells that detect and transmit sensations of pain. This was discovered in 2003 by studying the variation in reactions of larvae of the common fruitfly Drosophila to the touch of a heated probe and an unheated one. The larvae reacted to the touch of the heated probe with a stereotypical rolling behavior that was not exhibited when the larvae were touched by the unheated probe. Although nociception has been demonstrated in insects, there is not a consensus that insects feel pain consciously.

消化系統

An insect uses its digestive system to extract nutrients and other substances from the food it consumes. Most of this food is ingested in the form of macromolecules and other complex substances like proteins, polysaccharides, fats, and nucleic acids. These macromolecules must be broken down by catabolic reactions into smaller molecules like amino acids and simple sugars before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as digestion. The main structure of an insect's digestive system is a long enclosed tube called the alimentary canal, which runs lengthwise through the body. The alimentary canal directs food in one direction: from the mouth to the anus. It has three sections, each of which performs a different process of digestion. In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax, adjacent to the foregut. The gut is where almost all of insects' digestion takes place. It can be divided into the foregut, midgut and hindgut.

前腸

Stylized diagram of insect digestive tract showing malpighian tubule, from an insect of the order Orthoptera.

The first section of the alimentary canal is the foregut （element 27 in numbered diagram）, or stomodaeum. The foregut is lined with a cuticular lining made of chitin and proteins as protection from tough food. The foregut includes the buccal cavity （mouth）, pharynx, esophagus, and Crop and proventriculus （any part may be highly modified）, which both store food and signify when to continue passing onward to the midgut. Here, digestion starts as partially chewed food is broken down by saliva from the salivary glands. As the salivary glands produce fluid and carbohydrate-digesting enzymes （mostly amylases）, strong muscles in the pharynx pump fluid into the buccal cavity, lubricating the food like the salivarium does, and helping blood feeders, and xylem and phloem feeders.

From there, the pharynx passes food to the esophagus, which could be just a simple tube passing it on to the crop and proventriculus, and then on ward to the midgut, as in most insects. Alternately, the foregut may expand into a very enlarged crop and proventriculus, or the crop could just be a diverticulum, or fluid filled structure, as in some Diptera species.

Bee defecating. Note the contraction of the anus, which provides internal pressure.

The salivary glands （element 30 in numbered diagram） in an insect's mouth produce saliva. The salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium, located behind the hypopharynx. By moving its mouthparts （element 32 in numbered diagram） the insect can mix its food with saliva. The mixture of saliva and food then travels through the salivary tubes into the mouth, where it begins to break down. Some insects, like flies, have extra-oral digestion. Insects using extra-oral digestion expel digestive enzymes onto their food to break it down. This strategy allows insects to extract a significant proportion of the available nutrients from the food source.

中腸

Once food leaves the crop, it passes to the midgut （element 13 in numbered diagram）, also known as the mesenteron, where the majority of digestion takes place. Microscopic projections from the midgut wall, called microvilli, increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. In some insects, the role of the microvilli and where they are located may vary. For example, specialized microvilli producing digestive enzymes may more likely be near the end of the midgut, and absorption near the origin or beginning of the midgut.

後腸

In the hindgut （element 16 in numbered diagram）, or proctodaeum, undigested food particles are joined by uric acid to form fecal pellets. The rectum absorbs 90% of the water in these fecal pellets, and the dry pellet is then eliminated through the anus （element 17）, completing the process of digestion. The uric acid is formed using hemolymph waste products diffused from the Malpighian tubules （element 20）. It is then emptied directly into the alimentary canal, at the junction between the midgut and hindgut. The number of Malpighian tubules possessed by a given insect varies between species, ranging from only two tubules in some insects to over 100 tubules in others.

呼吸系統

Insect respiration is accomplished without lungs. Instead, the insect respiratory system uses a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to tissues that need it via their trachea （element 8 in numbered diagram）. Since oxygen is delivered directly, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. The insect circulatory system has no veins or arteries, and instead consists of little more than a single, perforated dorsal tube that pulses peristaltically. Toward the thorax, the dorsal tube （element 14） divides into chambers and acts like the insect's heart. The opposite end of the dorsal tube is like the aorta of the insect circulating the hemolymph, arthropods' fluid analog of blood, inside the body cavity. Air is taken in through openings on the sides of the abdomen called spiracles.

