Dictionary of Human Evolution and Biology

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Embryonic Stage

Interval during human gestation following the preembryonic stage that extends from the second to the eighth week (14th to the 56th day) after conception (shorter in other primates). The embryonic stage is characterized by rapid structural development and differentiation of tissues in utero: the placenta forms, the main internal organs develop, and the major external body structures develop; only the heart and circulation are functioning, however.

Cf. fetal stage.

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