Figure 11.

Comparison of unpaired midline neuropils in an arthropod and various polychaete worms. (a) Serotonin immunoreactivity in the brain of the hexapod Leucophaea maderae. The central body of the arthropod brain is a characteristic unpaired midline neuropil comprising columnar and tangential components. (b) Histamine immunoreactivity reveals a small, crescent-shaped neuropil in the brain of Nereis diversicolor. (c) FMRFamide-like immunoreactivity shows a neuropil composed of tangential and columnar elements in the brain of the polychaete Eunice torquata. Tangential fibers projecting from laterally arranged cell bodies give rise to crescent-shaped fiber tangles in the brain of Harmothoe areolata (d, FMRFamide immunoreactivity) and Lepidonotus clava (e, serotonin immunoreactivity). Scale bars: 80 μm.