First Picture Book of Animals [antikvár]

Moving About Some animals move only once in their lives. Baby oysters and sponges, for example, swim until they find a good place to stay. Then they fasten themselves on to rocks and never move again. But most creatures travel to find food, warmth or a mate. They move to escape enemies, heat, frost or floods. To move in any direction, an animal must push something in the opposite direction. A horse trots by pushing back against the ground. A bird flies forward by pushing air backwards. A fish swims forward by thrusting water back. Animals have bodies which help them move whether they walk, swim or fly. Like cars, planes or ships, animals have 'engines' giving them the power to move themselves from place to place. A creature's engines are its muscles. Like a car's engine, muscles burn up fuel. An animal's fuel is the food it eats. Pistons move a car by turning wheels, but muscles move most animals by pulling levers. These levers are the limbs. Muscles tend to work in pairs. As one muscle shortens, the other in the same pair lengthens, and so on. Pairs of muscles fixed to long hinged bones movethemtoandfro. Limb bones worked like this help a dog to run ore bird to flap its wings. These animals push back with each limb, then bring each limb forward ready for another push. When a bird flaps its wings or a kangaroo leaps, the limbs work together as a pair. But when a horse or a dog walks or runs, the limbs work in turn. Not all animals have legs or wings to help them travel. A squid shoots itself along by squirting water out of its body. A fish swims along by bending its body from side to side and thrusting water back with its tail. Adam has one foot that it uses to dig into mud or sand. A slug slides forward by pushing against the ground with its muscular foot. Worms have no legs at all. They use bristles and plates on their skin to pull themselves along the ground. ˇ The pictures show how a horse moves from walking to trotting to galloping. In a gallop only two feet touch the ground at once. fC M ft ^ff ^ ^