Neuronal parts list and wiring diagram for a visual system.

A catalogue of neuronal cell types has often been called a 'parts list' of the brain, and regarded as a prerequisite for understanding brain function. In the optic lobe of Drosophila, rules of connectivity between cell types have already proven to be essential for understanding fly vision. Here we analyse the fly connectome to complete the list of cell types intrinsic to the optic lobe, as well as the rules governing their connectivity.