Figure 4.

(a) Four nested optic lobe neuropils (lamina, medulla, lobula and lobula plate) and two successive chiasmata are shared by malacostracan and insect optic lobes. (b) Entomostracans possess only a lamina and a tectum, linked by uncrossed fibres (from Sinakevitch et al. 2003). An intermediate morphology that consists of a second plexiform layer (the medulla) but still lacking a lobula has not been seen in any extant taxon other than in the secondarily reduced visual system of the Zygentoma (Strausfeld 2005). (c) The homologue of the entomostracan tectum in malacostracans and insects is the lobula plate, here from the fly Phaenicia (from Sinakevitch et al. 2003), which receives uncrossed axons from the inner face of the medulla and from the lobula.