The Nerves and Muscles of Medusae

Abstract

ABSTRACT The compensatory movements of Cyanea (Semaeostomeae) and Cassiopea (Rhizostomeae) are described. The asymmetry of these responses is not compatible with the properties of the through-conducting giant fibre net which propagates the contraction wave. Stimulation experiments with Cyanea show that a second nerve net, called the diffuse net, acts locally on the muscles of the bell and delays the process of relaxation. In Cassiopea, the responses of a ring of tissue containing a continuously circulating contraction wave are also evidence of a double innervation. The responses of Nausithose (Coronatae) are described and are interpreted in a similar manner. In all three orders the two nerve nets are in places superimposed but are independent except where they meet at the marginal ganglia. Here the diffusenet acts irreversibly on the rhythmical units, which are known to be within the giant fibre net.