Figure 12. The excretory organ of barnacles is a pair of maxillary glands that lie on each side of the foregut. Each gland is composed of an end-sac, an efferent duct (divided into proximal and distal regions) and a terminal duct that opens to outside at the base of second maxilla. A) The front view (Adapted from Anderson 1994) B) The side view. (Adapted from White and Walker 1981).