410 THE ORIGIN OF SPECIES 



lesser relative size in the adult. If, for 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 be- 

 come 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 obliterated? It is scarcely 

 possible that disuse can go on producing 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 augmenta- 

 tion of size, then we should be able to understand how an organ 

 which has become useless would be rendered, indep)endently 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 econ- 

 omy of growth, explained in a former chapter, by which the ma- 

 terials 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 some- 

 times 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 pronuncia- 

 tion, but which serve as a clew for its derivation. On the view of 

 descent with modification, we may conclude that the existence of 

 organs in a rudimentary, imperfect, and useless condition, or quite 



