Development of lung, kidney and skin in the brushtail possum, Trichosurus vulpecula.

The thyroid gland is not present at birth in marsupials and thyroid function begins during the latter half of pouch life. The hormonal output of the thyroid gland is important for normal development. In this study the structure of the lung, kidney and skin of the developing possum was examined and the structural development of these three organs was described. The lung of the newborn brushtail possum was functional and continued to develop during pouch life, alveolar formation beginning at day 39 and concluding at day 113 postpartum. The mesonephric kidneys of the newborn possum degenerated and were replaced by the metanephric kidneys, the nephrogenic zone of the metanephric kidney being present from 35 to 96 days postpartum. No new nephrons were formed after day 96. After the completion of nephrogenesis, the kidney increases in size through glomerular and tubular growth. The sequence of steps in the development of the possum skin was identical to that observed in other marsupials. The epidermis of the possum was thickest at 60 microns on about day 28 postpartum and as development proceeded the epidermis gradually decreased in thickness. A sparse number of primordia of hair follicles were observed at day 10 and the possum had a good covering of hair by day 129 postpartum. Correlation between the development of the lung, kidney and skin with the previously published plasma thyroxine concentration in the young possum suggests that thyroxine from the mother and from the young is important in the development of these three organs.