Functional kidney of mammals is:

Options

A. Archinephros type
B. Opisthonephros type
C. Pronephros type
D. Metanephros type

Explanation

**Step-by-Step Solution:**

1. **Identify the Types of Kidneys**: Understand that there are four types of kidneys in animals: Archinephros, Opistonephros, Pronephros, and Metanephros.

2. **Define Each Type**:
- **Archinephros**: This is the most primitive type of kidney found in organisms like hagfish. It has a simple structure and minimal development.
- **Opistonephros**: This type is a modification of the Archinephros and is found in jawless fishes, such as Cyclostomes.
- **Pronephros**: This is a basic type of kidney that appears in the embryonic stage of mammals.
- **Metanephros**: This is the final and mature type of kidney that is present in adult mammals and other more developed organisms.

3. **Determine the Functional Kidney in Mammals**: Among the types mentioned, the Metanephros is the only kidney that is functional in adult mammals.

4. **Conclude the Answer**: The functional kidney of mammals is the Metanephros.

**Final Answer**: The functional kidney of mammals is the Metanephros.

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