On The Origin of Species by Charles Darwin Chapter 5 Page 42

necessary compensation the reduction of some adjoining part.

6. Multiple, Rudimentary, And Lowly-Organised Structures Are Variable

It seems to be a rule, as remarked by Is.

Geoffroy St. Hilaire, both with varieties and species, that when any part or organ is repeated many times in the same individual (as the vertebrae in snakes, and the stamens in polyandrous flowers) the number is variable; whereas the number of the same part or organ, when it occurs in lesser numbers, is constant. The same author as well as some botanists, have further remarked that multiple parts are extremely liable to vary in structure. As “vegetative repetition,” to use Professor Owen’s expression, is a sign of low organisation; the foregoing statements