Nephridia are present in all the segments of earthworm except

Options

A. Last segment
B. First 3 segments
C. First 2 segments
D. First and last segments

Answer

**Step-by-Step Solution:**

1. **Understanding Nephridia**: Nephridia are excretory organs found in earthworms. They play a crucial role in the excretion of waste products from the body.

2. **Identifying the Segments of Earthworm**: The earthworm's body is divided into segments. Each segment typically contains a pair of nephridia, except for certain segments.

3. **Identifying the Segments Without Nephridia**: The question specifically asks for the segments where nephridia are absent. It is noted that nephridia are not present in the first three segments of the earthworm.

4. **Naming the Segments**:
- The **first segment** is called the **Prostomium**, which is a flap-like structure that covers the mouth.
- The **second segment** is the **Peristomium**, which is the segment that contains the mouth.
- The **third segment** is the **first Metameric segment**, where the body starts to show segmentation.

5. **Conclusion**: Since nephridia are absent in the first three segments (Prostomium, Peristomium, and the first Metameric segment), the correct answer to the question is that nephridia are present in all segments of the earthworm except for these first three segments.

**Final Answer**: Nephridia are present in all segments of the earthworm except the first three segments: Prostomium, Peristomium, and the first Metameric segment.

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