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evo·ca·tor 'ē-vō-.kāt-ər, 'ev-ə- n the specific chemical constituent responsible for the physiological effects of an organizer
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evo·ca·tor (evґo-ka″tər) a chemical substance emitted by an organizer region of an embryo that evokes a specific morphogenetic response from competent embryonic tissue in contact with it.Medical dictionary. 2011.