302 Dwellers of the Sea and Shore 



Green crabs, when kept In partial darkness, turned 

 brown; these, when kept in total darkness, turned red. 

 On this account it has been suggested that the colors of 

 crustaceans may be taken as an Index to the depths in 

 which they naturally belong. Thus, those of a pale hue 

 find life more enduring when farthest removed from 

 the sunlight; while the pink, red, crimson, and, finally, 

 purple, blue, green, anci heterogeneous forms are nor- 

 mal for each succeeding higher level. But this sup- 

 position cannot now^ be accepted without considerable 

 modification. And to speak of a bathymetrlcal (depth- 

 level) succession of colors in crustaceans would not be 

 quite true. 



Deep-sea crustaceans which rest or move about on 

 the soft ooze of the bottom indicate by some very ob- 

 vious peculiarities of structure their manner of over- 

 coming the difficulties of that mode of life. The crabs 

 are mostly long-legged or spiderlike; and in a number 

 of instances the legs are fringed with long stiff hairs, 

 and others have spines on the body and legs, all of 

 which may prevent them from sinking in the yielding 

 ooze. The extremely long, slender legs of certain 

 praw^ns are undoubtedly used as stilts by their pos- 

 sessors when making their way over the floor. 



Since the temperature is constant and uniform 

 throughout the world at certain depths, this renders it 

 possible for many crustaceans to live in the tropical 

 deep waters, which are identical with, or nearly related 

 to, the shallow-water species of the colder seas. Hence, 

 lobsters have been found in comparatively deep regions 

 of the Indian Ocean which were very closely allied to 

 a species known to occur along the shores of Norway. 



