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A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamates (snakes, lizards and worm lizards).〔(【引用サイトリンク】title=Hemipenes )〕 Hemipenes are usually held inverted, within the body, and are everted for reproduction via erectile tissue, much like that in the human penis.〔(【引用サイトリンク】title=Iguana Anatomy )〕 Only one is used at a time, and evidence indicates males alternate use between copulations as a behavioral means of increasing sperm transfer when the interval between copulations is relatively brief.〔Tokarz, R. and Slowinski,J.Alternation of hemipenis use as a behavioural means of increasing spermtransfer in the lizard Anolis sagrei. AnimalBehaviour. 40: 374–379. 1990.〕 The hemipenis itself has a variety of shapes, depending on species. Often, the hemipenis bears spines or hooks, in order to anchor the male within the female. Some species even have forked hemipenes (each hemipenis has two tips). Sexual conflict over copulation duration may have shaped the evolution of hemipenis morphology, favoring more elaborate organs in species in which a long duration of copulation is especially beneficial to males, despite the associated costs to females.〔KING, RICHARD B.; JADIN, ROBERT C.; GRUE, MICHAEL; WALLEY, HARLAN D. Biological Journal of the Linnean Society. Sep2009, Vol. 98 Issue 1, p110-120. 11p.〕 Because they are everted and inverted, hemipenes do not have a completely enclosed channel for the conduction of sperm, but rather a seminal groove which seals as the erectile tissue expands. The word ''hemipenis'' (plural "hemipenes") comes from the word "hemi", meaning half, and "penis". == See also == * Reproduction of snakes 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「hemipenis」の詳細全文を読む スポンサード リンク
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