186 THE OCEAN 



rents, the general conditions being very uni- 

 form throughout the year. In the inter- 

 mediate depths between the surface and the 

 bottom there are curious adaptations to twi- 

 light, to changing viscosity, depth, pressure, 

 and to variations in other physical and bio- 

 logical conditions. 



The oceanic faunal and floral areas are 

 indicated diagrammatically in Fig. 8, and 

 may be briefly described as follows : — 



I. The Photic Zone is the superficial region 

 of the ocean illumined by sunlight, extending 

 deeper in the open ocean and in equatorial 

 regions than near land and in high latitudes. 

 It is subdivided into the neritic and oceanic 

 areas. The neritic area surrounds all con- 

 tinents and islands from surface to bottom 

 within the limits of the 100 fathoms line of 

 depth. The waters of this area are much 

 agitated by winds, waves and currents, and 

 present great variations in composition, salin- 

 ity, temperature and viscosity ; they con- 

 tain plants and animals and a large proportion 

 of pelagic larvae of benthonic animals living 

 on the continental shelf. The nature of 

 the bottom on this neritic area likewise varies 

 greatly, and may be composed of rocks, 

 boulders, sands, marls and muds. The oceanic 

 area of the photic zone, being removed from 

 the immediate influence of the dry land 



