PLANKTONIC STUDIES. 633 



tlio higher unit of the person or of the colony, which is composed of 

 many cells. If we actually wish to cany out exactly the method, held 

 by Henseu as indispensable, of counting the individuals, and wish to 

 obtain useful results for his statistical work, then nothing remains ex- 

 cept a counting of all single cells which live in the sea. For only the 

 single cells, as the '' organic elementary individual," can form the 

 natural arithmetical unit of such statistical calculations and the com- 

 putations based thereon. If Henseu in his long " numerical protocols 

 and comparisons of captures" (9, pp. xi-xxxiii) places close to one 

 another as counted individuals — as coordinated categories — the uni- 

 cellular radiolaria, the cormi of siphonophores and tunicates, the per- 

 sons of medusae, ctenophores, echiuoderms, and Crustacea, the eggs 

 and persons of fishes, then he places together vastly incommensurable 

 bulks of quite different individual value. These can only be compar- 

 able for his purpose if all single cells are counted. But since each fish 

 and each whale in the ocean daily destroj^s milliards of these planktonic 

 organisms, so, in order to gain an ''exact" insight into the "cycle of 

 matter in the sea," the cell milliards which compose the bodies of these 

 gigantic animals must be counted and placed in the reckoning. 



ECONOMIC YIELD OF THE OCEAN. 



Hansen holds the quantitative determinations of the plankton not 

 only as of the highest importance in theoretical interest to science, but 

 also in practical interest to national economy. He thinks " that we 

 Avill be able to invent correct modes of action in the interest of the 

 fisheries,* only if we are in position to/orm a judgment upon the iiro- 

 ductive possibilities of the sea" (9, p. 2). Accordingly he regards it as 

 the most pressing problem to determine the economic yield of the 

 o(teaii in the same way as the farmer determines the useful yield of his 

 fields and meadows, tlie yearly production of grass and grain. By the 

 counting of the i)lanktonic individuals which Henseu has carried on for 

 a long time for a small part of the Baltic Sea, he thinks he has become 

 convinced that the "entire production of the Baltic in organic sub- 

 stance is only a little inferior to the yield of grass upon an equally 

 large area of meadow land." 



The farmer determines the yield of his meadows, garden, and field 

 by quantity and Aveight, not by counting the individuals. If instead 

 of this he wished to introduce Hensen's new exact method of deter- 



* How the practical interests of the fisheries can be advanced hy quantitative 

 plankton analysis I am not able to understand. The most important modes of 

 action which we can employ for the increase of the lish production of the ocean — 

 artificial propagation, increase and xirotection of the fry, increase of their food 

 supply, destruction of the predaceous fishes, etc. — are entirely independent of the 

 numerical tables which Hensen's enumeration of individuals gives. That the number 

 of swimming fish eggs furnishes no safe conclusion upon the nuiaber of mature fish 

 has been pointed out above. 



