1H Ghar vewPs 125 
play of certain chemical processes in which 
oxidation plays a central part. Incandescence 
is light given off under the influence of great 
heat, but animal luminescence is a “cold ight” 
with little or nothing in the way of heat rays. 
In the cases which have been most studied, 
the boring bivalve called Pholas, the lumi- 
nous beetles called fire-flies, and the luminous 
water-flea called Cypridina, there are always 
two substances involved in the animal light. 
There is a substance called /uctferin, which is 
oxidised, and there is a substance called Juci- 
ferase, which acts on its neighbour like a fer- 
ment. Sometimes the light is given out by a 
stuff manufactured in scattered or definitely 
arranged glands, and then it may stream into 
the water, or the whole clammy surface of the 
animal may sparkle. In other cases, the light 
is only seen inside special organs, the lumi- 
nous organs, which are often very complex and 
curiously like eyes. It is strange that organs 
which produce light should sometimes show a 
very striking resemblance to organs which de- 
tect light, namely, eyes. If you say that it is 
not so very strange, for the cat’s eyes shine in 
the dark, you are perhaps not altogether wrong, 
for although the shining of the cat’s eyes is 
