Airn ABORTED ORGANS. 473 



same mature age, but will seldom affect it in the embryo. 

 Thus we can understand the greater size of rudimentary 

 organs in the embryo relatively to the adjoining parts, and 

 their 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 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 difflculty. 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 ex- 

 planation is here requisite which I cannot give. If, for 

 instance, it could be proved that every part of the organ- 

 ization 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 prin- 

 ciple will almost necessarially 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 cellu- 

 lar tissue, could 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 condi- 

 tion, 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 



