PHOSPHORESCENCE 67 



fish of many kinds, and the minute noctiluca, no bigger 

 than a pin's head, and the three-horned animalcule 

 Ceratium tripos are the usual cause of the phosphor- 

 escence of the sea on our own coast. Deep-sea fishes 

 are provided with large phosphorescent discs or plates 

 on the surface of the body, which are sometimes 

 furnished with lenses like a bull's-eye lantern. Glow- 

 worms and fire-flies and some tropical beetles are 

 examples of insects which have fatty phosphorescent 

 organs which they can illuminate (oxidise) at pleasure, 

 under the control of the nervous system. Some of the 

 West Indian phosphorescent beetles are remarkable for 

 having " lights " of two different colours. In the 

 marshes around Mantua the fire-flies are so abundant 

 at the end of June that the air for miles is full of 

 them, and the sight so extraordinary and beautiful as 

 to be worth a long journey to see. I have seen fire- 

 flies as far north as Bonn on the Rhine. Once I 

 was nearly upset by a horse shying at a glow-worm 

 on a bank in Worcestershire. Some moulds and well- 

 grown toadstools are phosphorescent, and a phosphor- 

 escent earthworm, a peculiar species, now well known, 

 was first of all discovered in the South of Ireland by 

 the late Professor Allman. In the autumn I have 

 often picked up the phosphorescent centipede, which 

 is remarkable for the fact that the phosphorescent 

 material is a kind of slime which exudes from the 

 body the creature leaving thus a luminous trail 

 behind it as it crawls. The piddock, or pholas a 

 boring sort of mussel has brilliant phosphorescent 

 glands, and the boys at Naples love to munch these 

 shell-fish at night, and then to alarm the passer-by 

 by opening their mouths, and showing a brilliant green 

 light within. Cases are recorded, but not recently, of 

 persons suffering from tuberculosis becoming phosphor- 

 escent; a possible, but certainly a rare, occurrence. 

 Animal and vegetable phosphorescence is varied in 



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