A) Staining of the nervous system of DH planarians from Day 7 to Day 43 using synapsin antibody staining shows the different sizes of the brain in the primary and secondary head at the early time points. Animals are oriented with the primary head towards the top. B) Quantification of relative brain length in secondary and primary brain over time in untreated double-headed animals (red), and animals irradiated at Day 7 and stained at Day 28 (grey), which shows a reduction in the variability of brain size over time, except for irradiated samples. Brain length was measured in synapsin stains from base of brain where ventral nerve cords (VNCs) widen, to the tip of the brain, where the two halves meet. Scale bar 1 mm ***p < 0.0001.