. Cold-blooded vertebrates: part I. Fishes. Fishes; Amphibians; Reptiles. FISHES The word ganoid, used to describe one of the two time- honored groups of the subclass ray-fins, refers to the sub- stance which covers the outer surface of the bony plates protecting members of this great group of fishes. This substance resembles dentine and is called ganoin. The ganoid plates on the American gar pike (Fig. i6), which may be taken as the most typical example of this kind of covering, are large, bony, and rectangular, arranged in rows and placed edge to edge, in contrast to the over- lapping scales
. Cold-blooded vertebrates: part I. Fishes. Fishes; Amphibians; Reptiles. FISHES The word ganoid, used to describe one of the two time- honored groups of the subclass ray-fins, refers to the sub- stance which covers the outer surface of the bony plates protecting members of this great group of fishes. This substance resembles dentine and is called ganoin. The ganoid plates on the American gar pike (Fig. i6), which may be taken as the most typical example of this kind of covering, are large, bony, and rectangular, arranged in rows and placed edge to edge, in contrast to the over- lapping scales already described. These plates are very hard and form an excellent armor. Although interlocked for additional strength, they do not make the body rigid,' as they may separate or partly slide over each other when the fish moves its body from side to side. The free edges of the plates are so sharp that a large live fish, when held in the hands, can cut deep wounds by throwing its body from side to side in its effort to escape, thereby pinching the hands and fingers between the margins of the plates. In the sturgeons—among the largest fishes of our sea- shores, rivers, and lakes—the ganoid plates only partly cov- er the body (see Fig. ii). Generally two rows of plates lie on the back, one along the side, and another along the edge of the abdomen. Those Fig. i6. Ganoid plates of the scctions Unprotected by bony American gar pike, Lepisosteus shields are COVCrcd with rOUgh, osseus. After Lankester . R, leathery skm. Fmally, m the paddlefishes the ganoid plates have disappeared entirely, leaving the skin almost smooth (see Plate 4). The porcupine fishes, already referred to because of their spherical or globular body, derive their name from the sharp spines with which they are covered. The spines often are so broad at the base that, together with the roots they bear, a continuous coat of mail is formed. [36]. Please note that these images are extracted from scanned page images
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Keywords: ., bookcentury1900, booksubj, booksubjectfishes, booksubjectreptiles
