1. Ball, P., Knuppen, R., Haupt, M. and Breuer, H. (1976)J. Clin. Endocrinol.,34, 736.
2. Castracane, V. D. and Jordon, V. D. (1976)Prostaglandins,12, 243.
3. Chasalow, F. I., Marr, H. and Taylor, G. (1982)Steroids,39, 617.
4. Corner, G. W. (1947) inThe Hormones in Human Reproduction, ed. G. W. Corner (New Jersey: Princeton University Press, Princeton), p. 259.
5. Crombi, P. R. (1972)The Morphology and Ultrastructure of the Pig’s Placenta Throughout Pregnancy, Ph. D. Thesis, University of Cambridge, UK.