OoTOKSB 25, 1907] 



SCIENCE 



553 



These conclusions need not lead us to be 

 discouraged as to the ultimate success of sci- 

 entific 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 conclu- 

 sions upon them. 



I do not doubt that in limited, circum- 

 scribed areas of water, in the case of organisms 

 that reproduce with great rapidity, the plank- 

 ton becomes more uniformly distributed, 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 I 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 enor- 

 mously, and under such circumstances they 

 seem to be very evenly spread over all parts 

 and to pervade the water at all depths; but 

 that is emphatically not the case with the 

 Copepoda and other constituents of the plank- 

 ton, 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. Y. 

 Ladyhird, of the sea ofi Port Erin at the 

 southwest corner of the Isle of Man. We 

 ■worked on 23 days and obtained 276 samples, 

 an average of 12 per day. [Particulars were 

 here given of the localities, the methods and 

 the various nets used.] 



All the gatherings obtained are now being 

 worked up in detail, and the results will be 

 published in the Lancashire Sea-Fisheries Re- 

 port during next winter by Mr. Andrew 

 Scott and myself. 



One or two broad features of the collec- 

 tions 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 sur- 



face. Day after day we found that the two 

 closing vertical nets hauled up from 20 

 fathoms to 10 fathoms were of a brownish- 

 green color and contained (especially the Nan- 

 sen net) an abundant gathering of diatoms. 

 The surface nets during this time contained 

 more Copepoda. On April 15 and 19, how- 

 ever, when the change in plankton was taking 

 place, the diatoms were found to be mainly on 

 the surface and the Copepoda below. As an 

 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 Cope- 

 poda 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 " along- 

 shore " station III., north of Port Erin, ofE 

 the " Cronk," one mile out, I took six simul- 

 taneous gatherings in both surface and deeper 

 waters. Two of the nets were the exactly 

 similar surface tow-nets which I have called 

 B and C. 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 Cope- 

 poda, some diatoms and some larvse, but no 

 Crah Zoeas. At the end of the fifteen min- 

 utes, when all the nets were hauled on board, 

 all the gatherings, including B, showed an 

 extraordinary number of Crab Zoeas rendering 

 the ends of the nets quite dark in color. 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 not been for 

 the chance observation of the contents of B at 

 half-time, it would naturally have been sup- 

 posed that, as all the nets agreed in their 

 evidence, the catches were fair samples of 



