PHOSPHORESCENT LIGHT 41 



only in deep water, we have no reason to suppose are 

 rigidly restricted to depths that are quite beyond the 

 reach of solar illumination, we do find a considerable 

 number of species that have far larger eyes than their 

 shallow-water relatives — some of the fishes having these 

 organs of startling size. 



Again, further to complicate the matter, although 

 the depths below 200 fathoms may be impervious to 

 sunlight, we do not know to what extent these sunless 

 depths may be lit up by the animals themselves that 

 live in them. Everyone is familiar with the nocturnal 

 "phosphorescence" of the sea. Now this ''phosphor- 

 escence " would almost seem to be one of the properties 

 of marine animals, so constantly and universally is it 

 exhibited. But beyond this general source of light, 

 there are many species of deep-sea fishes which possess 

 special luminous organs comparable in efficiency with 

 those of fire-flies and glow-worms, so that it is quite 

 possible that the depths may in places have a weird 

 and imperfect illumination of their own. And this 

 will give us another explanation of the curious, and 

 at first sight paradoxical, fact that many species of 

 these animals that live away from sunlight possess 

 eyes of wonderful size. 



If the light of the sun is cut off by a thick screen 

 of water, so also, as we know from our sensations on 

 a cloudy day, is his heat. For instance, in the open 



