The retroperitoneal kidney is
(a) Kidney of fish
(b) Kidney covered by peritonium on ventral side
(c) Kidney covered by peritoneum on dorsal side
(d) Kidney uncovered by peritoneum on dorsal side.

Options

A. Kidney of fish
B. Kidney covered by peritonium on ventral side
C. Kidney covered by peritoneum on dorsal side
D. Kidney uncovered by peritoneum on dorsal side.

Answer

To determine the correct answer to the question regarding the retroperitoneal kidney, we can analyze the options step by step.

### Step-by-Step Solution:

1. **Understanding the Term "Retroperitoneal":**
- The term "retroperitoneal" refers to the anatomical space behind the peritoneum. Organs that are retroperitoneal are located behind the peritoneum and are only covered by peritoneum on their anterior (ventral) side.

2. **Analyzing Each Option:**
- **Option (a): Kidney of fish**
- Fish kidneys are not classified as retroperitoneal. This option is incorrect.

- **Option (b): Kidney covered by peritoneum on ventral side**
- This describes a retroperitoneal organ correctly. The kidney is covered by peritoneum only on the ventral side, which fits the definition of a retroperitoneal kidney. This option is correct.

- **Option (c): Kidney covered by peritoneum on dorsal side**
- This is incorrect because retroperitoneal organs are not covered by peritoneum on the dorsal side.

- **Option (d): Kidney uncovered by peritoneum on dorsal side**
- This option is misleading. While it is true that retroperitoneal organs are not covered by peritoneum on the dorsal side, it does not accurately describe the retroperitoneal kidney, which is specifically covered by peritoneum on the ventral side.

3. **Conclusion:**
- Based on the analysis, the correct answer is **(b) Kidney covered by peritoneum on ventral side.**

### Final Answer:
**(b) Kidney covered by peritoneum on ventral side.**