The postbranchial digestive tract of the ascidian, Polyandrocarpa misakiensis (Tunicata: Ascidiacea). 2. Stomach.

The organization of the stomach in the compound styelid ascidian, Polyandrocarpa misakiensis, is described, and the morphology and cell types of the stomach is discussed from the phylogenetic viewpoint. The stomach is a sac-like organ whose wall is formed into longitudinal folds. The stomach consists of external and internal epithelium.

Tunic phagocytes are involved in allorejection reaction in the colonial tunicate Aplidium yamazii (Polyclinidae, Ascidiacea).

The colonial ascidian Aplidium yamazii exhibited an allorejection reaction when two allogeneic colonies were brought into contact at their growing edges or at artificial cut surfaces. This species has no vascular network in the tunic, unlike the botryllid ascidians, which have a vascular network throughout the colony's common tunic. In the allorejection reaction induced by contact at the growing edges, some small, hard-packed tunic masses were formed at the contact points.

Comparative studies on the circulatory system of the compound ascidians, Botryllus, Botrylloides and Symplegma.

The circulatory systems of four polystyelids, Botryllus schlosseri, B. primigenus, Botrylloides violaceus and Symplegma reptans, were compared. The palleal buds are connected to the parent zooid by a peduncle and to the colonial vascular system by connecting vessels.