2A. Early gastrula stage (10-) S. tropicalis embryo in which bottle cell formation at the dorsal lip of the blastopore can be observed as a darkly pigmented area (arrowhead).
2B. An internal view of an early gastrula stage S. tropicalis embryo. Arrowhead illustrates involuted dorsal endomesoderm.
2C. A slightly later stage (10+) S. tropicalis embryo. Arrowhead denotes dorsal lip.
2D, 2E. Internal views of two 10+ S. tropicalis embryos illustrating consistent extent of involution of endomesoderm. Small arrowheads denote the ventral side, large arrowheads the dorsal side.
2F. Early gastrula stage (10-) X. laevis embryo. Arrowhead denotes dorsal lip.
2G. An example of an internal view of an X. laevis stage 10- embryo in which endomesoderm has already attached to overlying ectoderm (arrow), normally indicative of a later stage embryo. X. laevis embryos are often brittle internally and fracture during such dissections (arrowheads at top of figure).
2H. Defective gastrula stage X. laevis embryo showing defective boundary between vegetal endoderm and marginal zone indicated by lack of bottle cell formation (arrow).
2I, 2J. Variant gastrula stage X. laevis embryos in which the
involuting marginal zone (arrowheads) forms more torward the animal and
vegetal poles, respectively, than in the normal case.