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A love dart (also known as a gypsobelum) is a sharp, calcareous or chitinous dart which some hermaphroditic land snails and slugs create. Love darts are made in sexually mature animals only, and are used as part of the sequence of events during courtship, before actual mating takes place. Darts are quite large compared to the size of the animal: in the case of the semi-slug genus ''Parmarion'', the length of a dart can be up to one fifth that of the semi-slug's foot.〔 The process of using love darts in snails is a form of sexual selection.〔(Tales of two snails: sexual selection and sexual conflict in Lymnaea stagnalis and Helix aspersa Oxford Journals )〕 Prior to copulation, each of the two snails (or slugs) attempts to "shoot" one (or more) darts into the other snail (or slug). There is no organ to receive the dart; this action is more analogous to a stabbing, or to being shot with an arrow or flechette. The dart does not fly through the air to reach its target however; instead it is fired as a contact shot. The love dart is not a penial stylet (in other words this is ''not'' an accessory organ for sperm transfer). The exchange of sperm between both of the two land snails is a completely separate part of the mating progression. Nevertheless, recent research shows that use of the dart can strongly favor the reproductive outcome for the snail that is able to lodge a dart in its partner. This is because mucus on the dart introduces a hormone-like substance that allows far more of its sperm to survive. Love darts, also known as shooting darts, or just as darts, are shaped in many distinctive ways which vary considerably between species. What all the shapes of love darts have in common is their harpoon-like or needle-like ability to pierce. ==The mating dance== Mating begins with a courting ritual. For example, in land snails of the genus ''Helix'', including the escargot ''Helix pomatia'', and the common garden snail ''Helix aspersa'' (also known as ''Cornu aspersum'' and ''Cantareus aspersus''), copulation is preceded by an elaborate tactile courtship. The two snails circle around each other for up to six hours, touching with their tentacles, and biting lips and the area of the genital pore, which shows some preliminary signs of the eversion of the penis. As the snails approach mating, hydraulic pressure builds up in the blood sinus surrounding the organ housing the dart. Each snail manoeuvres to get its genital pore in the best position, close to the other snail's body. Then, when the body of one snail touches the other snail's genital pore, it triggers the firing of the dart. The darting can sometimes be so forceful that the dart ends up buried in the internal organs.〔(Reproductive behaviour ) (2008) In Encyclopædia Britannica. Retrieved 3 October 2008, from Encyclopædia Britannica Online〕 It can also happen that a dart will pierce the body or head entirely, and protrude on the other side.〔('Love darts' double snail's chance of offspring ) ''New Scientist'', 20 March 2006. The photo in this article shows a dart which has pierced the body entirely, and is protruding on the other side.〕 After both snails have fired their darts, the snails copulate and exchange sperm. A snail does not have a dart to fire the very first time it mates, because the first mating is necessary to trigger the process of dart formation.〔 Once a snail has mated, it fires a dart before some, but not all, subsequent matings. A snail often mates without having a dart to use,〔(Mating and Copulation ) written by Robert Nordsieck, Retrieved 8 August 2009〕 because it takes time to create a replacement dart. In the case of the garden snail ''Helix aspersa'', it takes a week for a new dart to form.〔() In New Scientist, Roxanne Khamsi, published 20 March 2006, cited 5 August 2009〕 The dart is shot with some variation in force, and with considerable inaccuracy, such that one-third of the darts that are fired in ''Helix aspersa'' either fail to penetrate the skin, or miss the target altogether.〔(Are Snails' ''Love Darts'' Source of Cupid Lore? ) McGill Tribune, 13 February 2002.〕 Snails have only very simple visual systems and cannot see well enough to use vision to help aim the darts. 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「Love dart」の詳細全文を読む スポンサード リンク
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