414 SURGEON J. 0. THOMPSON ON THE 32. Contributions to the Anatomy o£ the Ophidia. By Joseph C. Thompson, Surgeon, United States Navy *. [Received April 25, 1913 : Read June 3, 1913.] (Text-figures 77 & 78.) Index. Page Sugeestiou as to the Possible Origin of the so-called Tracheal "Lung 414 Notes upon the Anatomy of : — ■ JCenopeltis tmicolor 415 Cyclocorus lineatus 419 Chrysopelea ornata 420 Crotalus confluentus 422 The Intromittent Organ in : — Folyodontophis bivittatus 423 Tropidonotus vihakari 423 Selicops angulatus 424 Cyclocorus lineatus 425 Spilotes pullatus 425 S3' stein atic : Sebius, gen. nov 424 /Stcggestion as to the Possible Origin of the so-called Tracheal Lung. It is suggested that the tracheal membrane has been developed as a device originally contributing to the required flexibility of the tube. The cartilaginovis rings being interrupted behind, or on one side, permit that the structure be subject to a much greater pressure, especially when bulky morsels are being swallowed, than would be the case were the rings complete. The tracheal membrane, being continuous with the lung, appears to have afforded a convenient foundation for the extension of pulmonary tissue when the need for an increased breathing surface has arisen, or when the lung has been encroached upon by other organs. In the Hydrophidse an increased pulmonary area is required both to give buoyancy and to enable the sea-snakes to remain some time beneath the surface. The most specialized species in the genus Hydrophis Daudin, those in \\\q fasciatus group, possess a lung that extends nearly to the vent, and a tracheal lung of due proportion. In the Acrochordinfe, the members of which are of aquatic habits, there is also a highly developed tracheal lung. Owing to the abnormal size of the heart the respiratory tissue on the trachea is widely separated from the lung itself. In the Viperidse the elaboration of venom requires a large liver. These serpents as a rule have short and thick bodies, and the liver invades the region just caudad of the heart. As a * Communicated by Dr. F. E. Beddaed, M.A., F.R.S., F.Z.S.