The percentages of total observations for the three types of displays 

 are as follows: 



Glowing-ball type 50^ 



Sheet type • 27^ 



Spark type 22$ 



The various types of displays are quite evenly distributed through- 

 out the year, although there are some exceptions. A maximum number of 

 glowing-ball and sheet- type displays occur from January through March, 

 whereas glowing -ball displays are least frequent from April through 

 June. Spark- type displays are least frequent from October through 

 December . 



South of the Tropic of Capricorn, data are relatively meager. 

 Except for the shipping lanes from southwest Africa and southeast South 

 America, large regions of open ocean are seldom traversed by vessels. 

 Although intense displays probably occur south of this tropic, the 

 frequency of the different types of displays is not known; glowing-ball 

 displays probably predominate in the open ocean and sheet-type displays 

 near the coasts. Spark-type displays might be expected to occur more 

 often toward the south. The sparse data available appear to indicate 

 that displays occur evenly throughout the year in this vast southern 

 portion of the Atlantic. 



In tropical waters containing the Equatorial currents, more bio- 

 luminescence has been observed east of the 30 W meridian, especially 

 toward the bulge of Africa, than west of this meridian. A number of 

 rather spectacular displays, principally glowing ball, have been ob- 

 served in this region. Near Sao Tome, observers on boaxd the whale 

 catcher ENERM noted a display of blue light in which the wake glowed 

 and the sea surface appeared as if fireworks were going off. The dis- 

 play was due to Pyrosoma , millions of which covered the sea surface to 

 the horizon. The German research vessel METEOR, while sailing back and 

 forth across the Equator in December, January, and February 1926, noted 

 continuous bioluminescence in the water night after night. The prin- 

 cipal organism creating the light also was Pyrosoma , often in great 

 numbers . 



Sheet-type displays occur most often in coastal regions, although 

 some strong displays have been observed in oceanic equatorial waters. 

 A typical sheet-type display was observed from the SS HERMINIUS in 

 December 1931 while sailing toward Capetown. The sea appeared com- 

 pletely "phosphorescent," and it gave the "effect of the sea being 

 illuminated by some unseen light underneath." The vessel 



"ran suddenly into a mass of pale, but intense green sea 

 with silvery-white edges to the waves, somewhat similar 

 in appearance to the illuminated dial of a wrist-watch, 

 when observed in the dark, only of much greater intensity. 



16 



