The structure and function of certain neuromuscular systems in echinoderms

Abstract

1. Physiological experiments were devised to study the electrical responses of ochinoderm muscle during contraction. The smooth muscle forming the lantern retractors of Eching conducts spike potentials at a speed off 4 cms. A sec. 2. Three muscle systems examined with the electron microscope reveal a layout that varies in complexity. The muscle cells give rise to processes that are synapsed upon by nerves. 3. The area containing the ribbon axons described by Smith (1950) was examined and the ribbon axons shown to be selectively stained muscle cells. 4. In the three muscle systems examined controlling ganglion was found to be associated sytams. 5. The ganglia contained large numbers of structures that are described as synapses. These synapses are of a simple type and do not possess the specialisations that are present in the synapses of some other invertebrate phyla. 6. The sensory cells of the epithalium are described and an examination has indicated that the cells of the general epithelial are all sensory and contribute axons to the nerve plexus. Some of these epithalial cells are modified into probable chemoreceptors, light receptors and are found in statocysts. 7. A hypothesis to account for the co-ordination of the behaviour of echinoderms in propounded.