No^t:mbeb 20, 1909] 



SCIENCE 



745 



other microscopic organisms as much as the 

 fishes. 



Two years ago, at the Leicester meeting 

 of the British Association, I showed that if 

 an intensive study of a small area be made, 

 hauls being taken not once a quarter or 

 once a month, but at the rate of ten or 

 twelve a day, abundant evidence will be 

 obtained as to: (1) variations in the dis- 

 tribution of the organisms, and (2) irregu- 

 larities in the action of the nets. [Ex- 

 amples shown.] Great care is necessary in 

 order to 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 un- 

 equally distributed over the depths, the 

 localities and the dates. One net may en- 

 counter a swarm of organisms which a 

 neighboring 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, accord- 

 ing 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 in- 

 tervals of months can scarcely give any 

 sure foundation for calculations as to the 

 population of wide sea areas. It seems, 

 from our present knowledge, that unifoi-m 

 hydrographic conditions do not determine 

 a uniform distribution of plankton. 

 [Some statistics of hauls shown.] 



These conclusions need not lead us to be 

 discouraged as to the ultimate success of 

 scientific methods in solving world-wide 



plankton and fisheries 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 ac- 

 curately the representative value of our 

 samples before we base conclusions upon 

 them. 



I do not doubt that in limited, circum- 

 scribed areas of water, in the case of or- 

 ganisms that reproduce with great rapidity, 

 the plankton becomes more uniformly 

 distributed, and a comparatively small 

 number of samples may then be fairly 

 representative of the whole. That is prob- 

 ably 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 two years ago at the end 

 of September, the diatoms may increase 

 enormously, and in such circumstances 

 they seem to be very evenly spread over all 

 parts and to pervade the water to some 

 depth; but that is emphatically not the 

 case with the Copepoda and other constit- 

 uents of the plankton, and it was not the 

 case even with the diatoms during the suc- 

 ceeding year. 



I have published elsewhere an observa- 

 tion that showed very definite limitation of 

 a large shoal of crab Zoeas, so that none 

 were present in one net while in another 

 adjacent haul they multiplied several times 

 the bulk of the catch and introduced a new 

 animal in enormous numbers. [Diagrams 

 shown.] Had two expeditions taken 

 samples that evening at what might well be 

 considered as the same station, but a few 

 hundred yards apart, they might have ar- 

 rived at very different conclusions as to the 

 constitution of the plankton in that part 

 of the ocean. 



It is possible to obtain a great deal of in- 

 teresting information in regard to the 

 "hylokinesis" of the sea without attempt- 



