the resemblance of organs or parts located serially along the longitudinal axis of an animal’s body. The term “homodynamy” was proposed by the German biologist E. Haeckel in 1866. Some examples of homodynamy are the vertebrae, ribs, and anterior and posterior extremities in vertebrates; and the body segments of arthropods and all their parts, including extremities. If homodynamic organs are adapted to the performance of different functions, they may have dissimilar structures (for example, the wings and legs of birds). A synonym of “homodynamy” is “serial homology”; the latter term was proposed by the English biologist R. Owen (1843).