TRANSACTIONS OF SECTION D. 5d1 
importance in connection with the fishing industries. Notable methods of work, 
and instruments for the purpose of capturing and measuring the organisms present, 
have been devised by some of the German investigators, and these methods will 
always be associated with the name of Professor 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 imperfections or limi- 
tations in the methods employed should be recognised. 
The Hensen methods are based upon the assumption that the distribution of 
the plankton, or minute floating organisms in the sea, is so uniform over wide areas 
under much the same conditions that total populations can be calculated from re- 
jiatively 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 of the plankton methods 
have appeared which are based upon imperfections of the instruments, variations 
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 distribu- 
tion of the organisms. 
At the time, five years ago, when I served as a member of the Ichthyological 
Research Committee, I was much struck by the evidence obtained of irregularity 
in distribution of marine organisms, and of the inadequacy of small samples taken 
at considerable distances apart, either in time or space, and further observations 
since have confirmed this impression. It has been a matter of common observation 
amongst naturalists that many of the larger organisms, such as Copepoda, occur in 
swarms ; and this not merely around our coasts and in the narrow seas, but also 
in the open ocean. Trichodesmium, again, is found in the Indian Ocean occurring 
in enormous profusion over narrow bands. At the last meeting of the Association 
Dr. Fowler gave some interesting results he had obtained in regard to irregularity 
of distribution in the open Atlantic. These and other results which have been 
obtained, I believe, are not yet published. 
Convinced of the fundamental importance of such work, I spent the greater 
part of my last summer vacation in experimenting day after day with various 
plankton nets under 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 diversity. 
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 en- 
counter a swarm of some organism which a neighbouring net escaped, aud 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 previous 
weeks, being composed mainly of Cheetoceros 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 plankton 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 evidence for as many 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. 
These conclusions need not lead us to be discouraged as to the ultimate success 
