In every animal which has not passed the limit of its development, a more frequent and continuous use of any organ gradually strengthens, develops and enlarges that organ, and gives it a power proportional to the length of time it has been so used; while the permanent disuse of any organ imperceptibly weakens and deteriorates it, and progressively diminishes its functional capacity, until it finally disappears.

Zoological Philosophy: An Exposition with Regard to the Natural History of Animals (ed. Cambridge University Press, 2011) - ISBN: 9781108038423