PLANKTONIC STUDIES. 607 
V.—COMPOSITION OF THE PLANKTON. 
The composition of the plankton ts in qualitative as well as quantitative 
relations very irregular, and the distribution of the same in place and 
time in the ocean also very unequal. These two axioms apply to the 
oceanic as well as to the neritic plankton. In both these important 
axioms, which in my opinion must form the starting-point and the 
foundation for the wcology and chorology of the plankton, are embodied 
the concordant fundamental conceptions of all those naturalists who 
have hitherto studied carefully for a long time the natural history of 
the pelagic fauna and flora. 
The surprise was general when Prof. Hensen this year advanced an 
entirely opposite opinion, “that in the ocean the plankton was dis- 
tributed so equally that from a few hauls a correct estimate could be 
made of the condition in a very much greater area of the sea” (22, p. 
243). He says himself that the plankton expedition of Kiel, directed 
by him, started on this ‘ purely theoretical view,” and that it had “full 
results because this hypothesis was proven far more completely than 
couid have been hoped” (22, p. 244).* 
These highly remarkable opinions of Hensen, contradictory to all 
previous conceptions, demand the most thorough investigation; for if 
they are true, then all naturalists who many years previously, and in 
the most extensive compass, have studied the composition and distri- 
bution of the plankton are completely in error and have arrived at 
entirely false conclusions. If, on the other hand, these propositions of 
Hensen are false, then his entire plankton theory based thereon falls, 
and all his painstaking computations (on which in the last six years he 
has spent 17,000 hours, which he wishes to have number the individ- 
uals distributed in the plankton) are utterly worthless. 
In the first place, the empirical basis upon which Hensen founded his 
assumptions must be proved, ‘starting from a purely theoretical point 
of view.” The plankton expedition of Kiel was 93 days at sea, and in 
the months of late summer (July 15 to November 7) which, as is known, 
offer in the northern hemisphere the most unfavorable time of all for 
pelagic fishery (28, p. 16, 18). Hensen himself says that it bore the 
“character of a trial trip” (22, p. 10), and his companion Brandt names 
ita “reconnaissance ” upon which they had come to investigate rapidly 
* Hensen speaks of this in the following terms: ‘‘Titherto it was the prevailing 
view that the inhabitants of the sea were distributed in schools, and that one, ac- 
cording to luck and chance, according to wind, current, and season, sometimes came 
upon thick masses, sometimes upon uninhabited parts. This in fact applies only in 
a certain degree for the harbors. For the open sea our knowledge teaches that nor- 
mally regular distribution obtains there, which changes in thickness and ingredients 
only within wide zones corresponding to the climatic conditions. In any case one 
must seck the variation from such condition according to the cause which has pro- 
duced it, and the occurrence of inequality is not to be taken as the given starting- 
point for relative investigation” (22, p. 244). 
