Gastrulation in a Megalecithal Embryo
The Early Chick Embryo
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Whole Mount of Chick Blastoderm AO = area opaca, AP = area pellucida P = region of thick blastoderm that marks the future posterior region of the embryo; area where gastrulation begins Arrows = movement of rapidly dividing cells of epiblast layer |
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Chick Embryo - Primitive Streak Stage AO = area opaca, AP = area pellucida, P= posterior The primitive streak is the region where epiblast cells converge (solid arrows) and move through a groove into the blastocoel (dashed arrows). The primitive steak consists of a lightly staining groove bordered on each side by darker staining ridges. Hensen's node marks the anterior of the streak and P marks the posterior. |
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Cross sections through Primitive streak Key to Upper Cross section: AO = area opaca, . AP = area pellucida, ^^ = remnants of yolk granules, arrows = direction of ingression of embryonic cells Lower Cross Section shows the three germ layers formed by the process of gastrulation. |
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