An accessory organ of the circulatory system in Sepia and Loligo

Abstract

SUMMARYAn accessory organ of the circulatory system has been found in Sepia officinalis and Loligo forbesi, situated on the inner surface of the mantle around the posterior pallial vessels. It is spheroidal in shape and consists chiefly of muscle fibres forming bundles anastomosing with one another, most of them taking a general circular course round the artery and the vein. In Sepia the muscle bundles are more loosely arranged, being imbedded in connective tissue of soft consistency; they are not continuous either with the musculature of the vessels or with that of the mantle, and show certain structural differences from them. The nerves approaching this organ from various directions carry elements of two systems: (a) fibres given off by the branches innervating the neighbouring mantle muscles; (b) elements of the vasomotor system; these are 3 trunks consisting of fibres of small calibre and containing groups or rows of ganglion cells. One of these trunks associates with one of the main mantle nerves, another runs through the retractor muscle of the branchia. Within the accessory organ they intermingle with the motor fibres, but the nerve bundles passing to the posterior pallial vessels consist of fibres of the vasomotor system only; it is possible that the muscles of the accessory organ are supplied, in addition to their motor innervation, with fibres of the vasomotor system.