There are many different patterns of gas exchange demonstrated by different groups of insects. Gas exchange patterns in insects can range from continuous and diffusive ventilation, to discontinuous gas exchange. During continuous gas exchange, oxygen is taken in and carbon dioxide is released in a continuous cycle. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest. Diffusive ventilation is simply a form of continuous gas exchange that occurs by diffusion rather than physically taking in the oxygen. Some species of insect that are submerged also have adaptations to aid in respiration. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies, which may be held or trapped in special structures.

循環系統

Insect blood or haemolymph's main function is that of transport and it bathes the insect's body organs. Making up usually less than 25% of an insect's body weight, it transports hormones, nutrients and wastes and has a role in, osmoregulation, temperature control, immunity, storage （water, carbohydrates and fats） and skeletal function. It also plays an essential part in the moulting process. An additional role of the haemolymph in some orders, can be that of predatory defence. It can contain unpalatable and malodourous chemicals that will act as a deterrent to predators. Haemolymph contains molecules, ions and cells; regulating chemical exchanges between tissues, haemolymph is encased in the insect body cavity or haemocoel. It is transported around the body by combined heart （posterior） and aorta （anterior） pulsations, which are located dorsally just under the surface of the body. It differs from vertebrate blood in that it doesn't contain any red blood cells and therefore is without high oxygen carrying capacity, and is more similar to lymph found in vertebrates.

Body fluids enter through one-way valved ostia, which are openings situated along the length of the combined aorta and heart organ. Pumping of the haemolymph occurs by waves of peristaltic contraction, originating at the body's posterior end, pumping forwards into the dorsal vessel, out via the aorta and then into the head where it flows out into the haemocoel. The haemolymph is circulated to the appendages unidirectionally with the aid of muscular pumps or accessory pulsatile organs usually found at the base of the antennae or wings and sometimes in the legs, with pumping rates accelerating with periods of increased activity. Movement of haemolymph is particularly important for thermoregulation in orders such as Odonata, Lepidoptera, Hymenoptera and Diptera.

內分泌系統

These glands are part of the endocrine system:

1. Neurosecretory cells

2. Corpora cardiaca

3. Prothoracic glands

4. Corpora allata

生殖系統

主條目：Insect reproductive system

雌性

Female insects are able make eggs, receive and store sperm, manipulate sperm from different males, and lay eggs. Their reproductive systems are made up of a pair of ovaries, accessory glands, one or more spermathecae, and ducts connecting these parts. The ovaries make eggs and accessory glands produce the substances to help package and lay the eggs. Spermathecae store sperm for varying periods of time and, along with portions of the oviducts, can control sperm use. The ducts and spermathecae are lined with a cuticle.

The ovaries are made up of a number of egg tubes, called ovarioles, which vary in size and number by species. The number of eggs that the insect is able to make vary by the number of ovarioles with the rate that eggs can be developed being also influenced by ovariole design. In meroistic ovaries, the eggs-to-be divide repeatedly and most of the daughter cells become helper cells for a single oocyte in the cluster. In panoistic ovaries, each egg-to-be produced by stem germ cells develops into an oocyte; there are no helper cells from the germ line. Production of eggs by panoistic ovaries tends to be slower than that by meroistic ovaries.

Accessory glands or glandular parts of the oviducts produce a variety of substances for sperm maintenance, transport, and fertilization, as well as for protection of eggs. They can produce glue and protective substances for coating eggs or tough coverings for a batch of eggs called oothecae. Spermathecae are tubes or sacs in which sperm can be stored between the time of mating and the time an egg is fertilized. Paternity testing of insects has revealed that some, and probably many, female insects use the spermatheca and various ducts to control or bias sperm used in favor of some males over others.

