Photoreceptors in Pheretima are present

Options

A. On the ventral side of skin
B. On the dorsal side of skin
C. On both sides
D. In clitellum

Answer

### Step-by-Step Solution:

1. **Understanding Photoreceptors**: Photoreceptors are specialized cells that detect light. In the case of Pheretima (earthworm), these cells are characterized by having a single nucleus and clear cytoplasm.

2. **Structure of Photoreceptors**: The cytoplasm of these photoreceptors contains a network of neurofibrilli, which are essential for transmitting nerve impulses. Additionally, they have a small transparent L-shaped lens, known as the optic organelle, that helps focus light rays.

3. **Location of Photoreceptors**: Photoreceptors in Pheretima are located in the inner parts of the epidermis.

4. **Dorsal vs. Ventral Surface**: The photoreceptors are specifically found on the dorsal surface of the skin, meaning they are not present on the ventral side.

5. **Abundance of Photoreceptors**: These photoreceptors are more numerous on the prostonium (the anterior part of the earthworm) and the first segment of the body.

6. **Final Conclusion**: Therefore, the photoreceptors in Pheretima are present on the dorsal side of the skin.

### Final Answer:
Photoreceptors in Pheretima are present on the dorsal side of the skin.

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