The correct answer to the question is:
- Cleavage
During the cleavage stage of embryonic development, the zygote undergoes rapid cell divisions without an increase in overall size. This process leads to the formation of blastomeres, which are a group of cells resulting from these initial divisions. As cleavage progresses, the blastomeres arrange themselves to form the three primary germ layers known as ectoderm, mesoderm, and endoderm. These germ layers are essential as they give rise to various tissues and organs in the developing embryo. Once the blastomeres have organized into these three germ layers, the cleavage stage is considered complete.
Therefore, cleavage is the developmental stage that is complete once the blastomeres arrange to form the three primary germ layers. This marks an important milestone in embryonic development as it sets the foundation for the differentiation and specialization of cells that will ultimately give rise to the various structures of the organism.
