Integration assay in planarian. (A) Schematic illustration of the assay method used to investigate the integration of external stimuli is shown. A container made using glass as described in Materials and Methods was used for the experiments. A planarian was placed in Zone 3 (indicated by a circle). Three microliters of chemoattractant (C. A.) was dropped into Zone 1 (indicated by a cross). The chamber was illuminated from Zone 1 in the direction of Zone 5. (B) The behaviors of 10 planarians without any stimulation were analyzed independently in the chamber; they showed random movements. (C) The chamber was illuminated with 400 lux of light from the side of Zone 1. The planarians immediately moved away from the light toward Zone 5. (D) Chemoattractant (C. A.) was dropped into Zone 1. Planarians moved to Zone 1, where the chemoattractant was most highly concentrated. (E) Chemoattractant was dropped into Zone 1, which was then exposed to 400, 800, or 1600 lux of light. (F) Time spent in Zone 1 (white columns) and Zone 5 (black columns). (G) Trajectories of 10 planarians starting from the circle in Zone 3 without any stimulation (left) and with exposure to both 800 lux of light and chemoattractant simultaneously. Two representative trajectories were colored in orange and blue. Although no significant difference was seen in time spent in Zone 1 or 5 between no stimulation and multiple stimulation of 800 lux light plus chemoattractant, each control planarian moved extensively in the container, whereas each planarian given 800 lux of light and chemoattractant moved toward the chemoattractant or moved away from the light toward the dark region.