Lung development in the marsupial bandicoot, Isoodon macrourus.

The transformation of the terminal sacs present in the newborn into the alveoli observed in the adult, and the tissue and cellular composition of the interalveolar septum at various stages of lung development, were examined in the developing bandicoot. Lungs from 22 bandicoots, aged from 1 day postpartum to adult, were fixed with a glutaraldehyde/formaldehyde fixative and processed for examination of their structure. The respiratory region of the newborn lung is formed from terminating sacs, approximately 300-500 microns in diameter, which are delineated by thick connective tissue septa, have a highly vascularised internal lining and are present from birth until approximately Day 35 postpartum. The large blind sacs are then gradually replaced by alveoli, approximately 80 microns in diameter. In the juvenile and adult bandicoot, the connective tissue septa of the sacs are no longer discernible and a larger area of the blood capillaries of the lung is adjacent to the air within the alveoli. The changes in lung structure throughout pouch life probably reflect the increased respiratory requirements of the developing young. Although the time sequence of lung development in the eutherian differs from that in the marsupial, the adult form of the lung in both animal groups is similar in structure.