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, can- 

 not 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 



Fig. 1. — A, Female of an ant {Monomorium rothsteini) with 

 normal wings; B, Female of an ant {Alouomorinm 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 



[35] 



