The Ocean watched the reptiles in the great salt marsh, and saw many wonderful things. As the water in the marsh got lower and lower, being dried up by the Sun, the mud in the marsh got harder and firmer, and the reptiles in it, who lived partly on land and partly in the water, found after a while that there wasn't enough water left for them all to live in, so thousands of them crept inland, away from the sea, and made their homes in the great fern forests, or among the rocks on the bare hillsides and plains. And no matter what sort of a life they lived, they changed to suit it. Some made their homes in the soft earth along the edges of the marsh, squirming along on their stomachs, and as they did not need feet and legs to squirm with, their feet and legs got smaller and smaller, until they did not have any at all, and they became snakes. Some dug holes in the hard ground with their feet, to make homes for themselves, and from digging and digging, their feet became very strong, with hard, sharp nails on them. And those that lived under the ground all the time, feeding on the roots of plants, lost their eyes and became blind, because they no longer needed eyes to see with, in their dark burrows, just like the moles we see digging under our lawns to-day. Some, like the frogs and the turtles, stayed in the marshes. The frogs made holes in the mud to live in, but the turtles grew hard shells on their backs, so that they could carry their homes about with them, and sleep on the open ground without any fear that other animals could harm them. Some of the reptiles, who liked the water best, crawled out of the marshes into the rivers, and became crocodiles, and alligators, while those that went inland forgot all about the water, and instead of scales, or shiny skins, like the reptiles, they grew hair on their bodies, to protect them and keep them warm. Some, who took to living in the trees, grew sharp claws, and long legs, to climb with, while others, who did not care for climbing, but ran around on their four feet all day, found that after a time their feet grew very hard and strong, and because they did not use their toes any more, they gradually lost them, and grew hoofs, like the horse, or the deer. And some, who liked the trees better than the ground, because there were always plenty of berries and fruits to be found there, stayed in the tree-tops all the time, and never came to the ground. Their front fins had gradually become larger, from flopping them in the air all the time, and at last, after many thousands of years, these fins became wings, and the trees in the forest were full of birds.