DEEP-SEA FAUNA 263 



or skeletons of the microscopic Radiolarians, Fora- 

 minifera, or Diatoms, which swarm in the waters 

 above. This does not mean that the whole of the 

 food supply consists of microscopic matter, for in the 

 upper waters representatives of almost every order of 

 marine animals, from whales downwards, may be 

 found. 



In the early days of deep-sea exploration it was 

 believed by many naturalists that the unknown depths 

 of the ocean would be found to harbour survivors of 

 an earlier geological epoch which would fill gaps in 

 the known pedigree of the Animal Kingdom. This 

 expectation has not, save in a few instances, been 

 realized, for, although an immense number of deep- 

 sea species have been discovered, they are, on the 

 whole, either very like those from shallow water or 

 else have been specially modified to adapt them to 

 the changed conditions of life. On account of this 

 general resemblance of the abysmal fauna to the 

 animals inhabiting shallow water at the present time, 

 rather than to those of a remote geological period, 

 it is generally believed that the inhabitants of the 

 deep sea have migrated thither at some comparatively 

 recent geological age, the migration probably beginning 

 at the close of the Mesozoic Period, and continuing to 

 the present day. 



It is hard to. point out any features in which, as a 

 whole, the animals of the deep sea differ from those of 

 more shallow waters. Their colours are, as a rule, 

 peculiar. Fishes are usually black, while Crustacea 

 are mostly red or pink. The Echinoderms show a 

 great range of colour, from yellow through orange and 

 red to crimson and purple. Uniform colours are the 

 rule, rather than blotches or stripes, such as are often 

 found in shallow water. These markings may perhaps 



