Four-cell Embryo (IMAGE) Indiana University Caption This early-stage embryo is protected by a fertilization envelope, seen here as a white line encircling the embryo cells. Credit E.C. Raff and R.A. Raff Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.