. Animal biology. Zoology; Biology. CLASS ELASMOBRANCHII 345 The body of the dogfish is covered with placoid scales (Fig. 250), each of which is composed of a sharp toothUke portion projecting through the skin and attached to a plate lying in the dermis. They neither overlap nor touch one another. The points of these scales are directed. Fig. 241.—Spiral valve of a ray. The arrow shows the direction in which the food passes. {From Wieman, "General Zoology,'' modified from Mayer, by the courtesy of McGraw- Hill Book CoTnpany, Inc.) backward. They thus offer no resistance to the hand if the
. Animal biology. Zoology; Biology. CLASS ELASMOBRANCHII 345 The body of the dogfish is covered with placoid scales (Fig. 250), each of which is composed of a sharp toothUke portion projecting through the skin and attached to a plate lying in the dermis. They neither overlap nor touch one another. The points of these scales are directed. Fig. 241.—Spiral valve of a ray. The arrow shows the direction in which the food passes. {From Wieman, "General Zoology,'' modified from Mayer, by the courtesy of McGraw- Hill Book CoTnpany, Inc.) backward. They thus offer no resistance to the hand if the animal is stroked from the head to the tail, but when an attempt is made to stroke it firmly in the opposite direction they effectively resist the movement. The stomach is U-shaped and is marked off from the intestine by a constriction containing a sphincter muscle. The characteristic feature of the digestive system of the dogfish is the presence in the intestine Carotid artery Precai^al vein ? Sinus venosus^ Efferent branciiial ortery , Dorsal V aorta - Cardinal i/ein Coeli'ac artery PatJCreas Jugular vein ~ 'er?al portal vein Caudal artery Caudal vein. 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 Wolcott, Robert Henry, 1868-1934; University of Nebraska (Lincoln campus). Dept. of Zoology. New York ; London : McGraw-Hill Book Company, Inc.
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Keywords: ., bookcentury1900, bookcoll, booksubjectbiology, booksubjectzoology
