Which of the following is present in first homeotherms ?

Options

A. Pronephric kindney
B. Opisthonephric kidney
C. Metanephric kidney
D. Archinephric kidney

Answer

### Step-by-Step Solution:

1. **Understanding Homeotherms**: Homeotherms are animals that maintain a constant body temperature regardless of the environmental temperature. This characteristic is essential for their survival and is achieved through a process called thermoregulation.

2. **Identifying the Types of Kidneys**: The question presents four types of kidneys:
- Pronephric kidney
- Opisthonephric kidney
- Metanephric kidney
- Archinephric kidney

3. **Analyzing Each Kidney Type**:
- **Pronephric Kidney**: This is the most primitive form of kidney and is not present in homeotherms.
- **Opisthonephric Kidney**: This kidney is a more developed form but still does not represent the advanced kidneys found in homeotherms.
- **Metanephric Kidney**: This is the most advanced kidney type and is found in amniotes, which include birds and mammals (the primary groups of homeotherms).
- **Archinephric Kidney**: This is a hypothetical and primitive kidney that predates the pronephric kidney and is not present in homeotherms.

4. **Conclusion**: Since metanephric kidneys are the most developed kidneys found in homeotherms (birds and mammals), the correct answer to the question is option 3: **Metanephric kidney**.