hills and they became plants. Others preferred to move about and they
grew strange jointed legs, like scorpions and began to crawl along
the bottom of the sea amidst the plants and the pale green things that
looked like jelly-fishes. Still others (covered with scales) depended
upon a swimming motion to go from place to place in their search for
food, and gradually they populated the ocean with myriads of fishes.

Meanwhile the plants had increased in number and they had to search for
new dwelling places. There was no more room for them at the bottom of
the sea. Reluctantly they left the water and made a new home in the
marshes and on the mud-banks that lay at the foot of the mountains.
Twice a day the tides of the ocean covered them with their brine. For
the rest of the time, the plants made the best of their uncomfortable
situation and tried to survive in the thin air which surrounded the
surface of the planet. After centuries of training, they learned how
to live as comfortably in the air as they had done in the water. They
increased in size and became shrubs and trees and at last they learned
how to grow lovely flowers which attracted the attention of the busy big
bumble-bees and the birds who carried the seeds far and wide until the
whole earth had become covered with green pastures, or lay dark under
the shadow of the big trees. But some of the fishes too had begun to
leave the sea, and they had learned how to breathe with lungs as well as
with gills. We call such creatures amphibious, which means that they
are able to live with equal ease on the land and in the water. The first
frog who crosses your path can tell you all about the pleasures of the
double existence of the amphibian.

Once outside of the water, these animals gradually adapted themselves
more and more to life on land. Some became reptiles (creatures who
crawl like lizards) and they shared the silence of the forests with
the insects. That they might move faster through the soft soil, they
improved upon their legs and their size increased until the world was
populated with gigantic forms (which the hand-books of biology list
under the names of Ichthyosaurus and Megalosaurus and Brontosaurus)
who grew to be thirty to forty feet long and who could have played with
elephants as a full grown cat plays with her kittens.

Some of the members of this reptilian family began to live in the tops
of the trees, which were then often more than a hundred feet high