72 THE SEAS 



doxically, in some deep-sea animals losing their eyes com- 

 pletely, while others have developed especially large ones, 

 sometimes on the ends of long stalks, like telescopes, perhaps 

 capable of detecting any gleam of phosphorescent light. 



Many deep-sea animals are of graceful and slender build, 

 a result, probably, of the complete lack of movement, for 

 there is no need for a strong skeleton and powerful muscles 

 if water currents and tides are absent. Striped and spotted 

 animals, so numerous in shallower water, are remarkable 

 by their absence, practically all deep-water animals being of 

 a uniform colour, usually white, grey, black or red ; blue 

 and green animals are never found. Many of the fish have 

 great jaws and powerful teeth by means of which they 

 prey upon one another, other animals feed on the dead 

 bodies which rain down from the surface miles above, while 

 others again, such as the numerous many-coloured sea 

 cucumbers, plough their way through the ooze, swallowing 

 it as they go and extracting such nourishment as they are 

 able. 



Associations 



In each of the areas we have considered. Littoral, Sub- 

 littoral, Continental Deep-sea, and Abyssal zones, we find 

 definite associations of animals in different localities and on 

 different types of bottom. Just as on the shore, the 

 animals composing the associations are especially suited 

 to the particular conditions and also probably assist one 

 another, for life is a unity and its various constituents are 

 dependent one upon another. Very little was known of 

 these associations of bottom-living animals until recent years, 

 when the Danish Biological Station commenced to study 

 them, using for the purpose, not the dredge which gathers 

 haphazard from the sea bottom, but the more exact grab 

 which takes definite samples of the bottom (see page 263). 



