1. Center for Reproductive Sciences, Departments of Anatomy and OB/GYN-RS, University of California, San Francisco, San Francisco, California 94143-0452
2. Department of Biological and Health Sciences, Texas A&M University-Kingsville, Kingsville, Texas 78363-8202
3. Department of Biology, University of Oklahoma, Norman, Oklahoma 73019
4. Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211