The process in which the germ layers are formed during embryonic development is called gastrulation. This stage is characterized by morphogenetic movements such as invagination, ingression, and involution.
In the invagination step, an epithelial lining of cells of the zygote moves inward.
In ingression, cells of the epithelial lining migrate to form the mesenchymal cells.
In involution, the embryonic tissue undergoes movement and folds inward giving rise to an underlying layer.
So the correct answer is Gastrula

Movement of Blastomeres in Gastrula Stage

In the process of embryonic development, blastomeres are the cells that are formed after the zygote undergoes multiple rounds of cell division. The movement of blastomeres is an essential aspect of embryogenesis, as it plays a crucial role in the formation of different germ layers and the establishment of the body plan.

What is Gastrula Stage?
The gastrula stage is a critical stage in embryonic development, which follows the blastula stage. During this stage, the blastula undergoes a process called gastrulation, where the cells undergo extensive rearrangement and movements to form three primary germ layers - ectoderm, endoderm, and mesoderm.

Movement of Blastomeres in Gastrula Stage
During gastrulation, the blastomeres undergo various movements to establish the three germ layers. These movements include:

1. Epiboly: This movement involves the spreading of the blastomeres to cover the entire surface of the embryo.

2. Invagination: In this movement, the cells at one end of the embryo fold inwards to form a depression called the blastopore. This process leads to the formation of the endoderm and mesoderm germ layers.

3. Delamination: This movement involves the splitting of a single layer of blastomeres into two layers. Delamination contributes to the formation of the ectoderm and endoderm.

4. Ingression: In this movement, individual cells detach from the outer layer and migrate into the embryo's interior. These cells form the mesoderm layer.

5. Migration: Once the germ layers are formed, the cells undergo further migration to their respective positions, contributing to the development of various organs and tissues.

Conclusion
The movement of blastomeres is a dynamic process that occurs during the gastrula stage of embryonic development. It involves complex cellular rearrangements that lead to the formation of the three germ layers and the establishment of the body plan. The gastrula stage is a crucial phase in embryogenesis, and the movement of blastomeres plays a significant role in shaping the developing embryo.