1. Department of Biological Sciences (P.W., N.D., D.D.C.), University of Delaware, Newark, Delaware 19716
2. Department of Biochemistry and Cell Biology (N.D., D.D.C.), Wiess School of Natural Sciences, Rice University, Houston, Texas 77251
3. Department of Reproductive Medicine (M.J.B.), University of California, San Diego, School of Medicine, La Jolla, California 92093