Which of the following embryonic membrane structure is excretory in function?

Options

A. Amnion
B. Allantois
C. Yolk sac
D. Vitelline chorion

Answer

To solve the question "Which of the following embryonic membrane structure is excretory in function?", we will analyze the given options one by one.

### Step-by-step Solution:

1. **Identify the Embryonic Membranes**:
- We have three embryonic membranes to consider: Amnion, Allantois, and Yolk Sac.

2. **Analyze the Function of Each Membrane**:
- **Amnion**: This membrane surrounds the embryo and contains amniotic fluid, which provides a protective environment for the developing embryo. It does not have an excretory function.
- **Allantois**: The allantois is an important structure that serves as a storage area for the embryo's waste products. It acts like a urinary bladder, collecting and storing waste until it can be excreted. This membrane is indeed excretory in function.
- **Yolk Sac**: The yolk sac is primarily responsible for nutrient uptake and secretion for the embryo. It provides nourishment but does not have an excretory function.

3. **Conclusion**:
- Based on the analysis, the only embryonic membrane that has an excretory function is the **Allantois**. Therefore, the correct answer is option number 2.

### Final Answer:
The embryonic membrane structure that is excretory in function is the **Allantois**.