雄性

The main component of the male reproductive system is the testis, suspended in the body cavity by tracheae and the fat body. The more primitive apterygote insects have a single testis, and in some lepidopterans the two maturing testes are secondarily fused into one structure during the later stages of larval development, although the ducts leading from them remain separate. However, most male insects have a pair of testes, inside of which are sperm tubes or follicles that are enclosed within a membranous sac. The follicles connect to the vas deferens by the vas efferens, and the two tubular vasa deferentia connect to a median ejaculatory duct that leads to the outside. A portion of the vas deferens is often enlarged to form the seminal vesicle, which stores the sperm before they are discharged into the female. The seminal vesicles have glandular linings that secrete nutrients for nourishment and maintenance of the sperm. The ejaculatory duct is derived from an invagination of the epidermal cells during development and, as a result, has a cuticular lining. The terminal portion of the ejaculatory duct may be sclerotized to form the intromittent organ, the aedeagus. The remainder of the male reproductive system is derived from embryonic mesoderm, except for the germ cells, or spermatogonia, which descend from the primordial pole cells very early during embryogenesis. The aedeagus can be quite pronounced or de minimis. The base of the aedeagus may be the partially sclerotized phallotheca, also called the phallosoma or theca. In some species the phallotheca contains a space, called the endosoma （internal holding pouch）, into which the tip end of the aedeagus may be withdrawn （retracted）. The vas deferens is sometimes drawn into （folded into） the phallotheca together with a seminal vesicle.

Internal of different taxa

蜚蠊目

Cockroaches are most common in tropical and subtropical climates. Some species are in close association with human dwellings and widely found around garbage or in the kitchen. Cockroaches are generally omnivorous with the exception of the wood-eating species such as Cryptocercus; these roaches are incapable of digesting cellulose themselves, but have symbiotic relationships with various protozoans and bacteria that digest the cellulose, allowing them to extract the nutrients. The similarity of these symbionts in the genus Cryptocercus to those in termites are such that it has been suggested that they are more closely related to termites than to other cockroaches, and current research strongly supports this hypothesis of relationships. All species studied so far carry the obligate mutualistic endosymbiont bacterium Blattabacterium, with the exception of Nocticola australiensis, an Australian cave dwelling species without eyes, pigment or wings, and which recent genetic studies indicates are very primitive cockroaches.

Cockroaches, like all insects, breathe through a system of tubes called tracheae. The tracheae of insects are attached to the spiracles, excluding the head. Thus cockroaches, like all insects, are not dependent on the mouth and windpipe to breathe. The valves open when the CO₂ level in the insect rises to a high level; then the CO₂ diffuses out of the tracheae to the outside and fresh O₂ diffuses in. Unlike in vertebrates that depend on blood for transporting O₂ and CO₂, the tracheal system brings the air directly to cells, the tracheal tubes branching continually like a tree until their finest divisions, tracheoles, are associated with each cell, allowing gaseous oxygen to dissolve in the cytoplasm lying across the fine cuticle lining of the tracheole. CO₂ diffuses out of the cell into the tracheole. While cockroaches do not have lungs and thus do not actively breathe in the vertebrate lung manner, in some very large species the body musculature may contract rhythmically to forcibly move air out and in the spiracles; this may be considered a form of breathing.

鞘翅目

The digestive system of beetles is primarily based on plants, which they for the most part feed upon, with mostly the anterior midgut performing digestion. However, in predatory species （e.g., Carabidae） most digestion occurs in the crop by means of midgut enzymes. In Elateridae species, the predatory larvae defecate enzymes on their prey, with digestion being extraorally. The alimentary canal basically comprises a short narrow pharynx, a widened expansion, the crop and a poorly developed gizzard. After there is a midgut, that varies in dimensions between species, with a large amount of cecum, with a hingut, with varying lengths. There are typically four to six Malpighian tubules.

The nervous system in beetles contains all the types found in insects, varying between different species. With three thoracic and seven or eight abdominal ganglia can be distinguished to that in which all the thoracic and abdominal ganglia are fused to form a composite structure. Oxygen is obtained via a tracheal system. Air enters a series of tubes along the body through openings called spiracles, and is then taken into increasingly finer fibers. Pumping movements of the body force the air through the system. Some species of diving beetles （Dytiscidae） carry a bubble of air with them whenever they dive beneath the water surface. This bubble may be held under the elytra or it may be trapped against the body using specialized hairs. The bubble usually covers one or more spiracles so the insect can breathe air from the bubble while submerged. An air bubble provides an insect with only a short-term supply of oxygen, but thanks to its unique physical properties, oxygen will diffuse into the bubble and displacing the nitrogen, called passive diffusion, however the volume of the bubble eventually diminishes and the beetle will have to return to the surface.

