Negative control sections (see Methods ). A. Peroxidase-antiperoxidase immunocytochemistry, transverse paraffin section of the radial nerve cord of E. fraudatrix. B. Immunofluorescent microscopy; transverse cryosection of the radial nerve cord of H. glaberrima. Nuclei are stained with Hoechst (blue). Dashed line shows the border between the ectoneural (en) and hyponeural (hn) parts of the radial nerve cord. C. Immunoelectron microscopy; the apical region of the ectoneural neuroepithelium of the radial nerve cord (E. fraudatrix). Note a single grain representing unspecific staining (arrowhead). ec, epinueral canal; re, non-neuronal roof epithelium. Scale bars = 20 μm in (A), 50 μm in (B), 5 μm in (C).