1. Medical Research Council Human Reproductive Sciences Unit (H.M.S., G.R.H., I.K.M., N.H., M.W., R.M.S.), Centre for Reproductive Biology, The Queen’s Medical Research Institute, Edinburgh EH16 4TJ, United Kingdom
2. Division of Biochemistry (K.D.G., G.V.), Catholic University of Leuven, B-300 Leuven, Belgium
3. Institute of Comparative Medicine (P.O.), University of Glasgow Veterinary School, Glasgow G61 1QH, United Kingdom