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PLANKTONIC STUDIES. 591 
monly only of a single species, Sargassum bacciferum; but this has the 
greatest importance, since, as is known, it alone forms the floating 
sargasso banks, which cover such extensive portions of the ocean. Be- 
sides this very important species, other fucoids are found floating in 
the ocean, especially species of Mucus (F. vesiculosus, F'. nodosus, and 
others). Still they never appear in such masses as the familiar “ berry 
weed.” The floating sargasso banks are well known to have their char- 
acteristic animal life, which Wyville Thompson accurately described 
and fittingly termed nomadie (14, If, pp. 9, 339). 
This remarkable sargasso fauna bears the same character in both the 
Atlantic and the Pacific oceans and consists partly of benthonie ani- 
mals, which live sessile or creeping on the sargasso weed, partly of plank- 
tonic organisms which swim among the weeds; the latter are more 
neritic than oceanic. Hensen has lately described this fauna as re- 
markably poor, and could only find 10 species of animals in it (9, p. 
246). The Challenger found more than five times aS many species in 
this same Atlantic sargasso, namely, 55 (6, p. 136). It is obvious that 
the remarkable negative results of Hensen on this as on other plank- 
tonic questions can have no value against the positive results of other 
investigators. 
C.—PROTOZOA OF THE PLANKTON. 
The two great chief groups of unicellular animals, Rhizopoda and 
Infusoria, occur mm the ocean in very different preportions, in the’ 
reverse condition to that in fresh water. 
The Infusoria (Flagellata and Ciliata), which chiefly form the pro- 
tozoic fauna in the latter, are indeed represented in the sea by a great 
number of species, but the most belong to the littoral benthos, and 
only a few swimming species occur in such quantities that they are of 
importance in the plankton, the Noctilucide among the Flagellata, the 
Tintinnoide among the Ciliatt. Much greater is the wealth of the 
ocean in Rhizopoda, calcareous-shelled Thalamophora and siliceous- 
shelled Radiolaria. The accumulated masses of these shells form the 
most important sediment of the ocean, while their unicellular soft bodies 
constitute the chief food supply for many planktonic animals. . 
Infusoria.—As is known, the Infusoria do not play so great a role 
in the life of the ocean as in that of the fresh water. It is true that a 
great number of Flagellata and Ciliata oceur in the neritic or littoral 
fauna, but neither on account of the number of individuals nor the 
richness of forms are they elsewhere of importance, and only a few 
small groups extend out into the open sea. It seems as if these tender 
and for the most part uncovered Protozoa are not suited for the contest 
which the wild “struggle for existence” offers here. The armored 
rhizopods take their place. Still two small and very peculiar groups of 
Infusoria are found in very great numbers in the plankton, and some- 
times in such quantities as to form the chief bulk; the octiluca among 
