PLANKTONIC STUDIES. 633 
the higher unit of the person or of the colony, which is composed of 
many cells. If we actually wish to carryout exactly the method, held 
by Hensen 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 caleulations and the com- 
putations based thereon. If Hensen in his long “ numerical protocols 
and comparisons of captures” (9, pp. XI-xXxx1II) places close to one 
another as counted individuals—as coérdinated categories—the uni- 
cellular radiolaria, the cormi of siphonophores and tunicates, the per- 
sons of meduse, ctenophores, echinoderms, 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- 
cable for his purpose if all single cells are counted. But since each fish 
‘and each whale in the ocean daily destroys milliards of these planktonic 
organisms, So, in order to gain an “exact” insight into the “eyele 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. 
Hensen 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 
will be able to invent correct modes of action in the interest of the 
fisheries,* only if we are in position to form a judgment upon the pro- 
ductive possibilities of the sea” (9, p. 2). Accordingly he regards it as 
the most pressing problem to determine the economic yield of the 
ocean in the same way as the farmer determines the useful yield of his 
tields and meadows, the yearly production of grass and grain. By the 
counting of the planktonic individuals which Hensen 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 weight, 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 by quantitative 
plankton analysis I am not able to understand. The most important modes of 
action which we can employ for the increase of the fish production of the ocean— 
artificial propagation, increase and protection 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 number of mature fish 
has been pointed out above. 
