Gross and fine structure of the antennal circulatory organ in cockroaches (Blattodea, Insecta)

The antennal circulatory organ of Periplaneta americana and Blaberus craniifer was investigated by light and electron microscopy. This organ consists of two pulsatile ampullae located near the antennal base which are interconnected by a large transverse muscle and associated blood vessels which run into the antennae. Diastole is caused simultaneously in both ampullae by the transverse muscle. Systole is produced passively by the elasticity of the wall of the ampullae and minute accessory tendons. Both elastic structures contain fine unbanded extracellular filaments. The antennal vessels possess two distinct regions: a proximal convoluted region lying within the hemocoel of the head and a narrower distal region running through the antenna and opening near the antennal apex. The length of the proximal portion increases markedly during ontogeny in correlation with the growing antenna. Its wall consists of a high-prismatic epithelium ensheathed by a thick layer of collagen fibrils. The structure of the wall cells is comparable to that found in some salt transporting epithelia: it shows a polar organization with basal infoldings, a large number of mitochondria, and typical arrangement of the junctions or mitochondrial-scalariform junctional complexes. The possible physiological function of this epithelium in ionic or osmoregulation of the hemolymph entering the antenna is discussed. The wall of the distal vessel region consists of a flat single-layered epithelium and seems to be specialized only for delivery of hemolymph to antennae. The structure and function of the antennal heart in cockroaches is compared to that found in other insects.