A treatise on zoology . ,more or less rhomboid scales in oblique rows corresponding niuneri-cally to the myotomes (Figs. 182, 183, 193). Each scale to someextent overlaps its neighbours from before backwards like the tilesof a roof, and the anterior deep-lying edge is often produced intoan articulating process. In the higher forms the scales becomethinner, more deeply imbricating, less closely articulated, and maylose their metameric disposition. Agassiz [4] classified the fish into the groups Placoidei,Ganoidei, Cycloidei, and Ctenoidei, according to the character of 210 DERMAL SKELETON their
A treatise on zoology . ,more or less rhomboid scales in oblique rows corresponding niuneri-cally to the myotomes (Figs. 182, 183, 193). Each scale to someextent overlaps its neighbours from before backwards like the tilesof a roof, and the anterior deep-lying edge is often produced intoan articulating process. In the higher forms the scales becomethinner, more deeply imbricating, less closely articulated, and maylose their metameric disposition. Agassiz [4] classified the fish into the groups Placoidei,Ganoidei, Cycloidei, and Ctenoidei, according to the character of 210 DERMAL SKELETON their scales. The first have only placoid scales (denticles,see p. 119). The second have the flat rhombic shiny scalesmentioned al)Ove. The third have thin rounded scales. Lastly,the Ctenoidei have similar thin scales, but provided with spiny. Leuoiscus rutilus. Left-side view, showiiif? the myotomes, two of wliicli are marked in , longitudinal transverse septum ; S, lateral line. (After A. llase.) projections. Recent work tends to show that the cycloid and ctenoid scales are closely allied forms derived from the moreprimitive ganoid scale, and that they all three differ very
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
