Half a billion years ago, there existed a wormlike creature the size of a grain of rice.

5亿年前，生存着一种体型如米粒大小的蠕虫状生物。

This creature—the fly's early, wormlike phase—is just about capable of sensing its environment, searching for food and avoiding predators.

这种生物——苍蝇的早期蠕虫阶段——几乎能够感知其环境、寻找食物和躲避捕食者。

" No, " Pyat screeched. " No, to me, come to me, to meeeeeee" . His face crumbled inward, changing to something pale and wormlike.

" ，" 俳雅尖叫。" ，，到我这里，到我这里里里里里——" 他的脸向内塌陷，逐渐变成苍白的蛆。

It's called a Pikaia and it's a little wormlike creature but it's thought that this is a chordate, and that is the branch of life that we're in, so it could that this is our earliest known ancestor.

它叫皮卡虫，确实和普通虫子差多，人们认为它是一种脊索动物，也就是说，它和我们是同一类动物，所以这也许是我们最早的祖先了。

So eggs are laid in and around sources of water, and then, when it rains, or tides come into the wetlands, these eggs hatch, and out of these eggs hatch these wormlike larvae that swim around in the water.

因此，卵产在水源中和水源周围， 然后，当下雨或潮汐进入湿地时，这些卵就会孵化， 并从这些卵中孵化出这些在水中游游去的蠕虫状幼虫。