Pharyngula

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In developmental biology, the pharyngula, also known as the phylotypic stage, is a stage in embryonic development.[1] Named by William Ballard,[2] the pharyngula stage follows the blastula, gastrula and neurula stages. At the pharyngula stage, all vertebrate embryos show remarkable similarities,[3] containing the following features:

The branchial grooves are matched on the inside by a series of paired gill pouches. In fish, the pouches and grooves eventually meet and form the gill slits, which allow water to pass from the pharynx over the gills and out the body.

In the other vertebrates, the grooves and pouches disappear. In humans, the chief trace of their existence is the eustachian tube and auditory canal which (interrupted only by the eardrum) connect the pharynx with the outside of the head.

The existence of a common pharyngula stage for vertebrates was first proposed by German biologist Ernst Haeckel (1834–1919) in 1874.[4]

See also

References

  1. ^ Gilbert SF (2000). Developmental mechanisms of evolutionary change. in: Developmental Biology (6th ed.). Sinauer Associates. ISBN 0-87893-243-7.
  2. ^ Ballard WW (1981). "Morphogenetic Movements and Fate Maps of Vertebrates". American Zoologist 21 (2): 391–9. doi:10.1093/icb/21.2.391. http://icb.oxfordjournals.org/cgi/content/abstract/21/2/391.
  3. ^ Sprague, J., et al. (2006). "ZFIN Pharyngula Period Description". Zebrafish Information Network. http://zfin.org/zf_info/zfbook/stages/phar.html. Retrieved 2007-07-18.
  4. ^ Haeckel E (1874) Anthropogenie oder Entwickelungsgeschichte des Menschen. Engelmann, Leipzig