1. Department of Biology (E.C., G.K., C.P.), York University, Toronto, Canada M3J 1P3
2. Marine Biological Laboratory (R.K.C.), Woods Hole, Massachusetts 02543
3. Serono Research Institute (R.K.C.), Rockland, Massachusetts 02370
4. Department of Reproductive Medicine (S.Sha., S.Shi.), University of California, San Diego, California 92093-0633