D'Arcy Thompson's method of transformations

    Differences in body forms among organisms may be more simply explained by pattern transformations than by rearrangement of physical component parts. The form of the puffer fish (Diodon) can evolve into that of an ocean sunfish (Mola) by a transformation of the rectangular coordinate system in (A) (red dots) into a curvilinear system in (B)  that "stretches" the posterior portion of the fish. [modified from Futuyma 1997, after Thompson 1917]