1. Beatty, R. A., Biol. Rev., 45, 73 (1970).
2. Patau, K., Pathol. Biol., 11, 1163 (1963).
3. Sumner, A. T., Robinson, J. A., and Evans, H. J., Nature New Biology, 229, 231 (1971).
4. Carr, D. H., Amer. J. Obstet. Gynec., 104, 327 (1969).
5. Carr, D. H., in Human Population Cytogenetics (edit. by Jacobs, P. A., Price, W. H., and law, P.), 103 (University Press, Edinburgh, 1970).