1. Xenopus laevis, the South African three clawed frog
Oocytes surgically removed

2. Stages of Xenopus development
Oocytes in the ovary. Note blood vessels
Unfertilized eggs, in jelly coats
Grey
crescent
Sperm
entry
point
Fertilized egg, 30 min.
4-cell stage, 2.5 hr

3. Stages of Xenopus development
Animal
pole
view
Blastopore
almost
closed
Late blastula, 9 hr. About 8000 cells
Late gastrula, 16 hr
Neural folds
Late neurula, 30 hr
Tadpoles, 2 weeks old, feeding

4. Fate maps, specification maps, competence maps, determination
Blastopore forms
at predicted
position
Fertilized eggs, marked with nile blue dye
Early gastrula, 10 hr
Cells injected
at 32 cell stage with
fluorescent dextrans,
as lineage tracers
32 cell
blastula
late gastrula

5. Embryonic induction by the Organizer
Hans
Spemann
( )

6. Xenopus conjoined twin produced by grafting Spemann’s organizer
M. Khokha and R. Harland