E. NEWTON HARVEY 9 



dusae, Polychaeta ( Tompteridae and Terebellidae ) , Nudibranchia, 

 Copepoda, Chilopoda, Lampyrid fireflies, and Macruroid fish. 



In many other kiminous organisms a yellow color cannot be estab- 

 lished with certainty although a faint yellow would be difficult to 

 detect. Of particular interest is the cephalic luminous organ of the 

 railroad worm (PhrixotJirix), whose bioluminescence is a bright red, 

 quite similar to the fluorescence of hematoporphyrin and to the chemi- 

 luminescence of metal porphyrin compounds. One might expect to 

 find a faint red tinge in the organ from a porphyrin, or a red fluores- 

 cence, but the tissue appears quite colorless to the eye and is non- 

 fluorescent in ultraviolet or in yellow to violet light (Harvey, 1944, 

 1945). It is certain that no red color screen is involved in the red 

 luminescence of PhrixotJirix. 



Another method of grouping luminous organisms involves the neces- 

 sity or non-necessity of oxygen for luminescence. The author (1926), 

 in a systematic study of oxygen requirements for luminescence of 

 various groups, was amazed to find that the ctenophores Beroe and 

 Eiicharis, the scyphomedusan Pelagia, and the radiolarians, Thalassi- 

 cola and Colozoum, require no dissolved oxygen for light production. 

 The result has been confirmed for another ctenophore, Mnemiopsis 

 (Harvey and Korr, 1938), and for the hydromedusan Aeqtiorea (An- 

 derson, private communication, 1939). It should be emphasized that 

 it is the luminescent system of extracts of various ctenophores which 

 emits light without dissolved oxygen, whereas the ability to stimulate 

 a ctenophore to luminescence through nerves may be lost in absence 

 of oxygen (Chase, 1941). The relation between oxygen pressure and 

 luminescence intensity should be studied for all organisms (see Has- 

 tings, 1952, 1953). 



Another basis for classification of luminous groups depends on their 

 relation to light, whether light inhibits the luminescence or not. Such 

 a division might involve inhibition of a nerve-stimulating mechanism, 

 or a photochemical action on the chemiluminescent system. Such an 

 efiFect of ultraviolet light and photosensitized visible light on Cypridina 

 luciferin will be referred to in the chapter on Cypridina chemistry. 

 The most important and best known case of light inhibition is to be 

 found among ctenophores. They do not luminesce in sunlight or strong 

 electric light but regain the ability after some twenty minutes in the 



