TLANKTONIC STUDIES. 579 



this here because iu plauktology the interesting- and complex vital 

 relations of pelagic organisms, their manner of life and economy, are 

 very often called biological instead of cecological problems.* 



PLANKTON AND BENTHOS. 



If under the term Halohios we embrace the totality of all organisms 

 living iu the sea, then these, in (ecological relation, fall into two great 

 chief groups, benthos and pJc.nkton. I give the term lenthos] (in opposi- 

 tion to plankton) to all the nou-swimining organisms of the sea, and to 

 all animals and plants which remain upon the sea bottom either lixed 

 (sessile) or capable of freely changing- their place by creeping or run- 

 ning (vagrant). The great ojcological differences in the entire mode of 

 life, and consequently in form, which exist between the benthonic and 

 planktonic organisms, justify this intelligible distinction, though here 

 as elsewhere a sharp limit is not to be drawn. The hentJios can itself 

 be divided into littoral and abyssal. The littoral-benthos embraces the 

 sessile and vagrant marine animals of the coast, as well as all the 

 plants fixed to the sea-bottom. The ahyssal-benthos, on the other 

 hand, comprises all the fixed or creeping- (but not the swimming) ani- 

 mals of the deep sea. Although as a whole tlie morphological char- 

 acter of the benthos, corresponding to the i)hysiological peculiarities 

 of the mode of life,, is very different from that of the plankton, still 

 these two chief groups of the halobios stand in manifold and intimate 

 correlation to one another. In part these relations are only phylo- 

 genetic, but also in part at the i^resent day of an ontogenetic nature, as, 

 for example, the alternationof generations of the benthonic polyps and 

 the planktonic medusiL\ The adai)tation of marine organisms to the 

 mode of life and the organization conditioned thereby may in both 

 chief groups be primary or secondary. These and other relations, as, 

 well as the general characteristics of the |)elagic fauna and tlora, have 

 already been thoroughly considered by Fuchs(lL') andMoseley(7). 



PLANKTON AND NEKTON. 



The term fiankton may be used in a wider and in a narrower sense; 

 either we understand it as embracing all organisms swimming in the 

 sea, those floating passively and those actively swimming; or we may 

 exclude these latter. Hensen comprehends under plankton " every- 

 thing which is in the water, whether near the surface or far down, 

 whether dead or living." The distinction is, v>hether the animals are 

 driven involuntarily with the water or whether they dis])lay a certain 

 degree of independence of this impetus. Fishes in the form of eggs 



* The terms biology and cecology are not intercliangeable, because the latter only 

 forms a part of physiology. Comp. my " Generelle Morphologie," 1866, Bd. i, j). 8, 

 21; Bd. II, p. 286; also my ''Ueber Etwickelungsgang und Aufgabe der Zoologie/'' 

 Jena. Zeitsch. fur Med. u. Nat., Bd. v, 1870. 



t/ieVQo?, the bottom of the ocean; hence the organisms living there. 



