On the Origin of Species · ¶687

On the principle of successive slight variations, not necessarily or generally supervening at a very early period of life, and being inherited at a corresponding period, we can understand the great leading facts in Embryology; namely, the resemblance in an individual embryo of the homologous parts, which when matured will become widely different from each other in structure and function; and the resemblance in different species of a class of the homologous parts or organs, though fitted in the adult members for purposes as different as possible. Larvæ are active embryos, which have become specially modified in relation to their habits of life, through the principle of modifications being inherited at corresponding ages. On this same principle—and bearing in mind, that when organs are reduced in size, either from disuse or selection, it will generally be at that period of life when the…

Charles Darwin · John Murray, London, 1859, first edition · Gutenberg #1228; original diagram from Darwin Online F373
Charles Darwin · John Murray, London, 1859, first edition · Gutenberg #1228; original diagram from Darwin Online F373
Passage preview. Read in context for the complete text, notes and references.