Amphibia 3 Amphibian 3 Animalia 3 Animals 3 Anura 3 Bufonidae 3 Electronic microscopic 3 Lung 3 Lung ultrastructure 3 Melanophryniscus stelzneri 3 Microscopy, Electron 3 Microscopy, Electron, Scanning Respiratory epithelium 3 Toad 3 Vertebrata 3 animal tissue article 3 cell ultrastructure 3 comparative anatomy 3 controlled study 3 female 3 lung alveolus cell type 1 3 lung alveolus cell type 2 3 lung parenchyma 3 lung structure 3 male 3 melanophryniscus stelzneri stelzneri 3 nonhuman 3 respiratory epithelium 3 scanning electron microscopy 3