302 THE STRUCTURE OF EVOLUTIONARY THEORY
between fishes and tetrapods for bones of (and around) the respiratory elements:
first on putative homology of opercular and hearing bones (incorrect in retrospect
of course), second on the sternum, third on the hyoid, fourth on the branchial
arches and their derivates (including the true homologs of the hearing bones, as
biologists later learned), and fifth on the shoulder girdle. Cuvier, not yet perceiving
(or at least not publicly admitting) his colleague's work as a comprehensive threat
to his functionalist system, proclaimed Geoffroy's publication as bold, challenging,
and worthy of respect— though almost surely wrong. He strongly doubted
Geoffroy's focal homology of opercular and hearing bones, for how could such
large, central, and functionally necessary bones of fishes represent the same
elements as tiny, almost superfluous nubbins ensconced within organs of differing
utility in tetrapods?
Geoffroy, who certainly equalled Cuvier in lack of modesty, proclaimed in
the introduction to the Philosophie anatomique that his work marked "a new
epoch, to which the publication of this book fixes the date" (1818, p. xxxi). He also
admitted, tweaking Cuvier's allegiance to the primacy of positive facts, that
formalist commitments come first. With such a proper conceptual key, the bones of
the skeleton fall into place: "I do not hide it; my direction has been given to me by
an a priori principle" (1818, p. 11)—although, he hastens to add, unity of type has
worked so well that the principle could now be inferred inductively from the
skeleton itself!
Geoffroy proceeds immediately to battle in defending formalism by explicit
contrast with false assumptions in Cuvier's functionalist alternative. He tells us on
page 3 that fishes, by virtue of their functional differences from other vertebrates,
seem to possess an anatomy of irreducible uniqueness. "It might appear to the
observer ... that fishes, in order to exist, must call upon the intervention of new
organs, and could only be complete in their construction by means of elements
destined for them alone, bones created uniquely for their profit" (1818).
But Geoffroy counterposes formalist unity of type to the functionalist
alternative of special organs for novel uses: "I can and will satisfy you by showing
you that all the elements used in the composition of fishes are exactly and entirely
the same as those that enter into the formation of man, mammals, birds, and
reptiles" (1818, p. 9).
Geoffroy then takes up the two key challenges previously mentioned. He must
first explicate the undeniable fact that the girdle, forelimbs and trunk organs have
shifted back in tetrapods relative to their anterior position in fishes—as a result of
the interposition of vertebral elements, and in apparent contradiction to the law of
connections. Geoffroy invokes his exceptional principle of metastasis and argues
that "the trunk exists under the milieu [sous le milieu] of the vertebral column" as a
whole (1818, p. 9), but not under any particular element in the series. Second, he
acknowledges that respiratory organs—with their maximally varying forms and
functions in vertebrates—do pose the chief challenge for his system: "In this case,
it would be entirely natural to assume in advance that the action of external
conditions would impose requirements capable of placing the respiratory apparatus
outside the condition of the other organs. From the two modes so rigidly ordained