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Fig. 1. Three-dimensional views of normal frog development. Normal embryos from
gastrulation stages are presented in mid-sagittal view. Internal events of
gastrulation are clearly visible, including blastopore groove formation (A),
archenteron formation (B), archenteron elongation (C) and archenteron
inflation (D-F). Mesendoderm migration over the blastocoel roof initiates on
the dorsal side (A), and spreads laterally (B) and ventrally (C) before
meeting at the animal pole. In a corresponding manner, the blastocoel shrinks
and shifts ventrally. (G-I) Three embryos with very similar blastopores, but
with significantly different degrees of archenteron elongation. bc,
blastocoel; ac, animal cap; dbpl, dorsal blastopore lip; cleft, cleft of
Brachet; vbpl, ventral blastopore lip; arc, archenteron; mm, mesodermal
mantle; v, ventral; d, dorsal.
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