PLANKTONIC STUDIES. 587 
4. Diatomee.—The inconceivable quantities in which the diatoms 
populate the whole ocean and the extraordinary importance which they 
possess as one of the most important constituents of the ‘fundamental 
food supply” (Urnahrung) in the cycle of matter in the sea has been 
considered so many times that it is sufficient here to point to the com- 
paratively recent accounts of Murray (5, p. 533; 6, p. 737, ete.), Fuchs 
(12, p. 49), Castracane (6, p. 930), and Hensen (9, p. 80). Harlier the 
chief attention was paid to the benthonic diatoms which everywhere 
cover the seacoast and the shallow depths of the sea bottom in aston- 
ishing quantities; in part fixed on stalks, in part slowly moving among 
the forests of seaweed and the fixed animal banks ( festsitzenden Thier- 
banken) of the coast. The importance of the planktonic diatoms was 
recognized much later, those abounding in the open ocean as well as in 
the coast waters furnishing one of the most important sources of food 
for the pelagic animals. The oceanic diatoms, which often cover the sur- 
face of the open sea as a thick layer of slime, form another flora, very 
insufficiently studied and characterized by many forms of colossal size 
(several millimeters in diameter), peculiarly regular in form, and with 
extremely thin-walled siliceous shells (species of Hthmodiscus, Coscino- 
discus, Rhizosolenia, etc., discovered in such numbers by the Challenger). 
The neritic diatoms, on the other hand, which, swimming free in no 
small numbers, populate the coast waters, are less in diameter and with 
thicker walls, and stand on the whole between the oceanic and littoral 
forms. The absolute and relative quantity of the planktonic diatoms 
seems to increase gradually from the equator towards both poles. 
In the tropical zone the pelagic diatoms are much less developed 
than in the temperate zone, and here again much less than in the polar 
zone. Wide stretches of the Arctic Ocean are often changed by incon- 
ceivable masses of diatoms into a thick dark slime, the “black water,” 
which forms the feeding-ground of whales. The pteropods and crus- 
taceans, upon which these cetaceans live, feed upon this diatom slime, 
the “black water” of the Arctie voyager. Not less wonderful are the 
vast masses of diatoms which fill the Antarctic Ocean south of the 
fiftieth degree of latitude, and whose siliceous shells, sinking to the 
bottom after the death of the organism, form the diatom ooze (Challenger, 
stations 152-157). The tow nets here were quickly filled with such 
masses of diatoms (for the most part composed of Chatoceros) that these 
when dried in the oven formed a thick matted felt (6, p. 920). 
5. Yanthellee.—A highly important share in the cycle of matter in the 
sea belongs to the remarkable wanthellew or ‘yellow cells,” which live 
in symbiosis in the bodies of many marine animals, in the plankton as 
well as in the benthos. I first proved that these “yellow cells,” which 
were observed by Huxley (1851) and by Johannes Miiller (1858) in the 
calymma of radiolarians, were “undoubted cells,” and also described 
their structure and increase by division (3, p. 84), and later (1870) 
showed that they constantly contained amylum (4, § 90). But Cien- 
