. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Ports of Entry 821 Only a trace of the parietal organ remains in birds, while among adult mammals it entirely disappears, in many cases in the embryo as well as in the adult. 6. Comparative Anatomy (a) Amphioxus.—Eyes are absent in amphioxus, but numerous photo- receptive cells occur in the nerve cord, thus rendering these primitive chor- dates sensitive to light as it penetrates through the semi-transparent tissues of the body. Each of these cells has a p
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Ports of Entry 821 Only a trace of the parietal organ remains in birds, while among adult mammals it entirely disappears, in many cases in the embryo as well as in the adult. 6. Comparative Anatomy (a) Amphioxus.—Eyes are absent in amphioxus, but numerous photo- receptive cells occur in the nerve cord, thus rendering these primitive chor- dates sensitive to light as it penetrates through the semi-transparent tissues of the body. Each of these cells has a pigment cup associated with it (Fig. 720).. 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 Walter, Herbert Eugene, b. 1867; Sayles, Leonard Perkins, 1902-. New York : Macmillan Co.
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