DEVELOPMENT OF LUNG, KIDNEY AND SKIN IN THE BRUSHTAIL POSSUM, TRICHOSURUS-VULPECULA

The thyroid gland is not present at birth in marsupials and thyroid fu nction begins during the latter half of pouch life. The hormonal outpu t of the thyroid gland is important for normal development. In this st udy the structure of the lung, kidney and skin of the developing possu m was examined and the structural development of these three organs wa s described. The lung of the newborn brushtail possum was functional a nd continued to develop during pouch life, alveolar formation beginnin g at day 39 and concluding at day 113 postpartum. The mesonephric kidn eys of the newborn possum degenerated and were replaced by the metanep hric kidneys, the nephrogenic zone of the metanephric kidney being pre sent 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 o ther marsupials. The epidermis of the possum was thickest at 60 mu m o n about day 28 postpartum and as development proceeded the epidermis g radually decreased in thickness. A sparse number of primordia of hair follicles were observed at day 10 and the possum had a good covering o f hair by day 129 postpartum. Correlation between the development of t he lung, kidney and skin with the previously published plasma thyroxin e concentration in the young possum suggests that thyroxine from the m other and from the young is important in the development of these thre e organs.