40 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY 



ensure that hauls intended for comparison are really 

 comparable. Two years' additional work since in the same 

 locality, off the south end of the Isle of Man, has only 

 confirmed these results, viz., that the Plankton is liable 

 to be very unequally distributed over the depths, the 

 localities, and the dates. One net may encounter a swarm 

 of organisms which a neighbouring net escapes, and a 

 sample taken on one day may be very different in quantity 

 from a sample taken under the same conditions next day. 

 If an observer were to take quarterly, or even monthly, 

 samples of the Plankton, he might obtain very different 

 results according to the date of his visit. For example, on 

 three successive weeks about the end of September he 

 might find evidence for as many different far-reaching 

 views as to the composition of the Plankton in that part 

 of the Irish Sea. Consequently, hauls taken many miles 

 apart and repeated only at intervals of months can scarcely 

 give any sure foundation for calculations as to the 

 population of wide sea areas. 



These conclusions need not lead us to be discouraged 

 as to the ultimate success of scientific methods in solving 

 what may be called world-wide problems, but they suggest 

 that it would 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 do not doubt that in limited, circumscribed areas of 

 water, in the case of organisms that reproduce with great 

 rapidity, the Plankton becomes more uniformly 

 distributed, and a comparatively small number of samples 

 ma}^ 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 



