In this volume outstanding specialists review the state of the art in nervous system research for all main invertebrate groups. They provide a comprehensive up-to-date analysis important for everyone working on neuronal aspects of single groups, as well as taking into account the phylogenesis of invertebrates. The articles report on recently gained knowledge about diversification in the invertebrate nervous systems, and demonstrate the analytical power of a comparative approach. Novel techniques in molecular and developmental biology are creating new perspectives that point toward a theoretical foundation for a modern organismic biology. The comparative approach, as documented here, will engage the interest of anyone challenged by the problem of structural diversification in biology.

Introductory remarks.- Coelenterata.- The nervous systems of Cnidarians.- Platyhelminthes.- The flatworm nervous system: Pattern and phylogeny.- Nematoda.- Repeating patterns of motoneurons in nematodes: The origin of segmentation?.- Annelida.- Genesis of segmental identity in the leech nervous system.- Mollusca.- Comparative aspects of gastropod neurobiology.- The cephalopod nervous system: What evolution has made of the molluscan design.- Onychophora.- Common and special features of the nervous system of Onychophora: A comparison with Arthropoda, Annelida and some other invertebrates.- Arthropoda Chelicerata.- Comparative aspects of the chelicerate nervous systems.- Mandibulata Embryogenesis.- Conservation versus change in early axonogenesis in arthropod embryos: A comparison between myriapods, crustaceans and insects.- Motoneurones.- Homologous structures, exemplified by motoneurones of Mandibulata.- Sensory neurones.- Developmental mechanisms, homology and evolution of the insect peripheral nervous system.- Interneurones.- Lineage analysis as an analytical tool in the insect central nervous system: Bringing order to interneurons.- Peptidergic neurones.- Comparative aspects of peptidergic signaling pathways in the nervous systems of arthropods.- The arthropod brain.- Ground plans, evolutionary changes and homologies in decapod crustacean brains.- The arthropod mushroom body: Its functional roles, evolutionary enigmas and mistaken identities.- Is the evolution of arthropod brains convergent?.- Echinodermata.- The nervous systems of Echinodermata: Recent results and new approaches.- Methodological comment.- The homology concept-still alive.- Coda.- Are the main grades of brains different principally in numbers of connections or also in quality?.