1. Formation of blastula

2. Gastrulation

3. Early gastrula
ectoderm: blue; dorsal lip of blastopore: green
endoderm: yellow; yolk: orange

4. Mid-gastrula
Blue: ectoderm; Green: chordomesoderm
Red: mesoderm (ventral lip); Yellow: endoderm

5. Late gastrula (yolk plug stage)
Green: notochord
Yellow: endoderm lining the archenteron

6. Formation of neural plate and early neurulation

7. Neural tube stage and late neurula

9. 3-4 mm frog embryo
Formation of brain vescicles:
prosencephalon
mesencephalon
rhombencephalon

11. In situ hybridization

12. Steps in the activation
of a receptor tyrosine
kinase:

13. Neural Induction

15. Mechanical factors which may contribute to
Neurulation:

16. Cadherins and cell adhesion

17. Example of
Cell-Cell
Recognition via
Cadherins: