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" I cm., or 6| 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 6| 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 : — 



Month. 



Number 

 1st Series. 



of Fish. 

 2nd Series. 



Difference 

 between the 

 Approximate 

 Means. 



Difference 

 between the 

 Modes or 

 Maximum 

 Ordinates. 









Cm. 



Cm. 



September. 



42 



167 



15-5 



16 



October, . 



75 



37 



16-5 



14 



November, 



• j • 



301 



20 



18-5 



19 



38 



178 



18 



21 



3 J « ' « 



78 



113 



15 



13 



December, 



91 



179 



15'5 



11 



July, 



29 



77 



17 



15 



August, 



90 



93 



15 



14 





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 IG^Ocro., or 6j 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: — 



Month. 



Number of Fish. 



Difference 

 between the 



Difference 

 between the 

 Modes or 

 Maximum 

 Ordinates. 



1st Series. 



2nd Series. 



Approximate 

 Means. 



November, 

 December, 



January, . 



May, .... 



178 

 41 

 179 

 280 

 268 



33 

 15 

 40 

 41 

 141 



Cm. 

 16 

 15 



17- 5 



18- 5 

 18 



Cm. 

 16 



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. 



