SEA-FISHERIES LABORATORY. 173 



To the question what light does a series of four to six 

 successive hauls throw upon the validity of a single haul, say 

 the first of that series, the answer seems to be that as regards 

 mere size (volume) and general nature (such as phytoplankton, 

 zooplankton or mixed) of the catch the series confirms the 

 representative nature of the single haul in a general way and 

 within limits. For example, in two out of the seven series 

 all the catches (six and four respectively) were alike in volume, 

 the additional hauls taken exactly confirming the evidence of 

 the first. In the remaining five series there was some diver- 

 gence from the average amounting in the most extreme case 

 to + 23 and — 26 per cent. ; so that as far as this experiment 

 shows if a single haul had been taken, in place of a series, it 

 might have given a result about 25 per cent, different in either 

 direction (either above or below the average of the series). 



Then again, in regard to the nature of the plankton, without 

 going into the exact statistics of the species or even of the groups 

 of species, it is evident to the eye at the time of collecting, 

 and this is confirmed by the microscopical examination, that 

 any one haul is very fairly representative of its series. If one 

 shows a phytoplankton catch, the others do also. 



But if one next proceeds to deal quantitatively with the 

 groups of species that make up the catches, it is found that the 

 individual hauls in a series may differ widely. The preceding 

 tables show that both in the main groups of the plankton and 

 in those species which have been taken out as examples fully 

 50 per cent, of the variations from the mean of the series 

 extend beyond the range of error, and are therefore not due 

 to possible imperfections in the experiment. Thus more than 

 half the differences between the hauls of a series remains 

 unaccounted for, and may naturally be interpreted as evidence 

 of an unequal distribution of the plankton in closely adjacent 

 areas of water, or in the same area in successive periods of time. 



Whether our present methods of collecting and of estimat- 

 ing are sufficiently accurate to enable us to determine the 



