. Text-book of zoology for junior students. Zoology. 22& VElfTEltrfATE ANIMALS. ICHTIIYOPSIDA. CHAPTER XXIII. CLASS I. PISCES. The fishes form the lowest chiss of the Vertebrata, and they may be broadly defined as being Vertebrate animals provided icit/i gills, whereby they are enabled to breathe air dissolved in water ; the heart, when present, con-nsts of a single auricle and ventricle (with the exception of the Mnd-fishes); and the limbs, when present, are in the form of fins, or expansions of the integument. In their external form, fishes are in most cases adapted for rapid locomotion
. Text-book of zoology for junior students. Zoology. 22& VElfTEltrfATE ANIMALS. ICHTIIYOPSIDA. CHAPTER XXIII. CLASS I. PISCES. The fishes form the lowest chiss of the Vertebrata, and they may be broadly defined as being Vertebrate animals provided icit/i gills, whereby they are enabled to breathe air dissolved in water ; the heart, when present, con-nsts of a single auricle and ventricle (with the exception of the Mnd-fishes); and the limbs, when present, are in the form of fins, or expansions of the integument. In their external form, fishes are in most cases adapted for rapid locomotion in water, the shape of the body being such as to cause the least possiljle friction in swimming. To this end, as well as for ])nrposes of defej)ce, the body is generally enveloped in a species of chain-mail formed by overla]i|)ing .scales, to Avliich bony plates, tubercles, and s|)ines are sometimes added. Val- uable characters can sometimes be drawn from the nature of the scales; and witli a view to this, the integu- mentary aii|iendages of fishes have been divided by Agassiz as follows (fig. 104) :— 1. t'l/cloid scales {<(), consisting of tlun, rtexible, horny , which iire circular or elliptical in .shape, and have a smooth outline. These scales occur in most of our common fishes ('-•.(/., the Pike). 2. Ctenoid scales {b).—Tiiese resendile the cycloid scales in being thin, , horny scales, but they are distinguished by having their hinder margins cut into comb-like projections, or fringed with. Fig. 104.—Scales of dillereut lisl a Cycloid scale (Pike); b Ck-u scalc(Pi'reh); c scalf(Tlu) Lack); d Placoid .scale nf Hhiin: Guiiniil scales (Puhctnihrn^.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Nicholson, Henry Alleyne, 1844-1899. New York, American Book Co
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
