The rats, sagacious creatures, instead of deserting their colony, showed that they possessed that species of wisdom which the Greek sage said was superior to all other knowledge—namely, the knowledge how to turn an evil to a good. Exploring this shallow lake which their carelessness had caused, they found several places still unsubmerged—islands, in fact. To one of these they swam, dug out new catacombs, and being now quite safe from interruption, and protected upon all sides, the Malthusian laws of population had full play, and soon proved its force, for the whole place swarmed with them. The axiom, however, that at the very point when empires are apparently most prosperous, their destruction is near at hand, to some extent applied even to the dominion of the water-rat. They were no longer to be the sole undisturbed possessors. Arguing _à priori_, one would have concluded that if this waste land was worthless before, now it was a marsh, and miasmatic vapours arose from it, it would be still more avoided. But the facts were exactly opposite. So soon as ever the water had spread over the level plain, and had well soaked into the sterile soil, there began to spring up tough aquatic grasses, commonly called bull-polls, from a supposed resemblance between their tangled appearance and the rough hair that hangs over the poll of a bull. These grasses are gregarious—that is to say, they prefer to grow in huge bunches. Each bunch increasing year after year, forms in time a small hillock or tuft, and, the roots spreading and spreading, these hillocks of grass almost covered the lake, leaving only narrow channels of water between. Upon these innumerable frogs and toads crawled up out of the water, and they were the chosen resorts of newts. In summer time the blue dragon-fly wheeled in mazes over them, or, while settled on the stiff blades of grass, looked like a species of blossom. The current of the brook brought down seeds, and soon the tall reed began to rear its slender stem, and rustle its feathery head in the breeze. The sedges came also, and fringed the marsh with a border of green. Meantime, the root which the rats had gnawed asunder beneath the ancient willow tree, felt the power of spring, and made one more effort. Freed from the incubus of the dead trunk, it threw out a shoot of its own. From this shoot there proceeded other shoots; and, in short, after a while the islands in the marsh became covered with willow trees and osier-beds. The reeds grew apace, and by the time the islands were clothed with willow, the rest of the marsh was occupied by them, saving only the fringe of sedge, and the almost immortal bull-polls, which were as tough as leather, and which nothing could kill.