YDS READING PASSAGES / TEST 3 49. Soru

- 17. THE SENSORY RECEPTORS of ANIMALS

Animals, like humans, use their ability to see, hear, smell, taste and touch to respond to the world around them. But a good many animals also have special sensory receptors that help them as they move about and search for food. Some birds use the sun and stars to navigate. But when the sun or stars are not visible, birds must rely on other senses. The barnacle geese, for example, can detect the magnetic forces that surround the Earth. This special sense helps them know where they are in relation to the Earth's poles. Dolphins use a similar ability to detect the magnetic landmarks around them as they swim and search for food in murky waters. Locust use their eyes and antennae to navigate and to regulate their flying speed. By looking at the ground, they can determine how fast they are going. And if their antennae bend too much in the wind, they will slow down. A group of mackerel are able to swim together, even in the dark, without bumping into each other. They can do this because of a lateral-line organ that runs the length of its body. This organ detects movement in the water, such as ripples made by other fish, and helps the mackerel navigate and avoid its enemies. The thornback ray, like many other fish, has the ability to sense the small amounts of electricity given off by nerve impulses or muscle contractions. Pores around the ray's mouth pick up these electrical discharges and help the ray as it hunts for food. Some snakes, like the North American cottonmouth, have a special pit organ underneath their eyes that senses the heat given off by animals. The organ helps the snake find its prey, even in the dark of night. These are but a few examples of animals with special senses. These senses help them detect a wide variety of stimuli in the world around them as they move about and search for food.

According to the passage, a great number of animals ------ .