Mammalian foetus is directly surrounded by

Options

A. yolk sac cavity
B. aminiotic cavity
C. allantoic cavity
D. primary digestive cavity

Answer

To answer the question "Mammalian foetus is directly surrounded by," we will analyze the options given and explain the correct answer step by step.

### Step-by-Step Solution:

1. **Understanding the Terms**:
- First, we need to clarify the difference between an embryo and a fetus. The term "embryo" refers to the developing organism from fertilization until about 11 weeks of gestation. After this period, it is referred to as a "fetus."

2. **Identifying Surrounding Structures**:
- The question asks what surrounds the mammalian fetus. The options provided are:
- Yolk sac cavity
- Amniotic cavity
- Allantoic cavity
- Primary digestive cavity

3. **Analyzing Each Option**:
- **Yolk Sac Cavity**: This structure is present during the early stages of development (embryo stage) and is primarily involved in nutrient transfer before the placenta is fully functional. It is not directly surrounding the fetus.
- **Amniotic Cavity**: This is a fluid-filled space that surrounds the fetus. It contains amniotic fluid, which cushions the fetus, provides a stable temperature, and allows for movement. This cavity is crucial for the protection and development of the fetus.
- **Allantoic Cavity**: This structure is an extension of the yolk sac and is involved in waste storage and umbilical cord formation. It does not directly surround the fetus.
- **Primary Digestive Cavity**: This is related to the digestive system and is not involved in surrounding the fetus.

4. **Conclusion**:
- Based on the analysis, the structure that directly surrounds the mammalian fetus is the **amniotic cavity**. This cavity plays a vital role in protecting and supporting the developing fetus.

### Final Answer:
The mammalian fetus is directly surrounded by the **amniotic cavity**.