THE AGE OF FISHES AND THE RATE AT WHICH THEY GROW. 411 
they are measured and marked, and only using such fish as appear to be 
quite uninjured and full of vigour. 
We must now pass on to consider some of the conclusions which have 
resulted from the use of these methods of investigating age and growth 
rate. In the case of the Plaice, the researches of Dr. Wallace, which were 
carried out at the Lowestoft Laboratory of the Marine Biological Associa- 
tion, are amongst the most important. The method he employed was 
the study of the otoliths, his results being based on a total of 20,000 fish, 
each of which was measured and its age determined. In addition to this 
Wallace makes use of the records of the otoliths of another 20,000 
measured Plaice collected by the Board of Agriculture and Fisheries (24). 
These numbers will give some idea of the extent of the investigations 
which have been made. 
The following table embodies the result of the analysis as regards age 
of two series of samples of Plaice trawled by Wallace along a line nearly 
at right angles to the Dutch coast, from Texel to the Leman Banks, 
commencing about three miles from the shore and running out some 
eighty or ninety miles into the North Sea. The samples were taken in 
May and September, 1905. (Wallace, 28, Rep. II, Pt. I, p. 26.) 
1. Males. 
The J group averaged 9-4cm. in May and 14-9 cm. in Sept. 
one ~ EE 16-2 cm. ud 19-9 em. co 
ee Jl 22-2 em. 5 25-4 em. 
SV : 21-2, cm. ‘ 29-3 em. ie 
ee ey us 31-6 em. a 3571 CMs 3 
VI - 34-8 cm. s 34-5 em. a 
2. Females. 
The I group averaged 10-3 cm. in May and 15-2 cm. in Sept. 
i ce 16-8 em. x 20-9 em. 5 
ie5! ct 23-6 cm. A: 25-8 cm. x 
ee * 28-3 cm. a 30-9 em. 2 
AN, Fe 34:3 cm. Hs ott Cm. 5 
VI i 38-5 em. 3 41-3 em. oy 
{A number of diagrams were also shown illustrating Wallace’s results. | 
The samples of fish from which these figures were derived were taken, 
as already stated, upon a line extending from the Dutch coast seawards 
to a distance of eighty or ninety miles. Wallace was the first to point out 
that if we are to obtain really accurate values for the average size of the 
Plaice belonging to any particular age-group in a given locality, we can. 
only do so by collecting samples uniformly in this way at different 
