From the Department of Obstetrics and Gynecology, Stanford University School of Medicine, San Francisco, Calif.

Supported by a research grant (RG 4034) from the National Institutes of Health, U. S. Public Health Service.

The author wishes to express his appreciation to Miss Ann Krepelka for her technical assistance and to Mr. W. E. Renner for the photomicrographs used in this study.