What are ommatidia? Define mosaic vision of cockroach.

Explanation

### Step-by-Step Solution:

1. **Definition of Ommatidia**:
- Ommatidia are the individual visual units that make up the compound eyes of certain arthropods, including cockroaches. Each ommatidium functions as a separate photoreceptive unit.

2. **Number of Ommatidia in Cockroach**:
- A cockroach has approximately 2000 ommatidia in each of its compound eyes. This large number allows for a wide field of vision.

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