___________ is a vestigial organ that acts as the site for the formation of blood cells in the developing embryo.

Options

A. Chorion
B. Amnion
C. Allantois
D. Yolk sac

Answer

**Step-by-Step Solution:**

1. **Identify the Function of the Organ**: The question asks for a vestigial organ that serves as a site for the formation of blood cells in a developing embryo.

2. **Consider the Options**: The options provided include Corion, Amniot, Allantois, and Yolk Sac. Each of these has different functions in the context of embryonic development.

3. **Analyze Each Option**:
- **Corion**: This is a protective layer that surrounds the embryo but does not form blood cells.
- **Amniot**: This is a fluid-filled structure that provides cushioning for the embryo but is not involved in blood cell formation.
- **Allantois**: This structure is primarily involved in waste management for the embryo, not blood cell formation.
- **Yolk Sac**: This organ is responsible for providing nutrition to the embryo in its early stages and is also the site where blood cells are formed.

4. **Determine the Vestigial Organ**: The Yolk Sac is considered a vestigial organ because, after the early stages of development, it is replaced by the placenta, which takes over its functions.

5. **Conclude the Answer**: Therefore, the correct answer to the question is "Yolk Sac".

**Final Answer**: Yolk Sac

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