Some characteristics of the mast cells of atrioventricular valves and pericardium of South American opossum ( Didelphis azarae ) - Soares, J. C; Ferreira, Affonso Luiz; Vugman, Ithamar (Zoologische Jahrbucher. Abteilung Fuer Anatomie und Ontogenie der Tiere, 1987)