1. Allen, G. (1955). Acta Genet. med. (Roma), 4, 143.
2. Anthony, D., and Thomas, J. G. Hugh. (1957). Brit. med. J., 2, 1546.
3. Guilbride, A. H. H. (1957). Ibid., 2, 1368.
4. Higgie, E. J. (1957). Ibid., 2, 1240.
5. Jacobs, P. A., Baikie, A. G., Court Brown, W. M., and Strong, J. A. (1959). Lancet, 1, 710.