SOME ASPECTS OF THE STRUCTURE OF THE NERVOUS SYSTEM IN THE ANEMONE CALLIACTIS

In the light of existing work on tbe behavioral physiology ofthis anemone, the structure of parts of the neuroimiscular systemhas been examined in detail. In the sphincter region, the morphologicalbasis for rapid through-conduction and motor innervation isa network of bipolar nerve cells, which is connected to thesimilar retractor nerve-nets of mesenteries. Sphincter musclefibers are arranged at the periphery of tubes, which form ameshwork within the mesogloea. Bipolar nerve cells appear torun in these tubes. Neurites also reach the sphincter from theendodermal nerve-net by penetrating the mesogloea directly.The nerve-net over the circular muscle is richer than in otherparts of the column, but shows similar features. It includessmall multipolar cells of unknown function. Coordination between different parts of the anemone is discussedin terms of possible pathways for the transmission of excitation.For example, bundles of retractor and parietobasilar musclefibers continue from both surfaces of mesenteries into the mesogloeaof the pedal disk, suggesting a possible route for neuritespassing to or from the ectoderm. If confirmed, the existenceof this route could throw light on a number of sequences ofbehavior.