Patterns of form and function in the central nervous system of Ariolimax.

Abstract

AbstractThe external and internal morphology of the central nervous system of the large terrestrial gastropod Ariolimax columbianus are shown to be typical of the general pattern for stylommatophoran pulmonates. This typicality recommends Ariolimax as a useful normal model for experimental investigation of the molluscan nervous system. The central nervous system of this form was reconstructed by tracing every section of a horizontally serially sectioned specimen onto transparent acetate tracing film at a magnification of 32 ×. The position of all cells greater than 50 m̈ in diameter as well as the locations of neuropil, septa, exits of the various nerves, etc., were all carefully indicated on this model. By comparing sections serially cut in different planes with the reconstruction it becomes apparent that many, if not most, of the larger cells and constellations of cells are identifiable from animal to animal. This finding is consistent with the assumption that basic stereotyped responses most probably reflect stereotyped anatomical patterns. Fixed neuronal patterns in turn suggest basic identifiable discharge patterns over the major nervous pathways. By double beam recording it is demonstrated that recognizable “core discharge” patterns from the central nervous system can indeed be distinguished following various controlled afferent inputs. The results of this study support the concept of a physiologically and anatomically patterned, as opposed to a randomly functioning, neuropil.