BEHAVIOR AND ELECTRICAL ACTIVITY IN THE HYDROZOAN PROBOSCIDACTYLA FLAVICIRRATA (BRANDT). II. THE MEDUSA

1. Feeding in the medusa of Proboscidactyla flavicirrata is accompanied by local, small amplitude impulses recorded from the bases of perradial tentacles. 2. Medusae, both attached and free, swim spontaneously with electrodes in place thus giving data on the temporal patterns of contractions of the swimming muscle. 3. Swimming pulses (SP's) can be recorded from the circular muscle of the subumbrella. Each SP is preceded by a pre-swim pulse (PSP) which is a neuronal pulse conducted in the marginal nerve(s). 4. Marginal pulses (MP's) are neuronal pulses conducted in the marginal nerve(s) which can trigger synchronous tentacle contraction. 5. MP's originate from pacemaker sites located in tentacle bulbs. When new tentacles first appear the firing of MP's from these new sites is not synchronized with established pacemakers: eventually they become linked to the original pacemaker system. 6. Synchrony between MP pacemakers is lost under Mg⁺⁺ anaesthesia. 7. Tentacle contraction pulses (TCP's) are the electrical accompaniment to local tentacle contraction. 8. Crumpling pulses (CrP's) are epithelial pulses causing the protective behavior known as crumpling. 9. CrP's show a decrease in conduction velocity and amplitude as a result of repetitive stimulation.