Petersen -- Flatworm Comparison (IMAGE) Northwestern University Caption When Northwestern University researchers inhibited the gene mob4 in planarian flatworms, the animal grew to twice its normal size (right). Credit Northwestern University Usage Restrictions Credit must be given 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.