7 
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628 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
few hundred meters, and at others several kilometers. Oceanic animal 
streams reach much greater extension. Their constitution is some- 
times polymixic, sometimes monotonic, often changing from day to- 
day. Highly remarkable is the sharp boundary of the smooth, thickly 
populated animal roads, especially if the less inhabited and plankton- 
poor water on both sides is rippled by the wind. What combination 
of causes produces this vast accumulation is still quite unknown; 
certainly wind and weather play a role in it; often, also, the ebb and 
flow of the tide and other local conditions of the regions, especially 
local currents. As whirlwinds on land drive together the scattered 
masses of dust and smaller objects and raise a column of dust upwards, 
so may the submarine whirlwind press closely together the bathypelagic— 
planktonic masses and carry them upward to the surface. But prob- 
ably, also, in the same connection, complicated cecological conditions 
come into play, e. g., sudden simultaneous development of quantities of 
eggs of one species of animal. A new study of the zodcurrents is one- 
of the most urgent problems of planktology. . 
VI—METHODS OF PLANKTOLOGY. 
The new aspects and methods which three years ago were introduced 
by Prof. Hensen into planktology, and of which I have already spceken, 
have for their main purpose the quantitative analysis of the plankton, 
i. e., the most exact determination possible of the quantity of organic 
substance which the swimming organisms of the sea produce. To 
solve this subject and come nearer to the question connected with 
it of the “cycle of matter in the sea,” Hensen devised a new mathe- 
matical method which ainis chiefly at the counting of the individuals of 
animals and plants which populate the ocean. This new method we 
can briefly term the oceanic population statistics of Hensen. The high 
value which this indefatigable physiologist attributes to his new arith- 
metical method is shown by the special mention which he makes of it 
in his first contribution (9, pp. 2-383), from the wonderful patience with 
which he counted for months the single Diatoms, Peridinew, Infusoria, 
Crustacea, and other pelagic individuals in a single haul of the Miiller 
‘net, and from the long tables of numbers, the numerical protocols, and 
records of captures which he has appended to his first plankton volume 
which appeared in 1887. . 
Any ordinary pelagic haul with the Miiller net or tow net brings up 
thousands of living beings from the sea; under most favorable circum- 
stances hundreds of thousands and millions of individuals.* How much 
labor and time was involved in the counting of these organisms (for the 
greater part microscopic) is Shown from the fact that ‘‘even the count- 
ing of one Baltic Sea catch, which is pretty uniform in its composi- 
tion, required eight full days, reckoning eight working hours to the 
*TIn a small catch, which filtered scarcely 2 cubic meters of Baltic Sea water, were 
found 5,700,000 organisms, including 5,000,000 microscopic peridinez, 630,000 diatoms, 
80,000 copepods and 70,000 other animals (23, p. 516). 