Like other insect species, beetles have hemolymph instead of blood. The open circulatory system of the beetle is driven by a tube-like heart attached to the top inside of the thorax.

Different glands specialize for different pheromones produced for finding mates. Pheromones from species of Rutelinea are produced from epithelial cells lining the inner surface of the apical abdominal segments or amino acid based pheromones of Melolonthinae from eversible glands on the abdominal apex. Other species produce different types of pheromones. Dermestids produce esters, and species of Elateridae produce fatty-acid-derived aldehydes and acetates. For means of finding a mate also, fireflies （Lampyridae） utilized modified fat body cells with transparent surfaces backed with reflective uric acid crystals to biosynthetically produce light, or bioluminescence. The light produce is highly efficient, as it is produced by oxidation of luciferin by the enzymes luciferase in the presence of ATP （adenosine triphospate） and oxygen, producing oxyluciferin, carbon dioxide, and light.

A notable number of species have developed special glands that produce chemicals for deterring predators （see Defense and predation）. The Ground beetle's （of Carabidae） defensive glands, located at the posterior, produce a variety of hydrocarbons, aldehydes, phenols, quinones, esters, and acids released from an opening at the end of the abdomen. While African carabid beetles （e.g., Anthia some of which used to comprise the genus Thermophilum） employ the same chemicals as ants: formic acid. While Bombardier beetles have well developed, like other carabid beetles, pygidial glands that empty from the lateral edges of the intersegment membranes between the seventh and eighth abdominal segments. The gland is made of two containing chambers. The first holds hydroquinones and hydrogen peroxide, with the second holding just hydrogen peroxide plus catalases. These chemicals mix and result in an explosive ejection, forming temperatures of around 100 C, with the breakdown of hydroquinone to H₂ + O₂ + quinone, with the O₂ propelling the excretion.

Tympanal organs are hearing organs. Such an organ is generally a membrane （tympanum） stretched across a frame backed by an air sac and associated sensory neurons. In the order Coleoptera, tympanal organs have been described in at least two families. Several species of the genus Cicindela in the family Cicindelidae have ears on the dorsal surface of the first abdominal segment beneath the wing; two tribes in the family Dynastinae （Scarabaeidae） have ears just beneath the pronotal shield or neck membrane. The ears of both families are to ultrasonic frequencies, with strong evidence that they function to detect the presence of bats via their ultrasonic echolocation. Even though beetles constitute a large order and live in a variety of niches, examples of hearing is surprisingly lacking in species, though it is likely that most are just undiscovered.

革翅目

The neuroendocrine system is typical of insects. There is a brain, a subesophageal ganglion, three thoracic ganglia, and six abdominal ganglia. Strong neuron connections connect the neurohemal corpora cardiaca to the brain and frontal ganglion, where the closely related median corpus allatum produces juvenile hormone III in close proximity to the neurohemal dorsal arota. The digestive system of earwigs is like all other insects, consisting of a fore-, mid-, and hindgut, but earwigs lack gastric caecae which are specialized for digestion in many species of insect. Long, slender （extratory） malpighian tubules can be found between the junction of the mid- and hind gut.

The reproductive system of females consist of paired ovaries, lateral oviducts, spermatheca, and a genital chamber. The lateral ducts are where the eggs leave the body, while the spermatheca is where sperm is stored. Unlike other insects, the gonopore, or genital opening is behind the seventh abdominal segment. The ovaries are primitive in that they are polytrophic （the nurse cells and oocytes alternate along the length of the ovariole）. In some species these long ovarioles branch off the lateral duct, while in others, short ovarioles appear around the duct.

