BOTH THE HEART AND PERICARDIUM IN THE CHITON ACANTHOPLEURA-JAPONICA RECEIVE DUAL INNERVATION FROM THE CENTRAL-NERVOUS-SYSTEM

The isolated heart or pericardium of the chiton Acanthopleura japonica each showed rhythmic automaticity, even after they were isolated from the body. Intracellular action potentials could be recorded from spon taneously active myocardial cells in the isolated heart and pericardiu m. They always appeared to be preceded by pacemaker potentials much as has been found for myocardial cells of other molluscs. These show tha t both heart and pericardial beats of Acanithopleura have a myogenic n ature. Stimuli applied to each of the lateral and ventral nerve cords produced both excitatory and inhibitory effects on the heart and the p ericardium. Both the heart and the pericardium in Acanthopleura may re ceive excitatory and inhibitory control from each of the lateral and v entral nerve cords. The dual innervation of the heart which is seen co mmonly in molluscs, at higher stages of evolution, may have been estab lished in Acanthopleura at the stage of the phylogenetic beginning of the Mollusca. On the contrary, the dual innervation which is required for acceleratory and inhibitory control of the spontaneously rhythmica lly active pericardium is different from the innervation seen in mollu scs at the higher stages.