A 1915 monograph by the Nobel Prize–winning neuroanatomist Santiago Ramón y Cajal and Domingo Sánchez y Sánchez, describing neurons and their organization in the optic lobes of insects, is now standard fare for those studying the microcircuitry of the insect visual system. The work contains prescient assumptions about possible functional arrangements, such as lateral interactions, centrifugal pathways, and the convergence of neurons onto wider dendritic trees, to provide central integration of information processed at peripheral levels of the system. This chapter will consider further indications of correspondence between the insect-crustacean and the vertebrate visual systems, with particular reference to the deep organization of the optic lobe’s third optic neuropil, the lobula, and part of the lateral forebrain (protocerebrum) that receives inputs from it. Together, the lobula and lateral protocerebrum suggest valid comparison with the visual cortex and olfactory centers.
