Gastrulation 

1. Gastrulation is the process through which the presumptive areas of organ specific rudimetns present on the surface of blastula move to their specific position where these occur in the adult.
2. The blastula forms gastrula and the process of formation of the gastrual is called as gastrulation.
3. The blastocoel is gradually lost and there is formation of new cavity called gastrocoel or archenterone.
4. In gastrulation, morphogenetic movements results in the formation of three germ layers.
5. The gastrocoel has a pore which is called as blastopore.
6. In protostomia, the blastopore forms mouth. Examples - Coelenterata to mollusca.
7. In deuterostomia, the blastopore forms anus. Examples - Echinodermata, hemichordata & chordata.
8. Initially, the gastrula is diploblastic i.e. it consists of ectoderm & endoderm lateron with the formation of mesoderm it becomes triploblastic.
9. Gastrula is also called as "pouch-within a pound" or "tube-within-a tube" stage.