Primary neoplasms of the pleura are among the very rare tumors. They occur considerably less frequently than primary growths of the lung or bronchi. Clinically and pathologically the malignant tumors of the pleura form the most interesting and important group. The pathogenesis and consequently the nomenclature of these tumors is still in confusion. Wagner,1 in 1870, described the classical pleural tumor under the name "tuberkelaehnliche lymphadenome," which opened a long controversy. Schultz,2 in 1875, reexamined the preparations of Wagner and gave a complete description of the above tumor, emphasizing the neoplastic nature of the growth and naming it "endothelial cancer." These two papers mark the beginning of a stubborn contention which, fifty years after its inception, still remains unsettled. Among the other designations which have been used to describe malignant pleural tumors may be mentioned: lymphangitis proliferans (Fraenkel, Schweninger); lymphangitis carcinomatodes (Neelson); sarcocarcinoma (Boehme), alveolar endothelial sarcoma (Podak), endothelioma (Eppinger