In Earthworm, dorsal blood vessel is collecting channel

Options

A. Behind 13th segment
B. Anterior 13 segment
C. Throughout
D. In typhlosolar region

Answer

### Step-by-Step Solution:

1. **Identify the Dorsal Blood Vessel**: The dorsal blood vessel in an earthworm is the largest blood vessel that runs along the dorsal side of the body. It is situated above the elementary canal (intestine).

2. **Location of the Dorsal Blood Vessel**: This vessel extends from the anterior (front) end to the posterior (back) end of the earthworm, running mid-dorsally. It is important to note that it runs above the intestine.

3. **Understanding the Segments**: The intestine of the earthworm begins at the 15th segment and runs towards the posterior end. The dorsal blood vessel, being situated above the intestine, runs behind the 13th segment.

4. **Function of the Dorsal Blood Vessel**: The dorsal blood vessel acts as a collecting channel, receiving blood from various parts of the earthworm's body. It contains valves that prevent the backflow of blood.

5. **Evaluation of Options**:
- The dorsal blood vessel runs behind the 13th segment, which is correct.
- The other options regarding its position relative to the 13th segment or its relation to the commissural blood vessels are incorrect, as they do not accurately describe the location of the dorsal blood vessel.

6. **Conclusion**: Therefore, the statement that "in earthworm, the dorsal blood vessel is a collecting channel behind the 13th segment, above the intestine" is correct.

### Final Answer:
In earthworm, the dorsal blood vessel is a collecting channel located behind the 13th segment and above the intestine.

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