Small angle dislocations of the newt limb axes can test the validity of several regeneration models

We describe two experiments on the regenerating forelimbs of the urodele Triturus cristatus. In the first, a contralateral grafting is performed where the anteroposterior axis of the regenerating blastema coincides with the dorsoventral axis of the host stump. In the second, the regenerating blastema is ipsilaterally rotated on the stump at angles 90 degrees or 270 degrees. For these experimental setups several regeneration models, each based on different reference frames (cartesian versus polar coordinates), have diverging predictions for the resulting supernumerary outgrowths. We have analyzed these outgrowths morphologically and histologically and we conclude that both experiments are well described by a hierarchical extension of the Polar Coordinate Model.