Coloured scanning electron micrograph (SEM) of a small area from the left eye of a common Fruitfly (Drosophila melanogaster).
These tiny creatures are widely used in genetic experiments, particularly in mutation experiments, because they reproduce rapidly and their genetic systems are well understood. Wildtype (i.e. normal) Fruitflies have two compound eyes (red) – one on each side of the head. Each eye is a regular structure built up with 750 repeating units, or single lenses. Each single lens sends signals to the fly’s brain where they are combined and arranged into a mosaic map of the visual “outside world”. Tiny bristles between single lens units make sure the compound eye cannot be covered with dust or dirt particles, although it has also been hypothesized they measure flight speed.