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