240 



ANIMALS OF LAND AND SEA 



autumn the peridinians become excessively abundant, and the 

 magniticent displays of phosphorescence sometimes seen are 

 due to them. Elsewhere, too, in the Mediterranean and on 

 the coast of western Europe and at various places in the tropics 

 the peridinians are abundant and important as light producing 



organisms. At Nassau, in the 

 Bahamas, in Waterloo or Fire 

 Lake the wonderful exhibition is 

 due to a local peridinian. 



In the North Sea, in the Yel- 

 low Sea, and elsewhere, the Nocti- 

 lucas, looking like minute spheres 

 of transparent jelly, take the place 

 of peridinians. Their light is blu- 

 ish or greenish, like that of peri- 

 dinians, and they are sometimes 

 present in enormous numbers, 

 30,000 or more to each cubic foot 

 of water. 



Fyrocystis, which caused the 

 display recorded by the people on 

 the " Challenger," gives a steadier 

 light than the peridinians or Noc- 

 tilucas. 



Some, at least, of the radio- 

 larians are phosphorescent, but 

 observations on these are very 

 few. 



The luminosity arising from 

 dead fishes on the beach is caused by the bacteria growing on 

 them, and the light generally appears about a day after they 

 have died. 



The light given off by living animals and plants is usually 

 bluish green to green or blue, sometimes lilac, purple, or even 

 pink or red. It sometimes varies in color with intensity. Its 

 spectrum is very short, falling mostly in the green and blue, 



Figs. 696-698. Two Sponges 

 and a Phoronid. 



For explanations of the figures 

 see p. xxxiii. 



