Morphological development of tammar wallaby lung. (A-H) Histological examination of H and E stained tammar pouch young lungs collected at (A) late gestation, ~ day 24; (B) postnatal day 1; (C) day 3; (D) day 20; (E) day 40: (F) day 60; (G) day 80 and (H) day 120 (H). (A) Fetal lungs at the canalicular stage of development. (B) The lungs of newborn consist of large terminal air sacs surrounded by a thick wall. (C,D) During early postnatal life, lung development was slow, with large air sacs still present at day 20 (D). (E-H) The alveoli-like structure appears by day 40 (E), however at day 40 they appear quite primitive and are transiting from sac-like stature to alveoli. Defined alveoli start appearing from day 60 (F) and progressively increased in number thereafter (F-H). Scale bar 1 mm.