IX THE SEA 353 



fathoms ; deeper than this complete darkness 

 prevails. Hence in many species the eyes 

 have more or less completely disappeared. 



Sir Wyville Thomson mentions a kind of 

 Crab (Ethusa granulata), which when living 

 near the surface has well developed eyes ; in 

 deeper water, 100 to 400 fathoms, eyestalks 

 are present, but the animal is apparently 

 blind, the eyes themselves being absent ; 

 while in specimens from a depth of 500-700 

 fathoms the eyestalks themselves have lost 

 their special character, and have become 

 fixed, their terminations being combined into 

 a strong, pointed beak. 



In other deep sea creatures, on the con- 

 trary, the eyes gradually become more and 

 more developed, so that while in some species 

 the eyes gradually dwindle, in others they 

 become unusually large. 



Many of the latter species may be said to 

 be a light to themselves, being provided with 

 a larger or smaller number of curious luminous 

 organs. The deep sea fish are either silvery, 

 pink, or in many cases black, sometimes re- 

 lieved with scarlet, and when the luminous 

 2 a 



