Clarias batrachus (Linn.) inhabits the fresh-waters of India, It is commonly known as "Magur fish." According to Hora ('35) sometimes it is found in slightly brackish waters also. The fish has attracted the attention of several naturalists This paper formed part of a thesis approved for the Ph.D. degree by the Banaras Hindu University in 1959. 115 116 J. S . DATTA MUNSHIlimits it posteriorly. The postero-medial part of the chamber is covered by the peritoneal membrane (pl. 5, fig. 8). The 4 leaf-like "fans" or gill plates which are developed on the 4 gill arches cut off the communication between the suprabranchid chamber and the opercular cavity.Inhalent aperture. The inhalent aperture is not so well defined as in the case of Anabas scandens. Nevertheless, the air makes its way into the supra-branchial chamber through the narrow gill slit existing between the second and the third gill arches (pl. 5, fig. 8). As the air crosses the gill cleft and escapes into the opercular cavity it is directed into the supra-branchial chamber by the action of the two fans borne by the second and third gill arches. The opening and closing of this gill cleft is controlled by the action of the Abductor muscles developed on the f a m

A comparative study of the skin, based on the micro‐anatomical investigation of skin fragments taken from a specific region of the body, has been made of three air‐breathing fishes, namely, Heteropneustes fossilis, Amphipnous cuchia and Mastacembelus pancalus. On the basis of their structure and histochemical nature, five types of skin glands have been distinguished in the epidermis of these fishes. The relative thickness of the epidermis (A. cuchia–119 μm (average value), H. fossilis– 98 μm (average value), M. pancalus–34 μm (average value)) and its vascularization has been considered and compared with other fishes and amphibians. The possibilities of cutaneous respiration in these air‐breathing fishes has been discussed. The presence of a well‐defined lymphatic system, comprising a series of lymph spaces containing small lymphocytes, in the stratum germinativum layer of the epidermis of these fishes has been established. The stratum laxum layer of the dermis in Amphipnous is characterized by the presence of definite areas containing “Substantia amorpha” having acidic mucopolysaccharides which may be related with the amphibious habit of the fishes. This is an adaptation against desiccation similar to that found in the Anura. In Mastacembelus elliptical areas of the stratum laxum penetrate into the epidermis thus making these areas of the epidermis considerably thin (about 7 μm) for cutaneous respiration. There is an inverse relationship between the thickness of the stratum compactum and squamation.

The vascular organization and endothelial cell specialization of the air-breathing organs of Anabas testudineus were examined by light and scanning electron microscopy of fixed tissue and vascular corrosion replicas. The vessels supplying blood to the lining of paired suprabranchial chambers and the plicated labyrinthine organs within the chambers are tripartite, having a median artery and paired, lateral veins. Hundreds of respiratory islets, the functional units of gas exchange, cover the surfaces of both the chamber and labyrinthine organ. A median islet artery supplies the central aspect of each islet and gives rise to numerous short arterioles from which the transverse channels are formed. Transverse channels are parallel capillary-sized vessels that extend in two rows away from the medial arterioles and drain laterally into one of two lateral islet veins. Basally situated single rows of endothelial cells lining the transverse channels form thick, evaginated, tongue-like cytoplasmic processes that project freely into the lumen from the tissue side of the channel. Other thin, septate, cytoplasmic extensions of the same cells form valve-like septa that extend across the channel. Both the septa and tongue-like processes appear to direct the red blood cells to the epithelial side of the channel and thus decrease the diffusion distance between the air and red cell. A large sinusoidal space lies under the transverse channels and may support the channels and even elevate them during increased oxygen demand. The epithelium covering the transverse channels is smooth, which enhances air convection and minimizes unstirred layer effects. The epithelium between the channels contains microvilli that may serve to trap bacteria or particulates and to humidify the air chambers.

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