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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Pharyngeal slit ： ウィキペディア英語版 Pharyngeal slit Pharyngeal slits are filter-feeding organs found in Invertebrate chordates (lancelets and tunicates) and hemichordates living in aquatic environments. These repeated segments are controlled by similar developmental mechanisms. Some hemichordate species can have as many as 200 gill slits. Pharyngeal slits resembling gill slits are transiently present during the embryonic stages of tetrapod development. The presence of gill-like slits in the neck of the developing human embryo famously led Ernst Haeckel to postulate that "ontogeny recapitulates phylogeny"; this hypothesis, while false, contains elements of truth, as explored by Stephen Jay Gould in ''Ontogeny and Phylogeny''.〔. Also ISBN 0-674-63941-3 (paperback)〕 However, it is now accepted that it is the vertebrate pharyngeal pouches and not the neck slits that are homologous to the pharyngeal slits of invertebrate chordates. Gill slits are, at some stage of life, found in all chordates. ==Pharyngeal arches in Vertebrates== (詳細はgerm layers. Neural crest cells enter these arches where they contribute to craniofacial features such as bone and cartilage.〔 However, the existence of pharyngeal structures before neural crest cells evolved is indicated by the existence of neural crest-independent mechanisms of pharyngeal arch development. The first, most anterior pharyngeal arch gives rise to the oral jaw. The second arch becomes the hyoid and jaw support.〔 In fish, the other posterior arches contribute to the brachial skeleton, which support the gills; in tetrapods the anterior arches develop into components of the ear, tonsils, and thymus. The genetic and developmental basis of pharyngeal arch development is well characterized. It has been shown that Hox genes and other developmental genes such as ''dlx'' are important for patterning the anterior/posterior and dorsal/ventral axes of the branchial arches. Some fish species have jaws in their throat, known as pharyngeal jaws, which develop using the same genetic pathways involved in oral jaw formation. 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「Pharyngeal slit」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.