742 



SCIENCE 



[N. S. Vol. XXX. No. 778 



the bottom to the surface, and having their 

 constants determined so that it is known 

 what volume of water passes through the 

 net under certain conditions, and yields a 

 certain quantity of plankton. 



[Examples of the nets and the methods 

 of working shown.] 



Now if this constancy of distribution 

 postulated by Hensen could be relied upon 

 over considerable areas of the sea, far- 

 reaching conclusions, having important 

 bearings upon fisheries questions, might be 

 arrived at ; and such have, in fact, been put 

 forward by the Kiel planktologists and 

 their followers — such as the calculation by 

 Hensen and Apstein that the North Sea in 

 the spring of 1895 contained at least 157 

 billions of the eggs and larvse of certain 

 edible fish; and from this figure and the 

 average numbers of eggs produced by the 

 fish, their further computation of the total 

 number of the mature fish population which 

 produced the eggs— a grand conclusion, but 

 one based upon only 158 samples, taken in 

 the proportion of one square meter sampled 

 for each 3,465,968 square meters of sea. 

 Or, again, Hensen 's estimation, from 120 

 samples, of the number of certain kinds of 

 fish eggs in a part of the West Baltic ; from 

 which, by comparing with the number^ of 

 such eggs that would normally be produced 

 by the fish captured in that area, he arrived 

 at the conclusion that the fisherman catches 

 about one fourth of the total fish population 

 — possibly a correct approximation, though 

 differing considerably from estimates that 

 have been made for the North Sea. 



Such generalizations are most attractive, 

 and if it can be established that they are 

 based upon sufficiently reliable data, their 

 practical utility to man in connection with 

 sea-fishery legislation may be very great. 

 But the comparatively small number of the 



^ It is probable that too high a iigure was taken 

 for this. 



samples, and the observed irregularity in 

 the distribution of the plankton (contain- 

 ing, for example, the fish eggs) over wide 

 areas, such as the North Sea, leave the 

 impression that further observations are re- 

 quired before such conclusions can be ac- 

 cepted as established. 



Of the criticisms that have appeared in 

 Germany, in the United States and else- 

 where, the two most fundamental are: (1) 

 That the samples are inadequate; and (2) 

 that there is no such constancy and regu- 

 larity in distribution as Hensen and some 

 others have supposed. It has been shown 

 by Kofoid, by Lohmann and by others that 

 there are imperfections in the methods 

 which were not at first realized, and that 

 under some circumstances anything from 

 50 to 98 per cent, of the more minute organ- 

 isms of the plankton may escape capture by 

 the finest silk quantitative nets. The mesh 

 of the silk is one two-hundredths inch 

 across, but many of the organisms are 

 only one three-thousandths inch in diam- 

 eter, and so can readily escape. 



[Examples shown.] 



Other methods have been devised to sup- 

 plement the Hensen nets, such as the filter- 

 ing of water pumped up through hose-pipes 

 let down to known depths, and also the 

 microscopic examination in the laboratory 

 of the centrifuged contents of compara- 

 tively small samples of water obtained by 

 means of closing water-bottles from various 

 zones in the ocean. But even if deficiencies 

 in the nets be thus made good by supple- 

 mentary methods, and be allowed for in the 

 calculations, there still remains the second 

 and more fundamental source of error, 

 namely, unequal distribution of the organ- 

 isms in the water; and in regard to this a 

 large amount of evidence has now been 

 accumulated, since the time when Darwin, 

 during the voyage of the Beagle on March 

 18, 1832, noticed off the coast of South 



