of the Fishery Board for Scotland. 225 
however, is 16°5cm., or very nearly the figure derived from the comparison 
of the mean sizes; and if the average be made of all the instances, the 
figure is 16*lem., or 63 inches. If the collections are selected according 
to the numbers of fishes they contain, as above described in dealing with 
the approximate means, we get in the nine cases an average of 15°33cm., 
or a trifle over 6 inches. It seems very probable, then, that the cod on 
the east coast of Scotland increases in length at this early period of its life 
by from 6 to 64 inches in the course of a year, and it is likely to be nearer 
the former figure than the latter. The particulars of the computation in 
the nine cases referred to are given in the accompanying Table :— 
Number of Fish. Difference Dimenenge 
between the etween the 
Month. Se prec Modes or 
foe Maximum 
Ist Series. |2nd Series. Means. Ordinates. 
Cm. Cm. 
September, ; ; 42 167 15°5 16 
October, . : ‘ 75 37 16°5 14 
November, j A 301 20 18°5 19 
3 : a 38 178 18 21 
a : OF 78 113 15 13 
December, , ; 91 179 ENS, 11 
July, ; : A 29 77 Wy 15 
August, . ; : 90 93 15 14 
rs : ; : 46 47 14°5 15 
16:2 15°33 
In my previous paper, in which I dealt with the growth of the cod, the 
number of collections as well as the number of fishes was much less; but 
in the ten cases where comparison was possible the mean difference between 
the arithmetic averages of the two series (the method then made use of) 
was 16°7 cm., and in the five instances with the greatest numbers of fish 
it was 16-Ocm., or 63 inches, 
With regard to the difference between the second and third groups, the 
collections in which this can be determined are much less numerous. The 
five cases are as follows:— 
Number of Fish. Difference Pan 
between the 5 
Month. ee 5 Modes or 
Approximate Maximum 
1st Series. |2nd Series, Means, Ordinates. 
Cm. Cm 
November, ; ‘ 178 33 16 = 
December, : : 41 15 15 16 
“e : F 179 40 17-5 = 
January, 280 41 18°5 - 
May, 268 141 18 17°5 
17 16°7 
| 
The last collection (May) represents fish a little over two and three 
years of age. In my last paper there was only one instance in which 
comparison between these groups could be made, and the difference 
(arithmetical averages) was 18°2cm.; when incorporated with the others 
given above the average remains 17cm., or 6}} inches. 
It is very desirable that complete observations should be made with 
exactitude as to the average size, and the limits of size, at which the cod 
becomes mature for the first time. Until this be done it is not possible 
to be quite certain as to the age at which reproduction begins. It is 
certainly not before four years, and it may be five years, of age. 
P 
