The centre sagittal section was stained with Nissl reagent. The scale bar represents 1 mm. (A–I) In situ hybridization with the DIG-labelled oct-GnRHR cRNA probe to fixed 5 μm-thick sections of Octopus brain. The scale bars represent 100 μm. Abbreviations: v., vertical lobe; fr.s.med., median superior frontal lobe; fr.i.med., median inferior frontal lobe; buc.s., superior buccal lobe; subv., subvertical lobe; b.d., dorsal basal lobe; b.a., anterior basal lobe; b.med., median basal lobe; br.po., posterior brachial lobe; pe.a., anterior pedal lobe; pe.p., posterior pedal lobe; pv., palliovisceral lobe; ch.p., posterior chromatophore lobe; vas.ven., ventral vasomotor lobe.