Evolutionary Trends in Invertebrate Ganglionic Structure

Abstract: Early Bilateria developed the basic characteristics of ganglionic organization. Features such as the divergence of longitudinal axon bundles into functionally unique tracts, the separation of centers for motor pattern generation and exteroceptive sensory integration, the segregation of limb motor centers to lateral neuropils, and the genesis of glomerular microarchitecture occur in representatives from many protostome phyla. Ancestors of the protostome and deuterostome lineages may have evolved these features of neuronal organization independently but parsimony would argue in favor of a conservative evolution, whereby phylogenetically early events formed the basis for the complex neural architectonics displayed by extant Chordata