1% 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 bemg 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 mer 
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: 
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