444 RUDIMENTARY, ATROPHIED 



their lesser relative size in the adult, it, ior instance, the 

 digit of an adult animal was used less and less during 

 many generations, owing to some change of habits, or if an 

 organ or gland was less and less functionally exercised, we 

 may infer that it would become reduced in size in the 

 adult descendants of this animal, but would retain nearly its 

 original standard of development in the embryo. 



There remains, however, this difficulty. After an organ 

 has ceased being used, and has become in consequence much 

 reduced, how can it be still further reduced in size until the 

 merest vestige is left ; and how can it be finally quite obliter- 

 ated ? It is scarcely possible that disuse can go on produ- 

 cing any further effect after the organ has once been rendered 

 functionless. Some additional explanation is here requisite 

 which I cannot give. If, for instance, it could be proved 

 that every part of the organization tends to vary in a greater 

 degree toward diminution than toward augmentation of size, 

 then we should be able to understand how an organ which 

 has become useless would be rendered, independently of the 

 effects of disuse, rudimentary, and would at last be wholly 

 suppressed ; for the variations toward diminished size would 

 no longer be checked by natural selection. The principle of 

 the economy of growth, explained in a former chapter, by 

 which the materials forming any part, if not useful to the 

 possessor, are saved as far as is possible, will perhaps come 

 into play in rendering a useless part rudimentary. But this 

 principle will almost necessarily be confined to the earlier 

 stages of the process of reduction ; for we cannot suppose 

 that a minute papilla, for instance, representing in a male 

 flower the pistil of the female flower, and formed merely of 

 cellular tissue, would be further reduced or absorbed for the 

 sake of economizing nutriment. 



Finally, as rudimentary organs, by whatever steps they 

 may have been degraded into their present useless condition, 

 are the record of a former state of things, and have been 

 retained solely through the power of inheritance — we can 

 understand, on the genealogical view of classification, how 

 it is that systematists, in placing organisms in their proper 

 places in the natural system, have often found rudimentary 

 parts as useful as, or even sometimes more useful than, parts 

 of high physiological importance. Rudimentary organs may 

 be compared with the letters in a word, still retained in the 

 spelling, but become useless in the pronunciation, but which 

 serve as a clew for its derivation. On the view of descent 



