. The Ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975 . Figure 2. A. Glomeruli from a koala kidney showing the two measurements taken. B. Renal medullary tissue of a koala showing tubules (t), blood vessels (b), and collecting ducts (c). animals with greater urine-concentrating capability (Schmidt-Nielsen and O'Dell, 1961), was for the koala. Relative medullary thickness in the koala (Fig- ure 3) indicates that maximum urine concentration is comparatively low, suggesting that the ko
. The Ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975 . Figure 2. A. Glomeruli from a koala kidney showing the two measurements taken. B. Renal medullary tissue of a koala showing tubules (t), blood vessels (b), and collecting ducts (c). animals with greater urine-concentrating capability (Schmidt-Nielsen and O'Dell, 1961), was for the koala. Relative medullary thickness in the koala (Fig- ure 3) indicates that maximum urine concentration is comparatively low, suggesting that the koala is adapted to a habitat where water is not limiting. Other aspects of kidney morphology support this suggestion. The length of the renal papilla (Figure 3), which in- creases with dry habitat and diet (Schmidt-Nielsen, 1958), lies between that of the platypus (Ornitho- rhynchus anatinus), a water-living monotreme, and that of the dry habitat dasyurid marsupial Antechi- nomys laniger (Sperber, 1944). The difference in vol- ume between the cortical and juxtamedullary glo- meruli is greater in species from dry habitats than in those from a water-rich habitat (Munkacsi and Pal- kovits, 1965). The difference in glomerular volume % * E 3 6 9 Relative medullary thickness 12 Figure 3. Relationship between maximum urine osmolality and relative medullary thickness for a number of animals. Eutherian data (open circles) from Schmidt-Nielsen and O'Dell (1961); peramelid marsupial data (solid circles) from Hulbert and Dawson (1974b); macropodid marsupial data (open triangles) from Denny (1973); koala figure denoted by solid triangle. for the koala (Figure 4) is 60 percent, considerably less than that for the jerboa (Jaculus jaculus), a desert ro- dent (101 percent), or the bush baby (Galago sene- galensis), a semidesert-inhabiting subprimate (161 percent) (Munkacsi and Palkovits, 1965). The rel- ative proportions of the cortex and medulla given over to filtration also suggest that the ko
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