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Stage 8 embryos are in the presomite period, have a greatest length of 0.5 to 2 mm and an estimated postfertilization age of approximately 21 to 25 days. The embryonic disc is ovoid or pyriform in shape when viewed from the dorsal aspect. The gastrulation (primitive) pit is present. Neural folds herald the beginning of primary neurulation. A primordial head-fold is not yet evident but a primordial tail-fold is present. A gastrulation (primitive) streak and node and notochordal canal are typically present.


New structures include cardiac mesoderm, lateral plate mesoderm, neural crest, neural plate, paraxial mesoderm, prechordal plate.

Section 120

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There are no published figures for this stage.