One of the ganglia connected with the visceral nerves in octopod Cephalopoda has been found to possess the peculiarity of contracting rhythmically with the same frequency as the organs of blood circulation. This ganglion for which the term cardiac ganglion has been adopted (syn. ganglion of the branchial heart, 2nd cardiac ganglion) has been examined in Eledone cirrhosa and Octopus vulgaris. It has been found that the pulsations which can also be observed in an excised ganglion are brought about by contractions of a spherical body situated inside the ganglion and occupying nearly half of its volume. This body for which the term intraganglionar body (abbr. IG body) is proposed is separated from the rest of the ganglion by a layer of connective tissue and of muscle fibres arranged in bundles running in various directions. Some muscle strands pass from this peripheral coat outwards and mix with the muscles of the vena cava near its entrance into the branchial heart. Inside the peripheral coat the following elements of the IG body can be distinguished: (1) a stroma consisting of connective tissue cells whose expansions form a spongy framework with small irregular meshes; (2) collagen fibres scattered in the stroma; (3) muscle trabeculae running in various directions; (4) blood vessels; (5) nerve fibres. The latter derive from the cells situated outside and among the peripheral muscle bundles; after passing through the peripheral coat they ramify forming a neuropile layer beneath the muscles. At some places several cell axons running in a common bundle ramify close together and breaking up into fine terminations form tree-like tufts with their tops directed inwards. They are often seen coming into contact with the muscle trabeculae. The function of this pulsating intraganglionar body is enigmatic. It may perhaps have neurosecretory properties and the contractions of its muscles may be instrumental either in liberating the products of secretion from the nerve terminations, or in squeezing them out of the ganglion, or in both these actions.