On The Origin of Species by Charles Darwin Chapter 14 Page 1

Mutual Affinities Of Organic Beings: Morphology -- Embryology -- Rudimentary Organs

Classification, groups subordinate to groups — Natural system — Rules and difficulties in classification, explained on the theory of descent with modification — Classification of varieties — Descent always used in classification — Analogical or adaptive characters — Affinities, general, complex and radiating — Extinction separates and defines groups — Morphology, between members of the same class, between parts of the same individual — Embryology, laws of, explained by variations not supervening at an early age, and being inherited at a corresponding age — Rudimentary organs; their origin explained — Summary.

1. Classification