42 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



almost identical results. With a view of testing the matter 

 further, on seven separate occasions, in April, May, August, 

 and September, when the conditions at sea seemed favourable, 

 I took from the motor-boat " Redwing " a series of four or six 

 hauls of the vertical Nansen net in rapid succession, from 

 depths of 8 to 20 fathoms up to the surface. Superficially, 

 at the time of emptying the catches from the net into their 

 bottles those of each series seemed very much alike, and even 

 when measured carefully in the laboratory some of the series 

 gave identical quantitative results — for example, six successive 

 hauls from 8 fathoms were all of them 0.2 c.c, and four out 

 of five from 20 fathoms were 0.6 c.c. ; but qualitatively the 

 volume was made up rather differently in the successive hauls 

 of a series. The same organisms were present for the most 

 part in all the hauls of each series, and allowing for the well- 

 known seasonal variations the chief groups of organisms are 

 present in much the same proportions. For example, in a 

 series where the Copepoda average about 100, the Dinoflagel- 

 lates average about 300 and the Diatoms about 8,000, but the 

 percentage deviation of individual hauls from the average may 

 be as much as plus or minus 50, or even occasionally 

 a good deal more. The estimated numbers of each organism 

 (about fifty species) in each of the thirty-four hauls have been 

 worked out, and the details will be published in the Sea-Fisheries 

 Report for 1920 ; but, pending further statistical treatment, 

 the impression one receives from looking at the figures is that 

 if on each occasion one haul only in place of four or six had 

 been taken, and if one had used that haul to estimate the 

 abundance of any one organism in that sea-area, one might 

 have been about 50 per cent, wrong in either direction — while 

 the probable error of the method allows of a range of only 

 from about 10 bo 15 per cent. This seems to indicate a greater 

 variation in the successive hauls than can be accounted for 

 by the probable error of the experiment. 



