Incomplete double circulation is found in which of the following animals?

Options

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

Answer

To determine which animals exhibit incomplete double circulation, we can analyze the options provided in the question.

### Step-by-Step Solution:

1. **Understanding Double Circulation**:
- Double circulation refers to the separation of oxygenated and deoxygenated blood. In complete double circulation, blood passes through the heart twice: once to the lungs for oxygenation and once to the rest of the body.
- Incomplete double circulation occurs when there is some mixing of oxygenated and deoxygenated blood.

2. **Analyzing the Options**:
- **Option 1: Birds**:
- Birds have a four-chambered heart (two atria and two ventricles), which allows for complete separation of oxygenated and deoxygenated blood. Therefore, this option is incorrect.

- **Option 2: Mammals**:
- Similar to birds, mammals also possess a four-chambered heart. This structure ensures complete double circulation, making this option incorrect as well.

- **Option 3: Birds and Mammals**:
- Since both birds and mammals have complete double circulation, this option is also incorrect.

- **Option 4: Amphibians and Reptiles**:
- Amphibians and reptiles typically have a three-chambered heart (two atria and one ventricle). In this setup, oxygenated and deoxygenated blood can mix in the single ventricle, leading to incomplete double circulation. Therefore, this option is correct.

3. **Conclusion**:
- The correct answer is **Option 4: Amphibians and Reptiles**.