Gastrula is the embryonic stage in which

Options

A. cleavage occurs
B. blastocoel form
C. germinal layers form
D. villi form.

Explanation

**Step-by-Step Solution:**

1. **Understanding Gastrula**: The gastrula is an important embryonic stage that follows the blastula stage in the development of an embryo. It is characterized by the formation of the three primary germ layers: ectoderm, mesoderm, and endoderm.

2. **Gastrulation Process**: Gastrulation is the process that transforms the blastula into the gastrula. During this process, cells undergo rearrangement and differentiation to form the germ layers.

3. **Identifying the Correct Option**: The question asks about the embryonic stage in which the gastrula is formed. The options provided are:
- Cleavage
- Formation of blastocele
- Germinal layer
- Villi formation

4. **Analyzing Each Option**:
- **Cleavage**: This is the series of rapid cell divisions that occur after fertilization, leading to the formation of the blastula, not the gastrula.
- **Formation of Blastocele**: This refers to the formation of the fluid-filled cavity within the blastula, which is prior to gastrulation.
- **Germinal Layer**: This option refers to the formation of the primary germ layers during gastrulation, which is indeed when the gastrula is formed.
- **Villi Formation**: This is related to the development of structures in the placenta and is not directly related to the formation of the gastrula.

5. **Conclusion**: The correct answer is the third option, "germinal layer," as it directly relates to the formation of the gastrula during the process of gastrulation.

**Final Answer**: The correct option is C. Germinal layer formation.

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