COMPARATIVE MORPHOLOGY OF THE LUNG WITH SPECIAL REFERENCE TO THE ALVEOLAR EPITHELIAL CELLS : I. LUNG OF THE AMPHIBIA

Abstract

Comparative morphological study on the lung of the frog and newt was made leading to the following conclusions : 1) The lung of the newt is the simplest among vertebrates and seems to work not only as a respiratory organ but also as static organ. 2) In the lung of the frog, the "Vorbronchus", which serves as a passage for air, and the "primitive alveoli", in which gas exchange is performed, are fairly well differentiated. 3) In the mammalian lung, the "alveolar epithelial cell" is often assumed to be of mesenchymal orgin. However, in the amphibian lung, the "alveolar wall cell" resembles the "alveolar epithelial cell", and it may be ascertained that the "alveolar wall cell" is of epithelial origin. 4) Osmiophilic bodies are found in the "alveolar wall cell" and in the "alveolar epithelial cell" of the frog, but not in those of the newt. It is assumed that these bodies are highly developed organelles, and therefore, are not found in the newt which is one of the lowest forms of vertebrates with lungs.