. Carnegie Institution of Washington publication. i8 CHBL^ROID FISHES AND THEIR DEVELOPMENT. The mode of breathing of the fish is somewhat remarkable. The mouth is very small, and its rims are motionless or almost motionless, scarcely parted in breath- ing; so nearly closed, in fact, that the movement of the breathing-valve can hardly be seen. A portion, probably a large portion, of the water—as in the case also of dipnoans—is breathed through the prominent nasal openings (fig. 4 a and c), whose cartilaginous marginal iiap is specialized to this end; and since the mouth is motion- less, it fol
. Carnegie Institution of Washington publication. i8 CHBL^ROID FISHES AND THEIR DEVELOPMENT. The mode of breathing of the fish is somewhat remarkable. The mouth is very small, and its rims are motionless or almost motionless, scarcely parted in breath- ing; so nearly closed, in fact, that the movement of the breathing-valve can hardly be seen. A portion, probably a large portion, of the water—as in the case also of dipnoans—is breathed through the prominent nasal openings (fig. 4 a and c), whose cartilaginous marginal iiap is specialized to this end; and since the mouth is motion- less, it follows that the branchio-opercular muscles are the efficient means of introducing water to the gills. In point of fact, in the living fish one readily observes an extensive dilation and contraction of the opercular flaps. In spite, however, of this extensive movement, the excurrent open- ing is remarkably small, and at this point the opercular fold puffs out conspicuously, like an opened valve, a small one at that, forming a slit about three-sixteenths of an inch in diameter. The rhythmic opening and closing of this slit gives a further suggestion of its valvular nature. The breathing, moreover, as in the case of other fishes, is rendered more effective by the presence of oral breath- ing-valves, operating so as to close not merely the open- ing of the mouth, but the nasal passage also. The respi- ratory movements are rajud, at least in captive fish. In such specimens there are counted as many as 100 respi- rations a minute, a number evidently abnormal. (3cca- sionally, when the fish is swimming, the mouth will open two or three times spasmodically. This occurs too rarely, however, to be of especial respiratory value ; and it is also to be observed, if the fish is a male, that the frontal clasping spine will at the same time be elevated and depressed. This correlated movement of clasping spine and jaw has already been suggested by Reis on anatomical grounds. In this connectio
Size: 799px × 3128px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcarnegie, bookcentury1900, bookdecade1900, bookyear1906
