Gaskell... had to keep his stately soldiers upright and uniformly oriented... by crafting the brain and spinal cord from an arthropod digestive tube, while forming a completely new gut below.... Gaskell thought that his move would rescue the theory of linear progress, with its necessary transition of arthropod into vertebrate, from the absurdities of the old inversion theory.

"Brotherhood by Inversion", p. 327 - Leonardo's Mountain of Clams and the Diet of Worms (1998)