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Taxis
A taxis (plural taxes〔http://www.thefreedictionary.com/taxis〕〔http://www.merriam-webster.com/dictionary/taxis〕〔http://dictionary.reference.com/browse/taxis〕 , from the Ancient Greek , meaning "arrangement"〔(τάξις ) in A Greek–English Lexicon by Liddell & Scott, Clarendon Press, Oxford, 1940〕) is the movement of an organism in response to a stimulus such as light or the presence of food. Taxes are innate behavioral responses. A taxis differs from a tropism (turning response, often growth towards or away from a stimulus) in that the organism has motility and demonstrates guided movement towards or away from the stimulus source.〔Dusenbery, David B. (2009). ''Living at Micro Scale'', Ch. 14. Harvard University Press, Cambridge, Mass. ISBN 978-0-674-03116-6.〕 It is sometimes distinguished from a kinesis, a non-directional change in activity in response to a stimulus.
== Classification ==
Taxes are classified based on the type of stimulus, and on whether the organism's response is to move towards or away from the stimulus. If the organism moves towards the stimulus, the taxis is positive, while if it moves away, the taxis is negative. For example, flagellate protozoans of the genus ''Euglena'' move towards a light source. This reaction or behaviour is called "positive phototaxis", since phototaxis refers to a response to light, and the organism is moving towards the stimulus.
Many types of taxis have been identified, including aerotaxis (stimulation by oxygen) anemotaxis (by wind), barotaxis (by pressure), chemotaxis (by chemicals), durotaxis (by stiffness), electrotaxis or galvanotaxis (by electric current), gravitaxis (gravity), hydrotaxis (by moisture), magnetotaxis (by magnetic field), phototaxis (by light), rheotaxis (by fluid flow), thermotaxis (by changes in temperature) and thigmotaxis (by physical contact).
Depending on the type of sensory organs present, a taxis can be classified as a klinotaxis, where an organism continuously samples the environment to determine the direction of a stimulus; a tropotaxis, where bilateral sense organs are used to determine the stimulus direction; and telotaxis, where a single organ suffices to establish the orientation of stimulus.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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