KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 53 



for stimuli of some sort for tlie production of the light, whether through contact 

 Tvith other organisms or debris, or through agitation of the water. 



To determine the ]ieriodidty of the production of the light, watch glasses 

 containing a single individual, as well as finger howls containing a quantity of 

 the plankton, were placed in the dark room and tested at various tunes during 

 the day. These were sometimes taken into the dai-k room during the day, or 

 as frequeutly were placed there on being brought in at the 12 and 4 o'clock 

 night hauls. They were thus kept continuously in the dark for twenty-four 

 hours. The results were invarial)ly the same in both cases, that is, light ceased 

 to ho produced with the early dawn and began again with the coming of late 

 dusk in the evening. No amount of stimulation was able to bring forth the 

 slightest response during the day. "With the coming of dusk stimulation would 

 produce a few flashes at first, and with the deepening darkness the number of 

 these increased until the bowl would show its maximum illumination. The 

 reverse of this procedure took place with the coming of dawn. 



The light given forth by these dinoflagellates is silvery white and lasts no 

 more than a single second. Dahlgren has noted another method of lighting, 

 which he calls the death glow or glow of exhaustion, caused by lifting Ceratium 

 out of the water on to the hand or a bit of clean cloth or paper. In these cases 

 the glow lasted from several seconds to several minutes. This probably explains 

 the phenomenon observed in the hauls that were made each night. When the 

 net was drawn up, nililiing it with the finger caused streaks of light which lasted 

 usually for a nmch greater length of time than the ordinary flash seen in the 

 water. This is probably produced by the organisms caught in the meshes of 

 the net and thus held cajjtive. The amount of light seen in this way is much 

 greater than that produced at any one time in the jars containing the hauls. 

 Tlie long-horned Ceratinui and other forms would most easily ])ecome entangled 

 in the threads of the net, allowing the smaller, smoother forms, such as 

 Gymnodinium, to escape altogether. 



During an out])reak of yellow water near the Biological Station, July 27 to 

 August 6, 3914, caused liy the presence of enormous quantities of Gijmnodinium 

 flavuni (see p. 209), the lu-eakers along the shore were brightly luminous. A 

 few forms of both Gont/aidax and Noctnuca were found in the hauls, but not 

 in sufficient numbers to account for this display. At the height of the outbreak 

 Gymnodhuum flavum was present almost to the exclusion of other forms. It 

 seems, tlierefore, certain that the phosphorescence observed was due to this 

 organism, though, unfortunateh', no tests were made in the laboratory to confirm 

 this conclusion. 



The very close similarity of structure between the naked and thecate dino- 

 flagellates leads to the belief that the capacities for huuinescence in the two 

 groups are much the same, and that the ability to produce light is not confined 

 to a few species alone. In the tests that were made at La Jolla during the 

 summers of 1916 and 1917 it was evident that no single group of dinoflagellates 



