Among the peculiarities of internal structure in the fishes of the Ganges, the most remarkable, in a physiological point of view, are those connected with the organs of respiration and the air-bladder, in certain species of the genera Ophiocephalus , Bola , Coius , Trichopodus , Macropteronotus , Pimelodus , Silurus , Mystus and Clupanadon .
The Macropteronotus , Magur , Coius Cobojius , Trichopodus Colisa , Ophiocephalus Gachua , and Silurus Singio , present, in addition to the usual number of gills observed in osseous fishes, certain respiratory organs, which admit, it would seem from the tenacity of life possessed by these species, of a higher degree of oxygenation of the blood than is effected by means of common branchiae.
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Ophiocephalus Gachua . The branchial arches of this species have also very short lamina,. The supernumerary organ of each side is divided into two portions supported upon two broad osseous plates, one projecting from the internal side of the articular bone of the head, and connected with the cornu of the os hyoides; the other, articulated with the anterior branchial arch, the superior limb of which is wanting. The substance composing the organ is situate upon the edge of these plates, and consists of a thick solid tissue, having a curled margin, not unlike that of the common species of alga, or seaweed. The branchial artery having given off branches to the laminae of the arches, runs for a short distance in a canal of the osseous plate, which is connected with the anterior arch, and afterwards proceeds upon its surface, where it divides and subdivides into minute branches, distributed to the tip of the supernumerary organ: the vessels that return the aerated blood unite into one branch, which joins those proceeding from the gills to form the aorta.
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All the species, possessing these supernumerary organs of respiration, are very tenacious of life; surviving the infliction of severe wounds, and living upon land for a much longer time than other fishes. «In China, the species of the Ophiocephalus,» according to Hamilton, «are often carried alive in pails of water, and slices are cut for sale as wanted, the fish selling dear while it retains life, while what remains after death is considered of little value.» The Coius Cobojius can be kept alive without water for five or six days, and, according to the same author, is often conveyed in that state to the Calcutta market, from marshes at the distance of one hundred and fifty miles. This species, and the Ophiocephalus Gachua , like the Doras Costala or hassar , Dr Hancock's Zoological Journal, No. xiv ., possess the power of locomotion on land to a considerable extent; and are the fishes so often met with, after a shower of rain, in fields at a distance from rivers or marshes; and hence supposed to fall from the clouds. - Hamilton's Account of the Fishes of the Ganges, p. 68 .
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The air-bladder, besides possessing the locomotive function generally ascribed to it, appears, from the connection that exists between it and a set of small bones, analogous to the ossicula auditus , to exert some influence on the sense of hearing. These bones correspond to the malleus , incus , and stapes of Mammalia, and are present, according to Professor Weber, by whom they were discovered, in all the osseous fishes, in the vicinity of the anterior or cervical vertebrae.-(Blumenbach's Comparative Anatomy , p. 285.) They exist in the different species of the genera Silurus , Pimelodus , and Cyprinus , I have had an opportunity of examining; but are apparently wanting in the genera Ophiocephalus , Coius and Trichopodus : and also in the Bola Pama , Mystus Chetala , and Clupanadon Misha , in which species their place is supplied by a direct connection between the two organs. The bone corresponding to the malleus is considerably larger than either of the other two, and is uniformly situate at the anterior extremity of the air-bladder, extending along the side of the pine to opposite the first vertebra.
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These passages were originally published under the above title in: The Edinburg Journal of Science , 1831, vol. 5 (new series), pp. 33-49.
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