A fixed specimen of Schmidtea mediterranea processed to detect expression of Smedwi. Anterior is to the left and displays the dark, prominent, and characteristic photoreceptors found in planarians. The remainder pigmentation indicates those cells in which Smedwi transcription is occurring. The pattern of expression matches the known distribution of proliferating stem cells in this organism. The stem cells are known as neoblasts, a term first used by Harriet Randolph in 1892 to describe the Photo Credit: Alejandro Sánchez Alvarado/University of Utah