REFERENCES

Charles Darwin, A Naturalist's Journal.

Francis Darwin, The Life and Letters of Charles Darwin.

W. A. Locy, Biology and its Makers (third revised edition), chap. XIX.

G. J. Romanes, Darwin and After Darwin, vol. I.

A. R. Wallace, Darwinism.

See also John W. Judd, The Coming of Evolution (The Cambridge Manuals of Science and Literature).