Fig. 2.

Planarians possess extraocular photoreception. Graph of extraocular responses to light using our extraocular assay. A spot of light was placed on the worm's tail, and the presence of the photophobic ‘tail thinning’ response was assessed. Thinning was determined by measuring the width of the tail (midway between the posterior edge of the pharynx and tip of tail) both before and after exposure to red, green and near-UV laser light. Photos: starred bracket designates the tail; double-headed black arrows designate the width measurement. Note that significant tail thinning was observed only with near-UV wavelengths. N=40 for control, red, and green; N=120 for near UV. Statistics: two-tailed independent t-test; ****P<0.0001 (as compared with no light controls); error bars=s.d.