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. They no longer needed their legs for the purpose
of walking, but it was necessary for them to move quickly from
branch to branch. And so they changed a part of their skin
into a sort of parachute, which stretched between the sides of
their bodies and the small toes of their fore-feet, and gradually
they covered this skinny parachute with feathers and made
their tails into a steering gear and flew from tree to tree and
developed into true birds.

Then a strange thing happened. All the gigantic reptiles
died within a short time. We do not know the reason. Perhaps
it was due to a sudden change in climate. Perhaps they
had grown so large that they could neither swim nor walk nor
crawl, and they starved to death within sight but not within
reach of the big ferns and trees. Whatever the cause, the
million year old world-empire of the big reptiles was over.

The world now began to be occupied by very different
creatures. They were the descendants of the reptiles but they
were quite unlike these because they fed their young from the
``mammae'' or the breasts of the mother. Wherefore modern
science calls these animals ``mammals.'' They had shed the
scales of the fish. They did not adopt the feathers of the bird,
but they covered their bodies with hair. The mammals however
developed other habits which gave their race a great advantage
over the other animals. The female of the species