Geoffrey also recognized that the opposite orientations of gut and nervous system posed a problem for his claim that insects and vertebrates represent different versions of the same archetypal animal - and he proposed the first account of the inversion theory to resolve this threat to unification.... Geoffroy pursued the... aim of establishing a "unity of type" that could generate both arthropods and vertebrates from the same basic blueprint.... The single grand design includes a gut in the middle and the main nerve cords somewhere on the periphery.

"Brotherhood by Inversion", p. 326 - Leonardo's Mountain of Clams and the Diet of Worms (1998)