What is nictitating membrane? Give its function.

Explanation

### Step-by-Step Solution:

1. **Definition of Nictitating Membrane**:
- The nictitating membrane is a transparent or translucent membrane that is found in certain animals, particularly amphibians like frogs. Unlike typical eyelids, which are opaque and cover the eye completely, the nictitating membrane can move across the eye without obstructing vision.

2. **Location**:
- In frogs, the nictitating membrane is located on the cornea of the eye. It acts as a protective layer that can be drawn across the eye when needed.

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