10 THE NATURE OF ANIMAL LIGHT 



The only groups of the plant kingdom which are known 

 to produce light are some of the bacteria and some of the 

 fungi and the dinoflagellates (PeridinecE) if one is to 

 include them among the plants. Many different species 

 of phosphorescent bacteria have been described, differing 

 in cultural characteristics and structural peculiarities and 

 grouped in the genera, Bacterium, Photohacterium, Bacil- 

 lus, Microspira, Pseudomonas, Micrococcus, and Vibrio. 

 Specific names indicating their light-producing power 

 such as pJiosphorescens, phosphor eum, luminosum, luci- 

 fera, etc., have been applied. 



All the fungi which are definitely known to pro- 

 duce light belong to the Basidiomycetes, the largest 

 and most highly developed of the true fungi. Either 

 the mycelium alone or the fruiting body alone, or both, 

 may be luminescent. 



Among animals the best known forms are the dino- 

 flagellates; Noctiluca; hydroids; jelly-fish; ctenophores; 

 sea pens; Chcetopterus and other marine worms; earth- 

 worms; brittle stars; various crustaceans; myriapods; 

 fireflies and glo^vworms, the larvge of fireflies; Pholas 

 dactylus and Phyllirrhoe hucephala, both molluscs ; squid; 

 Pyrosoma, a colonial ascidian; and fishes. 



Luminous animals are all either marine or terrestrial 

 forms. No examples of fresh water luminous organisms 

 are known. Of marine forms, the great majority are deep 

 sea animals, and it is among these that the development 

 of true luminous organs of a complicated nature is most 

 pronounced. Many of the luminous marine animals are 

 to be found in the plankton, while the littoral luminous 

 forms are in the minority. Some members of all the above 

 groups are found at one or another of our marine labora- 



