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Fig. 6. Light micrograph (A) and electron micrographs (B–E) of pineal
photoreceptor cells. (A) Pineal photoreceptor cells exist in the dorsal
(arrowheads) and ventral region (arrows). (B) The outer segment of lamprey
parapinopsin-containing cells (electron dense) is in the dorsal region. It is
similar in shape to that of cone-type photoreceptor cells. (C) The outer
segment of pineal photoreceptor cells, which is lamprey parapinopsin
immunonegative (electron lucent), is in the ventral region. (D,E) Synaptic
ribbons in the basal processes of dorsal (D, arrowheads) and ventral (E,
arrowheads) photoreceptor cells. l, lumen. Scale bars, 10 µm in (A), 1
µm in (B,C) and 0.5 µm in (D,E).