246 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



In these tables the unit of length is the centimetre ; and 

 the numbers of fish measured refer to means of length : 

 thus all the fish between n cms. and n + 1 cms. are 

 grouped as n'b cms. Tables of sex and age are also given : 

 the notation for the age-groups adopted is that usually 

 employed, that is, all fish under one year of age are 

 included in the group "0"; those over one year and 

 under two years of age are included in group " I," and so 

 on. Generally speaking, the plaice in Lancashire in- 

 shore waters belong to groups 0, I, II, and III. 



Summaries of these age-determinations are given in 

 the tables on pp. 267-8. In the table on p. 267 the 

 sexes are distinguished. But in that on p. 268 they are 

 grouped together. This is because the latter table 

 includes a considerable number of plaice belonging to 

 age-group 0, and the smaller fish in this group require a 

 rather detailed examination if the sex is to be determined 

 with certainty. Also the difference in the rate of growth 

 in the two sexes of plaice under about 10 cms. is quite 

 insignificant, so that the combination of the figures does 

 not matter. 



Although well over 10,000 plaice have been examined 

 in detail during the last four years, and their sex and age 

 determined, it is still impossible to say what is the mean 

 or modal lengths of Irish Sea plaice at the end of each 

 year of age up to the fifth year. The table on p. 268 

 shows that the mode in age-group O lies apparently about 

 length 7 and this is probably very near the truth. That 

 of age-group II is near 19 cms., and this estimate also is 

 very nearly accurate. The modes in age-groups III and 

 IY cannot be determined merely by inspection of the 

 frequencies, and, indeed, the numbers of fish in Group IV 

 are too small to be used for statistical purposes. In 

 Group I the mode lies somewhere near length 17 cms., 



