1. Kloosterman, G. J., Int. J. Gynaec. Obstet., 8, 895–912 (1970).
2. Altman, P. L., and Dittmer, D. S., Biology Data Book, 2nd ed., 1, 207–216 (Fed. Am. Soc. Exp. Biol., 1972).
3. Dawes, G. S., Foetal and Neonatal Physiology, A Comparative Study of the Changes at Birth, 4, 42–59 (Yearbook Medical Publishers, Chicago, 1968).
4. Ounsted C., and Ounsted, M., Lancet., ii, 857–858 (1970).
5. Barr, M., Jensh, R. P., and Brent, R. L., Teratology, 2, 241–246 (1969).