. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Kinds of Vertebrates 31 allies (Fig. 20a and c), all graceful, elongated, streamlined animals, actively prey upon other fishes. The rays, with the skates, torpedoes, guitar fishes, and their allies, on the contrary, are flattened sluggish bottom feeders (Fig. 20b). In the Batoidea the pectoral fins, considerably enlarged, are the organs of A. Squalus, Spiny Dogfish B. Raia, A Skafe Fig. 20. ELASMOBRANCHS. (a, after Dean; b, after Goode and Bea
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Kinds of Vertebrates 31 allies (Fig. 20a and c), all graceful, elongated, streamlined animals, actively prey upon other fishes. The rays, with the skates, torpedoes, guitar fishes, and their allies, on the contrary, are flattened sluggish bottom feeders (Fig. 20b). In the Batoidea the pectoral fins, considerably enlarged, are the organs of A. Squalus, Spiny Dogfish B. Raia, A Skafe Fig. 20. ELASMOBRANCHS. (a, after Dean; b, after Goode and Bean; c, after Boas.) An elasmobranch may be distinguished by the following characteristics: (1) a large mouth ventral in position rather than terminal; (2) separate openings of the gill slits (usually five pairs) not concealed as in other fishes behind a gill cover; (3) dorso-ventrally flattened head; (4) placoid scales, resembling tiny thumb tacks embedded, point up, in the skin without shin- gling over each other like ordinary fish scales; (5) tail heterocercal, that is, with the vertebral column extending into the dorsal part of the caudal fin; (6) paired pelvic fins modified into "clasping organs" in the male, permit- ting internal fertilization of the egg; and (7) the production of a relatively small number of eggs that in some species are covered with shells and then laid, while in others they develop into some size within the oviduct of the female before the young are born alive. (3) holocephalians.—Biological interest in the uncommon and bizarre "elephant fishes," or "spook fishes," centers in their intermediate anatomical position between elasmobranchs and other fishes. They differ from elasmobranchs in a number of respects among which are: (1) small size of mouth; (2) scarcity of scales; and (3) presence of a gill cover, or operculum, a fold of the body wall extending over the gill slits but with a free posterior margin under which the re
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
