Shown are in situ hybridization results depicting expression of xPer2 mRNA. Panels A, B, D, and F show a dorsal view of each embryo. Panels C and E show side views. All embryos are oriented with the anterior to the left. G–I show transverse sections and J shows a sagittal section of late tailbud stage embryos. Sections shown in G, H, and J are oriented with the dorsal side at the top right of the panel. Neural plate staining is shown in panel A (stage 16) and B (stage 18). C and D depict early tailbud embryos with continued expression in the CNS as well as in the eye (black arrow), otic vesicle (black arrowhead), cement gland (blue arrow) and somites (red arrowheads). In late tailbud embryos (E and F), xPer2 is expressed in the otic vesicle (E,I, black arrowhead), pineal (F,G, orange arrowhead), brain, retina, lens (G), and olfactory pit (I, green arrowhead), although cement gland staining was lost (E, blue arrow). xPer2 was also present at low levels in the heart (H, blue arrowhead) and notochord (J, orange arrow). J also shows somite staining (red arrowheads).