Responses of Higher Animals: The Effectors - 443 



H O 



K 



^C* ^C" V >"^C-C-OH 



1 " c-q I + </ 2 2 



H 



*^, 



- C -../ 



HO" ^"C" "-S 



I 

 H 



active luciferin (LH 2 ) 



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 



+ H 2 



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 (LH 2 ) 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.) 



