The cave-crabs which have lost their disused eyes but _not the disused
eye-stalks_ appear to illustrate the effects of natural selection rather
than of disuse. The loss of the exposed, sensitive, and
worse-than-useless eye, would be a decided gain, while the disused
eye-stalk, being no particular detriment to the crab, would be but
slightly affected by natural selection, though open to the cumulative
effects of disuse. The disused but better protected eyes of the blind
cave-rat are still "of large size" (_Origin of Species_, p. 110).