本帖最后由 taoyukun-daidai 于 2010-7-11 23:30 编辑
上午单词小马两遍结束但是还有不熟悉的单词，今天开始背后一半，（6）天文学 还有吴老师list4迅速过两遍。
Higher animals like dogs, horses, even human being look like their parents when they are born. There are some minor changes that occur as these animals grow. But the basic form and the structure stay the same. Now this is called direct development which is quiet different from that metamorphosis. When lower animals like ants, flies or sea-urchins emerge from the eggs, they don't look at all like their parents. Only after series of major changes do they take on the characteristic of their parents. Butterfly and moth provide the best example of what biologist call complete metamorphosis, because they pass through four stages of extreme changes. Here is the illustration of a butterfly at each of the four stages of complete metamorphosis.
The first stage is the egg. Butterflies usually lay their eggs on plants and these plants provide food when they transform into larvae- the second stage. After about months in this stage, a butterfly larva spins the cocoon of silk around itself. A larva in a cocoon is also called a pupa. So it is known as the pupil stage. The pupil stage is the period of inactivity when larva structures evolve into adult structure. Depending on the species, the pupil stage can last anywhere from a few days to several months. When the pupa finally mature into the adult butterfly, it pushes its way out of its cocoon and cross onto a twig or tree land and pumps blood into the trunk and wing until they are full size and strong. Now some insects like grasshopper and roaches have only three stages: egg, larva and adult. When an animal skips the pupil stage, it’s called incomplete metamorphosis. It is not only insects that undergo metamorphosis, frogs and toads are the most well known example of other form-changing animal. Frogs lay their eggs in water and the eggs hatch into tadpole. A tadpole looks more like little fish because it has tail and no legs, but it gradually loses its tail and develops into a four-legged frog.
For the next couple of weeks we'll be focusing on how animals communicate with each other. Up to now, we’ve had a rather narrow view of vocal warning that animals give each other. Some recent research indicates that this communication is a lot more complex than we’ve traditionally thought. Let me give you an example. Take prairie dogs. Of course they are not really dogs at all, but wild rodents who lived on the plains in the western part of United States. In case you can’t visualize them , let me describe them to you. There are about as big as squirrels, but without the bushy tail. And unlike squirrels, they live in holes in the ground and they spend a lot of time just outside their holes because they have a lot of enemies: hawks, coyotes, humans you name it. When they spot a potential threat they bark to warn their neighbor and then escape down into their holes. Big deal you say, well, it turns out, they can differentiate among predators. Researchers discovered that the bark differs for different predators. Coyote warnings are different from people warnings for instance. But it goes deeper than that, there is an actually evidence that the barks differentiate between individual predators of the same species. The researchers found for example, that the prairie dogs had different bark for each member of the research team. As we’ve discussed, the human eye has three different types of color receptors that respond to three basic colors red, green and blue or other colors are seem to combinations of these different types of the receptors. Birds, however, have receptors for these three basic colors and for ultraviolet or UV light. Thus, they have much greater color range. What is really interesting though, is the role that UV light plays in a bird's life. Scientists have discovered that bird's eye is extremely sensitive to ultraviolet light. In one experiment, robins were able to distinguish between two objects one complete unlit and one lit by very dim ultraviolet light. Even with the very dim UV light, the object was readily apparent to the robins. In another experiment, female birds were exposed to two male birds. One was behind the filter transparent UV light, and one was behind the filter blocked UV light. The female birds preferred the male bird behind the transparent filter. Those birds’ feathers may have appeared colorful. Hunting birds use UV light to track down small animals. This is possible because small animals use urine to mark the trails and urine absorbed UV light. The hunting birds can use the UV light to follow the trail to their prey.
听写3个老托。然后跟读20遍。然后学习冰冰再复述一下子。 读完第一篇了。。。
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楼主: taoyukun-daidai
发表于 2010-7-7 23:13:32
发表于 2010-7-10 07:23:37
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