well fitted for bounding over the open plains — those of the climbing, leaf-eating koala, equally well fitted for grasping the branches of trees — those of the ground-dwelling, insect or root-eating, bandicoots — and those of some other Australian marsupials — should all be constructed on the same extraordinary type, namely with the bones of the second and third digits extremely slender and enveloped within the same skin, so that they appear like a single toe furnished with two claws.

Notwithstanding this similarity of pattern, it is obvious that the hind feet of these several animals are used for as widely different purposes as it is possible to conceive. The case is rendered all the more striking by the American opossums, which follow nearly the same habits of life as some of their Australian