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| Richard Owen, Vertebrae 'Archetype' |
Later, in 1848, Owen distinguished between homologous and analogous organs. He defined a homologous organ as "the same organ in different animals under every variety of form and function" whereas an analogous organ was "a part or organ in one animal which has the same function as another part or organ in a different animal." This means that, for example, the fins of fishes are homologous to the limbs of tetrapods while the wings of an insect and those of a bird are analogous. Owen made a further distinction between special homology and general homology. Special homology exists between corresponding organs in different organisms, as previously described. General homology, however, refers to the relation "in which apart or series of parts stands to the fundamental type." In the first case, it is the empirical or sensible forms of organs which are being compared. But, in general homology, empirical forms are compared to an ideal or invented form; the tertium quid that acts as intermediate between two things. Owen went as far as suggesting some ideal representations of vertebrae and archetypal skeletons.
