Internalism and Laws of Form 305
of the greatest joys that I ever felt in my life" (1822, p. 99), for he had realized that
"insects formed another class of vertebrated animals, and that they were,
consequently, brought under the common law of uniformity of organization"
(1822, p. 99).
An attempt to homologize the Bauplan of insects and vertebrates implies
some wondrous correspondences, and Geoffroy did not shrink from the logically
necessary, but inherently curious implications. He argued that both phyla are
fundamentally metameric, with the idealized vertebra itself acting as the archetype
of each segment—and therefore, in repetition and regional specialization, of the
entire animal. If Goethe's leaf could generate all the organs of a plant, then
Geoffroy's vertebra would prefigure the entire skeleton of animals.
Since the arthropod skeleton overlies the internal organs, whereas vertebrate
bones lie below flesh and blood, their homology implies a remarkable conclusion,
endorsed in yet another motto devised by Geoffroy: insects must live within their
own vertebrae! Geoffroy wrote in 1822: "Every animal lives outside or inside its
vertebral column" (Tout animal habite en debars ou en dedans de sa colonne
vertebrate). Continuing the string of surprising implications, all explicitly endorsed
by Geoffroy, if exoskeletal body rings must be treated as homologs of vertebrae in
the spinal column, then arthropod appendages must be equated with vertebrate
ribs—and insects walk on their ribs!
Geoffroy's attempted comparisons posed two major challenges to his own
"law of connections" for establishing homology: how can inside and outside
become reversed if topology be inviolate; and how can arthropods, with their
ventral nerve tracts, be brought into structural harmony with the dorsal nerve cord
of vertebrates? Geoffroy proposed an ingenious explanation for the metastasis of
inside and outside: He argued that hard parts (and other organs) develop as
deposits or exudates on the outside of vessels. In vertebrates, the dorsal nerve cord
secretes the vertebrae around itself, while other organs emerge as exudates around
vessels of the circulatory system. But insects lack a heart, making their circulatory
system too weak to build organs. Therefore, only the nervous system can carry
material for the deposition of hard parts— and all other organs must form within
the resulting outer set of rings.
The inversion of orientation did not require such an elaborate rationale, but
only a repositioning of viewpoint. Geoffroy regarded "top" and "bottom" as
subjective terms of a secondary and derivative functionalism. (Geoffroy never
intended his homology of vertebrates and inverted arthropods as an evolutionary
claim for the origin of vertebrates from an arthropod that literally turned over onto
its back. For Geoffroy, the two orientations represented ecological alternatives for
a common design.) The primary topology of formalism puts little store by the
derivative ecology and function that leads the same side of an invariant
organization to turn towards the sun in some groups, and towards the ground in
others.
This solution is not, by any means, problem-free, for such changes of
topology must also be rationalized. In particular, and as a major stumbling-block