. Zoology : for students and general readers . Zoology. 404 The head of the sturgeon, garpike, and of other ganoid fishes, is protected by solid dermal bones, and the shells of turtles are dermal structures. The color of the skin of Vertebrates is due to pigment- granules situated either in the epidermis or dermis, and in the chameleon they are contained in special sacs (chromatophores) which are under the control of the nervous system. The muscular system of Vertebrates arises from the middle gerni- layer (mesoderm), and Pig. 385.—Placoid scale of dog-fish (vertical sec- ;„ „„
. Zoology : for students and general readers . Zoology. 404 The head of the sturgeon, garpike, and of other ganoid fishes, is protected by solid dermal bones, and the shells of turtles are dermal structures. The color of the skin of Vertebrates is due to pigment- granules situated either in the epidermis or dermis, and in the chameleon they are contained in special sacs (chromatophores) which are under the control of the nervous system. The muscular system of Vertebrates arises from the middle gerni- layer (mesoderm), and Pig. 385.—Placoid scale of dog-fish (vertical sec- ;„ „„,,,„ tl-,o mnQfloa tion magnified), o, enamel layer ; b, dentine of the ^H ^IC gei m tne mUSCleS spine on the Owen. Jj^ p^j,^ j^^.JgQ f ^qjj^ ^J^g primary segments indicated by the protoyertebrfe, while in the adults of fishes and certain salamanders, the muscular system is distinctly segmented, corresponding to the seg- mentation of the ver- tebral column, the four lateral trunk- muscles being divided into a number of seg- ments by tendinous bauds, which corre- spond in number to the vertebrfe (Gegen- baur). The eye in Verte- brates in its develop- mentalhistory belongs to a different type of structure from that of any invertebrates, Un pi^. gge.^cyloid scale of roach, magnified, seen in less it be the larval section, ^, and from the surface, B.—After Owen. Ascidians, for in both tyjoes tlie eye is said by Gegenbaur not to be directly developed from the ectoderm, but from the. 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 Packard, A. S. (Alpheus Spring), 1839-1905. New York : Henry Holt
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
