f)28 REPORT OF COMMISSIONER OF FISH A^'D 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 chansi;in,n' from day to 

 day. Highly remarkable is the sharp boundary of the smooth, tliickly 

 populated animal roads, especially if the less inhabit ed and plankton- 

 poor water on both sides is rippled by the wind. What cond)ination 

 of causes produces this vast accumulation is still (piitc unknown; 

 certainly wind and weather play a role in it; often, als(>, 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 obi(U-ts and raise a^ column of dust upwards, 

 so may the submarine whirlwind piess closely together the l)athypelagic 

 plauktonic masses and carry tliem upward to the surface. But prob- 

 ably, also, in the same connection, complicated (ecological conditions 

 come into play, c. g., sudden simultaneous development of (juan titles 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 thr(?e years ago were introduced 

 by Prof. Hensen into planktology, and of which I have already spoken, " 

 have for their main purpose the quantitative analysis of the planJdon, 

 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 aims (chiefly at the counting of the individuals of 

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

 can brielly term the oceanic population statistics of Ilenseu. The high 

 value which this indefatigable physiologist attributes to his new arith- 

 metical method is shown by the special mention which he niiikes of it 

 in his first contribution (9, pp. 2-33), from the wonderful i)atience 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 api)ended to his first plankton volume 

 which a])peared in 1<H87. 



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.* Ilowmuch 

 labor and time was involved in the counting of these organisms (for the 

 greater part microscoijic) is shown from the fact that "even the count- 

 ing of one Baltic Sea catch, which is pretty uniform in its composi- 

 tion, recpiired 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 r),7nO,0()Oor>j;aiiisiiis, in<du(liii,L;r>, 000,000 iiiicro.si'oijic pen(liue;e, 630,000 diatoms, 

 80,000 copepods and 70,000 oth(;r auimals (23, p. 516). 



