Internalism and Laws of Form 301
can be commandeered to construct the archetypal elements. If one part becomes
hypertrophied by utility, others must atrophy to secure the constancy of the
common fund. Geoffroy wrote succinctly in 1829 (quoted in Russell, 1916, p. 72):
"There is only a single animal modified by the inverse reciprocal variation of all or
some of its parts."
Most systems of thought achieve their exemplification in a canonical
document; how would natural selection be defined without the Origin? Geoffroy's
formalism received its codification in an 1818 book with a majestic title—
Philosophie anatomique (or Anatomical Philosophy, explicitly not the less
grandiose Anatomie philosophique, or Philosophical Anatomy). Geoffroy's subtitle
brought the subject down to earth and bone with the best test case that vertebrates
can offer—Pieces osseuses des organes respiratoires (the bony elements of the
respiratory organs). Geoffroy began this work with an interesting example that
highlights the contrast of formalism and functionalism, and that sowed the seeds
for his later public debate with Cuvier.
Cuvier had named and described four bones in the opercular series of teleost
fishes—operculum, preoperculum, suboperculum, and interoperculum. And he,
given his functionalist perspective, had treated these bones as unique to fishes and
necessarily present for their utility in respiration by gills. Geoffroy developed a
contrary interpretation based on his commitment to unity of the vertebral type, and
to a primary implication that these bones must be homologues of elements with
different functions in other vertebrates—for all vertebrates possess the same
archetypal pieces, and none can be gained or lost. Geoffroy worked on the
opercular bones from 1809 to 1812, without resolution. In 1812, a good year for
wars and overtures, Cuvier argued that he had located, in the skulls of fishes, the
homologs for all bones in the mammalian head—leaving no mammalian structures
to serve as potential homologues of opercular bones in fishes. Henri de Blainville,
Geoffroy's chief formalist supporter, then argued for homology between the
opercular elements of fishes and bones of the tetrapod lower jaw. But, in 1817,
Cuvier showed Geoffroy a preparation of a pike and convinced him that all bones
of the lower jaw could be matched with jaw elements of tetrapods, again leaving
no tetrapod bones to interpret as transformations of the opercular series. Geoffroy
then returned to this crucial problem and realized, in a flash as he later stated, that
he would have to investigate the only remaining elements in the tetrapod head for a
solution: the opercular bones must be homologs of the mammalian middle ear
bones! Geoffroy reminisced in 1830 (quoted in Appel, 1987, p. 97): "I regained
courage and recommenced my studies, never to abandon them again."
Respiratory bones set the crucial experiment for vertebrate unity of type
because such deciding tests must provoke maximal dangers of disconfirmation and
grapple with the most difficult issues of validation. The respiratory bones from fish
to tetrapods pose prima facie challenges to unity of type—for they present no
apparent homology from sea to land, and they also exhibit maximal difference of
function within vertebrates. If these bones could be won for formalism, then the
rest of the skeleton would fall into order.
The Philosophie anatomique includes five monographs on homologies