THE COORDINATION OF POTENTIAL PACEMAKERS IN THE HYDROID TUBULARIA.

Abstract

Sectioning experiments and electrical recording indicate that there are many potential pacemakers in polyps of the hydroid Tubularia. Functionally the pacemakers are organized primarily into pacemaker systems, groups within which there is tight coupling. The different pacemaker systems of a polyp are loosely coupled to one another. There are two principal systems in Tubularia, one in the polyp neck (the NP system) and one in the hydranth (the HP system). In addition, there are pacemakers controlling activities of individual tentacles. Activity in the NP system is usually not associated with observable polyp behavior. HP system activity is correlated with behavioral responses termed concerts. Concerts are probably digestive activities; they result in the mixing of food being digested and the distribution of the products of this digestion. The NP systems of polyps on a colony are loosely coupled to one another through one of the three conducting systems found in Tubularia stalks. The loose coupling between NP systems of polyps on a colony and the loose coupling between NP and HP systems within single polyps results in there being some coordination of concert activity throughout a colony.