G28 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 monotouic, 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 wateron both sides is rippled by the wind. What combination 

 ;0f 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 laud 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 l)athy[)clagic 

 l^lanktonic masses and carry them upward to the surface. But xirob- 

 ably, also, in the same connection, complicated <Ec<dogical conditions 

 come into play, e. .(/., sudden simultaneous develoi)ment of quantities of 

 eggs of one species of animal. A new study of the zoocurrents 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. Heusen into planktology, and of which I have already spoken, 

 have for their main jiurpose the qHantitative anah/sis of the planlion, 

 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 inatter in the sea," Hensen devised a new mathe- 

 matical method which aims chiefly at the counting of the individuals of 

 animals and plants which populate the ocean. This uew method we 

 can briefly term the ocean'i e j)(>pnlat ion 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. 2-33), from the wonderful i)atience with 

 which he counted for months the single Biatoms, Fcridinea', Infusoria, 

 Crustacea, and other pelagic individuals in a single haul of the Miiller 

 net, and from the long tables of numbers, the numerical j)rotocols, 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 favoral)le 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 



*In a small catch, which filtered scarcely 2 cubic meters of Baltic Sea water, were 

 found 5,700,000 organisms, including 5.000,000 mici-oscopic peridiuete, 630,000 diatoms, 

 80,000 copepods and 70,000 other animals (23, p. 516). 



