ABSTRACT
There is now strong evidence that the idea that complex behaviour is controlled by the circumoral ring and immediately adjacent radial nerve cords is not correct. The segmental ganglia of the radial nerves cords control whole animal behaviour and there is to date no evidence that any particular ganglia are more important than any others. This may have profound effects on the way in which we interpret behavioural responses and although the detailed neural mechanisms have hardly begun to be understood the significance should not be ignored. This review will attempt to show that the peculiarities of the nervous system have consequencies far beyond a study of the nervous system itself. Indeed, is it possible that the enigmas we face are the echoes of some extra-ordinary evolutionary mechanism associated with the inexplica bility of pentamery?
