Fig. 2. Immunohistochemical localization of lamprey parapinopsin in the pineal organ. (A) Lamprey parapinopsin immunoreactivity is localized in the outer segment of the dorsal and peripheral photoreceptor cells of the pineal organ. A weak immunoreaction is observed in the cell bodies and the basal processes. (B) The lamprey parapinopsin immunoreactivity is localized in the pineal stalk. (C) In the parapineal organ, lamprey parapinopsin immunoreactivity is mainly localized in the dorsal region. (D) In control staining for lamprey parapinosin, no immunoreactivity was observed. l, lumen. Scale bars, 100 µm.