Philip Parker King, Sir Francis Darwin, Robert Fitzroy, Charles Darwin (1839). “Narrative of the Surveying Voyages of His Majesty's Ships Adventure and Beagle: Between the Years 1826 and 1836 ...”, p.604
Charles Darwin, Sir Francis Darwin, Paul H. Barrett, R. B. Freeman (1990). “The Works of Charles Darwin, Volume 23: The Expression of the Emotions in Man and Animals”, p.275, NYU Press
Charles Darwin (1902). “Charles Darwin: His Life in an Autobiographical Chapter and in a Selected Series of His Published Letters”, p.267, Library of Alexandria