The nephridia present on both sides of inter segmental septa are located in 

Options

A. a. 4,5,6 seg
B. b. 15/16 - last
C. c. 16/17-last
D. d. 15/17 - last

Answer

To answer the question about the location of nephridia present on both sides of intersegmental septa in earthworms, we can follow these steps:

### Step-by-Step Solution:

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

2. **Location of Nephridia**:
- Nephridia are present in most segments of the earthworm, but not in all segments.

3. **Identifying Specific Segments**:
- The question specifically asks about the nephridia located on both sides of intersegmental septa. These septa are the walls that separate different segments of the earthworm.

4. **Determining the Range of Segments**:
- According to biological studies, the nephridia are found from the 15th segment to the last segment of the earthworm.

5. **Evaluating the Options**:
- Option A (4, 5, 6): These segments are part of the clitellum and do not contain nephridia.
- Option B (15, 16 to last): This option correctly identifies the segments where nephridia are present.
- Option C (16, 17 to last): This option is incorrect as it starts from the 16th segment.
- Option D (15, 17 to last): This option is also incorrect as it skips the 16th segment.

6. **Conclusion**:
- Based on the analysis, the correct answer is **Option B: 15, 16 to last segment**.