552 TRANSACTIONS OF SECTION D. 
of scientific methods in solving what may be called world-wide problems, but they 
suggest that it might be wise to secure by detailed local work a firm foundation 
upon which to build, and to ascertain more accurately the representative value of 
our samples before we base conclusions upon them. 
I donot doubt that in limited, circumscribed areas of water, in the case of 
organisms that reproduce with great rapidity, the plankton becomes more uni- 
formly disturbed, and a comparatively small number of samples may then be fairly 
representative of the whole. That is probably more or less the case with fresh- 
water lakes; and [have noticed it in Port Erin Bay in the case of diatoms. In 
spring, and again in autumn, when suitable weather occurs, as it did last year at 
the end of September, the diatoms may increase enormously, and under such cir- 
cumstances they seem to be very evenly spread over all parts and to pervade the 
water at all depths; but that is emphatically mot the case with the Copepoda and 
other constituents of the plankton, and it was not the case even with the diatoms 
during the present spring. 
With the view of testing plankton methods still further, at another time of 
year, I devoted a month this spring (March 28 to April 27) to a systematic 
exploration, from the S.V. ‘ Ladybird,’ of the sea off Port Erin at the south-west 
corner of the Isle of Man. We worked on twenty-three days and obtained 276 
samples, an average of twelve per day. 
[Particulars were here given of the localities, the methods, and the nets used. | 
All the gatherings obtained are now being worked up in detail, and the results 
will be published during next winter by Mr. Andrew Scott and myself. 
One or two broad features of the collections made were obvious. In the earlier 
part of the time, up to about the middle of April, diatoms were abundant, and 
nearly all the gatherings had a greenish tinge. During that period the plants 
were more abundant in the bottom waters, and the animals at the surface. Day 
after day we found that the two closing vertical nets hauled up from twenty to ten 
fathoms were of a brownish-green colour, and contained (especially the Nansen) an 
abundant gathering of diatoms. The surface nets during this time contained 
more Copepoda. On April 15 and 19, however, when the change in plankton was 
taking place, the diatoms were found to be mainly on the surface and the Copepoda 
below. Asan example of wide distribution I may cite April 10, when the nets 
gave consistent results all the afternoon at three localities north of Port Erin, the 
diatoms being in all cases more abundant at the bottom, and the Copepoda on the 
surface. 
We were fortunate enough on one occasion to obtain incontrovertible evidence of 
the sharply defined nature of a shoal of organisms, forming an instructive example of 
how nets hauled under similar circumstances a short distance apart may give very 
different results. On the evening of April 1, at the ‘alongshore’ Station IIL., 
north of Port Erin, off the ‘Cronk,’ one mile out, I took six simultaneous gatherings 
in both surface and deeper waters. Two of the nets were the exactly similar sur- 
face tow-nets which I havecalled Band. At half-time, as the result of a sudden 
thought, I hauled in B, emptied the contents into a jar, and promptly put the net 
out again. This half-gathering was of very ordinary character, containing a few 
Copepoda, some diatoms and some larve, but no Crab Zeas. At the end of the 
fifteen minutes, when all the nets were hauled on hoard, all the gatherings, 
including B, showed an extraordinary number of Crab Zceas, rendering the ends 
of the nets quite dark in colour. B was practically the same as C, although B had 
only been fishing for seven minutes. It was evident that at about half-time the 
nets had encountered a remarkable swarm of organisms which had multiplied 
several times the bulk of the catch, and had introduced a new animal in enormous 
numbers. Had it nct been for the chance observation of the contents of B at 
half-time, it would naturally have been supposed that, as all the nets agreed in 
their evidence, the catches were fair samples of what the water contained over at 
least the area traversed, whereas we now know that the Zoeas were confined to, 
at most, the latter half of the traverse, and may have been even more restricted. 
In these circumstances an observation made solely in the water traversed 
during the first seven minutes would have given a very different result from that 
