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Both sides of this batfi sh look the same.


Seeing Double T e batfish has a kind of symmetry called bilateral symmetry. It’s also called mirror symmetry. T at’s because it’s like looking in a mirror and seeing your ref lection. An exact copy of you looks back. Now imagine that the line you drew down the middle of the batfish is a mirror. T e fish’s right side looks like a ref lection of its leſt side. In nature, though, both sides aren’t always


exactly the same. You can see that if you draw a line of symmetry down the middle of your face. You might notice that one eyebrow is slightly higher than the other. Maybe when you smile, you’ve got only one dimple instead of two. Both sides of your face have an eye, an ear, and half a smile. Both are almost alike. So your face is still symmetrical.


Look at this funny fish. Its bright red


lips frown. Its eyes glare. It even has a tiny fishing rod hidden in its head. It sticks this body part out to catch its dinner. If this isn’t odd enough, check out the fish’s


four fins. It’s standing on them like they are feet! T is fish can swim. Yet it spends much of its time walking across the seaf loor on its fins. Meet the rosy-lipped batfish. T is batfish may be one of the weirder


looking animals in the sea. Yet in one way, it’s not odd at all. Like most animals, both sides of its body look the same. T is whacky fish is a great example of symmetry. Symmetry occurs when at least two sides of


something match. T at means it has parts that are similar in size and shape. Sometimes, these parts are evenly placed along a dividing line. Sometimes, they’re evenly spaced around a central point. Either way, it’s symmetry. Here’s how you can tell with the batfish.


Draw an imaginary line down the middle of the fish’s face. Each side has a bulging eye. Each side has two fins. T e line also divides the fishy frown in half. Both sides look the same. T at’s symmetry.


4 NATIONAL GEOGRAPHIC EXPLORER


Making Matches It’s even easier to see bilateral symmetry in a luna moth. Find one resting with its wings open. T en you can really see how its two sides look the same. A pair of pale green wings grows from each


side of the moth’s body. Two feathery antennae stick up from its head. Its body parts are about the same size and shape. T ey are evenly arranged along its white furry body. Now look at the pretty patterns on its green


and purple wings. You can see symmetry there, too. A ribbon of purple runs along the edges of its wings. T e matching spots on its wings look just like a pair of eyes staring at you. T e patterns are made by thousands of tiny overlapping, matching scales. Bilateral symmetry is all around you. Most


animals have it. Camels, beetles, pigeons, and frogs have it. You can even look at your pet for signs of symmetry. You can find symmetry other places in


nature, too. Look at a leaf. A vein runs down the middle and divides the leaf in half. It’s the same with some types of flowers. Take a look at a bleeding heart flower. Its curvy petals form


the shape of a heart. Both sides look the same.


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