PLANKTONIC STUDIES. 681 



OCEANIC AND NERITIC* PLANKTON. 



The maiiitold (lift'erences wliieli the character of the phiukton shows 

 according to its distribution in the sea, lead first, with reference to 

 its horizontal extension, to a distinction between oceanic and neritic 

 plankton. Occdnie planldon is that of the oi)eu ocean, exclusive of the 

 swimming hios of the coast. The region of oceanic plankton may from a 

 zoological point of view be divided into five great provinces : (1) the Arc- 

 tic Ocean; (2) the Atlantic; (3) the Indian; (4) the Pacific; (5) the Ant- 

 arctic. In each of these five great provinces the characteristic genera 

 of the i^lankton are apparent through the different species, even if tlie 

 differences in general are not so significant as in the different provinces 

 of the neritic and still more of the littoral fauna. 



The neritic plauktou embraces the swimming fauna and flora of the 

 coast regions of the continents as well as the archipelagos and islands. 

 This is in its composition essentially different from the oceanic plank- 

 ton, and is quantitatively as well as qualitatively richer. For along 

 the coast there develop, partly under protection of the littoral Mos, or 

 in genetic relation with it, numerous swimming animal and vegetable 

 forms which do not generally occur in the open ocean, or there quickly 

 die; but the floating organisms of the latter may be driven by currents 

 or storms to the coast and there mingled with the neritic plankton. 

 Aside from this the richness of the neritic plankton in genera and 

 species is much greater than that of the oceanic. The complicated and 

 manifold relations of the latter to the former, as well as the relations of 

 both to the benthos (littoral as well as abyssal), have been but little 

 investigated and contain a fund of interesting problems. One could 

 designate the neritic plankton also as "littoral plankton" if it were not 

 better to limit the concei)tion of the littoral bios to the non-swimming 

 organisms of the coast, the vagrant and sessile forms. 



PELAGIC, ZONARY, AND BATHYBIC PLANKTON. 



I keep the original meaning of the pelagic plankto7i as given forty-five 

 years ago by Johannes Miiller, and used since by the great majority 

 of authors. 1 also limit the meaning of the pelagic fauna and flora to 

 those actively swimming or passively floating animals and plants, which 

 are taken swimming at the surface of the sea, no matter whether they 

 are found here alone or also at a variable depth below the surface. 

 These are the superficial and interzonary organisms of Chun (15, p. 54). 

 On the other hand, I distinguish the zonary and hathi/Mo organisms; I 

 call zonary planldon those organisms which occur only in zones of defi- 

 nite depths of the ocean, and above this (at the surface of the sea) or 

 below (at the sea bottom) are only tbund occasionally, as for example 

 many phieod aria and Crustacea; also the deeiJ-sea siphonophores dis- 



• NrjpiTijc, sou of Nereus. 



