630 REPORT OF COMMISSIONER OF FisH AND FISHERIES. 



established than could have been hoped. 1 have already shown that 

 this fundamental premise is entirely wrong. The mass of i}lanldon in 

 the ocean is not perennial and constant, hut of highly variable and oscil- 

 lating size. The biological coniiiositiou is very diverse, dependent ui)on 

 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 zoocurrents. 



A comprehensive and fail- estimation of all these O'cological condi- 

 tions must a priori lead to the couvictiou that the distribution of the 

 2)lanMon in the ocean must be extremely irregular, and Ave find this 

 "purely theoretical view comi)letely established" a posteriori by the 

 comparative consideration and comparison of all the earlier above- 

 mentioned observations. These can not lie regardetl as refuted by the 

 opposing view of Henseii; 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 descrip- 

 tion v> hich Hensen gives of his technical methods for obtaining plankton 

 (or pelagic fishery) is very praiseworthy (0, pp. 3 to 14). The construc- 

 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 ca])ture more productively and 

 more completely than was possible with the previous simpler technical 

 apparatus of planktology; but 1 can not find that one of the projiosed 

 improvements of this pelagic technique shows a great advance in prin- 

 ciple and is at all comjiaiable 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 Mill always bring up only a part of the plankton 

 contained in the volume of water going through it, and by no means, 

 as Hensen 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 cur- 

 rents, especially of concealed deep streams, are left 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, J). 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. 



