CORAL-MAKERS AND JELLY-FISH 93 



can assign any life-saving value to the brilliant, gem- 

 like colouring of some of the sea-anemones which live in 

 the dark on the under-surface of rocks. 



The most probable view of the matter is that 

 neither the colourless transparency of the one set nor 

 the brilliant colouring of the other has any value ; it 

 just happens to be so, and is not harmful. So, for 

 instance, some crystals are colourless, some blue or 

 green or yellow or red, without any advantage to them ! 

 On the other hand, we know that a large number of 

 the animals which live in the dark unfathomed depths 

 themselves produce light, that is to say, are phosphor- 

 escent, and it seems probable that at great depths, though 

 there is no sunlight, the sea bottom is illuminated we 

 can only vaguely guess to what degree by the strange 

 living lanterns fish, crustaceans, worms, and even micro- 

 scopic creatures which move about in quest of their food, 

 carrying their own searchlight with them. Another sug- 

 gestion is that the eyes of these inhabitants of the dark 

 may be more sensitive than our own, and even be affected 

 by rays invisible to us. This, however, is not probable, 

 since whilst there are among them some with enormous 

 eyes, we find that at the greatest depths (2 to 4 

 miles) even the fishes have no eyes at all, and at a 

 depth of a mile there are many shrimp-like creatures 

 in which the eyes have been completely transformed 

 into peculiar " feelers," or otherwise aborted. So that 

 we cannot suppose there is a possibility of developing 

 the eye of the dwellers in deep-sea darkness to a degree 

 of sensitiveness greatly beyond that of terrestrial animals. 

 A limit of obscurity is reached at which it is of no use 

 having an eye at all, and eyes cease to have life-saving 

 value, and accordingly are not maintained by natural 

 selection, 



