144 SIR W. A, HERDMAN : RESULTS OF CONTINUOUS 
differences between the catches give, I believe, approximate results which are 
of value. When a number of similar hauls agree in their evidence, we must 
conclude that they are representative and give an approximation to a true 
picture of the contents of the sea at that place and time. When they differ 
widely we must, I think, be convinced that the plankton is very irregularly 
distributed and that therefore generalisations as to that sea-area must not 
be based upon any one or a few hauls. 
In drawing any conclusions as to uniformity of distribution it is not 
sufficient to find that two or more nets agree in the quantity of their catch. 
The quality must also be considered, and it is by no means always the two 
simultaneous hauls that are most alike in bulk that agree best in the kind 
and number of contained organisms. For example, on April 13th, 1907, two 
similar surface nets, “B” and “C,” towed together contained the one 
16 c.em. and the other 15:5 c.cm., but these were made up very differently 
in the two cases. [n C there were no Balanus nauplii and no immature 
Copepoda, while thousands of both were present in B. Then again in B 
there were very few adult Temora, while in C there were over 4000, B had 
650 larval Polychætes and C had none, B had 2000 Oikopleura and C only 
150, and so on *. 
During the diatom maximum, when the sea is swarming with these 
organisms, there is greater uniformity in adjacent hauls than at other times 
when a zooplankton is present, but even then the simultaneous hauls of two 
similar nets, though of the same general type, commonly differ to the extent 
that one may be double or some small multiple of the other—showing that we 
get a good general picture of the plankton by such hauls, but that they are 
not representative in minute detail f. 
For further details as to our nets and methods of use, and subsequent 
computations, reference must be made to the Annual Reports—and especially 
to the first three, for 1907-8-9 (loc. cit.). 
DISTRIBUTION OF THE PLANKTON. 
In regard to the first object of the investigation “ the distribution of the 
plankton as a whole and of its various constituents throughout the year,” I 
dealt in a former part of the present series f with the general distribution and 
the form of the annual curve for the total plankton, and in some detail with 
* The full list of between 20 and 30 organisms for each net is given in our first Annual 
Report, for 1907. 
t I find that W. E. Allen, in California, comes to much the same conclusions (loc. cit. 
p.218). He adds, * Hundreds of samples approximately enumerated will give a much better 
idea of actual conditions in the sea than ten samples enumerated with excruciating care." 
t “Spolia Runiana.—IL[I. The Distribution of certain Diatomis and Copepoda throughout 
the Year in the Irish Sea.” Journ. Linn. Soc., Zool. xxxiv. p. 95 (1918). 
