The first segment with nephridiopores is  

Options

A. `5^(th)`
B. `4^(th)`
C. `2^(nd)`
D. `3^(rd)`

Answer

To solve the question regarding the first segment with nephridiopores in earthworms, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Earthworm**:
- Earthworms have a segmented body structure. Each segment can have different organs and structures.

2. **Identify the Excretory Organ**:
- The main excretory organ in earthworms is called nephridia. These are responsible for excretion and osmoregulation.

3. **Types of Nephridia**:
- There are three types of nephridia based on their location in the segments:
- **Integumentary Nephridia**: These start from the third segment and continue throughout the body.
- **Pharyngeal Nephridia**: These are present from the fourth to the sixth segment.
- **Septal Nephridia**: These begin from the fifteenth segment and extend to the end of the body.

4. **Determine the First Segment with Nephridiopores**:
- Since integumentary nephridia start from the third segment, this segment is the first one that contains nephridiopores.

5. **Conclusion**:
- Therefore, the first segment with nephridiopores in an earthworm is the **third segment**.

### Final Answer:
The first segment with nephridiopores is the **third segment**.

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