英语听力：自然百科 大迁徙 Great Migrations—12（在线收听） |
It takes four days for the larva to emerge. It gorges on its own egg case, before turning to tender milkweed. It must grow fat, build up its reserves for the long migration ahead. After two weeks of manic feasting, its body mass now 2,000 times what it was at birth. The caterpillar is ready. Anchored by silk, it begins its miracle. Over the next two weeks, the caterpillar literally dissolves into a bag of rich fluid. Its cells sprout anew, giving rise to wings, legs, antennae... and then...
After a scant few hours, it's ready to fly. This is a creature truly born to move, born to outstrip its parents and grandparents' heroic efforts, carrying aloft the genetic hopes of the species. Incredibly, more than a billion super monarchs are now taking off. And for the first time in four generations, they're heading south, heading for their winter home. |
| 原文地址：http://www.tingroom.com/lesson/zrbaike/2010/259342.html |