雙翅目

The genitalia of female flies are rotated to a varying degree from the position found in other insects. In some flies this is a temporary rotation during mating, but in others it is a permanent torsion of the organs that occurs during the pupal stage. This torsion may lead to the anus being located below the genitals, or, in the case of 360° torsion, to the sperm duct being wrapped around the gut, despite the external organs being in their usual position. When flies mate, the male initially flies on top of the female, facing in the same direction, but then turns round to face in the opposite direction. This forces the male to lie on its back in order for its genitalia to remain engaged with those of the female, or the torsion of the male genitals allows the male to mate while remaining upright. This leads to flies having more reproduction abilities than most insects and at a much quicker rate. Flies come in great populations due ir ability to mate effectively and in a short period of time especially during the mating season.

The female lays her eggs as close to the food source as possible, and development is very rapid, allowing the larva to consume as much food as possible in a short period of time before transforming into the adult. The eggs hatch immediately after being laid, or the flies are ovoviviparous, with the larva hatching inside the mother. Larval flies, or maggots, have no true legs, and little demarcation between the thorax and abdomen; in the more derived species, the head is not clearly distinguishable from the rest of the body. Maggots are limbless, or else have small prolegs. The eyes and antennae are reduced or absent, and the abdomen also lacks appendages such as cerci. This lack of features is an adaptation to a food-rich environment, such as within rotting organic matter, or as an endoparasite. The pupae take various forms, and in some cases develop inside a silk cocoon. After emerging from the pupa, the adult fly rarely lives more than a few days, and serves mainly to reproduce and to disperse in search of new food sources.

鱗翅目

In reproductive system of butterflies and moths, the male genitalia are complex and unclear. In females there are three types of genitalia based on the relating taxa: monotrysian, exoporian, and dytresian. In the monotrysian type there is an opening on the fused segments of the sterna 9 and 10, which act as insemination and oviposition. In the exoporian type （in Hepaloidae and Mnesarchaeoidea） there are two separate places for insemination and oviposition, both occurring on the same sterna as the monotrysian type, 9/10. In most species the genitalia are flanked by two soft lobes, although they may be specialized and sclerotized in some species for ovipositing in area such as crevices and inside plant tissue. Hormones and the glands that produce them run the development of butterflies and moths as they go through their life cycle, called the endocrine system. The first insect hormone PTTH （Prothoracicotropic hormone） operates the species life cycle and diapause （see the relates section）. This hormone is produced by corpora allata and corpora cardiaca, where it is also stored. Some glands are specialized to perform certain task such as producing silk or producing saliva in the palpi. While the corpora cardiaca produce PTTH, the corpora allata also produces jeuvanile hormones, and the prothorocic glands produce moulting hormones.

In the digestive system, the anterior region of the foregut has been modified to form a pharyngial sucking pump as they need it for the food they eat, which are for the most part liquids. An esophagus follows and leads to the posterior of the pharynx and in some species forms a form of crop. The midgut is short and straight, with the hindgut being longer and coiled. Ancestors of lepidopteran species, stemming from Hymenoptera, had midgut ceca, although this is lost in current butterflies and moths. Instead, all the digestive enzymes other than initial digestion, are immobilized at the surface of the midgut cells. In larvae, long-necked and stalked goblet cells are found in the anterior and posterior midgut regions, respectively. In insects, the goblet cells excrete positive potassium ions, which are absorbed from leaves ingested by the larvae. Most butterflies and moths display the usual digestive cycle, however species that have a different diet require adaptations to meet these new demands.

In the circulatory system, hemolymph, or insect blood, is used to circulate heat in a form of thermoregulation, where muscles contraction produces heat, which is transferred to the rest of the body when conditions are unfavorable. In lepidopteran species, hemolymph is circulated through the veins in the wings by some form of pulsating organ, either by the heart or by the intake of air into the trachea. Air is taken in through spiracles along the sides of the abdomen and thorax supplying the trachea with oxygen as it goes through the lepidopteran's respiratory system. There are three different tracheae supplying oxygen diffusing oxygen throughout the species body: The dorsal, ventral, and visceral. The dorsal tracheae supply oxygen to the dorsal musculature and vessels, while the ventral tracheae supply the ventral musculature and nerve cord, and the visceral tracheae supply the guts, fat bodies, and gonads.

參見

• 形態學 （生物學）
• Insect physiology
• Lepidoptera morphology
• Insect ecology
• Insect flight
• 無脊椎動物
• 昆蟲
• 昆蟲學
• Prehistoric insect