SEA-FISHERIES LABORATORY. 187 
with regard to age, sexual condition, and weight. But 
this part of the work is very laborious, and with the 
resources at the present disposal of the Committee, the 
number of fish so examined cannot, probably, be 
exceeded. 
Tables are given, as in last year’s Report, and are 
constructed in the same manner. No comparisons are 
yet made between different years, so that the question of 
error has not been touched. But the data are given, 
just as they are collected, the only groupings being that 
of the inclusion of all fish caught on the same ground, 
during the same month, in the same column. Measure- 
ments are given in centimetres, the only satisfactory 
unit, as Professor Heincke has already insisted. 
Standard deviations and probable errors can then be 
easily ascertained. 
From the beginning of these investigations I 
recognised that an error was inherent in the system of 
examining fish some time after capture—that of the 
post-mortem contraction of the animal. Fortunately 
the mean magnitude of this error can easily be ascer- 
tained, for all samples of plaice sent to me by Captain 
Wignall have been measured immediately (less than 
half an hour) after capture. On reaching the laboratory 
they are again measured, and the Table on p. 206 shows 
in parallel columns the results of these two series of 
measurements. Obviously the point involved is one of 
some practical importance in view of the possible 
imposition of restrictions on trawl fishing with respect 
to the lengths of fish permitted to be taken; and Captain 
Wignall’s measurements form an important contribution 
to the solution of a question which might conceivably 
trouble the lawyers and magistrates who may have ta 
deal in the future with size-limits of trawled plaice. 
