Which is not correct about circulatory system of aves?
(a) Heart is four chambered
(b) Well developed renal portal system
(c) Sinus venosus and truncus arterious are lacking
(d) RBCs are nucleated

Options

A. Heart is four chambered
B. Well developed renal portal system
C. Sinus venosus and truncus arterious are lacking
D. RBCs are nucleated

Answer

To determine which statement is not correct about the circulatory system of birds (aves), we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Analyze Option (a): Heart is four chambered.**
- Birds have a well-developed four-chambered heart consisting of two atria and two ventricles. This is a characteristic feature of their circulatory system.
- **Conclusion:** This statement is correct.

2. **Analyze Option (b): Well developed renal portal system.**
- The renal portal system in birds is not well developed. Birds do not possess a well-developed renal portal system, which is a significant distinction from other vertebrates.
- **Conclusion:** This statement is not correct.

3. **Analyze Option (c): Sinus venosus and truncus arteriosus are lacking.**
- In birds, the sinus venosus and truncus arteriosus are indeed lacking. Instead, they have a more evolved structure for their circulatory system.
- **Conclusion:** This statement is correct.

4. **Analyze Option (d): RBCs are nucleated.**
- The red blood cells (RBCs) in birds are nucleated, which is a characteristic feature of avian physiology. This is different from mammals, where RBCs are typically enucleated.
- **Conclusion:** This statement is correct.

### Final Conclusion:
The only statement that is not correct about the circulatory system of birds is **(b) Well developed renal portal system**.