. Principles of modern biology. Biology. Responses of Higher Animals: The Effectors - 443 H O K ^C* ^C" V >"^C-C-OH 1 " c-q I + </2 02 H *^, HO" ^"C" "-S I H active luciferin (LH2) C—H H <^ H I H c \ /" c- i ii ;c-< i I o H oxidized luciferin (LO) inactive until reduced O II -C-OH + H20 Fig. 24-12. Molecular structure of the luciferins of the firefly. chain protein, consisting of about 1000 precisely ordered peptide units. Moreover, it has been shown that for each molecule of active luciferin (LH2) that is converted to the oxidized for
. Principles of modern biology. Biology. Responses of Higher Animals: The Effectors - 443 H O K ^C* ^C" V >"^C-C-OH 1 " c-q I + </2 02 H *^, HO" ^"C" "-S I H active luciferin (LH2) C—H H <^ H I H c \ /" c- i ii ;c-< i I o H oxidized luciferin (LO) inactive until reduced O II -C-OH + H20 Fig. 24-12. Molecular structure of the luciferins of the firefly. chain protein, consisting of about 1000 precisely ordered peptide units. Moreover, it has been shown that for each molecule of active luciferin (LH2) that is converted to the oxidized form (L:0), one quantum of light (and no heat) is produced. In other words, bioluminescence proceeds with re- markable efficiency and the frequently used term "cold light" is most appropriate. are usually multicellular organs in which the displacement of the pigment is controlled by muscles. But the chromatophores of verte- brates are single cells (Fig. 24-13), which are present in enormous numbers throughout the skin. The cytoplasm of these cells is densely packed with pigment granules, and the distribution of the pigment in the cells determines the shade and color of the skin PIGMENTARY EFFECTORS Chromatophores, which enable an animal to change color or shade quickly and drasti- cally, are possessed by a variety of creatures, including crustaceans, mollusks, fish, am- phibians, and reptiles. As to structure, the chromatophores vary in different animals, but all are mechanical effectors in the sense that the response always involves the move- ment of pigment granules, which may or may not be contained within the protoplasm of the specialized effector cells. Among invertebrates the chromatophores CHROMATOPHORES. EXPANDED * CONTRACTED Fig. 24-13. Unicellular chromatophores containing black pigment, from the scales of a fish {Fundulus). The light area at the center of the expanded cell marks the position of the nucleus. (After Spaeth.). Please note that these images are
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