In earthworm metameric segmentation is present. However, internal septa are absent in :

Options

A. 10 anterior segments
B. 8 posterior segments
C. 4 anterior segments
D. All segments

Answer

**Step-by-Step Solution:**

1. **Understanding Metameric Segmentation**:
- Earthworms exhibit metameric segmentation, which means their bodies are divided into repeated segments. Each segment is called a metamere.

2. **Identifying the Structure of Earthworm**:
- Earthworms belong to the phylum Annelida and typically have around 100 to 120 segments. Each segment is separated by internal septa.

3. **Locating the Anterior Segments**:
- The anterior region of the earthworm includes the first few segments, specifically segments 1 to 4.

4. **Examining the Internal Structure**:
- In the first four segments (1st to 4th), the internal septa are absent. This means that the coelom (body cavity) is continuous in these segments.

5. **Identifying the Specific Segments**:
- The first segment contains the mouth, the second and third segments contain the buccal cavity, and the fourth segment contains the pharynx.

6. **Analyzing the Options**:
- Given the options:
- Option 1: 10 anterior segments – Incorrect, as there are only 4 segments without internal septa.
- Option 2: 8 posterior segments – Incorrect, as the absence of internal septa is not in the posterior segments.
- Option 3: 4 anterior segments – Correct, as we have established that the first four segments lack internal septa.
- Option 4: All segments – Incorrect, as only the first four segments lack internal septa.

7. **Conclusion**:
- The correct answer is that internal septa are absent in the **four anterior segments** of the earthworm.

---