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The osmeterium is a defensive organ found in all Papilionid larvae, in all stages.〔 The organ is situated in the prothoracic segment and can be everted when the larva feels threatened. The everted organ resembles a fleshy forked tongue not unlike a snake tongue and this along with the large eye like spots on the body might be used to startle birds and small reptiles. The osmeterial organ remains inside the body in the thoracic region in an inverted position and is everted when the larva is disturbed in any way emitting a foul, disagreeable odor which serves to repel ants,〔 small spiders 〔 and mantids.〔 The constitution of the osmeterial secretion varies from species to species and contains monoterpene hydrocarbons, sesquiterpenic compounds or a mixture of aliphatic acids and esters The fine structure of the osmetrium of ''Papilio demoleus libanius'' Fruhstorfer has been studied and found to contain 3 types of specialised cells for synthesis, acid secretion,〔 and storage.〔 of the osmeterial secretion. ==Structure== The fine structure of the osmeterium gland of Papilio larvae consists of the following cell types. *Ellipsoid gland cells have an extensively infolded basal plasma membrane, abundant ribosomes and whorls of smooth endoplasmic reticulum. The apical plasma membrane bears long microvilli extending into a mass of granular material containing electron-lucid cavities. Tangential slits occur in the epicuticle. These cells are presumed to be organic acid-secreting cells. *Tubular arm cells contain heterogeneous, electron-dense inclusions, extensively-branched nuclei and large mitochondria sometimes distended with electron-dense material. The apical plasma membrane bears short microvilli. The inner, dense epicuticle forms a complex ramifying system. These glandular cells presumably synthesize and secrete the mature secretion.〔 Specific study of Papilio demoleus libanius Fruhstorfer shows the possible existence of a third type of cell *Slack cells, loosely surround the ellipsoid gland cells. These cells possess papillae, well-developed, rough endoplasmic reticulum, and numerous secretory vacuoles of various sizes and electron density. They may function as storage cells.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「osmeterium」の詳細全文を読む スポンサード リンク
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