THE KIDNEY STRUCTURE OF THE COMMON WOMBAT (VOMBATUS-URSINUS) AND THE HAIRY-NOSED WOMBAT (LASIORHINUS-LATIFRONS)

The common wombat (Vombatus ursinus) lives in a mesic habitat whereas the hairy-nosed wombat (Lasiorhinus latifrons) inhabits a xeric habita t. The kidney structure of these two wombats was studied and it was fo und that kidney size, kidney weight, and kidney weight as a percentage of body weight, were larger in V. ursinus. However, relative medullar y thickness, percentage medullary volume, and medullary thickness as a percentage of total thickness, were significantly greater in L. latif rons, suggesting that L. latifrons has a greater capacity to conserve water than does V. ursinus. The number of glomeruli and mean glomerula r area were the same in both species whereas the mean diameter of the proximal and distal tubules was larger in V. ursinus. There were more proximal tubules per square millimetre in L. latifrons. The larger num ber of collecting ducts per square millimetre in the medullary region in L. latifrons indicates that the nephrons join the collecting ducts deep in the medulla, a feature that has been associated with increased urinary concentrating ability. Urinary pH was significantly lower, an d urinary ammonia, creatinine and sodium levels were higher, in L. lat ifrons, as were plasma sodium and chloride levels. These data suggest that L. latifrons has a greater capacity to conserve water.