Developmental expression of Tt-c - opsin. (A, B) At the middle larva stage Tt-c-opsin is expressed in two laterally symmetrical punctate domains, just anterior of the dorsal rim of the apical lobe (black arrows), consistent with the location of the larval eye spots, as observed in (A) dorsal and (B) lateral views. A medial-anterior domain of weak expression is also observed (black arrowhead in panel A). (C, D) At the early gastrula stage broad expression of Tt-c-opsin is observed at the animal pole, opposite the blastopore (*). (E, F) By the middle gastrula stage the blastopore (*) has shifted 90° relative to the animal pole, and Tt-c-opsin expression becomes localized to a medial anterior domain, which persists through the early larva stage (G, H). (C, E, G) blastoporal views; (D, F, H) lateral views.