How Do Animals Grow and Change?动物是怎样成长和变化的？
I-8 / 008
How Do Animals Grow and Change?
Some animals change in form as they go through their lives. These animal babies hatch from eggs and do not look like the mother who laid the eggs. They go through changes as they grow. They begin to look like different kinds of animals. Scientists call these changes metamorphosis.
Invertebrates
A butterfly is an invertebrate that goes through metamorphosis. There are four stages in the metamorphosis of a butterfly. The female adult lays an egg that hatches into a larva. A larva looks somewhat like a worm but it is not a worm. If you look at a larva carefully, you can find six tiny legs at the end nearest to its head. You will also find other things that look like legs at the back end of the larva. These things are not legs, but they do help to hold larva to surfaces.
When the animal is in the larva stage of its life, it must eat much food in order to be strong and to grow. Its skin will not grow like yours. Larva must molt when the skin becomes too tight. There is a soft skin underneath that will get hard. Then later, that skin will have to be shed. This happens many times before larva is ready to go into the next stage.
Later the larva will go into a resting stage called the pupa. It will no longer look like a worm-like animal. It will work hard to make a strong safe place for itself on a twig. There the animal will remain for some time not moving or eating. A different kind of covering will form on the outside. The animal inside is changing. When everything is just right, an adult butterfly will come from the pupa skin.
An animal must be very strong to go through all four stages. Every time you see a butterfly, moth, or even a housefly, think about these stages of metamorphosis. The animal that you will be looking at had to survive these stages. The nature has a good plan for the animals of the earth to follow as they live, grow, and change.
必背词汇
练 习
Fill in the blanks.
1. (1) The four stages of metamorphosis of a butterfly are
____________ _____________
____________ _____________
(2) The skin of larva cannot grow and must be _____________ .
2. Arrange these words in proper order of growth.
adult larva egg pupa
(1) ________ (2) __________ (3) ___________ (4)_____________
译 文
动物是怎样成长和变化的？
一些动物的外形一生不断发生变化。这些小动物从卵中孵化，与产卵的母体长得并不像。它们随着成长而经历着变化，开始变得像不同种类的动物。科学家称这些变化为“变态”。
无脊椎动物
蝴蝶就是一种无脊椎变态动物。蝴蝶的变态过程分为四个阶段。雌蝴蝶产卵，卵孵化成幼虫。幼虫看起来像是一种蠕虫，但其实不是。如果你仔细观察，就会发现在接近它头部的末端有六只细小的脚。你还会在它背部的末端发现其他一些像脚的东西。这些其实不是脚，但却有助于支撑幼虫在地面上行动。
当蝴蝶处于幼虫阶段时，它需要吃很多东西以变得强壮并长大。它的皮肤的生长变化与我们的不同。当幼虫的皮肤变得非常紧时，它们必须要蜕皮。蜕皮后里层柔软的肌肤会逐渐变硬，不久后，这层皮肤会再次蜕掉。在幼虫进入下一个变态阶段前，这种现象会发生很多次。
随后，幼虫会进入一个被称为蛹的静止期。它看起来不再是蠕虫那样的动物了。它会在树枝上竭尽全力地为自己制造一个坚固而安全的居所。在那里，蛹不吃也不动，这种现象会持续一段时间。其间，一种不同的表皮会在身体外部形成，里面的动物也在发生变化。当一切时机都成熟时，一只成年的蝴蝶就会破蛹而出。
动物必须足够强壮，才能完成这四个阶段的转变。每次当你看到一只蝴蝶、飞蛾，或者家蝇时，想想它们所经历的这些变态阶段吧。你看到的动物必须成功地经历这些阶段才能够存活下来。大自然其实早已为地球上的动物妥善地安排好了生存、成长、变化的过程。
练 习
填空。
1. (1) 一只蝴蝶的四个变态阶段分别是
_____________ _____________
_____________ _____________
(2) 幼虫的皮肤不能生长，必须 ________________ 。
2. 按照成长顺序排列下面的单词。
成虫 幼虫 卵 蛹
(1) ___________ (2) ____________ (3) ____________ (4) _____________
答 案
1. (1) egg larva pupa adult
(2) shed
2. (1) egg (2) larva (3) pupa (4) adult