1. MAIN POINT: Gastrulation (folding) results in three embryonic germ layers: ectoderm which develop into skin and other topical structures, mesoderm which become bone and muscle, and endoderm which develop into organs.
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2. MAIN POINT: In amphibians, the dorsal lip contains the Spemann’s organizer which direct tissue “fate.”

3. Utility of Spemann’s Organizer in manipulating embryonic/tissue development.
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4. The elongated primitive streak (purple) of the chick embryo is the site of gastrulation. The dark, purplish apex is where the tissue “organizer” called Henson’s node lies.
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5. Neurulation results in the formation of the nervous system
Neurulation results in the formation of the nervous system. The central nervous system derives from the neural plate (B) and subsequent neural tube (E) while the peripheral nervous system derives from the neural crest (B, E).
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6. The rostral (front) portion of the neural tube develops into the telencephalon and diencephalon comprised of cortex and primitive structures such as the hypothalamus, thalamus, amygdala, hippocampus, etc. Behind this most rostral portion, the mesencephalon and rhombencephalon respectively develop into structures of the brainstem which are necessary for survival (breathing, consciousness). The most caudal (back) of the neural tube becomes the spinal cord.

7. Migration of neural crest cells and formation of central nervous system: P-proencephalon; forebrain, M-mesencephalon; midbrain

8. 33 hours, identify formation of areas of the central nervous and visual (optic vesicle) systems, heart, and localize the site of gastrulation.

9. 48 hours, further development of the central nervous and visual systems, and heart.

10. 72 hours, even further development of the systems and heart
72 hours, even further development of the systems and heart. Identify the major divisions of the brain (forebrain, midbrain, hindbrain), atrium and ventricles of heart, and optic cup/lens.