Complete loop of Henle is found in

Options

A. Amphibia
B. Reptilia
C. Birds
D. Mammals

Answer

### Step-by-Step Solution:

1. **Understanding the Loop of Henle**:
- The Loop of Henle is a U-shaped structure found in the nephron, which is the functional unit of the kidney. It plays a crucial role in the concentration of urine.

2. **Location of the Loop of Henle**:
- The Loop of Henle is located between the proximal convoluted tubule (PCT) and the distal convoluted tubule (DCT) within the nephron.

3. **Function of the Loop of Henle**:
- Its primary function is to absorb water and various ions from the filtrate (urine), which helps in the regulation of water balance and electrolyte levels in the body.

4. **Presence in Different Animal Groups**:
- The Loop of Henle is absent in fish and amphibians, as well as in reptiles.
- In birds, the Loop of Henle is rudimentary, meaning it is not fully developed.

5. **Complete Loop of Henle in Mammals**:
- In contrast, mammals possess a complete Loop of Henle, which is well-developed and functional, allowing for efficient water reabsorption and urine concentration.

6. **Conclusion**:
- Therefore, the complete Loop of Henle is found in mammals.

### Final Answer:
The complete Loop of Henle is found in **mammals**.

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