This volume had its inception at a symposium entitled Aneura1 Organisms: Their Significance for Neurobiology held at the Winter Conference on Brain Research in Vail, Colorado, in January, 1972. The original participants were Drs. Epstein, Hamilton, Kung, Wood and myself. However, since that time several other authors (Drs. Applewhite, Chen, Diehn and Ettienne) were asked to contri- bute papers and all were asked to update their presentations so as to present a broad perspective as to the role and significance of aneura1 systems for investigating neurobiological problems. This volume is the...