X.—On The Accessory Respiratory Organs of Heteropneustes fossilis Bloch

Abstract

Heteropneustes (Saccobranchus) fossilis Bloch. is a common airbreathing fish found in India. It possesses a respiratory sac on each side of the body embedded in the lateral myotomes. The structure of this organ, its respiratory function and the phenomenon of “drowning” when the fish is denied direct access to the air have engaged the attention of several workers in the past among whom Day (1868), Dobson (1874), Burne (1896), Das (1927), Hora (1935) and Marlier (1938) deserve mention. The only detailed account of the structure of the accessory organ of this fish is available to us from the work of Das (1927) who also paid some attention to its development. Dobson (1874) and Hora (1935) mainly concerned themselves with some experiments bearing on the “drowning” of the fish when compelled to live under water. Little information is obtainable from the existing literature on the following points which have an important bearing on evolution of its accessory respiratory organs:(i) the gross and minute structure of the respiratory sac, especially its vascularization;(ii) the origin and derivation of the accessory respiratory organs (=the “Fans” and the respiratory sac); and(iii) the muscles concerned with its breathing movements.