Introductory remarks. Part 1 Coelenterata: the nervous systems of cnidarians, C.J.P. Grimmelikhuijzen and J.A. Westfall. Part 2 Plathelminthes: the flatworm nervous system - pattern and phylogeny, M. Reuter and M.K.S. Gustafsson. Part 3 Nematoda: repeating patterns of motoneurons in nematodes - the origin of segmentation?, W.W. Walthall. Part 4 Annelida - genesis of segmental identity in the leech nervous system, G.O. Aisemberg et al. Part 5 Mollusca - comparative aspects of gastropod neurobiology, A.G.M. Bulloch and R.L. Ridgway; the cephalopod nervous system - what evolution has made of the molluscan design, B.U. Budelmann. Part 6 Onychophora - common and special features of the nervous system of onychophora - a comparison with arthropoda, annelida and some other invertebrates, F.W. Schurmann Part 7 Arthropoda: chelicerata - comparative aspects of the chelicerate nervous system, R. Wegerhoff and O. Breidbach; mandibulata - embryogenesis - conservation versus change in early axonogenesis in arthropod embryos - a comparison between myriapods, crustaceans and insects, P.M. Whittington, motoneurones - homologous structures, exemplified by motoneurones of mandibulata, W. Kutsch and R. Heckman, sensory neurones - developmental mechanisms, homology and evolution of the insect peripheral nervous system, T. Meier and H. Reichert, interneurones - lineage analysis as an analytical tool in the insect central nervous system - bringing order to interneurons, G.S. Boyan and J.L.D. Williams, peptidergic neurones - comparative aspects of peptidergic signalling pathways in the nervous systems of arthropods, H.-J. Agricola and P. Braunig; the arthropod brain - ground plans, evolutionary changes and homologies in decapod crustacean brains, D. Sandeman and G. Scholtz; the arthropod mushroom body - its functional roles, evolutionary enigmas and mistaken identities, N.J. Strausfeld et al; is the evolution of arthropod brains convergent?, O. Breidbach. Part 8 Echinodermata: the nervous systems of echinodermata - recent results and new approaches, J.L.S. Cobb. Part 9 Methodological comment: the homology concept - still alive, M. Schmitt. Part 10 Coda: are the main grades of brains different principally in numbers of connections or also in quality?, T.H. Bullock.