VESTIGIAL ORGANS
By George Howard Parker
Professor of Zoölogy, Harvard University
The body of an animal, like a piece of machinery, is made up of numerous parts that work together toward a common end. In an animal these parts are the organs, and each organ commonly has a definite use. Thus in man the eye, the hand, and the heart are three organs, the first for vision, the second for prehension, and the third for the propulsion of the blood. As in the machine, so in the animal, some parts are more important than others.
Just as there may be superfluous wheels and belts in a machine, so there may be organs in an animal that are not essential. A man may lose an arm or a leg and still live. Paired organs may be reduced by the removal of one. Thus a surgeon does not hesitate to excise a kidney provided its mate can be left intact. After such an operation the organ left behind usually enlarges and acts for two. Some single organs, such as the spleen, or even the stomach, may be removed without causing death. After its removal the function it ordinarily performs is taken over by other organs, and the life of the individual continues.
But in addition to organs of the kind just described there are others whose loss is followed by death. None of the higher animals can survive the loss of the heart, and every
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