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Some frogs found in South and Central America have the ability to turn on and off their nearly transparent(透明的）body.
During the day, these frogs sleep by going under tree leaves. Their small bodies do not create shadows, making them almost invisible(看不见的) to birds and other animals that might consider them food. But when glass frogs wake up and move in search of insects and mates(伴侣), they take on a partly clear, reddish-brown color.
Researchers recently published the findings in Science. Junjie Yao of Duke University was a co- writer of the study."When they're transparent，it's for their safety,”Yao said about the frogs. When the animals are awake, they can escape their natural enemies. But when they are sleeping,they are more likely to be eaten. Yao explained, "They make changes to remain hidden.”
Using special technology, the researchers discovered the frogs'secret. While asleep, the frogs“hide” nearly 90 percent of their red blood cells(红细胞). Exactly how the frogs carry out these changes and why they can survive with almost no blood flow remains unknown. For most animals, having very little blood for several hours would be deadly.
“Only a few animals, most living in the ocean, are naturally transparent,” said Richard White of Oxford University.“Being transparent is rare(罕见的）in nature.especially in land animals.It's unheard of outside of the glass frog." Those that are transparent include some fish,worms and insects—none of which move lots of blood through their bodies.Frogs seem to be the only animals able to hide blood while sleeping. “The frogs' ability is really amazing,” he said.
在南美洲和中美洲发现的一些青蛙有开关它们几乎透明的身体的能力。白天，它们在树叶下睡觉时，小小的身体不会产生影子，鸟类和其他可能把它们当作食物的动物几乎看不到它们。但当玻璃蛙醒来动身去寻找昆虫和伴侣时，它们的身体就会呈现出部分透明的红褐色。
研究人员最近在《自然》杂志上发表了这一研究发现。杜克大学的姚俊杰是这项研究报告的共同作者。姚俊杰谈及青蛙说道：“玻璃蛙变成透明是为了保证它们的安全。”当这些动物醒着的时候，它们可以逃避它们的天敌。但是当它们在睡觉时，就有可能被吃掉。姚俊杰解释说：“它们作出改变是为了藏起来。”
利用特殊技术，研究人员发现了青蛙的秘密。在睡觉时，青蛙“隐藏”了近90%的红细胞。这种青蛙究竟是如何进行这些变化的以及为什么它们在几乎没有血液流动的情况下能活下来还是个谜。对于大多数动物来说，连续几个小时血液稀少是致命的。
牛津大学的Richard White说：“只有少数动物是自然透明的，大多数生活在海洋中。在自然界中，动物的身体透明是罕见的，尤其是在陆地动物中。除了玻璃蛙之外，这是闻所未闻的。”那些身体透明的动物包括一些鱼类、蠕虫和昆虫，它们体内都没有大量的血液流动。青蛙似乎是唯一能够在睡觉时隐藏血液的动物。他说：“这正是它们的独特之处。”
在南美洲和中美洲有一种玻璃蛙，这些蛙在睡觉时可以通过控制血液流动进行隐身，从而避免被吃掉。但在没有血液流动的情况下它们是如何生存的呢？目前这还是个谜。
