VESTIGIAL ORGANS
such animal requires at least the most of one lung and of one kidney. Even such inconspicuous organs as the adrenal glands, small bodies lodged in the fat near the kidneys, cannot be removed without causing death. Organs that are thus absolutely essential to the continuance of life are called vital organs and stand in strong contrast to others whose functions are not so essential. Different organs thus vary
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A -
B
_p035_A_female_ant_with_normal_wings.png)
_p035_B_female_ant_with_vestigial_wings.png)
Fig. 1.—A, Female of an ant (Monomorium rothsteini) with normal wings; B, Female of an ant (Monomorium subapterum) with vestigial wings.
greatly in that some are essential and others are not essential to life.
Vestigial organs are those that are quite useless. Such organs are of course not necessary to their possessors. It is not always easy to prove that a given organ is vestigial. As might be inferred from what has been said, such proof requires that a given organ be not only removable without detriment from the animal of which it is a part but that it be shown to be without function. Conclusive evidence on this point is not always easy to obtain, for our ignorance may at times leave us in doubt as to the presence or absence
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