An embryo at the stage following the bastula,when it is a hollow - cup shaped structure having three layers of cell....

The differentiation of the three germinal layers occurs during the process of gastrulation.

- Gastrulation:
During gastrulation, the blastula undergoes a series of complex morphogenetic movements that result in the formation of three primary germ layers - ectoderm, mesoderm, and endoderm.

- Process:
1. Ectoderm: The outermost layer of cells gives rise to structures such as the skin, nervous system, and sensory organs.
2. Mesoderm: The middle layer of cells gives rise to structures such as muscles, bones, and the circulatory system.
3. Endoderm: The innermost layer of cells gives rise to structures such as the digestive system and respiratory system.

- Significance:
The differentiation of these germ layers is crucial as they give rise to all the tissues and organs in the developing embryo. Each germ layer contributes to specific structures and plays a vital role in the overall development of the organism.

- Importance:
Understanding the process of gastrulation and the differentiation of germ layers is essential in developmental biology as it lays the foundation for the formation of complex multicellular organisms.

Therefore, the differentiation of the three germinal layers occurs during gastrulation, marking a critical stage in embryonic development.