Stage 13 (13 hrs 0 min)
Early gastrula stage
Drown by T. Iwamatsu
(Abbr. dl: dorsal lip of blastopore)
Stage 13 (13 hrs 0 min) Early gastrula stage:
The blastoderm begins to expand (epiboly, about 1/4 of the yolk sphere) over the surface of the yolk sphere, and the pre- sumptive region of the embryonic shield arises as a thickened margin (dorsal lip) of the blastoderm. It is difficult to recognize the boundaries of theflattened marginal cells. The diameter of the cells in the central region of the blastoderm is 15-20 um.