<em>Hydra vulgaris</em> (IMAGE) Cell Press Caption Hydra vulgaris is shown with its two tissue layers transgenically labeled: ectoderm (outer layer) in green; endoderm (inner layer) in magenta. Credit Callen Hyland Usage Restrictions Credit Required. 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.