The Eyes Have It
Compound eyes come in two flavors. Fruitflies and houseflies have sophisticated open compound eyes with millions of light collecting neurons, all acting as independent light guides. In contrast beetles, bees and mosquitoes have primitive closed systems in which all light collecting neurons are fused. The open system is an evolutionary improvement and results in a significantly improved vision. Andrew Zelhof and Charles Zuker have found a protein that is responsible for directing the partioning of the eyes in the fruitfly. The absence of the protein called spacemaker (amusingly abbreviated spam) results in an open eye system being converted to a closed system. Addition of spacemaker converts a closed system to an open system.
Each of the 800 eye units of the fruit fly (center) has distinct light gathering units, they were formed under the direction of the spacemaker protein.