Fig. 1. Immunohistochemical staining of TTF-1 in the developing lung of the snapping turtle. (A–C) TTF-1 was detected in the nuclei of epithelial cells of the trabeculae (T) and gas-exchange area (arrows). The greatest degree of staining occurring at day 61 of incubation (A), and was seen in fewer cells after pipping (B), with the lowest number and intensity after hatching (C). (D–F) Tissues were incubated without primary antibody. Immunostaining was not observed at day 61 (D), after pipping (E) or after hatching (F). Scale bars, 50 µm.