This would explain how these active, furry, little beings of all sizes, from that of a good-sized cat to a rat, come to be sporting among the leaves of the grand forests of Brazil or on the edges of the Virginian swamps, sleeping during the day in the hollow trees, and prowling by night over the plantations, and among the rice-fields feeding on fruit and seeds, worms and insects, and even on young birds and rats. On the ground they walk heavily, with flat feet, but in the trees they swing from bough to bough (see Fig. 53), the little ones curling their tails round that of their mother and clinging to her back as she goes. Some of these opossums have even lost the pouch, and put their little ones at once on to the thick fur of their back as soon as they come out of their snug nests in the tree-hollows. They seem to have a happy time of it, these merry tree-climbers, and know well how to swing out of danger, or to feign death if they cannot escape, so that “cute as a ’possum” is a common American proverb. One kind, living in the swamps of Guiana, feeds almost entirely on crabs, while another, called the Yapock, has webbed feet and dives under water, feeding on fish and other water-animals. But here another question presents itself. How is it that these curious pouched animals have lived on in America as well as in Australia when they have been killed off in Europe and Asia? The answer to this is not far to seek if we remember that geology teaches us that there have been many changes of land and sea in past times, for the neck of land which joins South America to North America is very low and narrow, and a change of level of scarcely more than 2000 feet would break it up into islands; and as we know that such changes have taken place in past geological times, there is no doubt that once this neck was partially under the sea, and South America, like Australia, was a huge continental island, where the lower animals might struggle on and become settled, before the higher ones poured in to interfere with them. * * * * *