436 DISTRIBUTION IN SPACE AND TIME 



drift with the currents, against which the swimming powers that 

 many of them possess can make no headway, though useful in a 

 minor degree. Such are various animalcules, small crustaceans, 

 jelly-fishes, and salps. Floating eggs and innumerable larvae 

 also belong to the Plankton. 



THE NERITIC ZONE LIFE IN SHALLOW WATER 



The Neritic Zone embraces the area between tide-marks, i.e. 

 the littoral sub-zone and the shallow waters adjacent. There 

 being abundant light a great variety of colours and patterns are 

 exhibited by the animals, many of these being useful to their 

 possessors in one way or another. And, as might be anticipated, 

 neritic animals mostly possess well -developed eyes, unless they 

 happen to have become adapted to a burrowing mode of life. 

 The fauna of this zone is rich in the extreme, its character vary- 

 ing with climate and the nature of the sea-floor, among other 

 determining circumstances. The intertidal area is of particular 

 interest, for, being exposed to the action of the air at periodic 

 intervals, it is intermediate in character between sea and land, 

 presenting an environment which has rendered possible the 

 evolution of certain terrestrial forms (see vol. ii, p. 459), some of 

 which have again more or less reverted to the ancient aquatic 

 existence. Land-Crabs, for instance, have sprung from purely 

 marine forms, while Cetaceans have undergone a secondary 

 adaptation to the original mode of life that characterized their 

 exceedingly remote fish-like ancestors. 



Neritic Mammals (Mammalia], A number of forms which 

 partly belong to the land have more or less claim to be included 

 in the fauna of this zone, though some of them also spend more 

 or less of their time in the Pelagic area. Such in particular are 

 the Sea- Lions or Eared Seals (Otarida), Walruses (Trichechidce), 

 and Seals (Phocidte), which make up a special group (Pinnipedia) 

 of the Flesh- Eaters. The Sea-Cows (Sirenia), including the 

 Dugong (Halicore) and Manatee (Manatus\ have deserted th'e 

 land entirely, though the latter pass up into rivers and are there- 

 fore, in part, members of the freshwater fauna. 



Neritic Birds (Aves). The nature of the development of 

 birds prevents them from deserting the land altogether, but many 

 species spend so large a part of their lives on the shore or in 



