Gastrulation: the development of

1. 
   It begins with the appearance of the Primitive Streak. It determines the direction of the embryo (body axis) and causes the development of the notochord, which induces neurulation.
   
2. 
   The structural parts of the primitive streak include: the primitive node, primitive pit and the primitive groove.
   
3. 
   It involves the invagination of the epiblast and cellular migration.
   
4. 
   During gastrulation, the three primary germ layers are established.
   
5. 
   The basic body plan is established, including the physical construction of the rudimentary primary body axis.
   
6. 
   As a result of the movements of gastrulation, cells are brought into new positions, allowing them to interact with cells that were initially not near them. This paves the way for inductive interactions, which are the hallmark of neurulation and organogenesis.
   
7. 
   The cells that enter through the node will become the notochord.
   
8. 
   As the cells continue to move in and the primitive groove forms; 
   
9. 
   The cells that migrate internally first will become the endoderm which contains the presumptive notochordal tissue as well;
   
10. 
    The cells that move internally will later migrate over the endoderm and form the mesoderm; 
    
11. 
    The cells that remain on the surface will form ectoderm.
    

Mesenchymal cells migrate from the primitive knot to form a midline cellular cord known as the notochordal process.

The notochordal process grows cranially until it reaches the prechordal plate, the future site of the mouth. In this area the ectoderm is attached directly to the endoderm without intervening mesoderm. This area is known as the oropharyngeal membrane, and it will break down to become the mouth.

At the other end of the primitive streak the ectoderm is also fused directly to the endoderm; this is known as the cloacal membrane (proctodeum), or primordial anus.

1. 
   Creates the neural tube, which gives rise to the central nervous system.
   
2. 
   Creates the neural crest, which migrates away from the dorsal surface of the neural tube, and gives rise to a diverse set of cell types.
   
3. 
   Creates the bona fide epidermis, which covers over the neural tube once it is created.