A Swedish Professor at Natural History came out to the farm to ask me for help. He had come to Africa to find out at what stage of the embryo (胚胎) state the foot of the monkeys begins to differ from the human foot. For this purpose, he meant to go and shoot Colobus monkeys on Mount Elgon.

“You will never find out from the Colobus monkeys,” I said to him, “they live in the tops of the trees and are shy and difficult to shoot. It would be the greatest luck should you get the embryo you want.”

The Professor was hopeful. He was going to stay out till he had got his foot, he said, even if it was be for years. He had applied to the Game Department for permission to shoot the monkeys he wanted. The permission he was, in view of the high scientific object of his research, certain to get, but so far he had had no reply.

“How many monkeys have you asked to be allowed to shoot?” I asked him

He told me that he had, to begin with, asked for permission to shoot fifteen hundred monkeys.

Now I knew the people at the Game Department, and I assisted him to send in a second letter asking for a reply by return of post, since the Professor was keen to get off on his research. The answer from the Game Department did, for once, come by return of post. The Game Department, they wrote, were pleased to inform Professor Landgreen that, in view of the scientific object of his research, they had seen their way to make an exception from their rules, and to raise the number of monkeys on his license from four to six.

I had to read the letter over twice to the Professor. When the contents at last were clear to him, he became so deadly shocked and hurt, that he did not say a single word. To my expressions of sympathy he made no reply, but walked out of the house, got into his car and drove away sadly.

Modern zoos are different from those built fifty years ago. At that time zoos were places where people could go to see animals from many parts of the world. The animals lived in cages with iron bars (栅栏). Although the zoo keepers took good care of them, many of the animals did not feel comfortable，and they often fell ill.

In modern zoos, people can see animals in more natural conditions. The animals are given more freedom in larger places so that they can live as they would in nature. Even the appearance of zoos has changed. Trees and grass grow in cages, and water flows through the places the animals live in. There are few bars; instead, there is often a deep ditch (沟), filled with water, which surrounds a space where several sorts of animals live together as they would naturally. In an American zoo, the visitors can walk through a special huge cage that is filled with trees, some small animals and many birds, and large enough for the birds to live naturally. In a zoo in New York, with the use of special nights, people can observe certain animals that are active only at night, when most zoos are closed. Some zoos have special places for visitors to watch animals that live in the desert or under water.

Modern zoos not only show animals to visitors, but also keep and save rare animals. For this reason, fifty years from now, the grandchildren of today's visitors will still be able to enjoy watching these animals.

Native to forests of Central and South America, glass frogs in the Centrolenidae family get their name from their skin and muscles that help them be perfectly fit to live in their jungle environment. Turn the frogs over, where the effect is the most impressive, and you’ll make out their hearts, livers, and other organs through their hyaline bellies (肚子).

And in a study published in the journal Science, researchers have discovered an amazing mechanism (机制) the animals use to become so clear.

When glass frogs go to sleep, they take in 89 percent of their brightly colored red blood cells into sacs (液囊) in their livers, which reflect incoming light and make the frogs appear nearly unseen. With their red blood cells out of view, the frogs become twice to three times more clear — a trick scientists believe helps the animals avoid being killed and eaten by their natural enemies.

“The trick is really hard to do, because their tissues are full of things that take in and spread light. And transparency (透明) is normal for many creatures in water, but hard on land,” says study co-author Jesse Delia. “Red blood cells also take in a lot of light, and we found that the frogs can actually hide themselves by packing them into the liver.”

Not only are the findings interesting, but the researchers attach great importance to them. That’s because many red blood cells in one place usually form a clot (血块), which can block and lead to a potentially life-threatening condition. But the frogs can seemingly clot and expand their red blood cells at will — without any negative effects. This may mean the animals already have what medical researchers have been seeking for decades: a biological mechanism which prevents too much bleeding while also preventing too much clotting.