1. Literary Papers of the Late Professor Edward Forbes F.R.S. (Lovell Reeve London 1855).
2. Thomson C. W., The Depths of the Sea (Macmillan, London, 1873), p. 49.
3. Thomson C. W., The Voyage of the Challenger (John Murray Ltd., London, 1972), p. 276quoted in E. Linklater.
4. Huxley T. H., Autobiography and Selected Essays, , Snell A. L. F., Ed. (Houghton Mifflin, Boston, 1909)http://human-nature.com/darwin/huxley/autobiography.html.