E g y p t ELEVEN FIGURES
JNTRODIJCTTONThe vast majority of fishes are incapable of living f o r any length of time out of water. A few fish, however, are remarkable for being ablc to live out of their aquatic media for a comparatively long time, and also for their peculiar habit of going on excursions over surrounding marshy lands. These fishes usually possess special accessory air-breathing organs wliicli enable them to stay out of water. These organs arc generally met witli where the gill-filaments are reduced. Thus iii Amphipnous (Arnphipnoidae) there is a pharyngeal "lung" for breathing atmospheric air (Das, '27) ; whilc in Periophtlialrrius (Gobiidae ) aerial iwqiiration is pcrformed mainly by tlic pharyngeal diverticula assisted by both buccal and opcrcular cavitics. (Ilas, '40). Acccwory air-breathing organs are also found jn the Ophiocephalidae, Cllariidac, Ana-1)aiititlae and others in which the gill-apparatus is as complrtcl AS in ordinary fishes (Das, '27, '40 ; Moussa, '56). 111 a previous paper the author (Moussa, '56) lias described the accessory respiratory organs of Clarias lazera as consisting of a suprabraiichial chamber-on each side of the hody--c.~iclosing two highly vascular arborcsccnt organs surmounting the epibranchials of the second and 4th branchial arches. The suprahranchial cliambcr lies postero-dorsal to the opercular cavity and its outer \\.all is supported by four 419 420 TOHAMY A. MOUSSA branchial fans formed by the coalescence of the hranchial filaments at the distal end of the ceratobranchial of the first four gill-arches. The fans separate the suprabranchial chamber (air-chamber) from the opercular cavity proper. Between the second and third fans there is a notch which allows air to escape from the pharynx into the air-chamber when the mouth is widely opened for a gulp of air; thus the notch serves as an air-entrance. There is aiiotlier notch lying between the third arid fourth fans and connecting the air-charnbt?r with the opercular cavity; this is used as an air-exit when the operculum is raised.Each of the suprahrancliial air-charnlwrs is supplied by all afferent branchial vessels ; tlie oxygenated blood is conveyed by a separate vessel directly to the latcAral aorta; a condition which is absent in otliei-fishes. The anterior and posterior arborescent organs a r e supplied by the second and 4th afferent branchial vessels respectively ; the equivalent efferent vessels convey the oxygenated ldoocl to both the latc~a l aorta and the dorsal aorta respectively ; a n arrangement which has not been described before ill Clariitlae. l h c arboresceiit organs, charnlwix and fans are highly vascular and, therefore, very likely to be respiratory in function. So, iii this present contribution some cxpcrinieiits have been carried out by the author to t r y to untlerstaiicl more clearly the function of these organs. The experinients were carried out in the laboratory on specimens of Clarias lazcra obtained from the hiahmoudia Canal which supplies Alexandria with fresh water. They were kept ...
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