No. of corneal facets in one ocellus is

Options

A. 2,000
B. 200
C. 10
D. 1

Answer

To determine the number of corneal facets in one ocellus, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Ocellus**:
- An ocellus is a type of simple eye found in insects, such as cockroaches. It is different from compound eyes, which are made up of multiple units.

**Hint**: Remember that ocelli are simple eyes, while compound eyes consist of many facets.

2. **Identify the Structure of Ocellus**:
- The ocellus is composed of hexagonal units known as ommatidia. Each ommatidium contains a lens and photoreceptor cells.

**Hint**: Ommatidia are the building blocks of the ocellus, and they play a crucial role in vision.

3. **Count the Number of Ommatidia**:
- Each ocellus typically contains a large number of ommatidia. In the case of the cockroach, one ocellus has approximately 2,000 ommatidia.

**Hint**: Focus on the number associated with the ocellus in cockroaches, which is critical for understanding its vision.

4. **Determine the Number of Corneal Facets**:
- Each ommatidium has a corneal facet, which is the outer part of the ommatidium that contributes to light reception. Therefore, the number of corneal facets in one ocellus is equal to the number of ommatidia.

**Hint**: Remember that corneal facets and ommatidia are directly related; each ommatidium corresponds to one facet.

5. **Final Answer**:
- Since one ocellus contains approximately 2,000 ommatidia, it also has about 2,000 corneal facets.

**Hint**: The final number you arrive at should reflect the total count of ommatidia, as they are synonymous with corneal facets in this context.

### Conclusion:
The number of corneal facets in one ocellus is approximately **2,000**.