THE ORGANS OF PHOSPHORESCENCE 301 



colony is fully organised, like the common large sea- 

 squirt, but it is oat-shaped, being elongated in such a way 

 that the mouth is at one end of the oat and the opening 

 of the branchial chamber (often called the " atrium ") at 

 the other. Near the nerve-mass or brain one can see with 

 the miscroscope in the living creature a pair of granular 

 little lumps. Darken the room in which you are observing 

 and you will see these little lumps glowing independently, 

 and giving out a strong light. They are the phosphores- 

 cent organs of the " sea-candle " or Pyrosoma. If you 

 gently pinch one end of a Pyrosoma floating in a tank of 

 sea-water in a darkened room, you will see a wave of 

 light pass along the colony from the pinched end to the 

 other. The excitation caused by the pinch is transmitted 

 from one of the little " colonists " to the next, and so on 

 through the whole length. The phosphorescent matter is 

 a fatty chemical compound. It can be extracted from the 

 " sea-candle " (as from other marine phosphorescent 

 animals), dried, and kept for some weeks, when it can be 

 again made to give out light by wetting it with sea-water 

 and a little ether. Its property of giving out light is 

 dependent on its contact with oxygen, and during life this 

 contact is controlled by the nervous system of the little 

 Ascidian. It appears also that the cells which produce 

 the phosphorescent granules are stimulated by nerves, just 

 as are the cells which produce the saliva and other secre- 

 tions in higher animals. The same history is true with 

 regard to the phosphorescence of many marine animals 

 worms, shrimps, and jellyfish as well as of glow-worms, 

 fire-flies, and deep-sea fishes. In some cases, but not in 

 all, we can imagine what may be the use to its owner of 

 the phosphorescent gift. 



There is a whole world of transparent floating creatures 

 in the sea which live near the surface and never rest on 

 the bottom. They are all glass-like and often colourless, 



