DEEP-SEA FAUNA 261 



in coarse sandy gravel. In these instances the animals 

 find shelter by burrowing beneath the surface (though 

 in the case of the Norway lobster this burrowing habit 

 must be inferred, as it does not seem to have been 

 established by direct observation), and the medium 

 chosen is probably the one best suited to their ex- 

 cavating powers. 



The fauna of an area of soft mud affords many 

 instances of animals, either specially modified to meet 

 their peculiar conditions of life, or else adapting them- 

 selves to their circumstances without any special 

 structural alteration. Leaving aside those species 

 which are capable of burrowing beneath the surface, 

 we notice that the peculiarities of a mud fauna are due 

 mainly to the absence of any solid points of attachment 

 or support. 



The Deep Sea. 



Shortly after the edge of the Continental Shelf is 

 passed, we begin to meet with members of the true 

 deep-sea fauna, which peoples the abysses of the 

 ocean. With the rapidly increasing depth the pro- 

 portion of shallow- water forms becomes less and less, 

 till at a depth of 1,000 fathoms there is hardly a 

 species left of the abundant life of the Continental 

 Shelf. Their place has been taken by a fresh assem- 

 blage of animals, which, as a whole, present a very 

 different appearance. If, however, we take into 

 account the very much altered conditions under which 

 they exist, these differences are perhaps not so great as 

 might have been expected. In fact, except amongst 

 the fishes, and, perhaps, some of the sea-cucumbers 

 and Crustaceans, there is hardly an inhabitant of the 

 deep sea which differs so markedly from its nearest 

 allies which live in shallower water, that, were its 



