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Fish blastula. (A) Prior to
gastrulation, the deep cells are surrounded by the EVL. The animal surface
of the yolk cell is flat and contains the nuclei of the YSL. Microtubules
extend through the yolky cytoplasm and through the external region of the
YSL. (B) Late-blastula stage embryo of the minnow Fundulus, showing the
external YSL. The nuclei of these cells were derived from cells at the
margin of the blastoderm, which released their nuclei into the yolky
cytoplasm. (C) Fate map of the deep cells after cell mixing has stopped.
The lateral view is shown, and not all organ fates are labeled (for the
sake of clarity). (A and C after Langeland
and Kimmel 1997; B from Trinkaus
1993, photograph courtesy of the author.) |
