Light micrograph section through the eye of a mutant fruit fly (Drosophila sp.). Each of the fly's compound eyes contains hundreds of separate image-forming facets (ommatidia). These tiny cone-shaped facets are made up of a lens and seven rhabdoms (dark blue dots). The rhabdoms are light sensitive cells which transmit nerve signals to the sight centres of the brain. In this fly there are only six rhabdoms. To form one view of it's surroundings, the fly's eye combines the separate images from each facet. Magnification = 250x.