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.
同时那些植物也增加了数目。海底已无它们容身之地，
Reluctantly they left the water and made a new home in the marshes and on the mudbanks that lay at the foot of the mountains.
于是不得不离开海水，去到山脚的泥滩或湿地上另筑新家。
Twice a day the tides of the ocean covered them with their brine.
海潮每天上来两次，将它们全身泡在咸水内。
For the rest of the time, the plants made the best of their uncomfortable situation
其余时，它们就在不舒服的情况中将就对付，
and tried to survive in the thin air which surrounded the surface of the planet.
并且设法在包围星球表面的稀薄空气里生活着。
After centuries of training, they learned how to live as comfortably in the air as they had done in the water.
经过许多年代的训练，它们学会如何在空气内生活与当年在水里生活同样的舒服。
They increased in size and became shrubs and trees
它们的骨干长大了，长成大小的树木，
and at last they learned how to grow lovely flowers which attracted the attention of the busy big bumble-bees and the birds
到最后，学会如何开美丽的鲜花，引动大野蜂与飞鸟的注意，
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.
这些蜂与鸟替它们到处去传播种子，使全世界都铺满了绿沉沉的草地和阴森森的树林。
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.
有的鱼类也渐渐离开海水，学会了如何用肺呼吸与用鳃呼吸一样方便。
We call such creatures amphibious, which means that they are able to live with equal ease on the land and in the water.
我们称这类动物为两栖类，意思就是它们既可以陆居，又可以水居。
The first frog who crosses your path can tell you all about the pleasures of the double existence of the amphibian.
你在半路遇到的小青蛙就可以告诉你两栖类的二重生活的快乐。
Once outside of the water, these animals gradually adapted themselves more and more to life on land.
这些动物，一旦离开水，渐渐能适应于陆居的生活。
Some became reptiles (creatures who crawl like lizards) and they shared the silence of the forests with the insects.
有的变成爬虫类（像壁虎之类会爬的），它们与昆虫同享树林里的安静。
That they might move faster through the soft soil,
它们为要在松土上来去得快些，
they improved upon their legs and their size increased until the world was populated with gigantic forms
便把它们的腿改良了，体格增长了，直到这世上充满无数庞大的动物
(which the handbooks of biology list under the names of Ichthyosaurus and Megalosaurus and Brontosaurus)
〔生物学教科书上将它们分为鱼龙（Ichthyosaurus）、斑龙（Megalosaurus）、雷龙（Brontosaurus）三种〕，
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.
这种动物长大到三四丈之长。他们作为成年的猫跟大象一起玩耍。
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.
有的爬虫类开始迁居到树顶，那时的树往往高至十余丈。
They no longer needed their legs for the purpose of walking, but it was necessary for them to move quickly from branch to branch.
它们不用腿走，所以必须另有方法迅速地往来于树林间。
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,
于是它们把身体上一部分的皮肉变成一对翅膀与足趾间的掌皮，
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.
翅膀渐渐长满了羽毛，又把尾巴当作舵，如此便可以自由飞翔，最后就发展成真正的飞鸟。