 The conserved role of Hox genes in axial patterning is referred to as functionally homologous across animals (Manak and Scott 1994), over and above the relation of structural homology that obtains between DNA sequences. And yet “functional homology” is a contradiction in terms (Abouheif et al. 1997) because the definition of a homologue is “the same organ in different animals under every variety of form and function” (Owen 1843: 379)—the descendant, evolutionary distinction between homology (structure) and analogy (function) is founded on this recognition. Therefore, the idea of functional homology appears theoretically confused and there is a conceptual tension in its use by molecular developmental biologists.