Fig. 3. Immunohistochemical staining of mature SP-B in the developing lung of the snapping turtle. (A–C) SP-B was detected in the cytoplasm of subsets of epithelial cells in the gas-exchange area (arrows) at day 61 of incubation (A), after pipping (B) and after hatching, when staining intensified (C). (D–F) Tissues were incubated without primary antibody. Immunostaining was not observed at day 61 (D), after pipping (E) or after hatching (F). T, trabeculae. Scale bars, 50 µm.