Uropygial or preen glands occur in :-

Options

A. Reptiles
B. Birds
C. Amphibians
D. Mammals

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the occurrence of uropygial or preen glands. We need to identify which group of animals possesses these glands.

2. **Identifying the Options**: The options provided are:
- Reptiles
- Birds
- Amphibians
- Mammals

3. **Defining Uropygial or Preen Glands**: Uropygial glands, also known as preen glands, are specialized sebaceous glands that produce an oily substance. This substance is used by birds to coat their feathers, keeping them waterproof and in good condition.

4. **Locating Uropygial Glands**: These glands are typically found at the base of the tail in birds, specifically between the fourth caudal vertebra and the pygostyle.

5. **Analyzing Each Option**:
- **Reptiles**: Do not possess uropygial glands.
- **Birds**: Have well-developed uropygial glands that serve the purpose of preening their feathers.
- **Amphibians**: Do not have these glands.
- **Mammals**: Also do not have uropygial glands.

6. **Conclusion**: Based on the information, the correct answer is that uropygial or preen glands occur in **birds**.

### Final Answer:
**Birds**

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