630 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
established than could aave been hoped. I have already shown that 
this fundamental premise is entirely wrong. The mass of plenkton in 
the ocean is not perennial and constant, but of highly variable and oseil- 
lating size. The biological composition is very diverse, dependent upon 
temporal variations—year, season, weather, time of day, upon climatic 
conditions and especially upon the complicated currentic conditions of 
the streams of the sea, of the oceanic and littoral currents, the deep 
currents, and the local zodcurrents. | - 
A comprehensive and fair estimation of all these ecological condi- 
tions must a priori lead to the conviction that the distribution of the 
plankton in the ocean must be extremely irregular, and we find this 
‘“nurely theoretical view completely established” a posteriori by the 
comparative consideration and comparison of all the earlier above- 
mentioned observations. These can not be regarded as refuted by the 
opposing view of Hensen; for the empirical basis of the latter is, in 
regard to its time and place, much too scanty and incomplete. 
One might perhaps object that the technical methods of plankton 
capture which Hensen employed gave more complete results than the 
methods hitherto used; but this is not the case. The recent desecrip- 
tion which Hensen gives of his technica! methods for obtaining plankton 
(or pelagic fishery) is very praiseworthy (9, pp.3 to 14). The consirue- 
tion of the net (material, structure of the net, size of filtration), the 
management of the catch and of the craft, are there carefully described. 
The advance of the new technique there realized may indeed serve to 
carry on the pelagic fishery or plankton capture more productively and 
more completely than was possible with the previous simpler technical 
apparatus of planktology; but I can not find that one of the proposed 
improvements of this pelagic technique shows a great advance in prin- 
ciple and is at all comparable to the great advance which Palumbo 
and Chierchia made in 1884 by the invention of the closible net. 
Besides, I can not understand how the new “plankton net” constructed 
by Hensen could give more accurate results than the simple * Miiller 
net” hitherto employed, and the “tow net” used by the Challenger. 
Such a vertical net will always bring up only a part of the plankton 
contained in the volume of water going through it, and by no means, 
as Henseu and Brandt believe, is a column of water whose height and 
base area can be measured with sufficient accuracy perfectly filtered. 
In this supposition the incalculable disturbances by conditions of eur- 
rents, especially of concealed deep streams, are Jeft out of account, as 
already mentioned. Besides, Chierchia has lately shown how unreliable 
and little productive is the fishery with the vertical net on account of 
the considerable horizontal swimming movements of the pelagic animals 
(8, p. 79). At any rate, the improvements Hensen has introduced into 
the technical methods of plankton capture are not so important that 
the remarkable difference between his and the earlier results can 
thereby be explained. 
