PLANKTONIC STUDIES. 579 
this here because in planktology 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. 
Tf under the term Halobios we embrace the totality of all organisms 
living in the sea, then these, in ecological relation, fall into two great 
chief groups, benthos and plankton. I give the term benthost (in opposi- 
tion to plankton) to all the non-swimming organisms of the sea, and to 
all animals and plants which remain upon the sea bottom either fixed 
(sessile) or capable of freely changing their place by creeping or run- 
ning (vagrant). The great cecological 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 benthos 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 abyssal-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 the morphological char- 
acter of the benthos, corresponding to the physiological 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 present day of an ontogenetic nature, as, 
for example, the alternation of generations of the benthonie polyps and 
the planktonic meduse. The adaptation 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 pelagic fauna and flora, have 
already been thoroughly considered by Fuchs (12) and Moseley (7). — 
PLANKTON AND NEKTON. 
The term puankton 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, whether the animals are 
driven involuntarily with the water or whether they display a certain 
degree of independence of this impetus. Fishes in the form of eggs 
forms a part of physiology. Comp, my “ Generelle Morphologie,” 1866, Bd. 1, p. 8, 
21; Bd. 11, p. 286; also my ‘‘ Ueber Etwickelungsgang und Aufgabe der Zodlogie,” 
Jena. Zeitsch, fur Med. u. Nat., Bd. v, 1870. 
t BEvGos, the bottom of the ocean; hence the organisms living there. 
