Editorial note — Chapter I
Reading edition
[Footnote 2: With certain modifications accounted for in their historical "descent" with modification from a common ancestor. See Scott: Theory of Evolution.]
[Footnote 1: The difference between the two is largely one of complexity. By a reflex is meant a very simple and comparatively rigid response; by an instinct a series of reflexes such that when the first is set off, the remainder are set off in a regularly determinate succession.]