48 THE FAUNA OF THE DEEP SEA 



of all seas extending from the surface to a depth 

 which cannot at present be very accurately determined, 

 but is probably the same as the limit of the influence 

 of direct sunlight. 



The animals of this zone are frequently charac- 

 terised by a general transparency of their tissues, 

 a white or sea-water (i.e. blue or green) colour, 

 an organisation capable of prolonged swimming or 

 floating movement, and by giving birth to floating 

 eggs which hatch out transparent larvae or embryos. 



The pelagic zone may be divided into several 

 geographical regions and sub-regions, which it would 

 be beyond the scope of this book to enumerate here, 

 but there is one that calls for a few brief remarks. In 

 many parts of the ocean there may be found vast 

 areas of floating sea- weed, which carry with them a 

 population of Crustacea and other animals peculiarly 

 their own. This ' sargasso ' fauna presents so many 

 characteristics and so many features different from 

 that of the ordinary pelagic fauna, that the tracts of 

 sea bearing this weed must be considered to rank as 

 a special region of the pelagic zone, which may be 

 called the Sargasso region. 



The zone of shallow water for which we shall adopt 

 Professor Haeckel's term theNeritic zone embraces 



