CHAP. XIV.] AND ABORTED ORGANS. 377 



organ, and this will generally be when the being has come to 

 maturity and has to exert its full powers of action, the principle 

 of inheritance at corresponding ages will tend to reproduce the 

 organ in its reduced state at the 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 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 organisation 

 tends to vary in a greater degree towards diminution than 

 towards augmentation of size, then we should be able to under- 

 stand 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 towards 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, could 

 be further reduced or absorbed for the sake of economising 

 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 woru. 



