566 History of Luminescence 



radiolaria 



Although dinoflagellates are the most abundant microscopic or- 

 ganisms responsible for sea light, another group of protozoa is also 

 luminous. These forms, the Radiolaria, are few in number and 

 their light is weak. Their luminescence appears to have been dis- 

 covered by Tilesius, recorded in the account of the Russian voyage 

 of discovery around the world in 1803-1806, under the command of 

 von Krusenstern. A resume of the results appeared, arranged by 

 L. W. Gilbert, in the Annalen der Physik for 1819 with special 

 attention to light-emitting organisms. It is probable that figure 23 

 of plate II in this article is a radiolarian. W. Baird (1831) has 

 likewise been credited with observing the light of radiolarians but 

 K. Brandt (1885) considered his drawing questionable. 



A little later, F. J. F. Meyen (1834) studied the luminous forms 

 collected on a trip to Canton in a trading vessel. He gave more 

 recognizable figures of the Radiolaria, Sphairazoon fuscum, and 

 what he called Physaematium atlanticum and vermiculare, all new 

 species. Radiolarians are never responsible for the brilliant displays 

 of phosphorescence described by so many mariners but they may be 

 considered to add their mite to the light from other microscopic 

 protozoa. 



Knowledge of the morphology and physiology of these luminous 

 protozoa, which may be solitary or colonial, is almost entirely due 

 to Karl Brandt (1885) , whose great monograph on the Radiolaria 

 of the Gulf of Naples is beautifully illustrated with drawings of 

 many species. He noted that it was the central capsule of the radio- 

 larian which responded by luminescence after various kinds of stimu- 

 lation, recorded the onset of fatigue and recovery from fatigue, and 

 in general proved that these organisms behave like Noctiluca in 

 most respects, although their light is very much less intense. 



Jellyfish or Medusae 



Like the dactylus, the jellyfish or pulmo marinus of the Romans 

 is a well-known luminous animal. Pliny's story of the luminous 

 slime which adheres to the fingers and that " a walking stick rubbed 

 with the pulmo marinus will light the way like a torch," directed 

 the attention of the scientific world to luminous medusae. The large 

 scyphomedusan, Pelagia noctiluca of the Mediterranean, was un- 

 doubtedly the species seen by Pliny and described by such later 

 naturalists as Rondelet, Boussuet, Aldrovandi, Belon, and Gesner. 

 In the seventeenth century Kircher (1640) and Bartholin (1647) 

 also listed the pulmo marinus as a luminous animal. 



