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SCIENCE 



[N. S. Vol. XXVI. No. 669 



the purpose of capturing and measuring tlie 

 organisms present, have been devised by some 

 of the German investigators, and these will 

 alvrays be associated with the name of Pro- 

 fessor Hensen, of Kiel, to whom very great 

 credit is due for the ingenuity and scientific 

 enthusiasm with which he has conducted the 

 investigation. It is very important that any 

 criticisms which are required should be 

 brought forward before further researches 

 have been made and before further material 

 has been accumulated, and that any imper- 

 fections or limitations in the methods em- 

 ployed should be recognized. 



The Hensen methods are based upon the 

 assumption that the distribution of the plank- 

 ton, or assemblage of minute floating organ- 

 isms, in the sea is so uniform over wide areas 

 under much the same conditions that total 

 populations can be calculated from relatively 

 very small samples. [Examples were given of 

 several of the conclusions arrived at as the 

 result of such calculations by Hensen and his 

 fellow workers.] The correctness of these 

 conclusions, it will be noticed, depends entirely 

 upon the assumed uniformity of distribution 

 and upon the adequacy of a small number of 

 samples as representing the whole area. 

 Some criticisms have appeared which are based 

 upon imperfections of the instruments — varia- 

 tions in the nets employed and such matters. 

 These imperfections can be obviated or allowed 

 for; but I wish to bring before your attention 

 a much more fundamental difficulty, namely, 

 the marked irregularity or want of uniformity 

 in the distribution of the organisms. At the 

 time (five years ago) when I served as a mem- 

 ber of the Ichthyological Research Committee, 

 I was much struck by the evidence obtained of 

 irregularity in distribution of marine organ- 

 isms and of' the inadequacy of small samples 

 taken at considerable distances apart in either 

 time or space. It has been a matter of com- 

 mon observation amongst naturalists that 

 many of the larger organisms, such as Cope- 

 poda, occur in swarms; and this not merely 

 around our coasts and in the narrow seas, 

 but also in the open ocean. [Recorded in- 

 stances were given.] Trichodesmium, again, 

 is found in the Indian Ocean occurring in 



enormous profusion over narrow bands. At 

 the last meeting of this association, Dr. G. H. 

 Fowler gave some interesting results he had 

 obtained in regard to irregularity of distribu- 

 tion in the open Atlantic. These and some 

 other results which have been obtained, I be- 

 lieve, are unfortunately not yet published. 



Convinced of the fundamental importance of 

 such work, I spent the greater part of last 

 summer vacation in experimenting day after 

 day with various plankton nets imder similar 

 and under varying conditions in a limited 

 sea-area off Port Erin in the Isle of Man — 

 with results that were startling in their di- 

 versity. It was obvious that the plankton was 

 at that time very unequally distributed over 

 the depths, the localities, and the dates. It 

 seemed clear that one net might encounter a 

 swarm of some organism which a neighboring 

 net escaped, and that a sample taken on one 

 day might be very different in quantity from 

 a sample taken under the same conditions 

 next day. 



I stopped this series of observations on 

 September 17. After a few days of wind a 

 spell of quiet, calm weather followed, during 

 which I took some tow-nettings both inside 

 Port Erin Bay and outside, both in the day 

 and at night, and all of these differed entirely 

 in character from the gatherings of the previ- 

 ous weeks — being composed mainly of Chceto- 

 ceros and other diatoms. When the weather 

 broke again, at the end of September, another 

 abrupt change took place, and gatherings taken 

 at the beginning of October showed very few 

 diatoms, but many Copepoda. It is evident 

 that if any observer had been taking quarterly 

 or even monthly samples of the planliton in 

 that sea-area, he would have obtained very dif- 

 ferent results, according to the exact date of 

 his visit. On three successive weeks about the 

 end of September he might have found evi- 

 dence for as maiiy different far-reaching views 

 as to the composition of the plankton in that 

 part of the Irish Sea. How it can be supposed 

 that hauls taken miles apart and repeated 

 only at intervals of months, or even weeks, can 

 give any sure foundation for calculations as 

 to the population of wide sea areas, I fail 

 to see. 



