1. Berrill, N. J., The Origin of Vertebrates (Oxford, 1955).
2. Burdon-Jones, C., Univ. Bergen Årb. Naturv. R., 11, 1 (1954).
3. Hincks, T., History of British Marine Polyzoa (London, 1880).
4. Schepotieff, A., Zool. Jb. (Anat.), 23, 463 (1907).
5. Burdon-Jones, C., in Parker and Haswell's Textbook of Zoology, 2, Seventh edit. (revised by Marshall, A. J.) (London, 1964).