Fissioning in Planarians: Control by the Brain

Science  02 May 1969:
Vol. 164, Issue 3879, pp. 565-566
DOI: 10.1126/science.164.3879.565


Reduced population densities lead to increased rates of fissioning in planarians whereas higher population densities suppress fissioning. This effect is not primarily due to mucus deposition or substances secreted into the water. Experiments are presented which show a system of population feedback control. In the presence of other planarians, the brain exerts an influence (probably neurohormonal) to suppress fissioning. This influence becomes attenuated with axial distance from the brain.