The lizard spinal cord is necessary and sufficient for inducing regenerated tails in lizards. (A, B) Morphological comparison of lizard tails (A) with and (B) without intact spinal cords two weeks after tail loss. (A) Lizard tails with intact spinal cords regenerate new tails, but (B) tails with disrupted spinal cords fail to regenerate. Dashed line marks amputation plane. (C, D) Morphologies of lizard tails (C) with or (D) without spinal cord implants. After two weeks, (C) tails treated with exogenous spinal cord implants develop ectopic tails at implantation sites, while (D) control tails that did not receive exogenous spinal cord implants did not exhibit any growth. ect, ectopic tail. Bar = 1 mm.