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22 23 dorsiventrAlity the symmetry of moving creatures Animals, by definition, are multicellular, foodeating creatures, and practically all are capable of some form of motion naturally, these attributes govern their general form. Whether an animal walks on the ground or burrows through it, whether it swims through water or flies through the air, its body will be made up of left and right sides that are roughly mirror versions of each other. Since they also have a front and a back and usually a distinct top and bottom they are not merely bilateral, but dorsiventral. This is the best arrangement to have if you need to move in a directed way examples opposite. It is not only animals that express this symmetry forwardmoving vehicles, such as automobiles, boats, airplanes etc., are, by necessity, symmetrically disposed along similar lines. There are other characteristics of animal dorsiventrality that developed alongside the power of locomotion. A strong forward movement obviously requires a forwardplaced vision to see where one is going, and a forwardplaced mouth to feed efficiently. Fins and limbs, by contrast, are best placed laterally, in symmetrically balanced positions. Although, for the reasons given above, dorsiventrality is the abiding symmetry of the animal kingdom, it is also fairly common in the plant worldtypically in zygomorphic irregular flowers, in the great majority of leaf forms below, and in many leaf arrangements.
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