LUMINESCENCE 565 



response for several days (27). Chctetopterus is stimulated into luminesc- 

 ence as the concentration of the surrounding sea water is reduced to 

 50%. These hypotonic solutions could have a cytolytic action by causing 

 disruption of the cell, or could alter intracellular organization. The addition 

 of ammonia usually evokes bright and lasting luminescence in many 

 animals, whereas acids cause a transient flash. These, and other strong 

 poisons, may act initially through excitation of peripheral receptors (43). 



The effect of temperature on luminescence has been investigated in 

 some forms. These studies have involved the lethal effects of high tempera- 

 tures and the influence of temperature alterations on the mechanism of 

 stimulation. Noctiluca gives a normal response as the temperature is 

 raised to 42-43°C. A further increase to 48-49 c C causes a steady glow, 

 and then the light is extinguished, without the possibility of recovery on 

 cooling. On lowering the temperature to 5-0 = C the animal gives a constant 

 glow, and will recover if warmed immediately (27). The ctenophore 

 Mnemiopsis shows some adaptation to lowered temperature. When cooled 

 from 20°C to 9°C no luminescent response is elicitable, but if the tempera- 

 ture is lowered further to 3°C and then raised to 7 C luminescence re- 

 appears on stimulation. Furthermore, animals kept for some time at 

 3°C luminesce regularly at that temperature. Raising the temperature 

 above 36°C evokes luminescence in many metazoans. 



Effect of Illumination 



In most animals luminescence is not affected by previous exposure to 

 light, but there are a few interesting exceptions. Such include the sea- 

 pansy Renilla and various ctenophores, in which luminescence is inhibited 

 by light and regained after a period in the dark. Again there are some 

 animals, including various dinoflagellates, Pelagia, and Ptychodera, 

 which are said to display a true diurnal rhythm of luminescent ability 

 and will only shine at night, whether they have been kept previously in the 

 dark or not. 



A luminescent dinoflagellate Gonyaulax polyedra has been cultured suc- 

 cessfully and studied in the laboratory. This species shows a true diurnal 

 rhythmicity of luminescence, the light being dim during the day and 

 bright at night. When a culture is transferred from light to darkness, 

 the rhythm of luminescence continues in phase with other cells left in 

 daylight. Continuous exposure to light inhibits the rhythm, which may 

 be initiated once more by placing the cells in the dark. The rhythm per- 

 sists for about four days in darkness. It has been observed that the 

 amount of luminescence which develops at night depends on the amount 

 of light received during the day, apparently through energy stores derived 

 from photosynthesis (30a, 5\a). 



When the pennatulid Renilla is brought from daylight into darkness it 

 fails to luminesce at first, but after the first half-hour the ability to luminesce 

 gradually returns. Moreover luminescence in the dark-adapted animal 

 can be reduced by exposure to a weak light. When small areas of a dark- 



